柑桔果实糖酸比及线粒体乌头酸酶活性的变化

测定了尤力克柠檬(高酸Citrus limon Burm．F)、冰糖橙(低酸C．sinensis Osbeck)、锦橙(中酸C．sinensis Osbeck)、奉节脐橙(C.sinensis Osbeck)72—1及其低酸和晚熟芽变在果实发育过程中还原糖含量、糖酸比以及线粒体乌头酸酶(Aconitase，EC4．2．1．3)和苹果酸脱氢酶(Malate debydrogenase，MDH，EC1．1．1．37)活性变化。结果表明：各类型柑橘果实发育过程中糖的含量，随着果实的生长而增加，奉节脐橙的低酸芽变还原糖含量和糖酸比的增长速度最快，与其说它是低酸还不如说是早熟更为合理。各类型柑橘果实线粒体乌头酸酶活性变化一致随果实发育降低，表明果实发育后期有机酸降解与线粒体乌头酸酶活性的降低无关，而较低的细胞质乌头酸酶活性有利于酸的积累；柠檬MDH活性一直较低，但其他柑桔MDH活性变化与果实柠檬酸含量差异没有发现有明显的关系。

CHANGES IN SUGAR/ACID RATIO AND ACTIVITY OF MITOCHONDRIAL ACONIDASE IN DEVELOPING CITRUS FRUIT

Seasonal changes were investigated in mitochondrial aconitase and malate dehydrogenase (MDH) activities and soluble sugar contents during the development of citrus fruits of Eurieka lemon (Citrus limon), candy orange (C. sinensis), Jincheng orange (C. sinensis) and Fengjie navel orange (C. sinensis) and its low-acid mutant and late maturing mutant. The results showed that soluble sugars increased continually during the development of the fruit and that in the fruit of low-acid mutant of Fengjie navel orange, soluble sugar content rose very fast and was consistent with the change in sugar/acid ratio. It seemed more appropriate to rename the mutant "early maturing mutant". Changes in mitochondrial aconitase activity exhibited similar patterns in all the citrus genotypes studied, and its activity reduction was associated with a decrease in the acid level. Such a result suggested that lower cytololic aconitase activity, not mitochondrial aconitase activity, in later stages of fruit development led to higher acid accumulation. MDH remained at a relatively low level in the entire process of lemon fruit development, but no distinct relationship was observed between the changes in MDH and citric acid content in the fruit of other citrus genotypes.