CARBOHYDRATE CONTENT AND ENZYME METABOLISM IN DEVELOPING CANOLA SILIQUES

Little biochemical information is available on carbohydrate metabolism in developing canola (Brassica napes L.) silique (pod) wall and seed tissues. This research examines the carbohydrate contents and sucrose (Sue) metabolic enzyme activities in different aged silique wall and s eed tissues during oil filling. The silique wall partitioned photosynt hate into Suc over starch and predominantly accumulated hexose. The si lique wall hexose content and soluble acid invertase activity rapidly fell as embryos progressed from the early- to late-cotyledon developme ntal stages. A similar trend was not evident for alkaline invertase, S uc synthase (SuSy), and Suc-phosphate synthase. Silique wall SuSy acti vities were much higher than source leaves at all times and may serve to supply the substrate for secondary cell wall thickening. In young s eeds starch was the predominant accumulated carbohydrate over the samp led developmental range. Seed hexose levels dropped as embryos develop ed from the early- to midcotyledon stage. Hexose and starch were local ized to the testa or liquid endosperm, whereas Suc was evenly distribu ted among seed components. With the switch to oil accumulation, seed S uSy activity increased by 3.6-fold and soluble acid invertase activity decreased by 76%. These data provide valuable baseline knowledge for the genetic manipulation of canola seed carbon partitioning.