University of Jena, Institute of General Botany and Plant Physiology, Jena, Germany.
Plant Biol (Stuttg). 2015 Jan;17 Suppl 1:125-9. doi: 10.1111/plb.12154. Epub 2014 Jan 24.
Turions play an important role in the survival strategy of the duckweed Spirodela polyrhiza. Therefore, factors influencing the formation of these survival organs were studied. Phosphate deficiency is the main natural factor inducing turion formation and the specific turion yield (SY), i.e. the number of turions formed per frond, varied widely for five different clones from different climate zones. The concentrations of phosphate and nitrate in the nutrient media were investigated at the onset of turion formation, with SY ranging from 0.22 to 5.9. Tissue P and N content was also investigated in vegetative fronds at the onset of turion formation and in newly formed turions. The clones were selected to test possible correlations between SY and threshold nutrient concentration for turion formation. Only one correlation, between SY and external phosphate concentration, was significant: clones with high SY started turion formation at higher external phosphate concentrations. Turion formation is thus mainly induced by the external phosphate concentration, below a defined, clone-dependent threshold. We propose the following mechanism: a switch of the developmental programme of frond primordia from vegetative frond to turion formation at a higher phosphate threshold saves more phosphate for turion formation instead of using it for a further vegetative growth. However, the period of growth preceding turion formation does not depend on this threshold value, but rather on the growth rate of the vegetative fronds, which actually produce the phosphate shortage by taking it up from the surrounding medium.
原叶体在浮萍的生存策略中起着重要作用。因此，研究了影响这些生存器官形成的因素。缺磷是诱导原叶体形成的主要自然因素，特定原叶体产量（SY），即每片叶子形成的原叶体数量，因来自不同气候带的五个不同克隆体而有很大差异。在原叶体形成开始时，研究了营养介质中磷酸盐和硝酸盐的浓度，SY 范围从 0.22 到 5.9。还在原叶体形成开始时和新形成的原叶体中调查了营养叶中的组织 P 和 N 含量。选择克隆体来测试 SY 与原叶体形成的阈值营养浓度之间的可能相关性。只有一个相关性，即 SY 与外部磷酸盐浓度之间的相关性，是显著的：SY 较高的克隆体在较高的外部磷酸盐浓度下开始原叶体形成。因此，原叶体的形成主要是由外部磷酸盐浓度诱导的，低于一个定义的、克隆体依赖的阈值。我们提出以下机制：在较高的磷酸盐阈值下，叶原基的发育程序从营养叶转变为原叶体形成，从而为原叶体形成节省更多的磷酸盐，而不是将其用于进一步的营养生长。然而，原叶体形成前的生长阶段并不依赖于这个阈值，而是依赖于营养叶的生长速度，实际上是通过从周围介质中吸收磷酸盐来造成磷酸盐短缺。
