Saether N, Iversen T H
Department of Botany, University of Trondheim, Dragvoll, Norway.
Planta. 1991 Jul;184(4):491-7. doi: 10.1007/BF00197897.
The mutant TC 7 of Arabidopsis thaliana (L.) Heynh. has been reported to be starch-free and still exhibit root gravitropism (T. Caspar and B. G. Pickard 1989, Planta 177, 185-197). This is not consistent with the hypothesis that plastid starch has a statolith function in gravity perception. In the present study, initial light microscopy using the same mutant showed apparently starch-free statocytes. However, ultrastructural examination detected residues of amyloplast starch grains in addition to the starch-depleted amyloplasts. Applying a point-counting morphometric method, the starch grains in the individual amyloplasts in the mutant were generally found to occupy more than 20% and in a few cases up to 60% of the amyloplast area. In the wild type (WT) the starch occupied on average 98% of the amyloplast area and appeared as densely packed grains. The amyloplasts occupied 13.9% of the area of the statocyte in the mutant and 23.3% of the statocyte area in the WT. Sedimentation of starch-depleted amyloplasts in the mutant was not detected after 40 min of inversion while in the WT the amyloplasts sedimented at a speed of 6 micrometers h-1. The gravitropic reactivity and the curvature pattern were also examined in the WT and the mutant. The time-courses of root curvature in the WT and the mutant showed that when cultivated under standard conditions for 60 h in darkness, the curvatures were 83 degrees and 44 degrees, respectively, after 25 h of continuous stimulation in the horizontal position. The WT roots curved significantly more rapidly and with a more normal gravitropic pattern than those of the mutant. These results are discussed in relation to the results previously obtained with the mutant and with respect to the starch-statolith hypothesis.
据报道，拟南芥（Arabidopsis thaliana (L.) Heynh.）的突变体TC 7不含淀粉，但仍表现出根的向重力性（T. Caspar和B. G. Pickard，1989年，《植物》177卷，185 - 197页）。这与质体淀粉在重力感知中具有平衡石功能的假设不一致。在本研究中，使用同一突变体进行的初步光学显微镜观察显示，平衡细胞明显不含淀粉。然而，超微结构检查除了发现淀粉耗尽的造粉体之外，还检测到了造粉体淀粉粒的残留物。应用点计数形态测量法，通常发现突变体单个造粉体内的淀粉粒占据造粉体面积的20%以上，在少数情况下高达60%。在野生型（WT）中，淀粉平均占据造粉体面积的98%，呈现为紧密堆积的颗粒。突变体中造粉体占据平衡细胞面积的13.9%，而在野生型中造粉体占据平衡细胞面积的23.3%。倒置40分钟后，未检测到突变体中淀粉耗尽的造粉体沉降，而野生型中的造粉体以6微米/小时的速度沉降。还对野生型和突变体的向重力反应性和弯曲模式进行了研究。野生型和突变体根弯曲的时间进程表明，在黑暗中于标准条件下培养60小时后，水平位置连续刺激25小时后，弯曲度分别为83度和44度。野生型根的弯曲明显比突变体根更快，且向重力模式更正常。结合先前对该突变体获得的结果以及淀粉平衡石假说对这些结果进行了讨论。
