Abstract
Although seed oil production and composition are genetically controlled, changes of oil level and oil composition across genotypes and environments such as drought and temperature were observed. The mechanisms of how genotypes interact with environment, affecting oil production and composition, are still not well understood. The objective of this research was to investigate the effect of drought/water stress and temperature on soybean genotypes. Two soybean genotypes of maturity group (MG) II (PI 597411 B and PI 597408) and two of MG VI (Arksoy and PI 437726) were used. A repeated greenhouse experiment to study the effect of water stress and a repeated growth chamber experiment to study the effect of temperature were conducted. The results showed that both water stress and high temperature altered seed oil composition by increasing oleic acid and decreasing linoleic and linolenic acid concentrations. Severe water stress (soil water potential between -150 to -200 kPa) or high temperature (40/33℃, day/night) resulted in higher palmitic acid and lower stearic acid. Genotypes differed in their responses to water stress or temperature. Analyses of seed carbohydrates (glucose, fructose, sucrose, raffinose, and stachyose) showed a significant decline of glucose, fructose, and sucrose and a significant increase of stachyose concentration by water stress and high temperature. Analyses of natural abundance of δ15N and δ13C isotopes showed changes in sources of nitrogen and carbon fixation, possibly affecting nitrogen and carbon metabolism pathways. The research demonstrated that both water stress and high temperature altered oil production and composition, and this could be partially related to limited availability and movement of carbohydrates from leaves to seed. Further research to investigate the enzymes controlling fatty acids conversion and nitrogen and carbon metabolism is needed.
Highlights
Soybean oil composition determines the oil quality
Linoleic, and linolenic acid concentrations were the main constituents that were affected by water stress, and palmitic, stearic, and to some extent total oil concentrations were the least affected by water stress
Effect of Water Stress In maturity group (MG) II, water stress resulted in a significant decrease in oil, linoleic and linolenic concentrations compared with seed in well watered (W) plants (Table 5)
Summary
Soybean oil is composed of saturated and unsaturated fatty acids. All carbon atoms are occupied by hydrogen with no double bonds between the carbon atoms. Major saturated fatty acids are palmitic (C16:0; 10 to 12%) and stearic (C18:0, 3 to 5%), and major unsaturated fatty acids are oleic (C18:1; 24%), linoleic (C18:2; 54%), and linolenic (C18:3, 8.0%). Soybeans with higher levels of monounsaturated fatty acids such as oleic acid or polyunsaturated fatty acids such as linoleic or linolenic are more desirable for human consumption than saturated fatty acids. From soybean processing perspective, higher levels of polyunsaturated fatty acids contribute to oil oxidative instability, short shelf life, and rancidity. Soybean seed with higher levels of oleic acids and lower levels of linoleic or linolenic acids are desirable to minimize hydrogenation of the oil.
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