Distribution of Minerals in Young and Mature Leaves of Different Leaf Vegetable Crops Cultivated in a Field

Home , Glebionis coronaria, Komatsuna, Leaf vegetable

Open Journal of Plant Science

Toshihiro Watanabe1*, Eriko Maejima1, Research Article Masaru Urayama1, Masako Owadano1, Aiko Yamauchi1, Ryosuke Okada1, Takuro Shinano2 and Mitsuru Osaki1 Distribution of Minerals in Young 1Research Faculty of Agriculture, Hokkaido University, Kita-9, Nishi-9, Kitaku, Sapporo, and Mature Leaves of Different Leaf 0608589, Japan 2Agricultural Radiation Research Center, NARO Vegetable Crops Cultivated in a Field Tohoku Agricultural Research Center, 50 Aza Harajyukuminami, Arai, Fukushima, 9602156, Japan Abstract Dates: Received: 02 May, 2016; Accepted: 17 May, At least 17 elements are known to be essential for plants; however, plants also absorb and 2016;Published: 18 May, 2016 accumulate various nonessential elements. Plants re-translocate different elements, including essential and nonessential elements, with differing efficiencies from mature to young developing organs via *Corresponding author: Dr. Toshihiro the phloem transport, resulting in different distributions of minerals in these organs. Therefore, in this Watanabe, Research Faculty of Agriculture, study, we analyzed the concentrations of 23 elements in young and mature leaves of different leaf Hokkaido University, Kita-9, Nishi-9, Kitaku, vegetable crops to comprehensively understand the mineral dynamics in plants. The allocation profiles Sapporo, 0608589, Japan, Tel: +81-11- of minerals in leaves of varying ages differed among species. For example, a higher molybdenum 706-2498; Fax: +81-11-706-2498; E-mail: allocation profile was observed in young crown daisyGlebionis ( coronaria) leaves, which might be related to the efficient nitrate assimilation in young leaves of this species. Thus, this study provides a www.peertechz.com new insight into the mineral uptake and transport mechanisms in plants.

Keywords: Minerals; Ionome; Leaf; Bok choy; Komatsuna; Turnip; Crown daisy this study, we analyzed the concentrations of 23 elements in young and mature leaves of different leaf vegetable crops and attempted to Introduction examine whether there was a phylogenetic influence on the elemental distribution profile and elemental concentration profile in leaves. To date, 17 elements have been recognized as essential for In this study, we selected the leaf vegetable crops because we could plants [1]. However, soil contains various nonessential and essential obtain plants of uniform size during field cultivation and their plant elements, and plants growing in fields absorb and accumulate both the type was suitable for collecting leaves of varying ages. elements. The accumulation of minerals in plants is largely affected by genetic variation and growth environment [2,3]. In particular, Materials and Methods compared with normal plants, specific plant species, known as Cultivation hyperaccumulators, accumulate extremely high concentrations of In 2012, four vegetable crop species/varieties were cultivated nonessential or trace elements, including aluminum (Al), sodium in an experimental field of the Hokkaido University, Japan. For (Na), silicon, and heavy metals, in their above-ground organs [4-6]. all cultivations, N, P, and K fertilizers were uniformly applied as Minerals are transported via the xylem and phloem vascular −1 ammonium sulfate (140 kg N ha ), superphosphate (130 kg P2O5 systems in plants. Essential elements are re-translocated from old or −1 −1 ha ), and potassium sulfate (100 kg K2O ha ), respectively. For mature organs to young developing organs via the phloem transport each species/variety, two different commercial cultivars were used. to increase their efficiency of use1 [ ]. However, the mobilities of Seeds of bok choy (Brassica rapa var. chinensis cv. Fuyushomi and essential elements in the phloem differ among elements. For example, cv. Shikizanmai), komatsuna (B. rapa var. perviridis cv. Shoten and the mobilities of nitrogen, potassium (K), phosphorus (P), sulfur (S), cv. Hitomikomatsuna), turnip (B. rapa var. rapa cv. Taibyohikari and magnesium (Mg) are high, whereas those of calcium (Ca) and and cv. Fukukomachi), and crown daisy (Glebionis coronaria cv. manganese (Mn) are low [1]. Moreover, some nonessential elements Kiwamechuba and cv. Chubashingiku) were sown on June 14 in the were found in high concentrations in the phloem sap [7,8]. field. General properties of the field soil are detailed in a previous Ionomics is the study of the accumulation of all metals, metalloids, study [3]. All species used in this study have similar growth rate, and and nonmetals (ionome) in living organisms [9]. Ionomics aims to are usually cultivated in this prefecture during spring to autumn. systematically profile all elements found in a certain organism and Young and mature leaves were sampled on July 23, with three considers the genetic links among the elements, thereby providing replicates from at least three plants each. The row and hill spacing insight into the functional status of a complex biological organism. used was 13 × 13 cm. Leaf samples were dried in an oven at 70°C for Moreover, ionomics can be applied to the study of the phylogenetic 72 h and ground with a vibrating sample mill (TI-100; CMT, Saitama, influence on mineral accumulation. Our previous broad survey of Japan) for mineral analysis. various plant species investigated higher-level phylogenetic effects Mineral analysis that influenced the leaf composition of a wide range of elements [10]. However, the ionome profile of leaves may not be constant and Plant samples were digested in 2 mL of 61% (w/v) HNO3 (EL may change with leaf senescence as described above. Therefore, in grade; Kanto Chemical, Tokyo, Japan) at 110 °C in a DigiPREP

Citation: Watanabe T, Maejima E, Urayama M, Owadano M, Yamauchi A, et al. (2016) Distribution of Minerals in Young and Mature Leaves of Different Leaf Vegetable Crops Cultivated in a Field. Open J Plant Sci 1(1): 005-009. 005 Watanabe et al. (2016)

6 apparatus (SCP Science, QC, Canada) for approximately 2 h until Bok choy 1 the solution had almost disappeared. After the samples had cooled, Bok choy 2 4 Komatsuna 1 0.5 mL H2O2 (semiconductor grade; Santoku Chemical, Tokyo, Komatsuna 2 2 Crown daisy 1 Japan) was added, and the samples were heated at 110 °C for a further Crown daisy 2 20 min. Once digestion was complete, the tubes were cooled and Turnip 1 0 Turnip 2 made up to a volume of 10 mL by adding 2% (w/v) HNO3 in Milli-Q PC2 (16.8%) water. The concentrations of the following elements were measured -2 Q%J$ using inductively coupled plasma-mass spectrometry (ELAN DRC-e;

-4 Perkin Elmer, Waltham, MA, USA): lithium (Li), boron (B), Na, K, -4 -2 0 2 4 6 chromium (Cr), cobalt (Co), nickel (Ni), arsenic (As), molybdenum PC1 (45.7%) (Mo), cadmium (Cd), Mg, Al, P, Ca, Mn, iron (Fe), copper (Cu), zinc 0.6 (Zn), strontium (Sr), barium (Ba), and cesium (Cs). Li 0.4 Fe Mg Mn Statistical analyses Co Cs As 0.2 Mo Ba Al All statistical analyses were performed using the Sigmaplot 11.0 Sr Cr Ni V Zn 0.0 Ca Cu B Cd (Systat Software, Inc., San Jose, CA, USA) and Minitab 14 (Minitab Na Rb Inc., State College, PA, USA) softwares. PC2 (16.8%) -0.2 P

K -0.4 Results and Discussion

-0.6 First, we comprehensively compared the characteristics of -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 element accumulation in leaves by comparing the ionomes of young PC1 (45.7%) and mature leaves among species, varieties, and cultivars using the principal component analysis (PCA). PCA provides a dimension Figure 1: Principal component analysis (PCA) of elements in the young leaves reduction method for ionome data and is widely used in ionomics [11]. of plants analyzed in this study. Scores on PC1 and PC2 with all elements included (A) and the corresponding loading plot (B). Bok choy 1: cv. Fuyushomi, The PCA scores were then presented according to the combinations Bok choy 2: cv. Shikizanmai, Komatsuna 1: cv. Shoten, Komatsuna 2: cv. of PC1 and PC2. In the score plots of both young and mature leaves, Hitomikomatsuna, Turnip 1: cv. Taibyohikari, Turnip 2: cv. Fukukomachi, Crown Brassicaceae (bok choy, komatsuna, and turnip) and Asteraceae daisy 1: cv. Kiwamechuba, and Crown daisy 2: cv. Chubashingiku. (crown daisy) were separately plotted along PC1 (Figures 1,2, both significant atP < 0.01, Student’s t-test). Moreover, different varieties of 4 Bok choy 1 B. rapa were separately plotted along PC2, and a significant difference Bok choy 2 2 Komatsuna 1 (P < 0.05, Tukey’s multiple comparison test) between turnip and the Komatsuna 2 other B. rapa varieties was observed. These differences in PC2 might 0 Crown daisy 1 Crown daisy 2 be because of their phylogenetic distance [12]. Differences in the Turnip 1 -2 Turnip 2 ionome profile between two different commercial cultivars were small PC2 (15.9%) for all species/varieties (Figures 1,2, closed and opened symbols). The -4 : %`V loading plot shows which variables (element concentrations) had

-6 the greater discriminating power to each PC1 and PC2. Results of -6 -4 -2 0 2 4 6 8 loading plots for both young and mature leaves indicated that the PC1 (56.3%) concentrations of Ca, Sr, Ba, and Mo negatively contributed, whereas 0.6 those of many other elements positively contributed to the PC1 score 0.4 K (Figures 1,2). The concentrations of elements with higher negative (Ca, Sr, Ba, and Mo) or positive (Na, Ni, Cu, and As) contributions Rb 0.2 P B V Al to PC1 are shown in Figure 3. As expected, Ca, Sr, Ba, and Mo Mo Cr Na 0.0 Cd Ca As Ba Zn concentrations were higher in Brassicaceae, whereas Na, Ni, Cu, and Sr Cu

PC2 (15.9%) -0.2 Cs Ni as concentrations were higher in crown daisy. Because Ca, Sr, and Mg Mn Fe Ba are homologous elements, the same absorption and transport -0.4 Li Co mechanisms may be involved in the accumulation of these elements. -0.6 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 In the following step, the young/mature ratio of the leaf PC1 (56.3%) concentration of each element was calculated. These ratios were then used as variables for PCA. The score plot of these ratios revealed a Figure 2: Principal component analysis (PCA) of elements in the mature clear significant separation between Brassicaceae and crown daisy leaves of plants analyzed in this study. Scores on PC1 and PC2 with all (Figure 4, P < 0.01, Student’s t-test), suggesting that the allocation elements included (A) and the corresponding loading plot (B). Bok choy 1: cv. Fuyushomi, Bok choy 2: cv. Shikizanmai, Komatsuna 1: cv. Shoten, Komatsuna profiles of minerals in leaves of varying ages are also phylogenetically 2: cv. Hitomikomatsuna, Turnip 1: cv. Taibyohikari, Turnip 2: cv. Fukukomachi, influenced. Minerals are transported from mature leaves (source) to Crown daisy 1: cv. Kiwamechuba, and Crown daisy 2: cv. Chubashingiku. young leaves (sink, newly developing tissue) via the phloem along

50 10 ) ) -1 40 Ca -1 8 Na

30 6

20 4

10 2 Concentration (mg g (mg Concentration g (mg Concentration 0 0 0.18 0.0030

) 0.16 ) -1 Sr -1 0.0025 Ni 0.14 0.12 0.0020 0.10 0.0015 0.08 0.06 0.0010 0.04 0.0005

Concentration (mg g Concentration 0.02 (mg g Concentration 0.00 0.0000 0.06 0.008 ) )

-1 0.05 Ba -1 Cu 0.006 0.04

0.03 0.004

0.02 0.002 0.01 Concentration (mg g Concentration (mg g Concentration 0.00 0.000 0.0020 0.0007

) 0.0018 ) 0.0006 -1 0.0016 Mo -1 As 0.0014 0.0005 0.0012 0.0004 0.0010 0.0008 0.0003 0.0006 0.0002 0.0004 0.0001 Concentration (mg g Concentration 0.0002 (mg g Concentration 0.0000 0.0000 Turnip 1 Turnip 2 Turnip Turnip 1 Turnip 2 Turnip Bok choy 1 choy Bok 2 choy Bok 1 choy Bok 2 choy Bok Komatsuna 1 Komatsuna 2 Komatsuna Komatsuna 1 Komatsuna 2 Komatsuna Crown daisy 1 daisy Crown 2 daisy Crown Crown daisy 1 daisy Crown 2 daisy Crown

Figure 3: Concentration of Ca, Sr, Ba, Mo, Na, Ni, Cu, and As in mature leaves of each plant. Bars represent ± SEs (n=3). Bok choy 1: cv. Fuyushomi, Bok choy 2: cv. Shikizanmai, Komatsuna 1: cv. Shoten, Komatsuna 2: cv. Hitomikomatsuna, Turnip 1: cv. Taibyohikari, Turnip 2: cv. Fukukomachi, Crown daisy 1: cv. Kiwamechuba, and Crown daisy 2: cv. Chubashingiku. with the translocation of photosynthates [1]. However, as described essential element in the phloem [1], indicating that the young/mature in the Introduction, the mobilities of elements in the phloem sap ratio of the leaf concentration of the element can reflect its mobility in differ, which can be because of their different availability in source the phloem. The young/mature ratio of the leaf K concentration was cells and/or different efficiencies of phloem loading. These differences relatively low (Figure 5) and did not correspond with the mobility are possibly related to the different allocation profiles of minerals in the phloem [1]. This might be because of the high K supply from in leaves of varying ages as observed in this study. Transporters the xylem sap in mature leaves. In contrast, when comparing the and channels responsible for phloem loading of minerals have been young/mature ratio of the leaf concentration of each element between reported for some elements, such as K+ [13], phosphate [14], and Na+ Brassicaceae and crown daisy, several differences were found. The [15], but not for other elements, particularly nonessential elements. most remarkable difference was that the young/mature ratio of the leaf Mo concentration was much higher in crown daisy than in the When comparing the young/mature ratio of the leaf concentrations three varieties of Brassicaceae (Figure 5). One of the most important of each element among different varieties of Brassicaceae, the order roles of Mo is as a component of nitrate reductase. Pate [16], found and value of the ratio was almost the same among different varieties that the ratio of nitrate-N to total-N was very low (<20%) in radish (Figure 5). The order was partly correlated with the mobility of each (Brassicaceae), whereas this ratio was >50% in sunflower (Asteraceae).

4 Bok choy 1 2 Bok choy 2 Komatsuna 1 0 Komatsuna 2 Crown daisy 1 Crown daisy 2 -2 Turnip 1 Turnip 2

PC2 (22.8%) -4

-6 Q%J$LCR

-8 -6 -4 -2 0 2 4

PC1 (34.4%)

0.6 0.4 Ca Sr Mg Ba Cd Na 0.2 Mn Li As Mo 0.0 Cs B Fe K

PC2 (22.8%) Co Al V P Cu -0.2 Cr Zn Ni Rb

-0.4 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 PC1 (34.4%)

Figure 4: Principal component analysis (PCA) of the young/mature ratio in leaf concentration of each element analyzed in this study. Scores on PC1 and PC2 with all elements included (A) and the corresponding loading plot (B). Bok choy 1: cv. Fuyushomi, Bok choy 2: cv. Shikizanmai, Komatsuna 1: cv. Shoten, Komatsuna 2: cv. Hitomikomatsuna, Turnip 1: cv. Taibyohikari, Turnip 2: cv. Fukukomachi, Crown daisy 1: cv. Kiwamechuba, and Crown daisy 2: cv. Chubashingiku.

Bok choy Komatsuna Turnip Crown daisy

P P Cu Mo Cu Cs P P Cs Cu Cs Cu Cr Zn Cr Cs Zn Rb Rb Ni Rb Cr Zn Cr B B Ni Rb Mo Na Mo Zn Na Mo B Na K Ni K Cd Ni Mn Na B Co K Al Sr Mn Al Co Mg Mg Fe Fe Fe Cd Mg Mg K Fe Cd Mn Mn Al Co Cd Ca Ca Li V Co Sr Ca As Ba Li As Li Li As Sr Ca As Ba V Sr Al V Ba Ba V

0.0 0.5 1.0 1.5 2.0 0.0 0.5 1.0 1.5 2.0 2.5 0.0 0.5 1.0 1.5 2.0 2.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Young/Mature ratio Young/Mature ratio Young/Mature ratio Young/Mature ratio

Figure 5: Young/mature ratio in leaf concentration of each element in each plant species or variety. Bars represent ± SEs (n=6). Bok choy 1: cv. Fuyushomi, Bok choy 2: cv. Shikizanmai, Komatsuna 1: cv. Shoten, Komatsuna 2: cv. Hitomikomatsuna, Turnip 1: cv. Taibyohikari, Turnip 2: cv. Fukukomachi, Crown daisy 1: cv. Kiwamechuba, and Crown daisy 2: cv. Chubashingiku.

This may imply that crown daisy (Asteraceae) efficiently translocates 5. Ma LQ, Komar KM, Tu C, Zhang W, Cai Y, et al. (2001) A fern that Mo from mature leaves to newly developing leaves via the phloem to hyperaccumulates arsenic. Nature 409: 579. enhance its nitrate assimilation. 6. Shen ZG, Liu YL (1998) Progress in the study on the plants that hyperaccumulate heavy metal. Plant Physiol Commun 34: 133–139. Conclusion 7. Mendoza-Cóatl DG, Butko E, Springer F, Torpey JW, Komives EA, et Using ionomics, this study first demonstrated that the allocation al. (2008) Identification of high levels of phytochelatins, glutathione and cadmium in the phloem sap of Brassica napus. A role for thiol-peptides in profiles of minerals in leaves of varying ages differed among species. the long-distance transport of cadmium and the effect of cadmium on iron Moreover, we provided the possibility to estimate the efficiency translocation Plant J 54: 249-259. of mineral re-translocation via the phloem for each element by 8. Hocking PJ (1980) The composition of phloem exudate and xylem sap from comparing the ionome between developing and mature tissues. tree tobacco (Nicotiana glauca Grah). Ann Bot 45: 633-643. In the future, we can determine the mineral dynamics in plants in 9. Lahner B, Gong J, Mahmoudian M, Smith EL, Abid KB, et al. (2003) Genomic greater detail by comparing the ionome profiles between leaves scale profiling of nutrient and trace elements in Arabidopsis thaliana. Nat and other organs (e.g., fruit) or between different growth stages. Biotechnol 21: 1215-1221.

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