Sucrose Metabolic Mechanism Of Lilium Asiatic Bulb During Bulb Development And Cooling Storage

Sucrose is the main photosynthesis product of higher plants and the main form of the carbohydrate long-distance transport between the bulblet and aerial part of lily. The study of sucrose metabolic mechanism is significant for definituding development mechanism and producing high quality bulb. In present study, we explore the effects of different buffers, pH values, durations and temperatures on SAI activity, and research the sucrose metabolic mechanism of lily bulb during bulb development and cooling storage. The main results are as follow.SAI activity detection system was established for the first time. The exterior scales of lily bulb were used in present study to explore the effects of different buffers, pH values, durations and temperatures on SAI activity. The results indicated that the optimal extraction and reaction buffers were Hepes-NaOH(pH 8.0) and HAc-K3PO4(pH 4.8), respectively. And SAI has an optimum reaction duration and temperature of 30 min and 40℃. These were different from other plants. SAI has different sensitive to external influence in different plants. It is important to activity establish the detection system for soluble acid invertase in lily bulb.The development of different size was varied. At flower bub stage, bulb I became bigger and heavier, but bulbⅡwas at 20 days after emergence. Bulb I had a rapid growth between flower bub and 20 days after anthesis, and a rapid growth of bulbⅡwas between 20 days after emergence and 80 days after emergence.During bulb development, bulb I and II had the similar trend of changes in starch and sucrose content. In early stage, there were a net breakdown of starch and a decline of sucrose; in later developmental stage, both starch and sucrose increased. Starch was closely related to sucrose metabolism.SAI and SuSy are the key enzymes of sucrose metabolism in lily bulb. During bulb development, cleavage activity of SuSy was far less than synthetic activity, it indicated that cleavage activity plays a major role. SAI activity and SuSy cleavage direction had a similar trend, but SAI had a higher activity than SuSy cleavage direction. SAI plays a leading role and sucrose lysosomal enzymes work together in sucrose metabolism during bulb development. The activity of SAI and SuSy increased, which results in the significant decrease of sucrose in later developmental stage. It formed a sucrose concentration gradient bettween bulb and aerial part, which promoted sucrose moving to bulb and provid the carbon skeleton for starch synthesis.During cooling storage, SuSy cleavage activity still plays a major role in SuSy. SuSy had a low activity in synthetic direction and the change trend was consistent with sucrose basically. It illustrated SuSy synthetic direction has a certain influence on formation of sucrose. The SuSy cleavage direction acticity kept a high level in apical bud. SAI activity rised sustaining after 20 days cooling storage. Moreover, it rised sharply during 40-60 days. It resulted that the sprout of buds was related to the higher activity of SAI. The sucrose lysosomal enzymes at a high level promoted that sucrose resolve into reducing sugar which could boost the buds sprouting.Starch content in bulb scales was continue to decline during cooling storage. Compared with exterior scales, starch content of middle scales is higher and the descending range is larger, starch content is have shown a sharp decline at the beginning of cooling storage. This indicated that nutrient metabolism started earlier and more quickly. Sucrose content in scales increased significantly and reached a peak after 60 days, sucrose content of middle scales is higher than exterior scales, it indicated that middle scales was more important position of sucrose accumulation. No matter exterior scales or middle scales, compared with apical parts, central and basal part have higher starch and sucrose content, SuSy synthetic activity and lower sucrose lysosomal enzymes, it shows that central and basal part are the important position of sucrose accumulation and transshipment.