Influence of photoperiod response on the expression of cold hardiness in wheat and barley

Vernalization and photoperiod requirements regulate the timing of the veget ative/reproductive transition in plants. Cereals adapted to cold winter cli mates regulate this developmental transition mainly through vernalization r equirements, which delay transition from the vegetative to the reproductive growth stage. Recent research indicates that vernalization requirements al so influence the expression of low-temperature (LT) tolerance genes in cere als exposed to acclimating temperatures. The objective of the present study was to determine if LT tolerance expression was also developmentally regul ated by photoperiod response. The nonhardy, short day (SD) sensitive, wheat (Triticum aestivum L. em Thell) cultivar AC Minto, the LT tolerant, highly SD sensitive barley (Hordeum vulgare L.) cultivar Dicktoo, and a barley se lection with very low sensitivity to SD were subjected to 8-h (SD) and 20-h (LD) days at cold acclimating temperatures over a period of 98 d. Final le af number (FLN) was used to measure photoperiod sensitivity and determine t he vegetative/reproductive transition point. The LT tolerance of the less S D sensitive barley genotype was similar for LD and SD treatments. In contra st, a delay in the transition from the vegetative to the reproductive stage in AC Minto and Dicktoo grown under SD resulted in an increased level and/ or longer retention of LT tolerance. These results support the hypothesis t hat not only the level, but also the duration of gene expression determines the degree of LT tolerance in cereals. Consequently, any factor that lengt hens the vegetative stage, such as vernalization or photoperiod sensitivity , also increases the duration of expression of LT tolerance genes.