Wagner T A, Sack F D
Department of Plant Biology, Ohio State University, Columbus 43210, USA.
Planta. 1998 Jul;205(3):352-8. doi: 10.1007/s004250050330.
Wild-type (WT) protonemata of the moss Ceratodon purpureus grow upwards in darkness (negative gravitropism), whereas protonemata of the mutant, wrong-way response (wwr-1) grow down. Since Ceratodon protoplasts regenerate to form new protonemata, we analyzed whether the direction of filament emergence was influenced by gravity (gravimorphism) and determined the cytological events that correlated with the onset of gravitropism in WT and wwr-1 filaments formed de novo. In the WT the direction of filament emergence appeared to be gravimorphic as more than 66% of the new filaments emerged above the horizontal. In contrast, the direction of filament emergence was random in wwr-1. Tip-growing cells of both genotypes became gravitropic within a total of one to two cell divisions. Gravitropic curvature in wwr-1 was opposite in direction to that of WT, and the timing of curvature was comparable, indicating that the wwr-1 mutation acts during the onset of gravitropic competence. In time-lapse studies of both genotypes, neither a plastid-free zone nor obvious and extensive plastid sedimentation characteristic of mature dark-grown protonemata was observed in the new filaments prior to gravitropic curvature. Thus, it appears that these latter two features are not required for gravitropism in new protonemal filaments from protoplasts.
紫萼藓（Ceratodon purpureus）的野生型（WT）原丝体在黑暗中向上生长（负向重力性），而突变体“错误方向反应”（wwr-1）的原丝体则向下生长。由于紫萼藓原生质体可再生形成新的原丝体，我们分析了丝状体出现的方向是否受重力影响（重力形态发生），并确定了与WT和从头形成的wwr-1丝状体中重力性起始相关的细胞学事件。在WT中，丝状体出现的方向似乎具有重力形态性，因为超过66%的新丝状体在水平上方出现。相比之下，wwr-1中丝状体出现的方向是随机的。两种基因型的顶端生长细胞在总共一到两个细胞分裂内变成重力性的。wwr-1中的重力性弯曲方向与WT相反，且弯曲时间相当，这表明wwr-1突变在重力性能力起始期间起作用。在对两种基因型的延时研究中，在重力性弯曲之前，新丝状体中未观察到成熟黑暗生长原丝体特有的无质体区或明显且广泛的质体沉降。因此，对于原生质体产生的新原丝体丝状体的重力性而言，后两个特征似乎并非必需。
