Pivotal role of sugar fluxes between the inner integument and endosperm in lipid synthesis during seed ontogeny in Jatropha curcas L.

Abstract

Jatropha curcas seed matures in 42 days after anthesis (DAA) with ~40% oil on dry weight basis. In this study, we report significant alterations in sugar fluxes in the inner integument, which might play a significant role in endosperm development during course of seed ontogeny in Jatropha. The inner integument significantly contributed to seed weight up to 32 DAA which was followed by endosperm development and maturity by 40 DAA. The inner integument rapidly lost its weight from 34 to 40 DAA, accompanied by a simultaneous gain in the weight of endosperm. Incorporation studies with 14C-label showed that the inner integument has the ability to take up both [14C] sucrose or [14C] glucose whereas the endosperm incorporated only [14C] glucose. The inner integument incorporated most of the 14C label into esters (80%), while the endosperm effectively incorporated [14C] glucose into glycerolipids and no label was found in the ester component. Starch and soluble sugar analysis of inner integument at 34 DAA revealed that ~54% of the dry weight of the tissue was starch while soluble sugars amounted to 10% of which sucrose content ranged from 20 to 30%. It can be inferred that the inner integument was specialised in sucrose uptake for its conversion mostly into starch and the remaining sugar was utilised for synthesis of esters. A rapid uptake of glucose by the developing endosperm fueled glycerolipid synthesis. Our data on sugar fluxes elucidate that the inner integument acts as a transient storage tissue and later the developing endosperm was responsible for synthesis and accumulation of lipids in Jatropha seed.