Soybean plants were grown at day/night temperatures of 24/19 C until the beginning of seed development, and then transferred to 5 different temperature regimes (18/13, 24/19, 27/22, 30/25 and 33/28 C) in the CSIRO phytotron. Mature seeds that developed under these conditions were analyzed for variances in composition. Fatty acid composition was strongly affected by temperature: linolenic and linoleic acids decreased markedly whereas oleic acid increased as the temperature increased; palmitic and stearic acids remained unchanged. Oil content was positively correlated with temperature, and protein content increased at the highest temperature. Of the sugars analyzed, sucrose concentration decreased by 56% with a 15 C increase in temperature, and stachyose showed a slight reduction; other sugars remained unchanged. Amino acid composition was generally stable; however, methionine increased with increased temperature during seed development. Moisture content was unaffected.

Effect of temperature on soybean seed constituents: Oil, protein, moisture, fatty acids, amino acids and sugars

Studies are reported on changes in fatty acid and lipid class composition in developing soybeans picked at intervals from ca. nine days after flowering to maturity. In the early stages of development of the bean, the lipid was virtually devoid of triglyceride and the major constituents consisted of glycolipids and phospholipids. As the bean developed, there was a rapid synthesis of triglyceride that paralleled the deposition of lipid. Simultaneously, unknown substances which occurred in relatively large amounts in the neutral, as well as the glycolipid and phospholipid, fractions of the immature bean diminished to less than 2% of the total lipid in the mature bean. The glycolipids and phospholipids also increased as the bean developed but at a much slower rate than the triglycerides and became minor components in the mature bean. The major component of the phospholipids in the immature bean was phosphatidic acid. It decreased as the phosphatidyl choline, phosphatidyl ethanolamine, and phosphatidyl inositol, as well as triglyceride, increased. The major component of the glycolipid fraction in the early stages of the development of the bean had the same migration pattern on two-dimensional thin layer chromatography as phosphatidic acid and gave a positive test for phosphorus; it also gave a positive test for glycolipids and was separated completely from phosphatidic acid and other phospholipids by column chromatography. It also decreased as the bean developed. Changes also occurred in the fatty acid composition of the developing bean. The percentage of saturated fatty acids decreased rapidly in the early stages of the development of the bean; oleic and linoleic increased rapidly as the bean developed. Linolenic acid increased rapidly to a maximum concentration in the early stages of the development of the bean and then gradually decreased as the bean matured.

Studies on the lipid composition of developing soybeans.

Mutants of Arabidopsis thaliana were identified by screening pedigreed M3 seed collections from EMS-treated plants for changes in fatty acid (FA) composition. The FA phenotypes of the most dramatic mutants are as follows: G30 and 1E5 (allelic) lack linolenic acid (18∶3) and are elevated in linoleic acid (18∶2); 4A5 is deficient in 18∶2 and 18∶3 and fourfold increased in oleic acid (18∶1); 9A1 lacks all FAs > C18 and is twofold increased in 18∶1; 1A9 is twofold increased in palmitic acid (16∶0) and decreased by one-half in 18∶1; 2A11 is two-to threefold increased in stearic acid (18∶0) and decreased by one-half in 18∶1. Based on segregation of F2 selfed plants derived from crosses to wild type, all of these phenotypes are the result of single gene mutations.

Isolation of EMS-induced mutants in Arabidopsis altered in seed fatty acid composition.

Soybean (Glycine max [L.] Merr. cv. Century) seeds were treated with ethylmethanesulfonate (EMS) and the M2 progeny were evaluated for fatty acid composition of the oil. Treatment with EMS significantly increased the variability in content of each of the fatty acids in comparison with those of the Century control. There was a strong inverse relationship between oleic and linoleic acids among seeds from M2 plants. This supports the hypothesis of sequential desaturation as the method of formation of unsaturated fatty acids in soybean oil. A genetically stable mutant with 3.4% linolenic acid was identified that was similar to the cultivar Century in days to maturity, plant height and resistance to lodging.

Genetic alteration of soybean oil composition by a chemical mutagen

Technological Innovations in Major World Oil Crops, Volume 1

Interest in changing composition of soybeans focuses on linolenic acid in the oil. Available germ plasm includes no lines with less than about 3.5% linolenic acid in the oil. Some breeding lines have been obtained with iodine values of about 115, reflecting higher oleic acid and somewhat lower than normal linoleic and linolenic acid levels. Radiation and other mutagenic agents have been investigated to a limited extent for potential usefulness in inducing a mutation in the direction of low linolenic acid. No such mutant has yet been found, and the task of identifying one is formidable. There is no research known at this time with the objective of altering amino acid distribution in soybeans.

R. W. Rinne

Papers

The plant geneticist’s contribution toward changing lipid and amino acid composition of soybeans