Zhang Hui-Ming, Imtiaz Mohammad S, Laver Derek R, McCurdy David W, Offler Christina E, van Helden Dirk F, Patrick John W
School of Environmental and Life Sciences, University of Newcastle, Callaghan, NSW 2308, Australia.
School of Biomedical Sciences and Pharmacy, University of Newcastle, Callaghan, NSW 2308, Australia.
J Exp Bot. 2015 Mar;66(5):1179-90. doi: 10.1093/jxb/eru460. Epub 2014 Dec 10.
Transfer cell morphology is characterized by a polarized ingrowth wall comprising a uniform wall upon which wall ingrowth papillae develop at right angles into the cytoplasm. The hypothesis that positional information directing construction of wall ingrowth papillae is mediated by Ca(2+) signals generated by spatiotemporal alterations in cytosolic Ca(2+) ([Ca(2+)]cyt) of cells trans-differentiating to a transfer cell morphology was tested. This hypothesis was examined using Vicia faba cotyledons. On transferring cotyledons to culture, their adaxial epidermal cells synchronously trans-differentiate to epidermal transfer cells. A polarized and persistent Ca(2+) signal, generated during epidermal cell trans-differentiation, was found to co-localize with the site of ingrowth wall formation. Dampening Ca(2+) signal intensity, by withdrawing extracellular Ca(2+) or blocking Ca(2+) channel activity, inhibited formation of wall ingrowth papillae. Maintenance of Ca(2+) signal polarity and persistence depended upon a rapid turnover (minutes) of cytosolic Ca(2+) by co-operative functioning of plasma membrane Ca(2+)-permeable channels and Ca(2+)-ATPases. Viewed paradermally, and proximal to the cytosol-plasma membrane interface, the Ca(2+) signal was organized into discrete patches that aligned spatially with clusters of Ca(2+)-permeable channels. Mathematical modelling demonstrated that these patches of cytosolic Ca(2+) were consistent with inward-directed plumes of elevated [Ca(2+)]cyt. Plume formation depended upon an alternating distribution of Ca(2+)-permeable channels and Ca(2+)-ATPase clusters. On further inward diffusion, the Ca(2+) plumes coalesced into a uniform Ca(2+) signal. Blocking or dispersing the Ca(2+) plumes inhibited deposition of wall ingrowth papillae, while uniform wall formation remained unaltered. A working model envisages that cytosolic Ca(2+) plumes define the loci at which wall ingrowth papillae are deposited.
传递细胞形态的特征是具有一个极化的内生长壁，该壁由一个均匀的壁组成，在这个壁上，壁内生长乳头以直角向细胞质中生长。我们测试了这样一个假设，即指导壁内生长乳头构建的位置信息是由向传递细胞形态转分化的细胞胞质Ca²⁺（[Ca²⁺]cyt）的时空变化所产生的Ca²⁺信号介导的。使用蚕豆子叶对这一假设进行了检验。将子叶转移到培养基上后，其近轴表皮细胞会同步转分化为表皮传递细胞。在表皮细胞转分化过程中产生的极化且持续的Ca²⁺信号，被发现与内生长壁形成的部位共定位。通过去除细胞外Ca²⁺或阻断Ca²⁺通道活性来减弱Ca²⁺信号强度，会抑制壁内生长乳头的形成。Ca²⁺信号极性和持续性的维持依赖于质膜Ca²⁺通透通道和Ca²⁺ - ATP酶的协同作用使胞质Ca²⁺快速周转（数分钟）。从平周面观察，且在靠近胞质 - 质膜界面处，Ca²⁺信号被组织成离散的斑块，这些斑块在空间上与Ca²⁺通透通道簇对齐。数学建模表明，这些胞质Ca²⁺斑块与[Ca²⁺]cyt升高的向内指向的羽流一致。羽流的形成依赖于Ca²⁺通透通道和Ca²⁺ - ATP酶簇的交替分布。进一步向内扩散时，Ca²⁺羽流合并成一个均匀的Ca²⁺信号。阻断或分散Ca²⁺羽流会抑制壁内生长乳头的沉积，而均匀壁的形成则保持不变。一个工作模型设想，胞质Ca²⁺羽流确定了壁内生长乳头沉积的位点。
