Seed Germination Behavior, Growth, Physiology and Antioxidant Metabolism of Four Contrasting Cultivars under Combined Drought and Salinity in Soybean

Abstract

Drought and salinity stresses are persistent threat to field crops and are frequently mentioned as major constraints on worldwide agricultural productivity. Moreover, their severity and frequency are predicted to rise in the near future. Therefore, in the present study we investigated the mechanisms underlying plant responses to drought (5, 10 and 15% polyethylene glycol, PEG-6000), salinity (50, 100, and 150 mM NaCl), and their combination, particularly at the seed germination stage, in terms of photosynthesis and antioxidant activity, in four soybean cultivars, viz., PI408105A (PI5A), PI567731 (PI31), PI567690 (PI90), and PI416937 (PI37). Results showed that seed germination was enhanced by 10% PEG and decreased by 15% PEG treatments compared to the control, while seed germination was drastically decreased under all levels of NaCl treatment. Furthermore, combined drought and salinity treatment reduced plant height and root length, shoot and root total weights, and relative water content compared with that of control. However, the reductions were not similar among the varieties, and definite growth retardations were observed in cultivar PI5A under drought and in PI37 under salinity. In addition, all treatments resulted in substantially reduced contents of chlorophyll pigment, anthocyanin, and chlorophyll fluorescence; and increased lipid peroxidation, electrolyte leakage, and non-photochemical quenching in all varieties of soybean as compared to the control plants. However, proline, amino acids, sugars, and secondary metabolites were increased with the drought and salinity stresses alone. Moreover, the reactive oxygen species accumulation was accompanied by improved enzymatic antioxidant activity, such as that of superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase. However, the enhancement was most noticeable in PI31 and PI90 under both treatments. In conclusion, the cultivar PI31 has efficient drought and salinity stress tolerance mechanisms, as illustrated by its superior photosynthesis, osmolyte accumulation, antioxidative enzyme activity, and secondary metabolite regulation, compared to the other cultivars, when stressed.

Silicon Supplementation Alleviates the Salinity Stress in Wheat Plants by Enhancing the Plant Water Status, Photosynthetic Pigments, Proline Content and Antioxidant Enzyme Activities

“…Salt stress causes physiological, biochemical, and metabolic alterations in plants, resulting in poor crop production. Under high-stress conditions, the water uptake is restricted in the plants from the soil, affecting the water status of the whole plant [ 6 , 7 ]. A reduction in water uptake results in decreased stomatal conductance and increased transpiration and hinders cell growth [ 8 ].…”

Seed Priming with Chitosan Improves Germination Characteristics Associated with Alterations in Antioxidant Defense and Dehydration-Responsive Pathway in White Clover under Water Stress

“…It has been found that drought-tolerant alfalfa ( Medicago sativa L.) cultivar Xinmu No.1 accumulated lower H 2 O 2 and malondialdehyde (MDA) contents through activating SOD, CAT, POD, and APX activities during seed germination under drought stress [ 11 ]. In response to drought, better antioxidant capacity and less ROS accumulation in soybean ( Glycine max L.) seedlings were positively correlated with higher seed-germination rate [ 12 ]. Exogenous silicon could improve tomato ( Lycopersicon esculentum L.) seed germination in relation to enhanced antioxidant enzymes activities and reduced oxidative stress [ 13 ].…”

Analysis of Physiological Indicators Associated with Drought Tolerance in Wheat under Drought and Re-Watering Conditions

“…This disrupts photosynthesis, and can lead to an imbalance between the photochemical activity of PSII and the electrons required for the Calvin–Benson cycle, which results in the excess absorption of excitation energy and subsequent photoinhibition damage to the PSII reaction centers [ 31 ], and ultimately leads to a decrease in crop photosynthesis [ 32 ]. Numerous studies have shown that severe drought stress can significantly reduce the photosynthetic capacity of crops, which causes a decrease in the chlorophyll content and net saturated photosynthetic rate (Asat), G s , and Fv/Fm [ 33 , 34 , 35 , 36 ]. However, drought stress leads to an increase in NPQ, which is an extremely important photoprotection mechanism in plants that helps them to maintain photosynthesis and consume light energy absorbed in PSII of leaves in the form of thermal energy [ 37 ].…”