Link B M, Wagner E R, Cosgrove D J
Wisconsin Center for Space Automation and Robotics, The University of Wisconsin, Madison, WI 53706, USA.
Physiol Plant. 2001 Oct;113(2):292-300. doi: 10.1034/j.1399-3054.2001.1130218.x.
In young cucumber seedlings, the peg is a polar outgrowth of tissue that functions by snagging the seed coat, thereby freeing the cotyledons. The development of the peg is thought to be gravity-dependent and has become a model system for plant-gravity response. Peg development requires rapid cell expansion, a process thought to be catalyzed by alpha-expansins, and thus was a good system to identify expansins that were regulated by gravity. This study identified 7 new alpha-expansin cDNAs from cucumber seedlings (Cucumis sativus L. cv Burpee Hybrid II) and examined their expression patterns. Two alpha-expansins (CsExp3 and CsExp4) were more highly expressed in the peg and the root. Earlier reports stated that pegs tend not to form in the absence of gravity, so the expression levels were compared in the pegs of seedlings grown in space (STS-95), on a clinostat, and on earth (1 g). Pegs were observed to form at high frequency on clinostat and space-grown seedlings, yet on clinostats there was more than a 4-fold reduction in the expression of CsExp3 in the pegs of seedlings grown on clinostats vs. those grown at 1 g, while the CsExp4 gene appeared to be turned off (below detection limits). There were no detectable differences in expansin gene expression levels for the pegs of seedlings grown in space or in the orbiter environmental simulator (OES) (1 g) at NASA. The microgravity environment did not affect the expression of CsExp3 or CsExp4, and the clinostat did not simulate the microgravity environment well.
在黄瓜幼苗中，胚轴是组织的极性突出物，其功能是钩住种皮，从而使子叶得以解放。胚轴的发育被认为依赖于重力，并已成为植物重力反应的一个模型系统。胚轴发育需要细胞快速扩张，这一过程被认为是由α-扩张蛋白催化的，因此它是鉴定受重力调节的扩张蛋白的良好系统。本研究从黄瓜幼苗（黄瓜品种Burpee Hybrid II）中鉴定出7个新的α-扩张蛋白cDNA，并研究了它们的表达模式。两种α-扩张蛋白（CsExp3和CsExp4）在胚轴和根中表达量更高。早期报告指出，在没有重力的情况下胚轴往往不会形成，因此比较了在太空（STS-95）、回转器和地球上（1g）生长的幼苗胚轴中的表达水平。观察到在回转器和太空生长的幼苗上胚轴高频形成，但在回转器上，与在1g条件下生长的幼苗相比，回转器上生长的幼苗胚轴中CsExp3的表达降低了4倍多，而CsExp4基因似乎被关闭（低于检测限）。在NASA的太空或轨道器环境模拟器（OES）（1g）中生长的幼苗胚轴，其扩张蛋白基因表达水平没有可检测到的差异。微重力环境不影响CsExp3或CsExp4的表达，回转器也不能很好地模拟微重力环境。
