Department of Molecular Biology and Radiobiology, Faculty of AgriSciences, Mendel University in Brno, Zemědělská 1, CZ-61300, Brno, Czech Republic.
Department of Plant Biotechnology and Bioinformatics, Ghent University, 9052, Ghent, Belgium.
Plant J. 2019 Mar;97(5):805-824. doi: 10.1111/tpj.14285.
The phytohormone cytokinin has been shown to affect many aspects of plant development ranging from the regulation of the shoot apical meristem to leaf senescence. However, some studies have reported contradictory effects of cytokinin on leaf physiology. Therefore cytokinin treatments cause both chlorosis and increased greening and both lead to decrease or increase in cell size. To elucidate this multifaceted role of cytokinin in leaf development, we have employed a system of temporal controls over the cytokinin pool and investigated the consequences of modulated cytokinin levels in the third leaf of Arabidopsis. We show that, at the cell proliferation phase, cytokinin is needed to maintain cell proliferation by blocking the transition to cell expansion and the onset of photosynthesis. Transcriptome profiling revealed regulation by cytokinin of a gene suite previously shown to affect cell proliferation and expansion and thereby a molecular mechanism by which cytokinin modulates a molecular network underlying the cellular responses. During the cell expansion phase, cytokinin stimulates cell expansion and differentiation. Consequently, a cytokinin excess at the cell expansion phase results in an increased leaf and rosette size fueled by higher cell expansion rate, yielding higher shoot biomass. Proteome profiling revealed the stimulation of primary metabolism by cytokinin, in line with an increased sugar content that is expected to increase turgor pressure, representing the driving force of cell expansion. Therefore, the developmental timing of cytokinin content fluctuations, together with a tight control of primary metabolism, is a key factor mediating transitions from cell proliferation to cell expansion in leaves.
植物激素细胞分裂素已被证明会影响植物发育的许多方面，从调节茎尖分生组织到叶片衰老。然而，一些研究报告称细胞分裂素对叶片生理学有相反的影响。因此，细胞分裂素处理既导致叶片黄化又增加绿色，同时导致细胞大小减少或增加。为了阐明细胞分裂素在叶片发育中的多方面作用，我们采用了一种对细胞分裂素库进行时间控制的系统，并研究了在拟南芥第三片中调节细胞分裂素水平的后果。我们表明，在细胞增殖阶段，细胞分裂素通过阻止向细胞扩展和光合作用的开始来维持细胞增殖，从而需要细胞分裂素。转录组分析显示，细胞分裂素调节先前显示影响细胞增殖和扩展的基因套件，从而调节细胞分裂素调节细胞反应下的分子网络的分子机制。在细胞扩展阶段，细胞分裂素刺激细胞扩展和分化。因此，在细胞扩展阶段细胞分裂素过多会导致叶片和莲座丛大小增加，这是由于更高的细胞扩展率导致更高的生物量。蛋白质组分析表明细胞分裂素刺激了初级代谢，这与预期增加膨压的糖含量增加一致，膨压是细胞扩展的驱动力。因此，细胞分裂素含量波动的发育时间以及对初级代谢的严格控制是介导叶片从细胞增殖到细胞扩展过渡的关键因素。
