Molecular mechanism of the osmoregulation during phtomorphogenesis in plant seedlings

干细胞的生长速度主要由两个参数决定，即渗透势和细胞壁的机械性能。大量证据表明，白光通过降低细胞壁的机械伸长率来抑制黄化幼苗的芽伸长。另一方面，有一份报告表明，白光增加渗透势，导致抑制黄化玉米幼苗的茎伸长(Parvez等人。1996年)。本文研究了白光对玉米幼苗渗透特性的调节机制。白光强烈抑制胚芽鞘的生长，而促进第一片叶的生长。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…的变化相关更具争议性。胚芽鞘和第一叶中的渗透性物质总量与可溶性糖的含量呈正相关。白光对结合在细胞壁上的酸性转化酶活性有抑制作用，而对第一片叶的酶活性有促进作用。酸性转化酶活性与胚芽鞘和第一叶中的可溶性糖含量呈正相关，除胚芽鞘和第一叶外，白光还提高了中胚轴的渗透势。白光照射后，中胚轴中酸性转化酶活性下降。在EDTA存在下，胚芽鞘和中胚轴切段的糖渗出在白光照射下被刺激。在颖果上方10 mm处切开中胚轴，研究光照对糖从颖果到中胚轴运输的影响。光照对中胚轴切段的糖分泌没有影响。质膜质子-ATPase的有效抑制剂--钒酸盐可抵消白光对胚芽鞘和中胚轴切段糖分分泌的影响。因此，白光通过控制细胞壁结合的酸性转化酶活性来控制玉米幼苗各器官间的糖分分配，从而控制玉米幼苗新梢的生长。目前，酸性转化酶基因的克隆工作正在进行中，研究玉米幼苗光形态建成过程中各器官酸性转化酶基因表达的调控机制。较少

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