RELATIONSHIP BETWEEN LOW-TEMPERATURE TOLERANCE AND VERNALIZATION RESPONSE IN WHEAT AND RYE

Vernalization response and low-temperature acclimation are survival me chanisms 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 respo nsible for the gradual loss in low-temperature tolerance observed in w inter cereals maintained for long periods of time at temperatures in t he 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 toleran ce in wheat (Triticum aestivum L.) and rye (Secale cereale L.). The pl ants of all cultivars began to low-temperature acclimate at a rapid ra te when exposed to a constant 4 degrees C. The rate of change in low-t emperature tolerance then gradually slowed and eventually started to d ecline, producing a curvilinear relationship between low-temperature t olerance and stage of acclimation. A close relationship was observed b etween the time to vemalization saturation and the start of the declin e in low-temperature tolerance of cultivars held at 4 degrees C. Howev er, cereal plants retained at least a partial ability to low-temperatu re acclimate following exposure to warm temperatures after vernalizati on saturation, indicating that vemalization saturation does not result in a ''switching off' of the low-temperature tolerance genes. The pos sibility that vernalization genes have a more subtle regulatory role i n the expression of low-temperature tolerance genes could not be ruled out, and future avenues for investigation are discussed.