刺梨果实中维生素C积累与相关酶活性的关系

刺梨果实发育过程中维生素C(AsA)积累呈"慢一快一慢"的模式,其中6月底至8月初是AsA积累最快和最重要的时期.半乳糖内酯脱氢酶(GalLDH)活性与AsA积累速率的变化趋势基本一致,二者间呈极显著的正相关关系.AsA分解酶抗坏血酸氧化酶(AAO)和抗坏血酸过氧化物酶(AAP)只在发育前期极短时间内表现活性,从而使AsA极少被氧化分解,这是刺梨果实能积累高水平AsA的重要原因之一;在果实发育过程中始终未能检测到单脱氢抗坏血酸还原酶(MDAR)和脱氢抗坏血酸还原酶(DHAR)的活性,表明它们不是刺梨果实积累高含量AsA的关键因素.

Relationship Between Ascorbic Acid Accumulation and Related Enzyme Activities in Fruit of Rosa roxburghii Tratt

Ascorbic acid (AsA) and sugar levels,together with activities of L-galactono-1,4-lac-tone dehydrogenase (GalLDH, a key enzyme inAsA biosynthesis in higher plant), AAO, AAP,MDAR and DHAR in fruit of Rosa roxburghiiTratt were measured during development. Theresult showed that AsA accumulated continuallybut with a slow, fast and slow accumulating ratein the R. roxburghii fruit during its development,in which the period from the end of June to theearly of August was the most important periodof AsA accumulation, since the AsA accumulatedin this stage accounting for approximately 90%of the final level (Fig.1B). Changes in GalLDHactivity coincided with AsA accumulating rateduring fruit development (Fig.2B). The ex-tremely significant positive correlation existedbetween the GalLDH activity and AsA accumu-lating rate (r2=0.783**) (Fig.3). Transitory andlow activities of AAO and AAP in the fruit were detected in the initial stage of development(Table 1), suggesting that little AsA degraded bythe activities of the two oxidative enzymes dur-ing the whole development. This data elucidated,at least in part, the reason for high accumulationof AsA in the R. roxburghii fruit. Furthermore,no activity of MDAR or DHAR in the fruit wasdetected during the whole development, imply-ing that the two enzymes are not key factors forcontribution of AsA level. No correlation wasfound between AsA content and sugar contentsin the R. roxburghii fruit.