Changes in fatty acid composition of sunflower (Helianthus annuus) seeds in response to time of nitrogen application, supply rates and defoliation

Abstract

AbstractThe fatty acid composition of sunflower (Helianthus annuus L ) seed oil was shown to respond to N supply rates and the time of N application in four glasshouse and two field experiments using five cultivars. Changes in individual fatty acids % total were smaller than those caused by differences in minimum temperatures during seed development but they were statistically significant. N supply rates before floret initiation affected the % fatty acid composition of mature seeds; the percentage of palmitic (16:0) and linoleic (18:2) acids responded positively to increases in N supply whereas % stearic (18:0) and oleic (18:1) acids responded negatively. The only fatty acid to respond to N supply rates between floret initiation and anthesis was 18:0 acid. The percentage of 18:1 responded positively and that of 18:2 acid negatively to high N supply rates after anthesis Responses to single N applications at different stages of plant development in the field confirmed these findings but results were more variable than in the glasshouse. Partial or complete defoliation at anthesis in the field caused the same changes in fatty acid composition as did a low N supply after anthesis.The results are difficult to interpret in terms of our current knowledge of lipid biosynthesis. N supply rates may affect the rate of hydrolysis of fatty acid complexes or their transport from the proplastid to the cytosolic compartment. There was no compelling support for the hypothesis that N supply rates bejore floret initiation were affecting fatty acid composition through their effects on other plant characters such as leaf mass, seed number or single seed weight.