Reduced Oil Accumulation in Cottonseeds Transformed with a Brassica Nonfunctional Allele of a Delta‐12 Fatty Acid Desaturase (FAD2)

Abstract

In an effort to better understand the mechanisms that regulate oil accumulation and packaging in seeds, transgenic cotton lines were generated using a Brassica napus nonfunctional delta‐12 fatty acid desaturase (FAD2) gene under control of the phaseolin promoter. Seeds of numerous transgenic plant lines had reduced oil content compared with null‐segregating siblings or nontransformed seeds. Seed oil content was quantified by 1H‐NMR, and was reduced to 12% or less of seed weight in transgenics from 20% by weight in nontransformed controls. Light‐ and electron‐microscopic analyses of severely lowered lines, showed a reduction in overall cotyledon thickness and a disruption in cellular and subcellular organization. Lipid bodies and protein bodies were fewer in transgenics, and their size and distribution in cells was different than that in nontransformed seeds. Coincident with reduced storage reserves, sucrose levels were elevated in transgenic seeds. The overall effect of oil suppression was to selectively reduce the size of the embryo, but the seed coat and fiber properties remained unaffected in seeds. In fact there was a significant increase in lint percentage in all oil‐suppressed lines examined. Overall we propose that expression of the nonfunctional Bnfad2 allele in cottonseeds disrupts normal oil biosynthesis and provides for redirection of carbon reserves.