Location: Crop Genetics Research Unit
Title: Responses of nitrogen metabolism and seed nutrition to drought stress in soybean genotypes differing in slow-wilting phenotype Authors
Submitted to: Frontiers in Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 19, 2013
Publication Date: December 10, 2013
Citation: Bellaloui, N., Gillen, A.M., Mengistu, A., Kebede, H.A., Fisher, D.K., Smith, J.R., Reddy, K.N. 2013. Responses of nitrogen metabolism and seed nutrition to drought stress in soybean genotypes differing in slow-wilting phenotype. Frontiers in Plant Physiology. 4:498. Interpretive Summary: Drought stress is a major environmental factor that negatively impacts crop growth and development, leading to yield loss and poor seed quality. Breeding for drought tolerance is still a major challenge, and this is mainly because the physiological and biochemical mechanisms of the drought tolerance remain unknown due to the complexity of the slow-wilting characteristic and environmental interactions. Recent advances in soybean breeding have resulted in a soybean variety that exhibited drought stress tolerance characteristic under drought. This characteristic (trait) is called slow-wilting. To advance our understanding of the mechanisms that control drought tolerance, an investigation of the physiology and biochemistry of leaves and seeds of soybean genotypes differing in slow-wilting characteristic was conducted. It was found that under well-watered conditions, nitrogen metabolism and leaf and seed composition differed between genotypes due to genotypic differences. Under drought stress, nitrogen metabolism and leaf and seed concentrations of potassium, phosphorus, calcium, copper, sodium, and boron were higher in slow-wilting genotypes than the check genotypes. Seed protein, oleic acid, and sugars were higher in slow-wilting genotypes, and oil and linoleic and linolenic acids were lower in slow-wilting genotypes. This research demonstrated that potassium, phosphorus, calcium, copper, sodium, and boron may be involved in slow-wilting trait by maintaining homeostasis and osmotic (salt) regulation. Selecting for higher accumulations of these specific minerals in leaves and seed could help increase drought tolerance in soybean.
Technical Abstract: Recent advances in soybean breeding have resulted in genotypes that express the slow-wilting phenotype (trait) under drought stress conditions. The physiological mechanisms of this trait remain unknown due to the complexity of trait × environment interactions. The objective of this research was to investigate nitrogen metabolism and leaf and seed nutrients composition of the slow-wilting soybean genotypes under drought stress conditions. We hypothesized that slow-wilting genotypes possess physiological and nutritional tolerance mechanisms exhibited under drought stress conditions. A repeated greenhouse experiment was conducted using check genotypes: NC-Roy (fast wilting), Boggs (intermediate in wilting); and NTCPR94-5157 and N04-9646 (slow-wilting, SLW) genotypes. Plants were either well-watered (soil water potential between -15 and -20 kPa) or drought stressed (soil water potential between -90 and -100 kPa). Nitrogen metabolism (nitrogen fixation, NF, and nitrogen assimilation, NA), seed protein, oil, fatty acids, sugars, and minerals were measured. Results showed that under well-watered conditions, NF, NA, and leaf and seed composition differed between genotypes. Under drought stress, NF and NA were higher in NTCPR94-5157 and N04-9646 than in NC-Roy and Boggs. Under severe water stress (soil water potential = -199 kPa), however, NA was low in all genotypes. Leaf water potential (LWP) was significantly lower in checks (-2.00 MPa) than in the SLW genotypes (-1.68 MPa). Leaf and seed concentrations of K, P, Ca, Cu, Na, B were higher in SLW genotypes than in the checks under drought stress conditions. Seed protein, oleic acid, and sugars were higher in SLW genotypes, and oil, linoleic and linolenic acids were lower in SLW genotypes. This research demonstrated that K, P, Ca, Cu, Na, and B may be involved in SLW trait by maintaining homeostasis and osmotic regulation. Maintaining higher leaf water potential in NTCPR94-5157 and N04-9646 under drought stress could be a possible water conservation mechanism to maintain leaf turgor pressure. Increases in seed oligosaccharides (sucrose, raffinose and stachyose) under drought stress in SLW genotypes reflect possible involvement of these sugars in drought and desiccation tolerance. The increase in osmoregulators such as minerals, raffinose and stachyose, and oleic acid could be beneficial for soybean breeders in selecting for drought stress tolerance.