Study on Changes in the Characteristics of Key Carbohydrates in Wheat during the After-ripening Period

Three wheat cultivars—Zhengmai 366(ZM366), Zhoumai 27(ZM27) and Yangmai 15(YM15)—were used in the present study. After storage at 25?C for 15, 30, 45, 60, 90, 120 and 150 d, the crude starch, amylose, amylopectin, damaged starch and reducing sugar contents in wheat during the after-ripening period were measured. The results revealed(1) a marginal decrease in the total starch content;(2) no significant change in the amylopectin content; and(3) significant change in the amylose and reducing sugar contents during the after-ripening period in all the three wheat cultivars. Further, the amylose content in the three cultivars exhibited an increasing trend during the initial phase of the after-ripening period. Among the cultivars, ZM366 exhibited the highest increase,which stabilized after 90 d. The reducing sugar content showed a significant decrease during the initial phase of the after-ripening period with ZM366 showing the highest decrease, which attained stability after 90 d. The damaged starch content in all the three wheat cultivars exhibited a decreasing trend with ZM27 showing the highest decrease, which stabilized after 90 d. There were no changes in the forms of starch crystal among the three wheat cultivars after the after-ripening period, with only ZM366 showing a significant increase in starch crystallinity. The reducing sugar content in all the three wheat cultivars exhibited a decreasing trend during the initial phase of the after-ripening period, which attained stability at around day 90.

Dormancy release and germination of Echinochloa crus-galli grains in relation to galactomannan-hydrolysing enzyme activity

Echinochloa crus-galli, one of the world＇s most serious weeds, influences seriously the yield and quality of cereal crop plant.It is well known that E.crus-galli grain is dormant, but its dormant type, as well as its dormancy release and germination in relation to galactomannan-hydrolysing enzyme activity were poorly understood.The cooperation of endo-β-mannanase（EC 3.2.1.78）, β-mannosidase（EC 3.2.1.25） and α-galactosidase（EC 3.2.1.22） can hydrolyze the cell walls rich in mannan-based polymers.In the present paper, the mature grains are used as experimental materials, we investigated the water uptake of grains, the effect of removing partial endosperm, after-ripening, stratification and phytohormone on grain germination, and the change in endo-β-mannanase, β-mannosidase and α-galactosidase activities of grains during after-ripening and germination.The results showed that the freshly-collected grains were water-permeable and had only phase I and II of water uptake, while the grains after-ripened for 150 d had an obvious phase III of water uptake.In alternating photoperiod, the germination of grains freshly-collected was zero at 10–35°C, and that of half grains was 11% at 20°C only.The grain germination was notably promoted by after-ripening and stratification, but not by gibberellic acid and 6-benzyladenine at 0.0001–1 mmol L–1.β-Mannosidase activity increased during 0 to 300 d of after-ripening and then decreased.The activity of endo-β-mannanase and α-galactosidase of grains decreased with after-ripening.During grain germination, endo-β-mannanase and β-mannosidase activities obviously increased, while α-galactosidase activity decreased.Our data showed that E.crus-galli grain was a deep physiological dormant, the dormancy release by after-ripening was related to an increasing β-mannosidase activity, and its germination was closely associated with an increasing endo-β-mannanase and β-mannosidase activity; which have provided new knowledge to decrease the harm of E.crus-galli on production of cereal crop plant.