Submitted to: American Journal of Plant Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 28, 2011
Publication Date: November 9, 2011
Citation: Bellaloui, N. 2011. Effect of water stress and foliar boron application on seed protein oil fatty acids and nitrogen metabolism in soybean. American Journal of Plant Sciences. 2:692-701. Interpretive Summary: Boron is an essential nutrient for crop growth, yield, and quality. The effects of foliar boron application on soybean yield and seed composition have not been well investigated, and information available is inconclusive. The source of inconsistency of previous results could be due to changes in environmental conditions such as drought and heat stress during the growing season. Therefore, the objective of this study was to investigate the effects of water stress and foliar boron fertilizer on seed protein, oil, and fatty acids. A repeated greenhouse experiment was conducted where soybean subjected to water stress and foliar boron application at a rate of 0.45 kg per hectare (0.40 pounds per acre) at flowering and seed-fill growth stages was compared with soybean receiving no water stress and no foliar boron fertilization. Protein and oil concentrations were significantly lower in water stressed soybean than in water stressed soybean receiving foliar application of boron or in watered soybean with or without foliar boron fertilization. The fatty acid oleic acid increased and linolenic acid decreased in water stressed soybean and in watered soybean receiving boron fertilization. These findings suggest that foliar application of boron may be needed under drought conditions to maintain seed yield and quality, and soybean breeders can use this knowledge in selecting for boron nutrition efficiency under stress environments.
Technical Abstract: Effects of water stress and foliar boron (FB) application on soybean (Glycine max (L) Merr.) seed composition and nitrogen metabolism have not been well investigated. Therefore, the objective of this study was to investigate the effects of water stress and FB on seed protein, oil, fatty acids, nitrate reductase activity (NRA), and nitrogenase activity (NA). A repeated greenhouse experiment was conducted where one set of soybean plants were subjected to water stress (WS) (soil water potential ranged from -90 to -100 kPa), and the other set was watered (W) (soil water potential ranged from -15 to -20 kPa), using tensiometers. Foliar boron (B) was applied at rate of 0.45 kg ha-1 at R1-R2 (flowering) and at R5-R6 (seed-fill) growth stages . Treatments were watered-plants with no FB (W), watered-plants with FB (WB), water-stress-plants with no FB (WS), and water-stress plants with FB (WSB). The results showed that seed protein and oil percentage were significantly (P< 0.05) higher in WB than other treatments. Oleic acid increased and linolenic acid decreased in WB and WSB. Significant (P< 0.05) increase in NRA in leaves and roots and NA occurred in WB compared to W. In WSB, NRA in leaves and roots or nitrogenase activities were higher than those in WS. Nitrate reductase activity in nodules was greater in WB than in W, and was higher in WSB than in WS. The concentration of B in leaves and seed were significantly (P<0.05) higher in W than in WS. Seed 15N/ 14N and 13C/12C natural abundance were altered between watered- and watered-stressed plants. These results suggest that water stress and FB can influence seed composition and nitrogen metabolism. Water stress can also alter 15N/ 14N and 13C/12C, reflecting environmental and metabolic changes in carbon and nitrogen fixation pathways. Lack of B translocation from leaves to seed under water stress may suggest a possible mechanism of limited B translocation under water stress. The limited B translocation from leaves to seed may also suggest the need of foliar B application under drought conditions. These findings may be beneficial to breeders to select for B translocation efficiency under drought conditions. Altered 15N/ 14N and 13C/12C under water stress can be used as a tool to select for drought tolerance using N and C isotopes in the breeding programs.