TRANSIENT FREEZING REGULATES EXPRESSION OF EXTENSIN-TGPE GENES IN WINTER OILSEED RAPE

In order to identify the molecular mechanisms underlying the process o f cold acclimation in plants, we examined the expression of extensin-t ype genes in Brassica napus L. var. oleifera L. leaves, subjected to v arious low temperature treatments. Northern analysis showed that two t ranscripts of 1260 nt and 1450 nt, strongly hybridized to the extA pro be and accumulated to high levels in leaves subjected to transient fre ezing treatments, giving rise to ca 20% membrane injury (2 h at - 3 de grees C for non-acclimated or at - 12 degrees C for cold-acclimated le aves). The accumulation of the frost-induced extensin mRNAs (especiall y of the 1450-nt transcript) was markedly higher than that seen upon m echanical wounding. Frost-dependent induction of extensin mRNAs was ma rkedly elevated both in extent and duration in cold-acclimated as comp ared to non-acclimated leaves. Post-incubation of cold-acclimated and frost-treated leaves on ice instead of at room temperature prolonged t he lime course of extensin mRNA accumulation and resulted in a marked increase of the level of the transcripts in the material studied. Fact ors possibly involved in the induction of extensin gene transcription are discussed, as well as the role of extensin cell wall proteins in p lant responses to freezing.