Cell Biology Laboratory, Graduate School of Kuroshio Science, Kochi University, 2-5-1 Akebono-cho, Kochi 780-8520, Japan.
Protoplasma. 2013 Feb;250(1):407-14. doi: 10.1007/s00709-012-0381-y. Epub 2012 Feb 4.
Cell differentiation and cell type commitment are an integral part of plant growth and development. Investigations on how environmental conditions affect the formation of shoots, roots, and rhizoids can help illustrate how plants determine cell fate and overall morphology. In this study, we evaluated the role of substratum and light on rhizoid differentiation in the coenocytic green alga, Valonia aegagropila. Elongating rhizoids displayed varying growth modes and cell shape upon exposure to different substrata and light conditions. It was found that soft substrata and dark incubation promoted rhizoid elongation via tip growth while subsequent exposure to light prevented tip growth and instead induced swelling in the apical region of rhizoids. Swelling was accompanied by the accumulation of protoplasm in the rhizoid tip through expansion of the cell wall and uninhibited cytoplasmic streaming. Subsequent diffuse growth led to the transformation from slender, rod-shaped rhizoids into spherical thallus-like structures that required photosynthesis. Further manipulation of light regimes caused vacillating cell growth redirections. An elongating V. aegagropila rhizoid cell thus appears capable of growth mode switching that is regulated by immediate environmental conditions thereby influencing ultimate cell shape and function. This is the first description of inducible, multiple growth mode shifts in a single intact plant cell that directly impact its differentiation.
细胞分化和细胞类型的决定是植物生长和发育的一个组成部分。研究环境条件如何影响芽、根和假根的形成，可以帮助阐明植物如何决定细胞命运和整体形态。在这项研究中，我们评估了基质和光照对多核绿藻 Valonia aegagropila 假根分化的影响。在不同的基质和光照条件下，伸长的假根表现出不同的生长模式和细胞形状。结果发现，软基质和暗培养通过顶端生长促进假根伸长，而随后暴露在光下会阻止顶端生长，反而会诱导假根顶端膨胀。膨胀伴随着细胞质通过细胞壁扩张和不受抑制的胞质流在假根顶端积累。随后的弥散生长导致从细长的、杆状的假根转变为需要光合作用的球形叶状体结构。进一步操纵光照条件会导致细胞生长方向的波动。因此，伸长的 V. aegagropila 假根细胞似乎能够进行由直接环境条件调节的生长模式转换，从而影响最终的细胞形状和功能。这是首次描述在单个完整植物细胞中诱导的、多种生长模式的转变，这些转变直接影响细胞的分化。
