植物钙吸收、转运及代谢的生理和分子机制

钙是植物必需的营养元素。酸性砂质土壤中含钙较少, 导致在其土壤上生长的作物容易缺钙。另外由于果树果实、果菜类和包心叶菜类的蒸腾作用弱, 导致果树和蔬菜普遍生理缺钙。根系维管束组织可能通过共质体和质外体两种途径进行钙素吸收, 而果实则可通过非维管束组织直接吸收钙素。Ca2+通过Ca2+通道内流进入胞质, 并通过Ca2+-ATPase 和Ca2+/H+反向转运蛋白外流以保持胞质内低Ca2+浓度。为了应对植物发育和环境胁迫信号, Ca2+由质膜、液泡膜和内质网膜的Ca2+通道内流进入胞质, 导致胞质Ca2+浓度迅速增加, 产生钙瞬变和钙振荡, 传递到钙信号靶蛋白, 如钙调素、钙依赖型蛋白激酶及钙调磷酸酶B类蛋白, 引起特异的生理生化反应。本文综述了植物钙素吸收、转运以及代谢研究的最新进展, 包括植物对钙的需求和作物缺钙的原因, 根系维管束组织及果实钙素吸收机理, Ca2+跨膜运输特性, 钙的信使作用以及钙信号靶蛋白等方面内容。

The physiological and molecular mechanisms of calcium uptake, transport, and metabolism in plants.

Calcium is an essential plant nutrient. Calcium deficiency may occur in acidic soils with low base saturation. Since the transpiration from enclosed tissues and fruit is low, Ca deficiency readily develops in fruit trees and vegetables with enclosed tissues or fruit. Calcium may traverse the root through an apoplastic or symplastic pathway. Calcium is also believed to be directly taken up by an actual fruit with a non-vascular bundle structure. At the molecular level, Ca enters plant cells through Ca2+-permeable ion channels in their plasma membranes, whereas low [Ca2+] in unstimulated cells is maintained by Ca2+-ATPase and Ca2+/H+ antiporters. The rapid influx of Ca2+ through cation channels in the plasma membranes, tonoplast and/or endoplasmic reticulum generates transient elevation and oscillation of [Ca2+]cyt that initiate cellular responses to a diverse range of developmental cues and environmental challenges. The cellular [Ca2+]cyt sensors include calmodulin, calcium-dependent protein kinases and calcineurin B-like proteins that allow plant cells to respond appropriately to [Ca2+]cyt signals. This article provides an overview of the mechanisms of Ca2+ transport across cellular membranes, the origins and specificity of [Ca2+]cyt signals and the characteristics of cellular [Ca2+]cyt sensors.