Changes in free and bound gibberellin levels in embryos of Pyrus malus cv. Golden delicious during a chilling treatment applied to the seeds

Abstract

The endogenous levels of free and bound forms of several gibberellins (GA 4 , GA 7 , GA 9 ) were studied in dormant as well as in partially or completely after-ripened embryos of Pyrus malus L. cv. Golden delicious, the seeds being submitted to a 4 °C chilling treatment for 1, 2 or 3 months. The GA s tested were isolated using thin-layer chromatographies which allowed the separation from ABA and IAA. Quantitative estimations were made using a lettuce hypocotyl test for GA 7 and GA 9 and an original amaranthin biossay for GA 4 . Very small quantities of GA S were found in dormant embryos under bound and free forms. Under the influence of chilling treatment, the content of GA 7 and GA 9 showed but slight modifications whereas free and bound forms of GA 4 underwent remarkable changes. In the cotyledons we found after 1 month after-npening treatment, a high GA 4 content essentially under the free form; after 2 or 3 months a similar level was detected under the bound form, the free form having disappeared. In the embryonic axes, free GA 4 was found in large amounts only after 2 months. Almost no bound form appeared whatever the length of the chilling treatment. The discussion is directed to the possible relation between the water content and GA 4 localization during the after-ripening treatment.