Drought stress is the main limiting factor in soybean production. However, no work has been done on how the application of a low dose of gamma rays could help to overcome water deficits during critical stages of soybean development. Gamma rays at a dose of 20 Gray (Gy) were applied to dry seeds of soybean before planting. Two levels of soil moisture (80% field capacity for well-watered control and 35% for drought-stressed treatment) were applied at pod initiation. Gamma irradiation increased biomass accumulation and seed yield in both treatments. It also increased the chlorophyll content, photosynthetic activity (14CO2 fixation) and leaf water potential and enhanced the enzyme activities of RuBPCase and PEPCase of control plants compared with drought-stressed plants. Gamma irradiation (20 Gy) increased the soluble sugars, protein and proline content and the activities of peroxidase and superoxide dismutase in drought-stressed soybean leaves. It also increased the chloroplast size, which was reduced by drought treatment, and rebuilt, to some extent, the chloroplast ultrastructure. However, it decreased the malondialdehyde concentration and the electrical conductivity of the leaves under drought stress. Overall, the results indicated that pre-treatment with gamma rays (20 Gy) to dry seeds of soybean before planting could be used to enhance drought tolerance and minimize the yield loss caused by water deficit.

Cadmium (100, 400 and 1000 µM CdCl 2 ) treatments resulted in the inhibition of root dry biomass, root elongation and increased Cd accumulation in wheat (Triticum aestivum L.) roots. Further, these treatments decreased relative water content, chlorophyll content, 14 CO 2 -fixation, activities of phosphoenolpyruvate carboxylase and ribulose-1,5-bisphosphate carboxylase and abscisic acid content while increased malondialdehyde, hydrogen peroxide and free proline contents. Chloroplast and root ultrastructure was also changed. Pretreatment of seeds with SA (500 µM) for 20 h resulted in amelioration of these effects.

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The effect of CdCl 2 (0-50 µM) on the growth, physiological parameters and leaf antioxidative enzymes of faba bean plants was studied in order to investigate the possible involvement of this metal in the generation of oxidative stress. In the roots and leaves of faba bean plants Cd produced a significant inhibition of growth, as well as a reduction in the transpiration rate, photosynthetic efficiency ( 14 CO 2 -fixation), ribulose-1,5-bisphosphate-carboxylase/oxygenase (Rubisco) activity and leaf pigment content, and an alteration in the nutrient status in booth roots and leaves. An increased level of free proline was also detected. The results suggest that the treatment of faba bean plants with CdCl 2 induced a concentration-dependent oxidative stress situation in the leaves, characterized by an accumulation of H 2 O 2 , as a result of the inhibition of the antioxidant enzymes glutathione reductase (GR) and catalase (CAT). These results point to the possible induction of leaf senescence by cadmium.