PROTEIN-CHANGES IN PEACH SEEDS DURING CHILLING ARE NOT ASSOCIATED WITH BREAKING DORMANCY

Siberian C peach (Prunus persica L.) seeds were stratified at 5 and 20 C. DWs and soluble protein content remained constant regardless of str atification temperature and duration. Seed extracts subjected to sodiu m dodecyl sulfate-polyacrylamide gel electrophoresis revealed a decrea se in the intensity of nine polypeptides in the cotyledons of seeds he ld at 5C during weeks 5 through 8, coinciding with an increase in germ ination capacity. These changes were confined to cotyledons held at 5C , and were observed only when the seeds were able to germinate. The ef fects of stratification and the imbibition degree on changes in the pr otein content of seeds of two additional peach biotypes ('Farouki' and 'Maloussi') were also evaluated. Germination of fully imbibed seeds a t 20C increased steadily as stratification time at 5C increased. Parti ally imbibed seeds (25% or 50% of full imbibition) did not germinate r egardless of stratification time. However, when these seeds were soake d in water after stratification, their germination paralleled that of fully imbibed seeds. Thus, dormancy was broken, even though the seeds could not germinate. Changes in protein profiles in fully imbibed seed s confirmed those previously reported for Siberian C seeds. Similar ch anges occurred in cotyledons of partially imbibed seeds during stratif ication at 5C, but at a slower rate. Those changes were, however, dela yed by partial imbibition, whereas germination capacity (ability to ge rminate when fully imbibed) was not. Changes in cotyledon protein prof iles were not affected by removing the embryonic axis before stratific ation, a result indicating that such changes are not controlled by the axis. Gibberellic acid (GA3) induced 35 % to 40 % germination of nonc hilled seeds. It hastened the loss of protein band intensity in 'Farou ki' but not in 'Maloussi'. However, GA3-treated seeds germinated befor e any visible changes occurred in protein profiles. We conclude that t he effects of chilling on breaking dormancy are independent of its eff ects on the protein changes observed in this study.