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) det ermine if expression of low-temperature (LT) tolerance genes is development ally regulated and (2) establish the interrelationships among the developme ntal stages and LT tolerance gene expression. LT response curves were deter mined for three photoperiod-sensitive LT tolerant winter wheal (Triticum ae stivum)2 L, em Thell) genotypes acclimated at 4 degreesC under 8 h short-da y (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 t hat had been de-acclimated at 20 degreesC LD. Before the vegetative/reprodu ctive transition, both the LD- and SD-treated plants were able to re-acclim ate to similar LT50 (temperature at which 50% of the plants are killed by L T 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 develop ment was reflected in the ability of SD plants to re-acclimate to a lower t emperature. These observations confirm the hypothesis that the point of tra nsition to the reproductive stage is pivotal in the expression of LT tolera nce genes, and the level and duration of LT acclimation are related to the stage of phenological development as regulated by vernalization and photope riod requirements. (C) 2001 Annals of Botany Company.