Gehring C A, Williams D A, Cody S H, Parish R W
Department of Botany, La Trobe University, Bundoora, Australia.
Nature. 1990 Jun 7;345:528-30. doi: 10.1038/345528a0.
Phototropism and gravitropism in the shoots and roots of higher plants are the result of asymmetric growth. This is explained by the redistribution of growth regulators following exposure to gravity or unilateral light (the Cholodny-Went hypothesis). The positive phototropism and the negative geotropism of grass seedling coleoptiles are believed to result from lateral movement of auxin from the irradiated to the shaded side and from the upper to the lower side, respectively. Many physiological processes in plants, including auxin-induced cell elongation, are reported to be under the control of calcium. Added auxin triggers oscillations in cytosolic free calcium ([Ca2+]cyt) and cytosolic pH (pHcyt) in epidermal cells of maize coleoptiles. Until recently, it has not been possible to visualize these changes spatially with the commonly used fluorescent cation indicators. Using a scanning laser confocal microscope, a new visible wavelength Ca2+ probe fluo-3 and the fluorescent pH indicator BCECF, we have recorded rapid light-induced increases in [Ca2+]cyt and a lowering of pHcyt of cells on the shaded side of maize coleoptiles. In horizontally orientated coleoptiles, [Ca2+]cyt increases and pHcyt decreases in the more rapidly elongating cells on the lower side. For the first time, rapid changes in [Ca2+]cyt and pHcyt are correlated directly with increases in cell elongation stimulated by light and gravity.
高等植物茎和根的向光性和向地性是不对称生长的结果。这可以通过重力或单侧光照后生长调节物质的重新分布来解释（ Cholodny-Went假说）。禾本科植物幼苗胚芽鞘的正向光性和负向地性被认为分别是由于生长素从受光一侧横向移动到背光一侧以及从上部移动到下部所致。据报道，植物中的许多生理过程，包括生长素诱导的细胞伸长，都受钙的调控。添加生长素会引发玉米胚芽鞘表皮细胞胞质游离钙（[Ca2+]cyt）和胞质pH值（pHcyt）的振荡。直到最近，使用常用的荧光阳离子指示剂还无法在空间上观察到这些变化。利用扫描激光共聚焦显微镜、一种新的可见波长Ca2+探针fluo-3和荧光pH指示剂BCECF，我们记录了玉米胚芽鞘背光侧细胞中光诱导的[Ca2+]cyt快速增加和pHcyt降低。在水平放置的胚芽鞘中，下侧伸长较快的细胞中[Ca2+]cyt增加而pHcyt降低。[Ca2+]cyt和pHcyt的快速变化首次与光和重力刺激引起的细胞伸长增加直接相关。
