番茄果实中乙烯与多聚半乳糖醛酸酶的关系

Relationship Between Ethylene and Polygalacturonase in Tomato Fruits

乙烯与多聚半乳糖醛酸酶(PG)都是果实成熟过程中关键的调节因子。一方面,在有乙烯合成缺陷的转反义ACS番茄和乙烯感受缺陷的Nr突变体番茄果实中PG基因表达量都明显下降,PG酶活性明显降低;用外源乙烯(100μL／L)处理绿熟期番茄果实使PG基因的表达明显增强,而1-甲基环丙烯(1-MCP,1 μL／L)处理转色期番茄果实明显抑制PG基因表达。另一方面,转反义PG基因番茄果实乙烯释放量在授粉后低于其野生型,番茄乙烯受体基因LeETR4和乙烯反应因子LeERF2基因表达量比野生种低。PG降解果胶的产物D-GA(100 mg／L)促进未熟期番茄果实中的乙烯生成和LeETR4、LeERF2基因的表达。

Ethylene and PG (polygalacturonase) are both key plant growth regulators in fruit ripening process. The expression of PG was markedly inhibited in either antisense ACS tomato (Lycopersicon esculentum cv. Lichun) where endogenous ethylene synthesis was suppressed, or in Nr mutant in which ethylene perception was severely damaged. Also, the PG activities in fruits of these mutants (Fig.1A) were significantly lower than that of wild-type tomato (Fig. 1B). PG gene expression was promoted in mature green tomato fruit by exogenous ethylene 100 μL/L treatment for 4 h, and was inhibited significantly in breaking tomato fruit after being treated with 1-MCP (1-methylcycloprane) 1 μL/ L (Fig.3), a specific ethylene reception inhibitor. Ethylene production of antisense PG tomato fruit during 45-50 DAP was lower than that of wild-type tomato (Fig.4), and the level of transcrip-tional expression of both the ethylene receptorgene LeETR4 and the ethylene response factor gene LeERF2 were lower in this transgenic tomato fruit (Fig.5). Ethylene production and the expression of LeETR4 and LeERF2 were both promoted by treatments with D-GA 100 mg/L, a product of enzymatic degradation of PG, in immature tomato fruit (Fig.6 and Fig.7). The relationship of PG and ethylene in tomato fruit in this study provided forceful evidences to support the mechanism by which PG and ethylene synergistically regulated climacteric fruit ripening and softening.