Relationship between low-temperature tolerance and vernalization response in wheat and rye

Vernalization response and low-temperature acclimation are survival mechanisms that cereals have evolved to cope with low-temperature stress. Both responses have similar optimum temperature ranges for induction, and they are controlled by genetic systems that are interrelated. It has also been suggested that the completion of vernalization is responsible for the gradual loss in low-temperature tolerance observed in winter cereals maintained for long periods of time at temperatures in the optimum range for low-temperature acclimation. In the present study, two experiments were conducted with the objective of clarifying the relationship between vemalization response and low-temperature tolerance in wheat (Triticum aestivum L.) and rye (Secale cereale L.). The plants of all cultivars began to low-temperature acclimate at a rapid rate when exposed to a constant 4 degrees C. The rate of change in low-temperature tolerance then gradually slowed and eventually started to decline, producing a curvilinear relationship between low-temperature tolerance and stage of acclimation. A close relationship was observed between the time to vemalization saturation and the start of the decline in low-temperature tolerance of cultivars held at 4 degrees C. However, cereal plants retained at least a partial ability to low-temperature acclimate following exposure to warm temperatures after vernalization saturation, indicating that vemalization saturation does not result in a ''switching off' of the low-temperature tolerance genes. The possibility that vernalization genes have a more subtle regulatory role in the expression of low-temperature tolerance genes could not be ruled out, and future avenues for investigation are discussed.