Investigation of Yield, Saponin Contents and Expressions of HMGS, FPPS and SS in Different Harvesting Mode of Asparagus

To study the effects of different asparagus harvesting mode on yield, saponin contents and genes' expression of saponin biosynthesis, by using three year-age asparagus cultivar Jersey Knight variety which were planned at asparagus base in Mile City of Yunnan as materials, in this study, 3 harvesting models, eg.white spears collection, bald green spears collection and green spears collection with mother stem were performed in 100 m2 experiment plots respectively in same tunnel green house. The yields were calculated, the contents of total saponins and diosgenin, an intermediate of asparagus saponins biosynthesis were determined. Based on asparagus EST data, primers were designed to amplified full coding sequence (CDS) of hydroxymethyl coenzyme A synthetase (AoHMGS), farnesene synthase (AoFPPS) and squalene synthase (AoSS) which were catalyze the key steps in early saponin biosynthesis pathway, and their expression were detected by method of q-RT-PCR amplification. The results showed that spear colleting with mother fern get the, highest contends of total saponins and diosgenin, while white spear collecting showed lowest yield and contents of diosgenin but total saponin was higher than green spear colleting with bald way. The q-RT-PCR amplification showed that the expression of AoHMGS, AoFPPS and AoSS genes and contents of total saponin and diosgenin presented a significant negative correlation among different harvesting mode, while there didn't exist correlation in different parts of the same spears cultivated in same mode. The possible reason is that the saponins and diosgenin synthesized in stalks are partially transferred to spears under the stalk maintained collection mode. It seems that the collecting spears with mother fern is the best way to get high quality of asparagus, even this mode needs more labors and times for spear colleting.