Annals of Agricultural Science (2015) 60(1), 53–60
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Root anatomy of some species of Amaranthus (Amaranthaceae) and formation of successive cambia
A.A. El-Ghamery a, Ahmed M. Sadek a, Ola H. Abd Elbar b,* a Botany and Microbiology Department, Faculty of Science, Al-Azhar University, Cairo, Egypt b Agriculture Botany Department, Faculty of Agriculture, Ain-Shams University, Cairo, Egypt
Received 26 February 2015; accepted 15 March 2015 Available online 4 July 2015
KEYWORDS Abstract The root anatomy of 12 Amaranthus taxa (Amaranthaceae) was studied. The internal Amaranthus root anatomy; structures were evaluated as an anatomical character to clarify the taxonomic complexity in the Secondary thickening; genus. Transactions of young roots of the studied species showed no variations. While the old roots Anomalous cambium; examination revealed differences in the products of the secondary thickening and their distribution, Taxonomy also differences in the anomalous cambium products were detected. Twelve characters with 26 char- acter stats were used to generate anatomical key using the DELTA key-generating programs. ª 2015 Production and hosting by Elsevier B.V. on behalf of Faculty of Agriculture, Ain Shams University. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).
Introduction known to be a taxonomically difficult group (Joshi and Rana, 1991) and the taxonomy of this genus has been confused The genus Amaranthus consists about 60–70 species (Costea by extremely wide range of phenotypic plasticity among and DeMason, 2001) includes many widely dispersed, econom- species and by the possible introgression involving weedy ically important species. The grain amaranths are ancient and crop species (Hauptli and Jain, 1978, 1984). Correct crops with increasing prospects as potential food and feed identification of Amaranthus weed species is important for effi- resources because of their high grain protein and starch quality cient weed control (Horak et al., 1994; Sweat et al., 1998). and high-nitrogen, highly digestible vegetative tissues Carlquist (2003) studied the stem of seven species of six (Cai et al., 1998a,b). Also, the family Amaranthaceae includes genera of Amaranthaceae, one species of genus Amaranthus some of the more prominent and aggressive annual weeds in (A. caudatus). Hong et al. (2005) studied the leaf anatomy of the Mideast (Wax, 1995). However, the genus Amaranthus is Amaranthus tricolor. Carlquist (2003) studied the root anatomy of Amaranthus caudatus. A little information on the pattern of secondary growth and the structure of the successive cambia in the old roots of Amaranthus was reported; for this * Corresponding author. reason the present study aims to elucidate the root anatomy E-mail addresses: [email protected], olhussein@yahoo. com (O.H. Abd Elbar). of some Amaranthus species. The structure of roots could help in defining the similarities among the genus and provide facil- Peer review under responsibility of Faculty of Agriculture, Ain-Shams University. ities in correct identification. http://dx.doi.org/10.1016/j.aoas.2015.03.001 0570-1783 ª 2015 Production and hosting by Elsevier B.V. on behalf of Faculty of Agriculture, Ain Shams University. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 54 A.A. El-Ghamery et al.
Table 1 Species and accessions of Amaranthus used in this study. No. Species Accession no. Origin Subgenus Habitat 1 A. albus L. 0022453 Germany Albersia Wild 2 A. blitum L. 0006563 France Albersia Cultiv. 3 A. caudatus L. 0003919 Unknown Amaranthus Wild 4 A. deflexus L. 0020275 Italy Albersia Cultiv. 5 A. dubius Mart. ex Thell. 0006574 Colombia Albersia Wild 6 A. graecizans L. 0020242 Portugal Amaranthus Wild 7 A. hybridus L. 0019657 Bolivia Amaranthus Wild 8 A. powellii S. Watson. 0030999 France Amaranthus Wild 9 A. retroflexus L. 0008394 Italy Amaranthus Wild 10 A. spinosus L. 0017882 Unknown Amaranthus Wild 11 A. tricolor L. – Egypt Amaranthus Cultiv. 12 A. x ozanonii Thell. 0008383 Unknown Amaranthus Cultiv. Cultiv. = Cultivated, – = unknown.
12
100µm 100µm
Sg Sg
R R 3 4
100µm 100µm
Figs. 1–4 (1) T.S. of the primary root of A. tricolor shows the common structure of the seedling root of the studied species. (2) T.S. of A. blitum root shows the beginning of the secondary thickening. (3) T.S. of A. dubius mature root reveals the massive secondary growth distributed in two groups with long-narrow parenchymatous ray. (4) T.S. of A. deflexus mature root shows the few secondary thickening with short, wide parenchymatous ray. R = Ray, Sg = Secondary growth.
Material and methods To examine the root structure five root segments (with length of 2–5 mm) at seedling and flowering stages adjacent Seeds of Amaranthus accessions were supplied by the Royal to lateral roots area were immediately fixed in FAA Botanic Garden at Kew, London, UK, while one taxon was (Formalin Acetic Acid). The schedule of paraffin method selected from one of the Botanic Gardens in Egypt. Twelve described by Johansen (1940) was followed. Serial transverse species of genus Amaranthus were used in this study sections (10–20 lm in thickness) were cut with a steel blade (Table 1). All the plants grown for study originated as seeds on IHC World KD-1508A rotary microtome and fixed on from open-pollinated plants. slides by means of Haupt’s adhesive. The sections were stained Root anatomy of some species and formation of successive cambia 55 with a safranin–fast green combination, and then mounted in endodermal cells appear slightly thickened with the Canada balsam (Sass, 1961). Observation: photomicrographs Casparian strips. The vascular cylinder is surrounded by a were achieved using XSZ-N107 Research Microscope fitted uniseriate thin walled wide pericycle and composed of two with Premiere MA88-900 digital camera. For microscopic exarch primary xylem strands alternating with two primary measurements ImageJ (ver. 1.49o) program standard in scien- phloem ones. Transection of Amaranthus tricolor was selected tific image analysis was used (software) and calibrated by using to represent the common structure of the primary stage in the a standard stage micrometer slide. Each recorded measure- root (Fig. 1). ment is the average of ten measurements. The secondary growth (at flowering stage) originates from two cambial strands arise on the inner edge of the primary Numerical analysis phloem. Subsequently, the pericycle cells outside the pro- toxylem poles begin to divide tangentially and constitute few Various data obtained from the description of the root anat- layers. The inner layer of the pericyclic derivatives contacts omy were subjected to automated key generation using version with the previous cambial strands. Then a complete cambial 4.12 of the DELTA suite of program (Dallwitz et al., 2000). cylinder has been developed. The vascular cambium continues to divide periclinally. The daughter cells that result from these divisions differentiate into secondary xylem cells if they divide Results off toward the inside of the root or secondary phloem cells if they divide toward the outer surface of the root. The later The examination of transverse sections of the young roots (at forces the primary one outwardly and becomes obliterated. seedling stage) of the studied species revealed that all species Transverse section of Amaranthus blitum (Fig. 2) represents (12) have the same general structure which consists of the com- this stage. As the dividing activity of the vascular cambium mon tissues, i.e., an epidermis, the cortex and the vascular increases the pericyclic cells undergo periclinal and anticlinal cylinder. The epidermis consists of narrow tangential cells with divisions around the circumference of the root. These divisions thin walls. The cortex is constructed of five layers of thin- cause an increase of the number of pericyclic derivative layers. walled, isodiametric or polygonal parenchyma with small Phellogen initiates from the outer row of the pericyclic intercellular spaces. The average thickness of the cortex derivatives. It produces 2–4 layers of phellem toward the reaches 50 lm. The innermost cortical cells, i.e., the surface while phelloderm was absent (Figs. 3 and 4). The
R
5 6
100µm 100µm
7 8
100µm 100µm
Figs. 5–8 (5) Magnification of the secondary growth divided into four groups in A. spinosus with thin parenchyma. (6) Magnification of the secondary growth divided into six groups in A. retroflexus with lignified parenchyma. (7) Magnified portion from the mature root of A. deflexus shows starch grains storage material. (8) Magnified portion from the mature root of A. dubius shows sandy cell. R = Ray. 56 A.A. El-Ghamery et al.
9 10
100µm 100µm
11 12
100µm 100µm
Figs. 9–12 (9 and 10) T.S. of A. caudatus root with magnified portions previews the initiation of the anomalous cambium from the pericyclic derivatives. (11 and 12) Magnified portion of A. caudatus root reveals the differentiation of the anomalous cambium products. accompanied increase in thickness of vascular tissues forces the divisions to form a wide band of cells. The transection of A. cortex outwardly and becomes ruptured. The periderm takes caudatus root showed this feature (Figs. 9 and 10). This band the role of protection. served as a site of the lateral meristem. The cells of the lateral In all the studied species of Amaranthus, the secondary meristem divided tangentially to produce conjunctive tissues growth of the old roots appeared as two groups of secondary and vascular cambium. The studied species varied in the distri- vascular tissues separated by two rays detected between them. bution, cell types and amounts of the conjunctive tissues as The amount of secondary vascular tissues (secondary phloem well the vascular cambium products. In most of the studied and secondary xylem) varied between the studied species. samples, the earliest cell divisions differentiate into thin walled Old roots of A. caudatus and A. dubius (Fig. 3) showed this parenchyma arranged radially in the innermost layers of the pattern by abundant or large products of secondary thickening first ring. This was followed by the differentiation of vascular which are mixed with thin parenchyma inwardly and few sec- cambium which divides into secondary phloem (with adjacent ondary phloem elements outwardly. So these secondary tissues parenchyma) outwardly, secondary vessels (solitary, pairs or constitute large portion of the old roots, while in the remaining clusters in radial chains) inwardly and then all are embedded species the old roots have constringent or few secondary thick- in a background of thin walled parenchyma (Figs. 11–14). ening products. It could be observed by few elements of sec- However, A. graecizans, A. powellii, A. retroflexus and A. x ondary xylem and secondary phloem, differentiated by ozanonii show maximal lignified parenchyma of the old roots. limited activity of vascular cambium which ceases to divide In the first ring of A. powellii and A. retroflexus the innermost early. Root of A. deflexus revealed this in Fig. 4. derivatives were lignified cells with rare xylem elements. It was Anomalous successive cambia phenomenon was illustrated followed by many vessels arranged in solitary, pairs or clusters in all studied species and causes the appearance of concentric of three to four elements with few lignified parenchyma. The rings in the old roots. Successive cambia produce bands or vessel clusters arranged in a radial direction and separated strands of secondary phloem and secondary xylem (vascular with wide zone of thin parenchyma cells ‘‘conjunctive tissue’’. increments), which are embedded in conjunctive tissues of par- The outermost part of the first anomalous ring is consisting of enchyma or fibers. In all the studied roots the first ring of the few phloem elements (Fig. 15). While in A. graecizans and A. x anomalous cambium developed from the pericyclic derivatives ozanonii the xylem vessels and phloem elements are completely outside the secondary phloem which produced by the normal embedded in a lignified parenchyma (Fig. 16), idioblasts con- secondary thickening. Prior to the initiation of the first ring, tain sand crystals or sometimes starch grains are common in these pericyclic derivative cells underwent repeated periclinal conjunctive tissue parenchyma. The formation of subsequent Root anatomy of some species and formation of successive cambia 57
13 14
100µm 100µm
15 16
100µm 100µm
Figs. 13–16 (13) Magnified part of A. dubius root shows the presence of thin and lignified parenchyma in the anomalous products and the formation of the successive cambia from the phloem parenchyma of the first anomalous ring. (14) Magnified portion of A. x ozanonii reveals the presence of lignified parenchyma only in the anomalous products. (15) T.S. of A. retroflexus root previews the lignified parenchyma at the innermost portion of the first anomalous ring and the distribution of xylem vessels (solitary, pairs or clusters) in radial way. (16) T.S. of A. x ozanonii root shows the continuous lignified parenchyma. cambia initiates from the parenchyma of the anomalous growth, the initiation of the anomalous cambium, the products phloem and followed a similar pattern of development of these successive anomalous cambia within the genus (Fig. 13). Amaranthus and to use this information to determine whether Observations of the old roots noticed two thin parench- they provide additional perspectives on the taxonomic prob- yma rays separate between the two mentioned groups of lems within the genus. The primary root vascular cylinder secondary thickening and reach to the protoxylem poles. showed full similarity in the populations studied (diarch). In A. albus, A. hybridus, A. powellii and A. spinosus these These results are identical to that reported by Kraehmer two rays were narrow in width (50–150 lm) and may not (2013). The normal secondary growth corresponded with that extend radially, A. spinosus revealed that in (Fig. 5). This found in the roots of most dicotyledons. It originates from two feature represented in the T.S. of the root of A. deflexus cambial strands arise on the inner edge of the primary phloem (Fig. 4). There are additional ray plates of parenchyma and subsequently, produces two groups of secondary vascular within the mentioned vascular groups and they make it tissues (secondary xylem and phloem) separated by two rays split into smaller groups of secondary xylem and phloem. detected between them. In addition few protected layers initi- These rays did not reach to the protoxylem poles (Figs. 5 ate from the outer row of the pericyclic derivatives. The num- and 6). Sometimes, the ray parenchyma cells contain sand ber and arrangement of the secondary tissues in the old roots crystals (Fig. 8) or starch grains (Fig. 7). The presence or are variable in the studied taxa. These results can be used to absence of each different character was treated and binary distinguish between the species studied. The first anomalous characters in data matrix i.e. coded 1 and 0 respectively cambial ring initiated from the pericyclic derivatives and there (Table 2). has been general agreement about this from Fahn and Zimmermann (1982), Kirchoff and Fahn (1984), and Discussion Carlquist (2003, 2007). Observations of successive cambia in old roots of Amaranthus have highly taxonomic value. This The objectives of this study were to look at the range of vari- phenomenon is present in Amaranthaceae and is considered ation of root structural characters including: the primary root to be a characteristic feature of the family (Fahn and vascular cylinder and the products of normal secondary Zimmermann, 1982; Carlquist, 2001). In Amaranthus deflexus, 26.three rings/ present (1), Absent (0). 12.Number of 26.three rings/25.two present rings/ (1), Absentpresent (0).(1), Absent (0). 12.Number ofanomalous rings 25.two rings/ present (1), Absent (0). anomalous rings 24.one ring/ present (1), Absent (0). 11.Storage24.one ring/ present23.Sand (1), crystals/ Absent present (0). (1), Absent (0).
A.A. El-Ghamery et al. 11.Storage materials23.Sand crystals/22.Starch/ present present (1), Absent (1), Absent (0). (0). materials 10.Distribution22.Starch/ of present 21.at (1),the Absentinnermost (0). part of the ring/ present (1), Absent (0). 10.Distributionthe oflignified 21.at the innermost20.between part of xylem the ring/ vessels/ present present (1), (1),Absent Absent (0). (0). parenchyma in the lignified 20.between xylem vessels/ present (1), Absent (0). parenchymathe in anomalous 19.in a continuous ring/ present (1), Absent (0). the anomalous 19.in a continuous18.Thin ring/ and present lignified (1), parenchyma/ Absent (0). present (1), Absent (0). 9.Anomalous 18.Thin and lignified17. Lignified parenchyma/ parenchyma present only/ (1), present Absent (1), (0). Absent (0). 9.Anomalouscambium 17. Lignified parenchyma only/ present (1), Absent (0). cambium products 16.Thin parenchyma only/ present (1), Absent (0). products 16.Thin parenchyma only/ present (1), Absent (0). 8.Anomalous 15.pericyclic derivatives/ present (1), Absent (0). 8.Anomalouscambium origin 15.pericyclic derivatives/ present (1), Absent (0). cambium origin7.Medullary ray 14.. Long (over 180 µm)/ present (1), Absent (0). 7.Medullary lengthray 14.. Long (over13. 180 Short µm)/ (up present to 180 (1), µm)/ Absent present (0). (1), Absent (0). length 13. Short (up to 180 µm)/ present (1), Absent (0). 6.Medullary ray 12.Narrow (till 150 µm)/ present (1), Absent (0). 6.Medullary widthray 12.Narrow (till11.Wide 150 µm)/ (over present 150 µm)/(1), Absent present (0). (1), Absent (0). width 5.Distribution11.Wide of(over 150 µm)/ present (1), Absent (0). 5.Distributionlignified of 10. In the ray & between secondary xylem vessels/ present (1), Absent (0).
lignified Characters Root parenchyma10. In thein ray & between secondary xylem vessels/ present (1), Absent (0).
Root Characters Root parenchymathe in secondary 9. between secondary xylem vessels only/ present (1), Absent (0). thickening the secondary 9. between secondary xylem vessels only/ present (1), Absent (0). thickening 8. Thin and lignified parenchyma/ present (1), Absent (0). 4.Secondary 8. Thin and lignified parenchyma/ present (1), Absent (0). 4.Secondary thickening 7. Lignified parenchyma only/ present (1), Absent (0). 7. Lignified parenchyma only/ present (1), Absent (0). thickening products 6. Thin parenchyma only/ present (1), Absent (0). products 6. Thin parenchyma only/ present (1), Absent (0). 3.Arrangement of 5. More than two/ present (1), Absent (0). 3.Arrangementsecondary of 5. More than two/ present (1), Absent (0). secondary thickness 4. Two groups/ present (1), Absent (0). 4. Two groups/ present (1), Absent (0). thickness 2.Ratio of 3. More than 7 %/ present (1), Absent (0). 2.Ratio of secondary3. More xylem than 7 %/ present (1), Absent (0). 2. Range from1–7 %/ present (1), Absent (0). secondary xylemto the section to the section 2. Range from1–7 %/ present (1), Absent (0). 1.primarry root 1. Diarch present (1), Absent (0).
Data1.primarry matrix of the observed characters in the different species. The following data-matrix based on tenroot characters with 26 1. Diarch present (1), Absent (0). 111001001100110100101001100 211010001101010101010001010 310110001100101100101001100 411010100001010110000011100 510110001101001100101001010 611010001101010101010001010 711001001010110100101001100 811001010010110100100101100 911001010011010100100101100
Characters Character Stats Species 10 111 1 0 112 0 1 1 1 0 0 0 01 1 1 1 0 0 1 01 0 1 0 0 10 01 10 1 0 1 10 01 0 0 1 01 0 00 10011 10 10 0 1 01 0 00 10011 0 10 1 01 00010 111001001100110100101001100 211010001101010101010001010 310110001100101100101001100 411010100001010110000011100 510110001101001100101001010 611010001101010101010001010 711001001010110100101001100 811001010010110100100101100 911001010011010100100101100
Characters Character Stats Species 10 111 1 0 112 0 1 1 1 0 0 0 01 1 1 1 0 0 1 01 0 1 0 0 10 01 10 1 0 1 10 01 0 0 1 01 0 00 10011 10 10 0 1 01 0 00 10011 0 10 1 01 00010 Table 2 character stats of the root anatomy, the species arranged (1–12) as mentioned in material and method. 58 Root anatomy of some species and formation of successive cambia 59
the old root has two small groups of secondary growth and the suggests optimal mechanical strength. Even the rays in these most of the products of the anomalous cambia were storage genera contribute to mechanical strength by having secondary parenchyma with few vessel elements (Fig. 4). The alternation walls. Carlquist (2002) observed that the vascular cambia of of vascular increments with parenchyma provided by the suc- Charpentiera (Amaranthaceae) produce radial rows of vessels cessive cambial mode of construction offers an ideal histolog- as well as associated fibers. The occurrence of fibers alongside ical plan for storage and retrieval of photosynthesis and water. vessels by the vascular cambium assures increase in mechanical That could be correspondent to the roots of Beta strength as well as prolonging the activity of the vascular path- (Artschwager, 1926) and Mirabilis (Mikesell and Popham, ways formed earlier. Unfortunately, the root characters of the 1976) which have thin cylindrical vascular increments spaced three abovementioned species were full similar. A. powellii and from each other by relatively wide zones of parenchyma. In A. retroflexus were clearly different from the other species by both genera, more recent vascular increments lack vessels, producing numerous lignified layers in the innermost portion although vessels do eventually differentiate in earlier-formed by the anomalous cambium activity. These results partially vascular increments. This seems clearly correlated with adapta- are compatible with the results of Wassom and Tranel tion to photosynthate storage and retrieval rather than water (2005), where they placed the two species of A. powellii and storage. The old roots of A. graecizans, A. x ozanonii, and A. A. retroflexus with A. hybridus together in the same group blitum species have slender of vascular increments embedded based on molecular genetic cluster analysis. The species A. cau- in a continuous background of fibers. This configuration datus and A. dubius are similar which aggregated with Afify 60 A.A. El-Ghamery et al.
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