Water Activity and Temperature

Water deficits and elevated temperatures are stressful conditions that negatively affect plant and leaf growth. Detailed kinematic analyses of leaf growth at non-stressful temperatures or a range of water activities have not been reported for Arabidopsis. However, in maize, a good correlation between leaf elongation and cell production rates was observed in a range of temperatures and when comparing watered plants with plants experiencing water stress (Granier et al. 2000). Moreover, CDK activity and cell division rate were strongly correlated, but not p34cdk abundance. This observation suggests that post-translational modification of p34cdk or transcriptional control of cyclin expression are potential targets for these signals. In a recent study (Rymen et al. 2007), the effect of cold nights on leaf growth in maize was examined. These conditions did not affect mature cell size, or the size of the meristem, but major changes were observed in the dividing cells of the meristem: cell size of dividing cells was reduced (hence the meristem had more, but smaller cells), and cell cycle duration was extended. This indicated that cell growth was strongly affected, and furthermore, that low temperature resets the size threshold for division. Interestingly, the latter is reminiscent of the response of budding yeast to growth at different levels of nutrient availability: in low nutrients, the size threshold for division is reduced, but when nutrients are abundant, cells divide with a larger mass (Tyson et al. 1979). Ploidy levels were not significantly changed, suggesting that all cell cycle phases were equally affected by the low temperatures, but the expression of some cell cycle regulators that function in the G1/S transition and in S-phase (e.g., cyclin CYCA3;1, CDKA1;1, E2F) was strongly down-regulated.

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