Welling Annikki, Rinne Päivi, Viherä-Aarnio Anneli, Kontunen-Soppela Sari, Heino Pekka, Palva E Tapio
Department of Biosciences, Division of Genetics, and Institute of Biotechnology, University of Helsinki, PO Box 56, FIN-00014 Helsinki, Finland.
J Exp Bot. 2004 Feb;55(396):507-16. doi: 10.1093/jxb/erh045.
The overwintering of trees in northern areas depends on processes regulated by photoperiod and temperature. To identify the physiological and genetic factors involved in this environmental control, three latitudinal ecotypes of pubescent birch (Betula pubescens Ehrh.) growing in a common garden experiment were used. Each ecotype responded to the shortening of the photoperiod according to its specific critical daylength, resulting in the induction of freezing tolerance and dehydration of buds first in the northern ecotype, followed by the central and southern ecotypes, respectively. By contrast, there was no clear difference in the timing of dormancy release, bud rehydration, and deacclimation in the spring, suggesting that these traits were controlled mainly by temperature. To elucidate the role of dehydrins (DHN) in the overwintering process, two DHN genomic clones were isolated from pubescent birch and expression of the corresponding genes, both in field and under controlled conditions, was characterized. BpuDhn1 was found to encode an Y(n)K(n)-type of basic DHN, while BpuDhn2 encoded an acidic, SK(n)-type of DHN. In field-grown trees the level of BpuDhn1 increased in buds during the autumn, while the level of BpuDhn2 was highest during the coldest winter months. Under controlled conditions BpuDhn1 increased in response to the combined effect of short daylength and low, non-freezing temperatures whereas the expression of BpuDhn2 was mainly controlled by low temperature while photoperiod had less effect on its expression. These results suggest that DHNs participate in the sensitive environmental regulation of the overwintering process in birch.
北方地区树木的越冬取决于受光周期和温度调节的过程。为了确定参与这种环境控制的生理和遗传因素，我们使用了在一个共同花园实验中生长的三种不同纬度生态型的毛桦（Betula pubescens Ehrh.）。每种生态型根据其特定的临界日长对光周期缩短做出反应，导致北部生态型的芽首先诱导出抗冻性和脱水，随后中部和南部生态型依次出现这种情况。相比之下，春季休眠解除、芽复水和脱锻炼的时间没有明显差异，这表明这些性状主要受温度控制。为了阐明脱水蛋白（DHN）在越冬过程中的作用，我们从毛桦中分离出两个DHN基因组克隆，并对相应基因在田间和受控条件下的表达进行了表征。发现BpuDhn1编码一种Y(n)K(n)型的碱性DHN，而BpuDhn2编码一种酸性的SK(n)型DHN。在田间生长的树木中，秋季芽中BpuDhn1的水平升高，而BpuDhn2的水平在最冷的冬季月份最高。在受控条件下，BpuDhn1因短日长和低温（非冰冻）的联合作用而增加，而BpuDhn2的表达主要受低温控制，光周期对其表达的影响较小。这些结果表明，DHN参与了桦树越冬过程的敏感环境调节。
