褪黑素对渗透胁迫下植物根系形态建成影响及调控机理研究进展

Progress in the effects of melatonin on plant root morphogenesis and its regulation mechanism under osmotic stress

  • 摘要: 根系作为植物主要器官之一, 常直接或间接遭受渗透胁迫, 如干旱、盐碱、高低温、重金属等对植物造成不可逆的伤害。调控根系生长是提升植物地上生存质量与植株抗逆性的最有效方式之一。外源激素对根系生长的调控尤为显著, 而褪黑素(melatonin, MT)作为一种新兴的植物生长调节物质在逆境研究中备受瞩目。本文综述了褪黑素的生物合成过程(以色氨酸为前体的酶促反应)、合成主要部位(叶绿体和线粒体)、分布(种子、叶和根系内皮层、中柱鞘与根尖伸长区等)及其与生长素、乙烯等激素的密切关系; 渗透胁迫下, MT促进种子萌发与胚根发育、调控主根与侧根生长(低浓度促进主根生长, 高浓度促进侧根形成)、改善根系形态特征(增加根毛数量、表面积、生物量及根系活性等)。该过程一方面通过MT与激素互作、调节相关基因表达,进而影响根系生长发育; 另一方面, 通过激活抗氧化系统,调控抗逆基因表达增强超氧化物歧化酶、过氧化氢酶等活性以清除羟基、单线态氧、过氧化氢与活性氧等有毒物质。此外, MT还通过影响根际微生物群落结构, 促进有益菌定殖、提升土壤养分利用率、改善根际环境来影响植物根系生长。综上,褪黑素抗逆具有广谱性、作用效果受浓度调控且单双子叶响应存在差异, 其核心机制包括激活抗氧化系统促进根系对水分的吸收、协同调控代谢通路增强植株耐渗透胁迫力以及整合跨胁迫多级信号转导网络形成快速感知-平衡系统。该综述阐明了褪黑素在协调“根系构型优化-抗逆性增强”方面的独特价值,为进一步利用褪黑素介导的根系构型调控和根际微环境改善提供了重要的理论参考, 也为利用生物技术调控植物内源褪黑素水平以增强抗逆性指明了方向。

     

    Abstract: The root system, as one of the primary organs of plants, often directly or indirectly suffers from osmotic stresses, such as drought, salinity, extreme temperatures, heavy metals, etc., which cause irreversible damage to plants. Regulating root growth is one of the most effective strategies to improve the aboveground survival quality and stress resistance of plants. Exogenous hormones have a particularly significant regulatory effects on root growth, and melatonin (MT), as an emerging plant growth regulator, has attracted much attention in stress response research. This article reviews the biosynthesis process of melatonin (which is derived from tryptophan and is produced through multiple enzymatic reactions), the main synthesis sites (chloroplasts and mitochondria), its distribution (seed, leaf, and the endodermis, pericycle, and root apical meristem zone of the root system, etc.), and its close relationship with hormones such as auxin, ethylene, etc. Under osmotic stress, MT promotes seed germination and hypocotyl development, regulates the growth of main root and lateral roots (low concentrations MT stimulate primary root elongation, while high concentration MT promote lateral root formation), and improves root morphological characteristics (increasing the number of root hairs, surface area, biomass, and root activity, etc.). This process, on the one hand, affects root growth and development through the interaction between MT and hormones and the regulation of related gene expression; on the other hand, it activates the antioxidant system, regulates the expression of stress resistance genes, and enhances the activities of superoxide dismutase, catalase, etc. to remove toxic substances such as hydroxyl groups, singlet oxygen, hydrogen peroxide and reactive oxygen species, etc. In addition, MT also affects plant root growth by influencing the structure of the rhizosphere microbial community, promoting the colonization of beneficial bacteria, improving soil nutrient utilization, and improving the root environment. In summary, melatonin's stress resistance has broad-spectrum properties, its effect is regulated by concentration, and there are differences in responses between monocotyledons and dicotyledons. Its core mechanism includes activating the antioxidant system to promote water absorption by the root system, coordinating the regulation of metabolic pathways to enhance the stress resistance of plants, and integrating the multi-level signal transduction network across stressors to form a rapid perception-balance system. This review clarifies the unique value of melatonin in coordinating "root system configuration optimization - stress resistance enhancement", providing important theoretical references for further using melatonin-mediated root system configuration regulation and rhizosphere microenvironment improvement, and also indicating the direction of using biotechnology to regulate the endogenous melatonin level of plants to enhance stress resistance.

     

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