Thermal Regulation and Physiological Responses of Flowering Plants Under Heat Stress: Effects of Flower Colour on Heat Tolerance
Keywords:
Flower colour, Heat stress, Thermal regulation, Transpiration, Heat toleranceAbstract
Flower colour is a poorly understood variable that can influence heat stress effects on floral function and reproductive performance, which poses an increasing threat. The colour-related differences in floral temperature, physiological responses and heat tolerance were assessed in this study by comparing dark-purple, light-purple and white flower morphs grown under different thermal environments. Thermal regulation was evaluated by measuring flower, petal and air temperature relationships and physiological responses were assessed by measuring transpiration, assimilation and boundary-layer conductance. Electrolyte leakage was used as a measure of heat tolerance across temperatures of 25 to 60°C, and nonlinear modelling was used to estimate the heat tolerance values (T50). The transpiration rate was highest for dark-purple flowers, the petal temperature was highest for purple flowers, and the white flowers showed almost no transpiration, indicating that the evaporative cooling was weakest. A reduction in assimilation occurred with increasing temperature, and this is thought to be due to metabolic impairment under heat stress. The progressive membrane damage was verified by the electrolyte leakage, which increased greatly with temperature. Cellular injury was most significantly related to temperature, with colour having a lesser effect. The estimated T50 values varied between the morphs, with the light-purple flower having the highest T50 value. In general, the colour of the flower influenced the thermal loading and physiological cooling, whereas cellular heat tolerance was largely dependent on absolute thermal exposure. The results shed light on the interactions of pigmentation with physiological regulation in determining floral responses to warming.
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