Comparison of ethylene- and wound-induced responses in fruit of wild-type, rin and nor tomatoes

Responses of wild-type, rin, and nor tomato (Lycopersicon esculentum Mill.) fruit to exogenous ethylene and wounding were compared to identify the events directly controlled by each mutation. When rin and nor fruit were exposed to exogenous ethylene, respiration and accumulation of E4, E8, and LE-ACO1 mRNAs increased to levels similar to those observed in the wild-type fruit, indicating that expression of these genes is independent of either mutations. In contrast, accumulation of LE-ACS4 and PG mRNAs was not restored by exogenous ethylene treatment in both mutants, indicating that the expression of both genes requires both RIN and NOR. Interestingly accumulation of LE-ACS2 mRNA was stimulated by ethylene treatment in rin fruit but not in nor fruit. This suggests that the signaling pathways of RIN and NOR affect the regulation of ripening-associated genes in distinct ways, at least with respect to the expression of LE-ACS2. Wounding induced ethylene biosynthesis and increased accumulation of LE-ACS2, LE-ACS6, LE-ACO1, and E4 mRNAs in both wild-type and the mutants to the same extent. Treatment with 1-methylcyclopropene (1-MCP), a potent inhibitor of ethylene perception, preceding wounding, inhibited the increase of E4 mRNA but did not affect the expression profile of other genes in all the lines tested. These results show that the wounding signal that controls LE-ACS2, LE-ACS6, and LE-ACO1 is independent of rin and nor mutations and ethylene signaling.