摘要
对采后番茄果实的电镜观察表明:当果实成熟衰老时,叶绿体数量减少,多数基粒结构丧失;成熟果实胞壁中胶层水解成中空的电子透明区,初生壁的纤丝也发生一定程度的水解,相邻细胞分离;外源 PG(多聚半乳糖醛酸酶)提取物处理绿熟期果实组织,也可引起胞壁结构和叶绿体发生与正常衰老相同的变化。Ca^(2+)、Mg^(2+)、Co^(2+)二价金属离子处理果实,可明显降低番茄红素含量和 PG 活性,延缓果实软化。外源乙烯处理果实,可促进番茄红素的形成,提高 PG活性,并能解除钙对 PG 活性的抑制。本文也对 PG 在乙烯和 Ca^(2+)调节果实成熟中的作用进行了讨论。
It has been reported that PG is a key enzyme related to the tomato fruit ripening,In this study tomato fruits were harvested at the mature-green stage and stored at room tempera- ture.The cell ultrastructure of pericarp tissue was observed at different ripening stages,and the effects of treatments with ethylene and calcium on PG activity and fruit ripening were ex- amined.The object of this study is to elucidate the role of PG in regulation of tomato fruit ripening by ethylene and calcium. PG activity was undetectable at mature-green stage,but it rose rapidly as fruit ripening. The rise in PG activity was coincided with the declining of fruit firmness during ripening of tomato fruits.The observation of cell ultrastructure showed that the most of grana in chloro- plast were lost and the mitochondrial cristae decreased as fruit ripening.Striking changes of cell wall structure was most noted,beginning with dissolution of the middle lamella and eventual disruption of primary cell wall.A similar pattern of changes of cell wall and chloro- plast have been observed in pericarp tissue treated with PG extract.In fruits treated with calcium and other divalent metal ions atmature-green stage,the lycopene content and PG activity decreased dramatically.Ethylene application enhanced the formation of lycopene and PG activity.The inhibition of Ca^(2+) on PG avtivity was removed by ethylene. Based on the above results,it was demonstrated that PG played a major role in ripening of tomato fruits,and suggested that the regulation of fruit ripening by ethylene and Ca^(2+) was all mediated by PG.PG induced the hydrolysis of cell wall and released the other hydrolytic enzymes,then effected the ripening processes follow up.
基金
国家自然科学基金资助课题
关键词
番茄
果实
成熟
PG
金属离子
乙烯
Tomato fruit
Ripening
Polygalacturonase
Divalent metal ions
Ethylene
