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 (8 2.7 kPa for 3 min) with methyl jasmonate (MJ) in aqueous suspension an d then stored at a chilling temperature of 5 degrees C. Control fruit were treated with distilled water and handled in a similar manner. Con trol fruit started to show chilling injury after 4 days of storage, wh ereas treated fruit had a 2-4 day delay in the onset of chilling injur y symptoms. The abscisic acid (ABA) level in exocarp tissue of the con trol fruit increased after chilling treatment. An even larger increase in ABA level was found in the MJ-treated tissue upon exposure to 5 de grees C, indicating that MJ may stimulate ABA synthesis at chilling te mperatures. The treated and control fruit had similar increases in put rescine content when exposed to chilling temperatures. Spermidine and spermine contents decreased during storage at 5 degrees C in treated a nd 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 in jury by a mechanism which involves regulation of ABA and polyamine lev els.