Hawkesbury Institute for the Environment, Western Sydney University, Locked Bag 1797, Penrith, New South Wales, 2751, Australia.
Instituto Nacional de Investigación Agropecuaria (INIA), La Estanzuela Research Station, Ruta 50, Km. 11, Colonia, Uruguay.
Physiol Plant. 2021 Mar;171(3):358-370. doi: 10.1111/ppl.13202. Epub 2020 Sep 16.
Silicon (Si) has been widely reported to improve plant resistance to water stress via various mechanisms including cuticular Si deposition to reduce leaf transpiration. However, there is limited understanding of the effects of Si on stomatal physiology, including the underlying mechanisms and implications for resistance to water stress. We grew tall fescue (Festuca arundinacea Schreb. cv. Fortuna) hydroponically, with or without Si, and treated half of the plants with 20% polyethylene glycol to impose physiological drought (osmotic stress). Scanning electron microscopy in conjunction with X-ray mapping found that Si was deposited on stomatal guard cells and as a sub-cuticular layer in Si-treated plants. Plants grown in Si had a 28% reduction in stomatal conductance and a 23% reduction in cuticular conductance. When abscisic acid was applied exogenously to epidermal leaf peels to promote stomatal closure, Si plants had 19% lower stomatal aperture compared to control plants (i.e. increased stomatal sensitivity) and an increased efflux of guard cell K ions. However, the changes in stomatal physiology with Si were not substantial enough to improve water stress resistance, as shown by a lack of significant effect of Si on water potential, growth, photosynthesis and water-use efficiency. Our findings suggest a novel underlying mechanism for reduced stomatal conductance with Si application; specifically, that Si deposition on stomatal guard cells promotes greater stomatal sensitivity as mediated by guard cell K efflux.
硅（Si）已被广泛报道可通过多种机制提高植物对水分胁迫的抗性，包括减少叶片蒸腾的角质层 Si 沉积。然而，对于 Si 对气孔生理的影响，包括其潜在机制及其对水分胁迫抗性的影响，我们的理解有限。我们用水培法种植高羊茅（Festuca arundinacea Schreb. cv. Fortuna），有无 Si 两种处理，并对一半植物用 20%聚乙二醇处理以施加生理干旱（渗透胁迫）。扫描电子显微镜结合 X 射线映射发现，Si 沉积在气孔保卫细胞上和 Si 处理植物的表皮下。在 Si 处理的植物中，气孔导度降低了 28%，角质层导度降低了 23%。当将外源脱落酸应用于表皮叶片剥离以促进气孔关闭时，与对照植物相比，Si 植物的气孔孔径低 19%（即气孔敏感性增加），保卫细胞 K 离子外流增加。然而，Si 对气孔生理的变化不足以提高水分胁迫抗性，因为 Si 对水势、生长、光合作用和水分利用效率没有显著影响。我们的研究结果表明，Si 应用降低气孔导度的一种新的潜在机制；具体来说，Si 沉积在气孔保卫细胞上促进了更大的气孔敏感性，这是由保卫细胞 K 外流介导的。
