Understanding Abiotic Stress Tolerance Mechanisms in Soybean (Glycine max.): Physiological, Biochemical and Cellular Responses to Drought and Flooding Stress.

Abstract

Soybean (Glycine max) is a major oil crop representing 56 percent of world oilseed production with 33 percent of this being produced in the United States. The demand for oil crops will continue to rise with the increase in global population; thus creating a need to improve productivity and ensure sustainable yields under changing environmental conditions. Even though sources of drought (slow wilting) and flooding tolerance have been identified, the mechanisms involved are poorly understood. There is therefore a need to dissect different responses with an aim of understanding the mechanisms that confer tolerance to these abiotic stresses in soybean. The objectives of this study were to: (i) evaluate variation in ultrastructure of leaf cells under drought and flooding stress for selected soybean lines and (ii) quantify these variations and infer their role in drought and flooding tolerance. Ten soybean lines were selected for this study and grown under greenhouse conditions. At the V6 stage, the plants were subjected to drought and flooding stress for 19 and 14 days respectively. These results showed that drought and flooding were significantly decreased (P<0.0001) for all physiological traits (photosynthesis, stomatal conductance, transpiration rate, and chlorophyll content) in all lines. At the cellular level, there was significant variation in the number of starch granules and Plastoglobule among lines in response to drought and flooding stress. Chloroplast size was also affected by drought and flooding. The results also revealed clear differences in the integrity of the thylakoid and mitochondria.

Key words: Plastoglobules, Drought, Flooding, slow wilting, hormones, soluble sugars