METHYL JASMONATE REDUCES CHILLING INJURY IN CUCURBITA-PEPO THROUGH ITS REGULATION OF ABSCISIC-ACID AND POLYAMINE LEVELS

Zucchini squash fruit (Cucurbita pepo L.) were pressure infiltrated (82.7 kPa for 3 min) with methyl jasmonate (MJ) in aqueous suspension and then stored at a chilling temperature of 5 degrees C. Control fruit were treated with distilled water and handled in a similar manner. Control fruit started to show chilling injury after 4 days of storage, whereas treated fruit had a 2-4 day delay in the onset of chilling injury symptoms. The abscisic acid (ABA) level in exocarp tissue of the control fruit increased after chilling treatment. An even larger increase in ABA level was found in the MJ-treated tissue upon exposure to 5 degrees C, indicating that MJ may stimulate ABA synthesis at chilling temperatures. The treated and control fruit had similar increases in putrescine content when exposed to chilling temperatures. Spermidine and spermine contents decreased during storage at 5 degrees C in treated and control squash. However, the treated fruit maintained higher levels of spermidine and spermine than the control fruit throughout storage at 5 degrees C. These results indicate that MJ may prevent chilling injury by a mechanism which involves regulation of ABA and polyamine levels.