Temperature response of vernalization in wheat: a developmental analysis

The vernalization response of wheat (Triticum aestivum L.) was reinterpreted from a developmental perspective, using current concepts of the developmental regulation of wheat morphology and phenology. At temperatures above 0 degrees C, the effects of the process of vernalization per se in wheat are confounded by the effects of concurrent vegetative development. These effects are manifested by differences in the number of leaves initiated by the shoot apex prior to floral initiation, which in turn affects the subsequent rate of development to ear emergence and anthesis. Leaf primordia development during vernalization and total leaf number at flowering were used to develop criteria to define both the progress and the point of saturation of the vernalization response. These criteria were then used to reinterpret the results of Chujo (Proceedings of the Crop Science Society of Japan 35: 177-186, 1966) and derive the temperature response of vernalization per se for plants grown under saturating long day conditions. The rate of vernalization increased linearly with temperature between 1 and 11 degrees C, such that the time taken to saturate the vernalization response decreased from 70 d at 1 degree C to 40 d at 11 degrees C. The rate declined again at temperatures above 11 degrees C, and 18 degrees C was apparently ineffective for vernalization. Total leaf number at saturation, however, increased consistently with temperature, as a result of the balance between the concurrent processes of leaf primordium initiation and vernalization. Total leaf number at saturation increased from 6 at 1 degree C to 13.3 at 15 degrees C, which in turn influenced the time taken to reach ear emergence. The advantages of using this developmental interpretation of vernalization as the basis for a mechanistic model of the vernalization response in wheat are discussed.