INFLUENCE OF VEGETATIVE/REPRODUCTIVE TRANSITION ON PROLINE AND PROTEIN ACCUMULATION AND EXPRESSION OF FREEZING TOLERANCE IN WHEAT CULTIVARS GROWN IN TEMPERATE AND COLD CLIMATES

This project was initiated to determine the effect of different hardening conditions on developmental traits, accumulation of compatible solutes and freezing tolerance (FT) in winter and spring habit cultivars grown under field conditions in Iran. For this purpose, three cultivars with different vernalization requirements were planted in the field during autumn at Zanjan and Karaj, which represent cold and temperate regions, respectively. FT, as measured by means of LT50 values and developmental progress estimated from final leaf number (FLN) and shoots apex morphology were monitored throughout the cold seasons. Result showed that ‘Pishtaz’ spring wheat quickly initiated reproductive growth in comparison with other cultivars as measured by minimum final leaf number (FLN) and timing of double ridge formation. The phenological development of the winter cultivars (CDC Osprey and Pishagam) in cold region was greatly delayed relative to temperate region, and this delay in development was associated with higher and longer FT expression. Cold and sub-zero temperatures, especially in cold region, resulted in slow advancement to the early reproductive phase after vernalization fulfilment and continuation of freezing tolerance. Soluble protein and proline concentrations in leaves of winter cultivars increased during cold acclimation and subsequently decreased by vegetative/reproductive transition. These observations confirm the hypothesis that the phenological development regulate accumulation of compatible solutes, expression of FT, and acclimation conditions of regions determine the level and duration of expression of FT in wheat.