Abstract
Melatonin is a pleiotropic signal molecule that plays critical roles in regulating plant growth and development, as well as providing physiological protections against various environmental stresses. Nonetheless, the mechanisms for melatonin-mediated pollen thermotolerance remain largely unknown. In this study, we report that irrigation treatment with melatonin (20 µM) effectively ameliorated high temperature-induced inactivation of pollen and inhibition of pollen germination in tomato (Solanum lycopersicum) plants. Melatonin alleviated reactive oxygen species production in tomato anthers under high temperature by the up-regulation of the transcription and activities of several antioxidant enzymes. Transmission electron micrograph results showed that high temperature-induced pollen abortion is associated with a premature degeneration of the tapetum cells and the formation of defective pollen grains with degenerated nuclei at the early uninuclear microspore stage, whilst melatonin protected degradation of organelles by enhancing the expression of heat shock protein genes to refold unfolded proteins and the expression of autophagy-related genes and formation of autophagosomes to degrade denatured proteins. These findings suggest a novel function of melatonin to protect pollen activity under high temperature and support the potential effects of melatonin on reproductive development of plants.
Highlights
IntroductionHigh temperature impacts plant vegetative growth and reproductive development, and especially inhibits flower bud differentiation, the development of female and male gametophytes, blooming and fruit set [1,2]
As the world warms up, plants are more vulnerable to extreme climates
This study deepens the understanding of melatonin functions in plant reproductive development and may have important implications for breeding heat-tolerant crops
Summary
High temperature impacts plant vegetative growth and reproductive development, and especially inhibits flower bud differentiation, the development of female and male gametophytes, blooming and fruit set [1,2]. The earliest high temperature-induced meiotic abnormalities occur in the pollen development [5,6]. Chromosome behavior and meiotic cell division is affected, which leads to unbalanced chromosome separation between spores and formation of 2n pollens after heat stress [5,7]. Heat stress reduces pollen number and viability, which are supported by tapetum cells [8]. The development and degeneration processes of tapetum cells are disturbed and reactive oxygen species (ROS) are accumulated under extreme heat or long-term mild heat stresses [9].
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