| Polygalacturonase (PG) plays major roles in fruit softening, organ abscission, pollination and seed development. The relationship between polygalacturonase and ethylene, other plant hormone, and the positions of PG in plant resistance and diseases responses were specially discussed in this paper. The multiformity of PG functions was indicated.Agrobacterium-mediated transformation had been used to introduce the Anti-PG gene into processing tomato (cv. 98-75). Four positive transformed tomato plants were confirmed by PCR and Southern hybridization. Fruit firmness and soluble solid of transgenic tomato were higher than those of control; fruit were full and lustrous; soluble pectin was lower than control at the same stage. The PG activity of transgenic tomato was 83%, 88%, 63%, 46% of control tomato respectively. Northern hybridization showed that all PG, LOX and LeEXPl mRNA decreased in transgenic tomato fruit compared with the wild tomato. These results suggest that the process of ripening and softening in transgenic anti-PG tomato were delayed.The expression patterns of PG, LeEXPl and LOX were studied in wild tomato, antisense ACS tomato and Nr mutant tomato. The result showed that PG played a major role in ripening and softening of tomato fruit, and cooperated with the regulation of LeEXPl and LOX.The relationship between ethylene and Polygalacturonase(PG) was thoroughly investigated in two aspects of the effect of ethylene on PG function and the regulation of PG on ethylene synthesis. With wild tomato, antisense ACS tomato, Nr mutant tomato and wild tomato treated with exogenous ethylene and 1-MCP as materials, it was showed that the expression of .PG gene and PG activity were inhibited significantly in antisense ACS tomato and Nr mutant tomato. The expression of PG was promoted with exogenous ethylene (100ul/L) and obviously inhibited with 1- MCP (1ul/L). These results suggested that expression of PG gene was regulated by ethylene. On the other hand, with antisense PG tomato and wild tomato treated with 100mg/L D-GA as materials, it was showed that the ethylene production of antisense PG tomato was lower than that of wild tomato, the expression of ethylene receptor gene LeETR4 and the ethylene response factor LeERF2 were inhibited. The ethylene synthesis was affected by changes of expression model on PG gene. The ethylene production and expression of LeETR4 and LeERF2 were promoted with the treatment of 100mg/L D-GA. These results implicated that the synthesis and action of ethylene were also feedback-regulated by PG gene in some case. There is an interaction between ethylene and PG.Wild tomato, antisense ACS tomato and Nr mutant tomato were treated with 0.1 mM ABA, 0.1 mM GA, 0.1 mM IAA , 0.1mM 6-BA and 1mM SA . The results suggested that the expression of PG in wild tomato was induced obviously by ABA, IAA, 6-BA and SA, but inhibited by GA. In antisense ACS tomato, expression of PG was promoted by ABA , 6-BA and IAA, but GA andSA had no affect on PG expression . In Nr mutant tomato, GA, IAA, 6-BA and SA induced whereas ABA had no obvious affect on PG expression. The expression of PG, LeEXPl and LOX in seedlings were promoted with ABA and SA.The expression of PG, LeEXPl, LeETR4 and LOX were significantly promoted with 0.2M NaCl in wild tomato fruit and seedlings. The results indicated that PG involved in plant stress response as early signaling gene.Treatment of wild tomato fruit and seedlings with Oligosaccharides elicitors -chitosan, significantly induced the expression of PG , the effect of chitosan was counteracted with EGTA treatment. The result implicated that Ca2+ may have an effect on PG in plant defense responses induced by elicitor.
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