Met

al(µ

g/g

shoo

tD

W)

Met

al(µ

g/g

shoo

tD

W)

P22-6

Mani Rajkumar・戴 清霞・○鈴木武志・藤嶽暢英・阿江教治（神大院農）

Combined application of plant growth regulators and metal chelatorsfor the improvement of heavy metal phytoextraction

The objective of this study is to evaluate the interactive effect of metalchelators and plant growth regulators on the biomass production and metalextraction by Zea mays and Sorghum bicolor.

Materials & Methods:20 d old plant seedlings weretransplanted into 500 g of metal spikedsoils (Cu-100 ppm; Zn-500 ppm; andCd-15 ppm) previously amended withEDTA or citric acid at theconcentrations of 5 mM kg-1 andallowed to grow in green housecondition (Z. mays – 60 d, S. bicolor -45d). The plant growth hormones,epibrassinolide (1 µM and 2.5 µM) andsalicylic acids (0.5 mM and 2 mM)were individually sprayed at five daysintervals until harvest. Each treatmentwas performed in triplicates. Aftergrowth, the plants were harvested andanalyzed for shoot fresh dry weightand metal accumulation (wet digestionand ICP-OES).

Application of EDTA or CA tometal contaminated soilsdecreased dry matter yield ofboth plants (Fig. 1). Theaddition of growth regulatorsincrease the shoot dry weight ofZ. mays and S. bicolor.However, plants treated with S1showed a maximum growthcompared with those plantstreated with B1 and B2. Forinstance shoot dry weight of theZ. mays was significantlyincreased by 24% and 97% withS1 and EDTA or CA treatment,respectively compared withthose treated with EDTA or CAalone. As for the S. bicolor, S1increased shoot dry weight by18% compared with thosetreated with CA alone.Previously, it has been reportedthat SA alleviated growthinhibition by metal toxicity inbarley and soybean (1,2).

Conclusion:

The present observations showed that the plant growth regulators application especially at the lower concentration of SAprotects the plants against the inhibitory effects of heavy metals and chelators. Although growth hormones treatment hadlittle influence on the accumulation of heavy metals in shoot system, it induced a larger biomass production. These resultssuggest that the addition of plant growth regulators might have some potential to improve chelate assisted phytoextractionin metal contaminated soils. Further combination experiments are required in order to gain insights into the mechanismsinvolved in heavy uptake using chelators and plant growth regulators.

References: (1) Metwally et al 2003 Plant Physiol 132272–281. (2) Drazic & Mihailovic 2005 Plant Sci 168 511–517. (3) Guo et al., 2007 Environ Pollut 2007 147 743–749.Abbreviations: B-Blank; M-Metal; EDTA- Ethylene-diaminetetraacetic acid; CA-Citric acid; S1- Salicylic acids(0.5 mM); S2- Salicylic acids (2 mM); B1- epibrassinolide(1 µM); B2- epibrassinolide (2.5 µM)

Fig.1. Plant growth

Fig. 2. Metal concentration in shoot of Z. mays Fig. 3. Metal concentration in shoot of S. bicolor

In this study, the metal concentration of shoots of both plants indicates that additionEDTA was more effective than CA in increasing the plant Cd, Cu and Zn concentrations ofshoot. In contrast, the addition of CA reduced the accumulation of Cu in the shoot tissues ofboth plants. The treatment S1 with EDTA increased the Cd and Cu accumulation in shoots of Z.mays by 14% and 20%, respectively compared with those treated with EDTA alone (Fig. 2).This may be due to the synergistic effects of salicylic acids and EDTA. In the case of S. bicolor,synergistic effect by the combination of EDTA and SA is not strong as compared with Z.mays, which may be due to the different uptake ability between two kinds of species under thetreatment (Fig. 3). Similarly, treatment of B1/B2 with CA did not greatly influence theaccumulation of heavy metals in the shoot systems of both plants.

Granite soil 500g

Crop (Zea mays andSorghum bicolor)

Spiked Heavy Meatl(Cu-100 ppm, Zn-500 ppm,and Cd-15 ppm)

Metal chelator(EDTA or citric acid)

Plant growth hormone(epibrassinolide orsalicylic acids)

Experimental design

Metal uptake by crops was calculated by shoot dry weight multiplied metal concentrationof crop shoot for consideration for phytoextraction ability of heavy metal. In the case of Cd,positive effect of heavy metal uptake was not shown by Z. mays and small (1.5 times lager ) byS. bicolor. In the case of Cu, the positive effect was not shown by S. bicolor and shown (2times larger) by Z. mays. In the case of Zn, the positive effect was shown in both plant (Z.mays: ten times larger uptake; S. bicolor: 1.2 times larger uptake). From these results, bestcombination of plant species, heavy metal, chelator and phytophormone will improve morethan ten times concentration of phytoextraction from contaminated soil.

Fig.5 Metal uptake by S. bicolorFig. 4 Metal uptake by Z. mays

Results: 2.Heavy Metal concentrations of Shoot

Results: 2.Heavy Metal concentrations of Shoot

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Results: 1.Yields of Shoot

Recently, Guo et al., (3) also reported that pretreatment of rice seeds with SAenhanced the antioxidant defense activities in Cd-stressed rice, thus enhancing Cdtolerance.

How to improve heavy metal (HM) phytoextraction ?

1.high contents of HM in the harvestable parts

Phytohormone

HMsoil

HM+Chelatorsoil

○×

Introduction:

2.Crops yield high biomass

Uptake HM which are hardlyabsorbed to soil constituent.

Metal chelator would be desorbedHM from soil constituents.

Crops shoul develop resistant to toxicity ofthe chelator and high concentration of HM

Phytochrome would facilitate growth ofthe crops.

Error bar show standard deviation. Different letter on error bar shows nosignificant difference (Tukey’s test p>0.05)

Error bar show standard deviation. Different letter on error bar shows nosignificant difference (Tukey’s test p>0.05)

Error bar show standard deviation. Different letter on error bar shows nosignificant difference (Tukey’s test p>0.05)

Error bar show standard deviation. Different letter on error bar shows nosignificant difference (Tukey’s test p>0.05)

Error bar show standard deviation. Different letter on error bar shows nosignificant difference (Tukey’s test p>0.05)

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