Some Perspectives on Rocket As a Vegetable Crop: a Review

Home , Diplotaxis (plant), Diplotaxis tenuifolia, Eruca vesicaria

2012 vol. 76, 21-41 DOI: 10.2478/v10032-012-0002-5 ______

SOME PERSPECTIVES ON ROCKET AS A VEGETABLE CROP: A REVIEW

Matthew K.D. HALL, Jenny J. JOBLING, Gordon S. ROGERS Faculty of Agriculture and Environment, The University of Sydney, Australian Technology Park, Eveleigh, NSW, Australia, 2015 Received: February 5, 2012; Accepted: April 21, 2012

Summary Baby leaf rocket is consumed worldwide as a salad vegetable. It is usually mixed with other baby leaf crops, such as spinach and lettuce, to form a mesclun-type salad. Rocket crops have become popular due to their distinct taste and textural appearance in mixed salads. There are two common forms of rocket that are commercially cultivated, a perennial species (Diplotaxis tenuifolia (L.) DC.) known as perennial wall rocket and an annual species (Eruca sativa Mill.) known as annual garden rocket. The popularity of baby leaf crops has increased in recent years due to consumer demand for a convenient, nutritious and easily accessible product. The baby leaf salad sector is now a significant part of the leafy vegetable market, with growth in this sector esti- mated to continue. The leaves of cultivars of perennial wall rocket and annual garden rocket have been bred to look similar, allowing for a year-round supply of produce. Despite this, there are many differences between the species that affect their responses to abiotic factors during growth and storage. This paper aims to provide some perspectives on the historical importance, botanical classification and cultivation techniques of these economically important plants. key words: arugula, baby leaf, botanical, glucosinolates, history, rucola, salad, vitamin C

HISTORICAL AND CULTURAL and many of its derivatives, including IMPORTANCE OF ROCKET rughetta, rucola, roquette and others, most likely descended from the Latin ‘Rocket’ is a common name used word roc, meaning harsh or rough for some species in the family (Pignone 1997). Common names cur- Brassicaceae that have a pungent rently used to describe these species aroma and a sharp taste. They are include roquette, rucola, arugula and native to the Mediterranean and Near rocket. As with all common names, East, and they possibly acquired their the choice of common name varies original common name from the Lat- with ethnicity, location and language in-speaking Roman citizens who in- group. habited this area. The common name

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22 VEGETABLE CROPS RESEARCH BULLETIN 76 ______These differences all contribute to the “Th’ eruca, plant, which gives jaded confusion surrounding the correct appetite the spur.” (Stark 1980). informal labeling of these species. This description emphasizes Rocket has been well-document- rocket’s aphrodisiac properties con- ed in ancient literature, where it is cerning the sexual appetite, which was called euzomon, gargir and oroth believed to be important during this (Yaniv et al. 1998). The leaves have period. The aphrodisiac properties of been used for thousands of years to rocket plants are still regarded as ex- season food and oil, for the produc- cellent today (Pratap & Gupta 2009). tion of deodorants and cosmetics and Rocket’s extensive and continued for medicinal purposes (Blangiforti & description as an aphrodisiac subse- Venora 1997, Pratap & Gupta 2009). quently led to the banning of these These plants have had an interesting plants in monastic gardens, as aphro- and turbulent journey, much of which disiac or mind-altering substances has occurred in the last 20 years, to were forbidden (Stark 1980, Mas- becoming the favored leafy greens cagno 1987). Despite this ban, rocket that they are today. To effectively species were extensively grown in describe rocket’s significance and monastic herb gardens, and they were popularity as a crop, it is useful to important for flavoring foods and place its recent global utilization into enhancing medicinal remedies. a historical context. Throughout the Abrahamic peri- “Th’ eruca, Priapus, near thee we od (500-300 B.C.), rocket was em- sow to rouse to duty husbands who ployed in a wide variety of applica- are slow.” (Davenport 1869). tions. Passages of the Old Testament The above inscription appears on describe the collection of leaves from the base of statues of the Greek God wild rocket plants, which in this peri- Priapus and refers to rocket’s reputa- od were called oroth: tion as an aphrodisiac. Rocket’s ability “One of them went out into the field to restore vigor to sexual organs is well- to gather oroth, and found a wild vine documented and celebrated throughout and gathered from it his lap full of ancient literature (Davenport 1869, wild gourds, and came and cut them Fernald 1993, Barillari et al. 2005). up into the pot of pottage, not know- Priapus was believed to be the protec- ing what they were. And they poured tor of the reproductive productivity of out for the men to eat.” II Kings 4: livestock, plants and human male geni- 39-40. talia. This inscription illustrates the significance that rocket plants played This passage illustrates that in the religious beliefs of ancient civi- rocket was a useful forage food during lizations of the Mediterranean region. this period. The mistake of the author Publius Vergilius Maro, who is in referring to oroth as growing from most commonly known by the Angli- a vine is comparable to other gram- cized name Virgil, was a famous natu- matical and translation discrepancies ralist and poet who lived in Rome contained in the Old Testament (Ni- between 70-19 B.C. Virgil is known cole 1959). Many scientists agree that to have described rocket as follows: the garden vegetable called oroth in

M.K.D. HALL et al. – SOME PERSPECTIVES ON ROCKET … 23 ______these verses is in fact rocket (Zohary with religious significance, but it also 1982, Yaniv et al. 1998, Duke et al. had a wide array of medicinal proper- 2008). ties. The uses of rocket species as During the Hellenistic period salads and spices were also recorded (323-146 B.C.), rocket was mentioned during this period by the Roman bota- many times, particularly in the Mish- nist Dioscorides, in Materia Medica na and Talmud. These Jewish manu- [therapeutic properties for healing], scripts describe rocket’s use as a spice, which was written in the first century food and medicine (Yaniv et al. 1998). A.D. (Gunther 1968). The uses of rocket recorded in these Although rocket species have manuscripts reflect the major ways in had a long and dubious journey to which rocket has been used since the their current widespread cultivation, it Hellenistic period across large geo- is interesting to note that the surge in graphical areas, including flavoring production did not occur until the foods and producing medicines. mid-1990’s. Increased interest in the- Rocket’s importance as a multi- se species was largely a result of the use vegetable was primarily recorded International Plant Genetic Resources by Caius Plinius Secundus, or Pliny Institute (IPGRI) workshops, which the Elder, who lived during the period were held in 1994 in Lisbon, Portugal 23-79 A.D. Pliny, like Virgil, shared a and in 1995 in Legnaro, Italy passion for naturalist writings and (Padulosi 1995, Padulosi & Pignone identified and recorded rocket’s po- 1997). These workshops aimed to tential for many different medicinal maintain genetic diversity and to uses. A total of twelve applications promote an improved understanding were recorded, an example of which of different rocket species, presenting includes the following: them as viable alternative crops for use in mixed salads. “So agreeable is its flavour as a sa- In the last quarter of a century, vouring for food, that the Greeks have three major changes have occurred given it the name of ‘euzomon’. It is that lead to the rise of rocket as an generally thought that rocket, lightly attractive alternate leafy crop. First, bruised, and employed as a fomenta- value-added products were developed, tion for the eyes, will restore the sight particularly in the processed market. to its original goodness, and that it Second, new leafy species were intro- allays coughs in young infants.” duced, particularly baby leaf crops (Bostock & Riley 1855). such as rocket. Third, consumers have Such medicinal claims are com- increasingly focused on the nutritional mon from Pliny, who is claimed to quality and value of the crops that have amassed a total of 20,000 gen- they consume (Ryder 2002). These eral facts contained in 36 volumes factors, combined with the unique (Fagan 2006). Nonetheless, rocket’s taste and visually pleasing texture of importance in the Mediterranean and rocket leaves, have facilitated the rise Near East increased significantly in of rocket’s popularity globally. Rock- the first century A.D. Not only was et plants have had an interesting jour- rocket believed to be an aphrodisiac ney to their current widespread culti-

24 VEGETABLE CROPS RESEARCH BULLETIN 76 ______vation, and the future of these crops 2009). Many of these species are used looks bright. for fibers, oils, condiments, vegetables and salads (Gómez-Campo 1980, BOTANICAL CLASSIFICATION 1999, Gómez-Campo & Prakash OF ROCKET SPECIES 1999). Perennial wall rocket and annual garden rocket belong to this large The Brassicaceae family and economically important family, The family Brassicaceae currently with their botanical classification includes 3,709 species and 338 genera illustrated in Fig. 1. (Rich 1991, Warwick et al. 2006,

Family Brassicaceae

Tribe Brassiceae

Subtribe Brassicinae

Lineage Rapa/Oleracea

Genus Diplotaxis Eruca

Species D. tenuifolia E. sativa

Fig. 1. Current botanical classification of perennial wall rocket (Diplotaxis tenuifolia (L.) DC.) and annual garden rocket (Eruca sativa Mill.).

The Brassiceae tribe The Brassiceae tribe constitutes a The tribe Brassiceae is one of the natural group, and it is the most eco- 13 to 19 disputed tribes recognized in nomically important and botanically the family Brassicaceae (Warwick et distinct tribe from the Brassicaceae al. 2009). Species in this tribe are family (Al-Shehbaz 1985, Gómez- characterized by conduplicate cotyle- Campo 1999). This tribe was original- dons and/or bi-segmented fruits, ly distributed around the Mediterrane- which contain seeds in either one or an region, Southwestern Asia and both segments (Gómez-Campo 1999). South Africa (Crespo et al. 2000). This tribe is comprised of 46 poorly Many of the species thrive in a tem- defined genera and approximately 230 perate environment and can grow species, across which a wide range of successfully over a wide range of soil diversity is present (Warwick et al. types, including infertile and heavily 2006, Koch & Al-Shehbaz 2009). leached profiles.

M.K.D. HALL et al. – SOME PERSPECTIVES ON ROCKET … 25 ______

Molecular markers, such as chlo- iterranean and Near East, with a major roplast DNA (ctDNA), have recently center of diversity in the Western Medi- been used to confirm that the terranean (Martínez-Laborde 1997, Brassiceae tribe does not conform to Eschmann-Grupe et al. 2003). the traditional generic morphological The taxonomy of Diplotaxis spp. boundaries recognized by Schulz has been revised several times and (1936) and Gómez-Campo (1999). remains problematic regarding the Some members of this tribe are mono- morphological characters, molecular phyletic, while the majority of species markers and diversity of glucosinolates form a phylogeny, as they do not share used to classify species (Eschmann- a common ancestor. Species in this Grupe et al. 2003, D’Antuono et at. grouping have been further classified 2008). There is little morphological into the Brassicinae subtribe (Warwick variability between species of this et al. 1992, Warwick & Sauder 2005). genus; however, the highest level of diversity exists in the Iberian Peninsula The Brassicinae subtribe and Northwestern Africa (Martín & The subtribe Brassicinae has Sánchez-Yélamo 2000). Some of the been further classified into the Ra- species extend eastward into present pa/Oleracea and Nigra lineages day Pakistan and India, with five en- (Pradhan et al. 1992, Prakash et al. demic species known in the Cape 2009). These lineages are morpholog- Verde Islands and one in Western Ne- ically similar and have been primarily pal (Martín & Sánchez-Yélamo 2000). classified using ctDNA and the diver- Until recently, the distribution of sity of glucosinolates. Perennial wall Diplotaxis spp. was restricted to the rocket and annual garden rocket have region of origin due to a lack of global been placed into the Rapa/Oleracea interest in their commercial utilization. lineage. In many regions, Diplotaxis spp. The Rapa/Oleracea lineage are weeds of economic importance. Ten genera belong to the lineage Perennial wall rocket is considered to Rapa/Oleracea. Four of these genera, be a weed in regions of Europe, the including Brassica, Diplotaxis, United States of America, Australia, Erucastrum and Eruca, are in the New Zealand and Argentina subtribe Brassicinae (Warwick & (Kleemann et al. 2007, Pratap & Gupta Black 1997). The classification of in- 2009). Its perennial nature, combined ter-generic species is primarily based with its capacity to produce large on chromosomal numbers (Warwick & numbers of viable seeds, makes this Hall 2009). species difficult to control as a weed. The Southern states of Australia, ex- The Diplotaxis genus The name Diplotaxis originates cluding Tasmania, have designated from the Greek words ‘diplos’, which perennial wall rocket as a noxious translates to double, and ‘taxis’, weed (Parsons & Cuthbertson 1992, which translates to row; these words Kleemann et al. 2007), with Victoria, reflect the way in which seeds are South Australia and Western Australia located in the silique (Bianco 1995). all attempting to control its spread. Diplotaxis spp. originated in the Med- Although perennial wall rocket is

26 VEGETABLE CROPS RESEARCH BULLETIN 76 ______considered to be a weed in many are- The fruits are cylindrical, rang- as, the commercial production of this ing in length from 2 to 4 cm, and they species is permitted. are semi-appressed along the stems (Pratap & Gupta 2009). Seeds are Botanical description of perennial light brown, with an average of 5,000 wall rocket seeds per gram. They are ellipsoid in Perennial wall rocket is an erect shape, slightly flattened with medium herbaceous plant that has elongated lumina, and are wingless with leaves and a deep tap root (Pratap & conduplicate cotyledons (De Leonardis Gupta 2009). Under natural condi- et al. 1997, Martínez-Laborde 1997). tions, the mature plant can grow to a Germination occurs during the autumn, height of 80 cm. The plant possesses a with plants forming slow growing coarse and woody base with retrorse rosettes and tap root systems. Flower- hairs in the lower parts (Bianco 1995). ing depends on seasonal conditions, Leaves are fleshy, oblong and deeply but it can occur 28 days after germina- lobed, with pointed apexes (Fig. 2). tion (Kenigsbuch et al. 2009). The Eruca genus There is disagreement over the number of species in this genus based on the ease with which members can cross pollinate. Some authorities only accept a single species, while others recognize up to four different species (D’Antuono et al. 2008). In this genus, the greatest genetic variability is found in Morocco and Spain (Pratap & Gupta 2009). Species exhibit a large range of morphological variability, ranging from round leaves to heavily serrated leaves. This genus, like the Diplotaxis, Fig. 2. Illustration of the structure and is native to the Mediterranean region form of perennial wall rocket (Pignone 1997, Pratap & Gupta (Diplotaxis tenuifolia (L.) DC.). The image is presented on a scale 2009). Annual garden rocket has been of 3/5 the actual size (Britton & cultivated as a salad and spice in areas Brown 1913). of Southern Europe and Central Asia for centuries (Ryder 2002, Pratap & Flowers are bright yellow, medi- Gupta 2009). The name Eruca origi- um in size and have four rounded nates from the Latin words ‘uro’ or petals 8 to 15 mm long. They are ar- ‘urere’, which translates to burn and ranged in racemes with oblong or relates to the acrid taste of the leaves linear sepals, and they have six sta- caused by the presence of mens and are tetradynamous (Pratap glucosinolates (Bianco 1995). & Gupta 2009). Annual garden rocket is the most commonly grown species in this ge-

M.K.D. HALL et al. – SOME PERSPECTIVES ON ROCKET … 27 ______nus and is cultivated throughout the Leaves of annual garden rocket Mediterranean, Central Europe, Af- are dark green and less than 20 cm ghanistan, Northern India, Continental long. They range in shape from America, South Africa and Australia smooth and round to heavily lobed or (Pratap & Gupta 2009). Leaves are serrated. Flowers are larger than those used in mixed salads, adding a unique of Diplotaxis spp. and are white or flavor to these dishes. Annual garden light yellow with purple venations. rocket is also cultivated in Pakistan Flowers contain four petals 15 to 20 and India where it is used as an indus- mm long and have tetradynamous trial oil crop. stamens (Bianco 1995). The number of flowers on a given plant is relative- Botanical description of annual ly low, and the flowers are borne on garden rocket small terminal racemes (Fig. 3). Annual garden rocket is a low- The siliques are ovate-oblong or growing herbaceous plant that, under oblong and range in length from 2 to 3 natural conditions, grows to a height of cm (Bianco 1995). Seeds are usually 40 cm. The lyrate-pinnatifid leaves are brown but can range from yellow arranged in a rosette (Pratap & Gupta brown to olive green (De Leonardis et 2009). This species has a slender tap al. 1997), with an average of 500 root and a rigid largely un-branched seeds per gram, making the seeds hairy stem. Leaves on upper parts of approximately ten times heavier then the plant are pinnatifid, with long- the seeds of perennial wall rocket. oblong terminal lobes, and are either coarsely toothed or lobed (Fig. 3). DIVERSITY AMONG ROCKET SPECIES Rocket is a common name used for both Diplotaxis and Eruca spp. (Bianco 1995, Gómez-Campo 1995, Martínez-Sánchez et al. 2007). It is used to group plants that have similar morphology and a bitter taste resulting from the presence of glucosinolates (Halkier & Gershenzon 2006). These two main factors, similar morphology and taste, are the basis for which the common name rocket and its various derivatives are used worldwide. Diplotaxis spp. generally have Fig. 3. Illustration of the structure and uniform leaf morphology, while form of annual garden rocket Eruca spp. have greater variability (Eruca sativa Mill.). The image is (Bianco 1995, Warwick 1995, Bennett presented on a scale of 1/2 actual et al. 2006). This natural variation has size (Britton & Brown 1913). been used in the breeding programs of both perennial wall rocket and annual

28 VEGETABLE CROPS RESEARCH BULLETIN 76 ______garden rocket for the development of populations of this species has, in commercial baby leaf cultivars for use recent years, led to the production of in the salad industry. These species cultivars of annual garden rocket that hybridize with other members of re- exhibit leaves resembling the heavily spective genera through sexual repro- serrated leaves of perennial wall rock- duction, ovary culture, embryo culture et. These cultivars are easily recog- and protoplast fusion (Salisbury 1989, nizable as rocket to consumers and Fahleson et al. 1997). Intergeneric have the superior vigor of the annual hybrids have also been produced be- form. tween perennial wall rocket and annu- The presence of glucosinolates in al garden rocket, suggesting that there the plant kingdom is unique to the is a high level of genetic similarity order Brassicales, with some minor between the species (Harberd & exceptions (Halkier & Gershenzon McArthur 1980, Bang et al. 2003). 2006). The expression of glucosino- Perennial wall rocket is unique lates in plants arose 10 to 15 million among the Brassicaceae family be- years ago as a result of evolutionary cause it is a C3-C4 intermediate. It has a pressures (Windsor et al. 2005, Wheat low CO2 compensation point and et al. 2007). The biological role of Kranz-like leaf anatomy, where the glucosinolates is to deter herbivores leaf veins are surrounded by bundle- and pathogens from feeding on plant sheath cells. This characteristic is im- parts and therefore most likely arose portant in breeding programs because as part of a defense mechanism. The C3-C4 intermediates exhibit low pho- presence and diversity of glucosinolates torespiration activity, and they are in both perennial wall rocket and annual better able to grow under hot dry con- garden rocket have been well-studied ditions than C3 plants. These plants and used in botanical classification also do not have the problem of high systems (Daxenbichler et al. 1991, Tsu- energy requirements associated with C4 kamoto et al. 1993, D’Antuono et al. carbon fixation. The use of perennial 2008). The major glucosinolates found wall rocket in hybridization programs in perennial wall rocket include gluco- between wild and cultivated crops is raphanin, 4-hydroxyglucobrassicin and also currently of interest, as a fertile glucoerucin, while in annual garden amphidiploid (Kaneko et al. 2009). rocket they include glucoraphanin, Selection techniques have been glucobrassicin and 4-methoxygluco- used to standardize the visual charac- brassicin (D’Antuono et al. 2008). teristics of rocket species for cultivation in the salad industry. Singh IMPORTANT NUTRITIONAL (1975) showed that crossing an annual COMPOUNDS garden rocket variant with deeply FOUND IN ROCKET serrated leaves with a normal leaf type The role of glucosinolates in plants resulted in a F dominant normal leaf 1 Glucosinolates are nitrogen- and shape. The F population had a 3:1 2 sulfur-rich compounds, with over 120 segregation ratio of normal to deeply different types having been identified serrated leaves. The ease of crossing (Halkier & Gershenzon 2006). They between morphologically different are nutritionally important to humans

M.K.D. HALL et al. – SOME PERSPECTIVES ON ROCKET … 29 ______because they have the capacity to Gershenzon 2006). These major steps provide protection against carcino- are well-known and supported by gens, mutagens and other forms of many studies of Arabidopsis. toxicity (Balch & Balch 2000, Ward The biosynthesis of gluco- 2002). Glucosinolates also contain sinolates is regulated by genetic and toxic, growth-inhibiting and feeding- environmental factors, but the mecha- deterrent signals to a wide variety of nisms are poorly understood (Felice et organisms (Burow et al. 2006, Kim & al. 2006, Zhang et al. 2006, Yan & Jander 2007, Hopkins et al. 2009). Chen 2007). The molecular structure The induction of glucosinolates is of glucosinolates can change in re- strongly associated with biotic stress sponse to biotic stress caused by cel- factors resulting from a range of lular damage, and the change increas- sources including fungal pathogens, es the plant’s deterrent characteristics bacterial infection, insect feeding and against further damage through direct generalist or specialist herbivores toxicity (Kim & Jander 2007). This (Rostás et al. 2002, Agerbirk et al. variability in glucosinolate formation 2009, Dam et al. 2009). partly explains the level of diversity in plants, with genetic factors directly The biosynthesis of glucosinolates influencing the type of glucosinolate Glucosinolates are formed from that can form. eight amino acids and are classified, Perennial wall rocket is known according to their amino acid precur- to contain 11 different glucosinolates, sors, into three distinct groups: ali- while annual garden rocket has 14 phatic, benzenic and indolic glucosinolates (D’Antuono et al. (Sønderby et al. 2010, Table 1). 2008). Of these, some are indolic

Table 1. The grouping of glucosinolate glucosinolates, most commonly found type based on their amino acid precursors. in the Rapa/Oleraceae lineage. The diversity of glucosinolates in rocket Aliphatic Benzenic Indolic species is related to their botanical glucosinolates glucosinolates glucosinolates classification, with glucoraphanin L-alanine L-phenylalanine L-tryptophan present in the leaves of both species at L-leucine L-tyrosine L-isoleucine high concentrations (Force et al. L-valine 2007, Kim & Ishii 2007). Most Methionine glucosinolates in these rocket species correspond to methionine-derived The biosynthesis of gluco- components, while both benzenic and sinolates occurs in three distinct phas- indolic glucosinolates have also been es. First, amino acids undergo chain identified in the leaves. elongation through the insertion of The glucosinolate-myrosinase system methylene groups into their side Glucosinolates are stored in plant chains. Second, the amino acid is vacuoles, while myrosinase is local- altered to produce the core structure ized in the cytosol and in specialized of the glucosinolate. Third, the myrosin cells (Bones & Rossiter glucosinolate is modified by second- 1996, Bennett et al. 2006). In Ara- ary transformations (Halkier & bidopsis, myrosinase has also been

30 VEGETABLE CROPS RESEARCH BULLETIN 76 ______shown to occur in S-cells and is found diate degradation of glucosinolates at in the pedicel. The wide distribution the site of damage. of myrosinase in plants means that this substance is available for imme-

Fig. 4. Depiction of the glucosinolate-myrosinase reaction and the various compounds produced under different conditions. ESP: epithiospecifier locus (Rask et al. 2000).

Once cellular damage occurs, the It is possible that variations between glucosinolate comes in contact with genetic factors of perennial wall rock- myrosinase, causing a reaction that et and annual garden rocket, com- releases glucose, sulfate and several bined with differences in their physi- hydrolysis products including ology, will result in a change in epithionitrile, thiocyanates, nitriles, glucosinolate profile and concentra- isothiocyanates, oxazolidine-thione tion when grown under different con- and other less-common compounds ditions. (Rask et al. 2000, Fig. 4). The role of vitamin C in plants The hydrolysis products formed Another important compound by this reaction are known to be de- found in rocket that is nutritionally pendent on the structure of the important and present at high concen- glucosinolate and the conditions under trations in the leaf is vitamin C. This which the reaction takes place. For compound is known to be effective in example, the pH during hydrolysis has neutralizing reactive oxygen species been shown to be an important factor (ROS), and its presence relates to the in the formation of nitriles in vitro. nutritional quality of crops. The term This reaction is most likely to occur at vitamin C is used to collectively refer a pH of 4 and/or in the presence of to L-ascorbic acid (AA), L-dehydro- Fe2+ ions (Bennett et al. 2006, Fig. 4).

M.K.D. HALL et al. – SOME PERSPECTIVES ON ROCKET … 31 ______ascorbic acid (DHAA) and their vari- these compounds is not neutralized by ous derivatives. Vitamin C is a me- vitamin C, cell damage can result tabolite with strong antioxidant prop- (Ishikawa & Shigeoka 2008). One of erties and is an important cofactor for the most common ROS found in enzymes. Humans cannot synthesize plants is hydrogen peroxide (H2O2); vitamin C because they lack the en- this compound has the ability to affect zyme L-gulonolactone oxidase, so cascade reactions if not neutralized, they must therefore obtain the vitamin leading to the production of more from food (Nishikimi et al. 1994, toxic molecules such as hydroxyle Woodall & Ames 1997). Vitamin C radicals and lipid peroxides (Noctor & has a direct effect on the health of Foyer 1998). AA is effective in neu- skin, gums and blood vessels, and it is tralizing H2O2 in the L-galactose also known to influence collagen for- pathway, the pathway through which mation, the absorption of inorganic vitamin C is synthesized in plants iron and the enhancement of the im- (Asada 1997). mune system (Conklin et al. 1999, The role of vitamin C in plants Lee & Kader 2000). has also been linked to a range of Vitamin C is abundant in plants biological processes including plant and can account for up to 10% of the growth, cell death, the response to total soluble carbohydrate levels pathogenic infection and senescence (Noctor & Foyer 1998, Smirnoff & (Pignocchi & Foyer 2003, Barth et al. Wheeler 2000). The pathway of vita- 2006, Linster & Clarke 2008). After min C biosynthesis in plants has been senescence occurs, there is a reduction described and is affected by develop- in AA concentration that is also corre- mental triggers and environmental lated with an increase in ROS (Zim- cues (Pastori et al. 2003). Vitamin C mermann & Zentgraf 2005). Vitamin concentration in the leaves of rocket C is also a protective agent against species is high compared to that of environmental factors including ozone other leafy crops, which means that stress, high levels of UV radiation and rocket has the potential to contribute high temperature exposures (Conklin high quantities of this antioxidant to & Barth 2004, Gao & Zhang 2008, the human diet (Bennett et al. 2006, Linster & Clarke 2008). In Arabidop- Kim & Ishii 2007, Martínez-Sánchez sis mutants, Larkindale et al. (2005) et al. 2008). have shown that AA plays an im- The biochemical roles of vitamin portant function in controlling ROS, C in plants include the elimination of particularly under high temperature ROS, ensuring that α-tocopherol re- and UV conditions. Although vitamin mains in a reduced state so that it can C is known to be influential in a wide be utilized, and its role as a substrate range of biochemical reactions, the for AA peroxidase, which is involved cascade of downstream reactions and in the production DHAA (Conklin et enzymes are poorly understood. al. 1999, Ishikawa & Shigeoka 2008). The synthesis of vitamin C in plants The highest concentration of ROS is The pathway for vitamin C for- found in the chloroplasts and mito- mation in plants is the L-galactose chondria of cells. If the production of pathway (Wheeler et al. 1998,

32 VEGETABLE CROPS RESEARCH BULLETIN 76 ______Giovannoni 2007), which converts and that translocation of AA from GDP-D-mannose to L-ascorbate source to sink occurs via phloem through four successive intermediates (DeBolt et al. 2007). A similar rela- that are enabled by six enzymes, as tionship has also been reported by described in Fig. 5. Tedone et al. (2004) in potato tubers. The transport of vitamin C occurs D-mannose 1-phosphate across a steep gradient, indicating the ↕ GTP-mannose pyrophosphorolase use of co-transport. The methods of transport around the plant are poorly GDP-D-mannose understood, with the majority of work ↕ GTP-mannose-3,5-epierimase focusing on AA, which makes up the GDP-L-galactose largest component of vitamin C in ↓ L-galactose guanyltransferase plants. L-galactose 1-phosphate ↓ L-galactose-1-P phosphatase SUMMARY L-galactose OF THE DIFFERENCES BETWEEN ROCKET SPECIES ↓ L-galactose dehydrogenase L-galactose-1,4-lactone Both species of rocket share ↓ L-galactono-1,4-lactone dehydrogenase characteristics consistent with their close botanical classification, includ- L-ascorbate ing similarities in morphology, origin

Fig. 5. Depiction of the L-galactose path- and the diversity of glucosinolates. It way of ascorbate synthesis in is understandable that informally, plants. Pathway metabolites from these species have been historically D-mannose-1-phosphate through L- grouped together for convenience. ascorbate are shown with the en- Breeding programs for annual zymes associated with the for- garden rocket have targeted cultivars mation to the right of the pathway. for use in the baby leaf salad market Figure adapted from Giovannoni and have primarily focused on the (2007). increased expression of heavily serrated leaves, which closely resemble The factors that control the dis- those of perennial wall rocket. This tribution and accumulation of vitamin has enabled the commercial produc- C in plant tissue are poorly under- tion of annual garden rocket during stood, particularly concerning vitamin seasons of plant growth that do not C accumulation in non-photosynthetic favor perennial germination and and storage tissue (DeBolt et al. growth. The combination of similari- 2007). The synthesis of AA in plants ties between cultivars of different occurs in the cytosol of cells (Loewus rocket species creates a problem be- 1999). The AA is then translocated to cause different cultivars look the same the chloroplast, vacuole and apoplast but do not respond equally to abiotic (Rautenkranz et al. 1994). Franceschi factors. & Tarlyn (2002) have shown that the accumulation of AA in plant organs is likely to follow localized synthesis

M.K.D. HALL et al. – SOME PERSPECTIVES ON ROCKET … 33 ______

Table 2. Illustration of the main differences between perennial wall rocket (Diplotaxis tenuifolia (L.) DC.) and annual garden rocket (Eruca sativa Mill.).

Variable Perennial wall rocket Annual garden rocket Form Perennial Annual Seed size 5,000 seeds/g 500 seeds/g Uses Salad, condiment Salad, condiment, oil, pesticide Carbon fixation C3-C4 intermediate C3 Root system 30 to 40 cm 10 to 20 cm Growth rate (summer) 30 to 40 days to harvest 20 to 30 days to harvest Glucosinolates 11 known types 14 known types

The major differences between respective species can continue to perennial wall rocket and annual gar- metabolize and grow, with perennial den rocket are summarized in Table 2. wall rocket better able to photosynthe- When compared to perennial wall size at higher temperatures than annual rocket, the seeds of annual garden garden rocket. The diversity of gluco- rocket are approximately 10 times sinolates is also different between heavier (Table 2). This difference rocket species, with 11 known gluco- influences the germination of rocket sinolates in perennial wall rocket and species, as larger seeds contain greater 14 in annual garden rocket (Table 2). stored reserves than smaller seeds The utilization of rocket species (Hall et al. 2012). Annual species are is similar for both perennial wall also known to develop more rapidly rocket and annual garden rocket, both than perennial species (Pitelka 1977, of which are extensively used around Jackson & Roy 1986), because they the world in salads (Table 2). Annual divert more energy into the produc- garden rocket is also used as an indus- tion of reproductive structures and trial oil and pesticide base due to its less into vegetative growth (Bazzaz et annual nature and large oil yield ca- al. 1987, Hancock & Pritts 1987, pacity. Garnier 1992). The root system of perennial plants is deeper than annual CULTIVARS OF PERENNIAL plants, which is relevant to a crop that WALL ROCKET AND ANNUAL is harvested multiple times by the GARDEN ROCKET removal of above-ground vegetation. Selective breeding of cultivars Therefore, the amount of stored re- from wild plants is performed to im- serves in the root system may be a prove the expression of desirable critical factor dictating the successful traits for commercial production regrowth of leaves after harvest. (Chahal & Gosal 2002, Acquaah The carbon fixation cycle is dif- 2007). These traits may include higher ferent between the different species; production and productivity, stress perennial wall rocket is a C -C in- 3 4 resistance and uniformity of growth termediate plant and annual garden (Kalia 2006). The breeding of culti- rocket is a C plant (Table 2). This 3 vars for commercial use invariably difference affects the range of envi- alters the response of species to environmental conditions under which ronmental conditions because plants

34 VEGETABLE CROPS RESEARCH BULLETIN 76 ______have been selected to remove natural ences between the species mean that, variation in the resulting population although they have been bred to look (Acquaah 2007). This means that, similar, these crops need to be man- between individual plants in the re- aged commercially in different ways. sulting cultivar, very little variation is In response to differences in plant experienced. The uniformity among responses to abiotic factors resulting plants allows for better crop manage- from differences in carbon systems, ment and superior plants for cultiva- habits and reproductive cycles. These tion compared to the wild plants from species clearly represent plants with which they were bred. Leaves of both important historical significance and species are usually harvested once high nutritional value for modern they reach a commercial size specifi- diets. If cultivation of these crops is to cation of 10 to 15 cm, further necessi- be improved, it is necessary to view tating the need for uniformity between the management of these crops sepa- plants. rately so that improvements in yield, In the last 20 years, with in- quality and nutrition can result. creased interest in rocket species for use in the salad market, many seed REFERENCES companies have included perennial wall rocket and annual garden rocket Acquaah G. 2007. Breeding hybrid culti- in their respective breeding programs. vars, pp.334-342. In: Acquaah G. The breeding of plants for appearance, (ed.). Principles of Plant Genetics and Breeding. Blackwell Publishing. commercial quality, shelf life, nutri- Carlton, Victoria. tional quality and other qualities is Agerbirk N., De Vos M., Kim J.H., Jander commonly performed during cultivar G. 2009. Indole glucosinolate development. These traits have there- breakdown and its biological ef- fore been considered in the breeding fects. Phytochemistry Reviews 8: of rocket species. It is impossible to 101-120. estimate the number of cultivars for Al-Shehbaz I.A. 1985. The genera of respective rocket species because seed Brassiceae (Cruciferae: Brassicaceae) companies hold many more cultivars in the southeastern United States. than they commercially sell and are Journal of the Arnold Arboretum 66: 279-351. reluctant to provide such information. Asada K. 1997. The role of ascorbate peroxidase and monodehydro- CONCLUSION ascorbate reductase in H2O2 scaveng- ing in plants, pp. 715-736. In: Through the detailed description Scandalios J.G. (ed.). Oxidative of perennial wall rocket and annual Stress and the Molecular Biology of garden rocket, it is clear that these Antioxidant Defenses. Cold Spring species share many similarities, as Harbor Laboratory Press. Cold reflected by their close botanical clas- Spring Harbor, New York. sifications and similar uses. However, Balch J.F., Balch P.A. 2000. Prescription for nutritional healing. Penguin Put- it is also clear that these species can- nam Inc. Avery, New York. not be considered similar from an Bang S.W., Mizuno Y., Kaneko Y., agronomic perspective. These differ- Matsuzawa Y., Bang K.S. 2003.

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38 VEGETABLE CROPS RESEARCH BULLETIN 76 ______Science of Food and Agriculture 87: Legnaro, Italy, 13-14 December, 966-973. 1996. Kim J.H., Jander G. 2007. Myzus persicae Martínez-Sánchez A., Llorach R., Gil (green peach aphid) feeding on Ara- M.I., Ferreres F. 2007. Identification bidopsis induces the formation of a of new flavonoid glycosides and deterrent indole glucosinolate. The flavonoid profiles to characterize Plant Journal 49: 1008-1019. rocket leafy salads (Eruca vesicaria Kleemann S.G.L., Chauhan B.S., Gill and Diplotaxis tenuifolia). Journal G.S. 2007. Factors affecting seed of Agricultural and Food Chemistry germination of perennial wall rocket 55: 1356-1363. (Diplotaxis tenuifolia) in Southern Martínez-Sánchez A., Gil-lzquierdo A., Australia. Weed Science 55: 481- Gil M.I., Ferreres F. 2008. A com- 485. parative study of flavonoid com- Koch M.A., Al-Shehbaz I.A. 2009. Mo- pounds, vitamin C, and antioxidant lecular systematics and evolution, properties of baby leaf Brassicaceae pp. 1-18. In: Gupta, S.K. (ed.). Bi- species. Journal of Agricultural and ology and Breeding of Crucifers. Food Chemistry 56: 2330-2340 CRC Press. Boca Raton, Florida. Mascagno V. 1987. Coltivata o selvatica Larkindale J., Hall J.D., Knight M.R., la rucola é ottima in insalata. Vita in Vierling E. 2005. Heat stress pheno- Campagna 5: 42-43. types of Arabidopsis mutants impli- Nicole R. 1959. New testament use of the cate multiple signaling pathways in old testament, pp. 137-151. In: Henry the acquisition of thermotolerance. C.F.H. (ed.). Revelation and the bible Plant Physiology 138: 882-897. - contemporary evangelical thought. Lee S.K, Kader A.A. 2000. Preharvest The Tyndale Press. Grand Rapids: and postharvest factors influencing Baker Book House, London. vitamin C content of horticultural Nishikimi M., Fukuyama R., Minoshima crops. Postharvest Biology and S., Shimizu N., Yagi K. 1994. Clon- Technology 20: 207-220. ing and chromosomal mapping of Linster C.L., Clarke S.G. 2008. L- the human nonfunctional gene for Ascorbate biosynthesis in higher L-gulono-gamma-lactone oxidase, plants: the role of VTC2. Trends in the enzyme for L-ascorbic acid bio- Plant Science 13: 567-573. synthesis missing in man. Journal of Loewus F.A. 1999. Biosynthesis and Biological Chemistry 269: 13685- metabolism of ascorbic acid in plants 13688. and of analogs of ascorbic acid in Noctor G., Foyer C.H. 1998. Ascorbate fungi. Phytochemistry 52: 193-210. and glutathione: keeping active ox- Martín J.P., Sánchez-Yélamo M.D. 2000. ygen under control. Annual Review Genetic relationships among species of Plant Physiology and Plant Mo- of the genus Diplotaxis (Brassica- lecular Biology 49: 249-279. ceae) using inter-simple sequence Padulosi S. 1995. Rocket genetic re- repeat markers. Theoretical and Ap- sources network. International Plant plied Genetics 101: 1234-1241. Genetic Resources Institute, Lisbon, Martínez-Laborde J.B. 1997. A brief Portugal, 13-15 November, 1994. account of the genus Diplotaxis, pp. Padulosi S., Pignone D. 1997. Rocket: a 13-22. In: Padulosi S. & Pignone D. Mediterranean crop for the world. (ed.). Rocket: a Mediterranean crop International Plant Genetic Re- for the world. International Plant sources Institute, Legnaro, Italy, 13- Genetic Resources Institute, 14 December, 1996.

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ROKIETTA JAKO ROŚLINA WARZYWNA: PRZEGLĄD

Streszczenie Młoda rokietta liściasta spożywana jest na całym świecie jako warzywo sałatko- we. Miesza się ją zazwyczaj z innymi młodymi warzywami liściastymi, takimi jak: szpinak i sałata, by otrzymać sałatkę typu mesclun. Rośliny rokietty stały się popularne ze względu na ich specyficzny smak i wygląd w sałatkach mieszanych. Istnieją dwa powszechnie spotykane rodzaje rokietty, które są uprawiane komercyjnie: gatunek wie- loletni – dwurząd wąskolistny (ang. perennial wall rocket) (Diplotaxis tenuifolia (L.) DC.) i gatunek jednoroczny – rokietta siewna (ang. garden rocket) (Eruca sativa Mill.). Popularność młodych roślin liściastych wzrosła w ostatnich latach ze względu na zapo- trzebowanie konsumentów na pożywne i łatwo dostępne produkty. Sektor sałatek z młodych liści stanowi już znaczącą część rynku warzyw liściastych i spodziewany jest dalszy rozwój w tym sektorze. Liście odmian uprawnych dwurządu wąskolistnego i rokietty siewnej wyhodowano tak, że są do siebie podobne, co pozwala na dostawę tego produktu przez cały rok. Pomimo tego, istnieje wiele różnic między tymi gatunka- mi, które mają wpływ na ich reakcje na czynniki abiotyczne w okresie wzrostu i prze- chowywania. Niniejszy artykuł ma na celu przedstawienie historycznego znaczenia, klasyfikacji botanicznej i techniki uprawy tych ważnych gospodarczo roślin.