Analysis of starch accumulation and differentially expressed proteins during the development of Chinese yam tuber

Objective  To understand the rules of starch accumulation during development of Chinese yam (Dioscoreaspp.) tuber, and provide theoretical references for breeding and cultivation of Chinese yam with high yield and quality.

Method  Using ‘GH16’ as material, starch accumulation during development process of Chinese yam tuber was measured. The changes of tuber tissues, cells and starch grains were studied through paraffin sectioning. The key proteins related to tuber development were discovered by two-dimensional electrophoresis.

Result  There was no starch accumulation in early stage of tuber formation (April to May). In the early expansion stage (June), starch grains distributed uniformly in parenchyma cells. With the development of yam tuber, tuber cells and starch grains enlarged gradually, and starch accumulated rapidly. In the mid and late expansion stages (after September), substantial starch grains distributed near parenchyma cells around vascular bundle. In the late expansion stage, tuber cell size reached the maximum in November with cell longitudinal diameter and transverse diameter reaching 121.685 and 89.572 μm respectively, and starch accumulation reached the peak with longitudinal diameter of starch grain being up to 27.608 μm (December), and transverse diameter being up to 16.450 μm (November). There were 179 differentially expressed proteins to be found. Among them, Fifty-two proteins with relatively larger differences in expression were analyzed by mass spectra, and 31 differentially expressed proteins were identified. Most of them were enzymes related to sugar metabolism and starch synthesis, such as glucose 6-phosphate acid dehydrogenase, fructose-bisphosphatealdolase cytoplasmic isozyme-like, ATP synthetase alpha subunit, UTP-glucose-1-phosphate uridylyltransferase and phosphoglycerate kinase 1, and these were up-regulated after the early stage of tuber formation. Chinese yam tuber specific protein, Dioscorin, was accumulated in the late stage of tuber expansion.

Conclusion  The expansion of Chinese yam tuber is the results of cell division, cell amplification and starch accumulation. The main differentially expressed proteins during development of Chinese yam tuber play the key roles of sugar metabolism and starch synthesis.