Molecular mechanism of the osmoregulation during phtomorphogenesis in plant seedlings

干细胞的生长速度主要由渗透电位和细胞壁的力学性能两个参数决定。大量证据表明，白光通过降低细胞壁的机械伸长性来抑制黄化幼苗的茎伸长。另一方面，有报道表明，白光增加渗透势，导致黄化玉米幼苗的茎伸长受到抑制（Parvez et al. 1996）。本文研究了白光调控渗透特性与玉米幼苗茎部生长的关系。白光对胚芽的生长有较强的抑制作用，而对第一片叶的生长有较强的促进作用。在白光照射下，胚芽鞘的渗透势增加。另一方面，白光降低了第一片叶片的渗透势。胚芽鞘和第一片叶生长速率的变化与渗透势的变化相关。胚芽鞘和第一片叶片的渗透总量与可溶性糖的总量呈正相关。白光抑制细胞壁酸性转化酶活性，而促进第一片叶片酸性转化酶活性。酸性转化酶活性与胚芽鞘和第一叶可溶性糖含量相关。除了胚芽鞘和第一叶外，白光也增加了中胚轴的渗透电位。在白光照射下，中胚轴酸性转化酶活性降低。在EDTA存在的情况下，白光照射刺激从胚芽和中胚轴切除的节段的切口中渗出糖。将中胚轴切至颖果上方10mm处，观察光对糖从颖果向中胚轴转运的影响。中胚轴切口的糖渗出量不受光照的影响。钒酸盐是一种有效的质膜质子atp酶抑制剂，可以消除白光对胚芽和中胚轴切割处糖渗出的影响。综上所述，白光通过控制细胞壁酸性转化酶的活性，控制了玉米幼苗各器官间糖的分配，从而控制了玉米幼苗的生长。目前，酸性转化酶基因的克隆正在进行中，旨在研究玉米幼苗光形态发生过程中酸性转化酶基因在各器官中的表达调控机制。少

The growth rate of the stem cells is mainly determined by two parameters, the osmotic potential and the mechanical properties of cell walls. Much evidence indicates that white light inhibits shoot elongation in etiolated seedlings by decreasing the mechanical extensibility of cell walls. On the other hand, there is a report suggesting that white light increases osmotic potential, resulting in inhibited stem elongation in etiolated maize seedlings (Parvez et al. 1996). In this report, the mechanism by which white light regulates osmotic properties was studied, in relation to stem growth in maize seedlings.White light strongly inhibited growth of the coleoptils, while it stimulated growth of the first leaf. Osmotic potential in the coleoptile was increased, in response to the irradiation of white light. On the other hand, white light decreased osmotic potential in the first leaf. Changes in the growth rate in the coleoptile and the first leaf were correlated with changes in osmotic poten … More tial. The total amount of osmotica in the coleoptile and first leaf was correlated with that a soluble sugars. White light inhibited the activity of acid invertase bound to cell walls, while it promoted the enzyme activity in the first leaf. The activity of the acid invertase was correlated with the content of soluble sugars in the coleoptile and the first leaf.In addition to the coleoptile and first leaf, white light also increased osmotic potential in the mesocotyl. In response to the irradiation of white light, the activity of acid invertase decreased in the mesocotyl. Sugar exudation from the cut of the segments excised from the coleoptile and the mesocotyl in the presence of EDTA was stimulated by white light irradiation. The mesocotyl was cut 10 mm above the caryopsis, to examine the effect of light on sugar transport from the caryopsis to the mesocotyl. Sugar exudation from the cut of the mesocotyl was not influenced by light irradiation. Vanadate a potent inhibitor of plasma membrane-proton ATPase nullified the effect of white light on sugar exudation from the cut of the coleoptile and the mesocotyl.From these experimental results, it was concluded that white light controls shoot growth in maize seedling by controlling sugar distribution among organs in maize seedlings via controlling the activity of acid invertase bound to cell walls. At present, the cloning of acid invertase gene is in progress, to study the regulatory mechanism of the gene expression on acid invertase in organs in maize seedlings during photomorphogenesis. Less