Chilling to zero degrees disrupts pollen formation but not meiotic microtubule arrays in Triticum aestivum L.

Throughout the wheat-growing regions of Australia, chilling temperatures below 2 degrees C occur periodically on consecutive nights during the period of floral development in spring wheat (Triticum aestivumL.). In this study, wheat plants showed significant reductions in fertility when exposed to prolonged chilling temperatures in controlled environment experiments. Among the cultivars tested, the Australian cultivars Kite and Hartog had among the lowest levels of seed set due to chilling and their responses were investigated further. The developmental stage at exposure, the chilling temperature and length of exposure all influenced the level of sterility. The early period of booting, and specifically the +4cm auricle distance class, was the most sensitive and corresponded to meiosis within the anthers. The response of microtubules to chilling during meiosis in Hartog was monitored, but there was little difference between chilled and control plants. Other abnormalities, such as plasmolysis and cytomixis increased in frequency, were associated with death of developing pollen cells, and could contribute to loss of fertility. The potential for an above-zero chilling sensitivity in Australian spring wheat varieties could have implications for exploring the tolerance of wheat flower development to chilling and freezing conditions in the field. In the field, spring wheat in Australia may experience extended periods of night time chilling during flower development. Prolonged cold treatment under controlled conditions was shown to induce pollen sterility and reduce yield substantially. The effect of seven consecutive nights of chilling on anther and pollen development (microsporogenesis) revealed that increased plasmolysis, cytomixis and death of developing pollen cells were associated with increased sterility. Microtubules, which are temperature sensitive, were unaffected by chilling treatments during meiosis.