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Limited information is available on the role of brassinosteroids (BRs) in response of plants to nutrient deficiency. To understand the functions of BRs in response to iron deficiency, we investigated the effect of 24-epibrassinolide (EBR) on activities of ferric-chelate reductase (FCR), H+-ATPase, Ca2+-ATPase, nitrate reductase (NR), antioxidant enzymes, Fe and other minerals content and distribution, chlorophylls, soluble protein, free proline, reactive oxygen species, and malondialdehyde in peanut (Arachis hypogea L.) plants subjected to Fe deficiency (10-5 M Fe(III)-EDTA) with foliar application of EBR (0, 10-8, 5.0×10-8, 10-7, 5.0×10-7, and10-6 M). Results show that EBR increased Fe translocation from roots to shoots and increased Fe content in cell organelles. Activities of antioxidant enzymes increased and so the ability of resistance to oxidative stress was enhanced. As result of enhancement of H+-ATPase and Ca2+-ATPase activities, the inhibition of Fe, Ca, Mg, and Zn uptake and distribution was ameliorated. Chlorophyll, soluble protein, and free proline content also increased and consequently, chlorosis induced by Fe deficiency was alleviated. The results demonstrate that EBR had a positive role in regulating peanut growth and development under Fe deficiency and an optimal concentration appeared to be 10-7 M.

The interactive effects of salicylic acid (SA) and nitric oxide (NO) on alleviating cadmium (Cd) toxicity in peanut (Arachis hypogaea L.) were studied. Seedlings of two cultivars (Huayu 22 - a big seed type, and Xiaobaisha - a small seed type) were treated with 200 μM CdCl2 without or with 0.1 mM SA or 0.25 mM sodium nitroprusside (SNP, an NO donor). Results show that the Cd exposure depressed the plant growth of both the cultivars but more of Huayu 22 than of Xiaobaisha. Exogenous SA and NO alleviated Cd toxicity in both the peanut cultivars: they improved growth, chlorophyll content, photosynthesis, and mineral nutrition. Furthermore, exogenous SA or NO decreased oxidative stress by increasing activities of antioxidant enzymes and content of non-enzymatic antioxidants. Besides, in roots and leaves of both the cultivars, exogenous SA and NO increased Cd accumulation in the cell wall and decreased Cd distribution to organelles. In particular, the effect of SA+SNP was most obvious.

Hydroponics experiments were conducted to study the effects of sodium nitroprusside (SNP, a donor of NO) on lead toxicity in ryegrass (Lolium perenne L.) seedlings. When the ryegrass seedlings were grown in a nutrient solution containing 500 μM Pb2+ for two weeks, the plant biomass as well as net photosynthetic rate, transpiration rate, chlorophyll and carotenoid content of leaves decreased. The Pb stress also induced the production of superoxide anion (O2 .-) and hydrogen peroxide (H2O2), leading to malondialdehyde (MDA) accumulation. Furthermore, the activities of superoxide dismutase (SOD), peroxidase (POD), and ascorbate peroxidase (APX) decreased in the Pb-treated seedlings, but the catalase (CAT) activity increased. Additionally, the content of Cu in shoots and the content of K, Mg, Fe, and Zn in both shoots and roots decreased, but the content of Ca in shoots and roots increased under the Pb stress. Moreover, Pb accumulated mostly in roots, whereas a small quantity was translocated to shoots. However, the addition of 50, 100, and 200 μM SNP into the solution containing Pb increased the chlorophyll content and net photosynthetic rate, reduced Pb-induced oxidative damages, improved antioxidant enzyme activities, and inhibited translocation of Pb from roots to shoots. In particular, 100 μM SNP had the best effect on promoting growth of the ryegrass seedlings under the Pb toxicity. However, the application of 400 μM SNP had no obvious alleviating effect on Pb toxicity in the ryegrass seedlings.