Developmental regulation of low-temperature tolerance in winter wheat

Vernalization and photoperiod genes have wide-ranging effects on the timing of gene expression in plants. The objectives of this study were to (1) determine if expression of low-temperature (LT) tolerance genes is developmentally regulated and (2) establish the interrelationships among the developmental stages and LT tolerance gene expression. LT response curves were determined for three photoperiod-sensitive LT tolerant winter wheal (Triticum aestivum)2 L, em Thell) genotypes acclimated at 4 degreesC under 8 h short-day (SD) and 20 h long-day (LD) photoperiods from 0 to 112 d. Also, three de-acclimation and re-acclimation cycles were used that bridged the vegetative/reproductive transition point for each LD and SD photoperiod treatment. A vernalization period of 49 d at 4 degreesC was sufficient for all genotypes to reach vernalization saturation as measured by minimum final leaf number (FLN) and confirmed by examination of shoot apices dissected from crowns that had been de-acclimated at 20 degreesC LD. Before the vegetative/reproductive transition, both the LD- and SD-treated plants were able to re-acclimate to similar LT50 (temperature at which 50% of the plants are killed by LT stress) levels following de-acclimation at 20 degreesC. De-acclimation of LD plants after vernalization saturation resulted in rapid progression to the reproductive phase and limited ability to re-acclimate. The comparative development of the SD (non-flowering-inductive photoperiod) de-acclimated plants was greatly delayed relative to LD plants, and this delay in development was reflected in the ability of SD plants to re-acclimate to a lower temperature. These observations confirm the hypothesis that the point of transition to the reproductive stage is pivotal in the expression of LT tolerance genes, and the level and duration of LT acclimation are related to the stage of phenological development as regulated by vernalization and photoperiod requirements. (C) 2001 Annals of Botany Company.