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，植物生长障碍在植物成功适应环境方面发挥了关键作用。陆生植物祖先中保存的基本因子为植物在陆地上的定殖提供了必要的工具。质外体（中层，细胞壁）中的角质层和复杂聚合物等屏障的发展是避免水分流失和防止疾病入侵的关键因素之一。因此，质外体复合物往往是植物对非生物和生物胁迫的抗性机制的核心。虽然多重压力之间的密切关系和它们的重要性，成功的植物适应是公认的，研究还没有广泛研究特定的结构质外体障碍的作用，作为一个共同的调解人在压力和发育过程。 细胞壁部分是由通过凝胶状基质保持在一起的纤维素微纤丝组成的双相结构。这种凝胶状基质占细胞壁干重的三分之二，由交联的伸展素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型细胞壁的孔隙率、渗透性以及因此的屏障的主要调节分子，但精确的机制仍然没有解决。 形成果胶凝胶、调节孔隙率和渗透性的功能能力通过果胶甲基酯酶（PME）、钙、蔗糖控制并通过温度改性。 然而，大多数证据来自食品加工文献。值得注意的是，只有有限数量的这样的研究在植物中存在，我们不知道任何目前专门集中在蔗糖，Ca 2+和PME作为调控点控制质外体渗透性障碍，以提高广泛的植物适应多种压力。全球变暖也使人们最近更加关注温度驱动的环境适应。假设：温度介导的植物胁迫和树休眠反应是通过改变由PME、钙和蔗糖调节的果胶质外体渗透屏障来诱导的。 目的：1）证明质外体透性的降低提高了抗冻性; 2）通过质外体透性的变化确定PME、蔗糖和/或钙水平是否是抗冻性、盐胁迫和干旱胁迫抗性的关键调节因子。 3)确定温度介导的休眠诱导是否受PME、蔗糖和/或钙离子介导的质外体透性变化的调节。发现质外体渗透性是一系列非生物胁迫抗性的核心，将产生广泛的影响，为作物改良创造新的工具，并开始深入了解障碍和水流调节的作用-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. ***