Temperature Effects on Cytokinin Accumulation and Kernel Mass in a Dwarf Wheat

The objectives of this study were: (1) to quantify post-anthesis kernel cytokinin levels in ‘Tibet Dwarf’, a dwarf wheat (Triticum aestivumL.) that accumulates elevated quantities of leaf cytokinins; and (2) to measure the effects of temperature on kernel cytokinin accumulation and mature kernel mass in this wheat. Post-anthesis kernel cytokinin accumulation was measured in control plants maintained at 25/12 °C (day/night) and treated plants which received a 7 d exposure to 35/25 °C beginning at anthesis and grown to maturity at 25/15 °C. Zeatin (Z), dihydrozeatin (diHZ) and their respective ribosides were the predominant cytokinins detected in control and treated plants. Minimal quantities of isopentenyl adenine-type cytokinins were detected. Kernel cytokinin content peaked within 3 d after anthesis in both groups and returned to baseline levels within 1–2 d. Relative to controls, exposure to high temperature reduced kernel cytokinin content approx. 80% within 1 d after anthesis. Because kernel cytokinin in control Tibet Dwarf plants exceeded that previously measured in other varieties by over 100-fold, the reduced content of treated plants still exceeded that of untreated plants of other varieties. The increased cytokinin content did not enhance thermotolerance. The temperature treatment reduced mature kernel weights approx. 27%, similar to reductions measured in other wheat varieties.