[Relationship between ethylene and polygalacturonase in tomato fruits]

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 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 microL/L treatment for 4 h, and was inhibited significantly in breaking tomato fruit after being treated with 1-MCP (1-methylcycloprane) 1 microL/L, 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 transcriptional expression of both the ethylene receptor gene 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.