Poster: Temperature Responses

Abs # 194: The leaf-order-dependent enhancement of freezing tolerance in cold-acclimated Arabidopsis rosettes is not correlated with the transcript levels of the cold-inducible transcription factors of CBF/DREB1

Presenter:	Nishida, Ikuo , nishida@biol.s.u-tokyo.ac.jp
Authors	Nishida, Ikuo  (A)   Nakamura, Masanobu  (A)   Takagi, Taro  (A)   Yano, Ryoichi  (A)   Hayashi, Hiroaki  (B)   Rie, Inatsugi  (A)
Affiliations:	(A): Department of Biological Sciences, Graduate Schooll of Science, The University of Tokyo (B): Department of Applied Biological Chemistry, Graduate School of Agriculture, The University of Tokyo

The central part of cold-acclimated Arabidopsis (Arabidopsis thaliana L. ecotype Columbia) rosettes survived freezing at lower temperatures better than did those at the rosette periphery. Electrolyte-leakage tests with detached rosette leaves verified that freezing tolerance in central (or young) leaves increased faster and to a greater extent than in peripheral (or aged and mature) leaves at 2ūC. Cold-induced accumulation of sugars could partly account for the leaf-order-dependent enhancement of freezing tolerance after 1 d at 2ūC, whereas the role of proline (Pro) remains to be determined. Cold-induced accumulation of the transcripts of stress-inducible CBF/DREB1 transcription factors apparently disagreed with the observed difference in the freezing tolerance in different leaf orders. However, the levels of COR78/RD29A transcripts were higher in central leaves than in peripheral leaves within 12 h at 2ūC and were almost the same between different leaf orders after 1 to 3 d at 2ūC. Thus, the accumulation of COR78/RD29A transcripts in central leaves at 2ūC seems to be enforced by post-transcriptional regulation of the CBF/DREB1 transcription factors. Consequently, COR78/RD29A content per total leaf protein was similar between different leaf orders after 7 d at 2ūC, although COR78/RD29A content per fresh weight in central leaves was twice that in peripheral leaves. Thus, cold-induced accumulation of COR78/RD29A does not seem to account for the observed difference in freezing tolerance in different leaf orders. All these data suggest that the leaf-order-dependent enhancement of freezing tolerance in Arabidopsis rosettes during cold acclimation is regulated by multiple components.