Apoplastic permeability barriers: a central regulating factor enabling plant resistance to abiotic stresses and dormancy induction.

在整个植物进化史中，屏障发挥了关键作用，使其能够成功地适应环境。陆地植物祖先保存的基本因子为植物在陆地上的定居提供了必要的工具。质外体(中层、细胞壁)中的角质层和复杂聚合物等屏障的形成是避免水分损失和防止疾病入侵的关键因素。因此，质外体复合体往往是高等植物对非生物和生物胁迫抗性机制的核心。虽然多种逆境及其对植物成功适应的重要性之间的密切关系已被广泛认识，但研究尚未广泛探讨特定的结构性质外体障碍作为跨越逆境和发育过程的共同媒介所起的作用。细胞壁部分是由纤维素微纤维通过凝胶状基质结合在一起的两相结构。这种凝胶状基质占细胞壁干重的三分之二，由交联性伸展蛋白、糖蛋白和包括果胶在内的非纤维素多糖组成。果胶是动态的，是决定I型细胞壁的孔隙度、渗透性和屏障的主要调节分子，但确切的机制仍未解决。形成果胶凝胶、调节孔隙度和渗透性的功能能力通过果胶甲基酯酶(PME)、钙、蔗糖和温度修饰来控制。然而，大部分证据来自食品加工文献。值得注意的是，目前在植物中的此类研究数量有限，我们目前还没有发现任何专门针对蔗糖、钙和PME作为调节点的研究，这些调节点控制质外体通透性障碍，以增强植物对多种胁迫的广泛适应。全球变暖最近也将重点放在了温度驱动的环境适应上。假设：温度介导的植物胁迫和树木休眠反应是通过改变PME、钙和蔗糖调节的果胶质外体渗透性屏障来诱导的。目的：1)证明质外体透性降低可提高抗寒性；2)通过质外体透性变化确定PME、蔗糖和/或钙水平是否是抗冻、盐和干旱胁迫的关键调节因子。3)确定温度诱导的休眠是否受质外体通过PME、蔗糖和/或钙的透性变化的调节。发现质外体渗透性处于一系列非生物胁迫抗性的中心将产生广泛的影响，为作物改良创造新的工具，并开始洞察屏障和水流调节的作用--所有植物生长、发育和适应环境的基本原则。***

Barriers have played a pivotal role enabling successful environmental adaptation throughout plant evolutionary history. Fundamental factors conserved in the progenitors of land plants provided essential tools for plant colonization on land. Development of barriers such as cuticular layers and complex polymers in the apoplast (middle lamella, cell wall) are among key factors enabling avoidance of water loss and preventing disease invasion. Thus, apoplastic complexes are often at the core of higher plant resistance mechanisms to both abiotic and biotic stresses. While the close relationship between multiple stresses and their importance to successful plant adaptation is well recognized, studies have not widely examined the role of specific structural apoplastic barriers as a common mediator across stresses and developmental processes. The cell wall fraction is a biphasic structure consisting of cellulose microfibrils held together by a gel-like matrix. This gel-like matrix constitutes up to two-thirds of the cell wall's dry weight and composed of cross-linking extensin glycoproteins and non-cellulosic polysaccharides including pectins. Pectins are dynamic, the major regulatory molecule dictating the porosity, permeability and therefore, barriers, of Type I cell walls but the precise mechanism is still not resolved. The functional ability to form pectin gels, regulate porosity and permeability is controlled through Pectin Methylesterase (PME), calcium, sucrose and modified by temperature. However, most of the evidence comes from the food processing literature. Remarkably, only a limited number of such studies in plants exist and we are not aware of any currently focussed specifically on sucrose, Ca2+ and PME as regulatory points controlling apoplast permeability barriers to enhance broad range plant adaptation to multiple stresses. Global warming has also placed more recent focus on temperature-driven environmental adaptation. Hypothesis: temperature-mediated plant stress and tree dormancy responses are induced through alterations in pectin apoplastic permeability barriers regulated by PME, calcium and sucrose. Objectives: 1) To demonstrate a reduction in apoplast permeability increases freezing stress resistance; 2) To determine if PME, sucrose and/or calcium levels are the key regulating factors to freezing, salt and drought stress resistance through apoplast permeability changes. 3) To determine if temperature-mediated dormancy induction is regulated by changes in apoplast permeability through PME, sucrose and/or calcium. Discovery apoplast permeability is at the centre of a range of abiotic stress resistances will have widespread impact, creating new tools for crop improvement and begins to provide insight into the role of barriers and regulation of water flow--fundamental principles to all plant growth, development and adaptation to the environment. ***