Abstract
The carbon flow balance is shifted to starch rather than oil accumulation during benzoin seed development stage (80–120 DAF) and thereby lipid deposition speed slows down. Benzoin [Styrax tonkinensis (Pierre) Craib ex Hartwich] is a woody oilseed species with potential value as a biofuel feedstock. However, the continuous drop in seed crude fat concentration during maturation had remained unexplained until it was investigated in this study. Seed filling began 60 days after flowering (DAF), when the hexose-to-sucrose ratio dropped, correlating with substantial morphological changes in kernels. Oil accumulated 20 days earlier than starch, as the concentrations of free fatty acid (50–70 DAF) and diacylglycerols (50–80 DAF) increased rapidly. Fatty acid synthesis slowed between 80 and 120 days, correlating with a sharp increase in the speed of starch deposition, while triacylglycerol accumulation and the profile of fatty acids remained stable. Phosphoglucose isomerase (PGI), pyruvate dehydrogenase complex (PDHC), and malate dehydrogenase (MDH) activities dropped progressively together with acetyl coenzyme carboxylase (ACCase) after 70 DAF before the reserve storage priority shifted from fatty acids to starch. PGI, PDHC, MDH, ACCase, and diglyceride acyltransferase (DAGT) activities rose again at 120 DAF, after which the speed of fatty acid accumulation increased, correlating with a 10-day lag phase in starch accumulation. High glucose 6-phosphate dehydrogenase (G6PDH) activity was observed during oil deposition. Soluble protein continued accumulating as protease activity decreased during benzoin seed development, while the total amylase activity rose twice between 30 and 70 DAF before the ADP-glucose pyrophosphorylase activity and starch content soared high simultaneously after 70 DAF. The collective results suggest that carbon partitioning between starch and lipid accumulation occurs during benzoin kernel development and is responsible for a reduction in the rate at which total fatty acids accumulate between 80 and 120 DAF.
Published Version
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