Department of Botany, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
Plant Cell. 2011 Oct;23(10):3684-95. doi: 10.1105/tpc.111.085852. Epub 2011 Oct 4.
Light is an important environmental information source that plants use to modify their growth and development. Palisade parenchyma cells in leaves develop cylindrical shapes in response to blue light; however, the photosensory mechanism for this response has not been elucidated. In this study, we analyzed the palisade cell response in phototropin-deficient mutants. First, we found that two different light-sensing mechanisms contributed to the response in different proportions depending on the light intensity. One response observed under lower intensities of blue light was mediated exclusively by a blue light photoreceptor, phototropin 2 (PHOT2). Another response was elicited under higher intensities of light in a phototropin-independent manner. To determine the tissue in which PHOT2 perceives the light stimulus to regulate the response, green fluorescent protein (GFP)-tagged PHOT2 (P2G) was expressed under the control of tissue-specific promoters in the phot1 phot2 mutant background. The results revealed that the expression of P2G in the mesophyll, but not in the epidermis, promoted palisade cell development. Furthermore, a constitutively active C-terminal kinase fragment of PHOT2 fused to GFP (P2CG) promoted the development of cylindrical palisade cells in the proper direction without the directional cue provided by light. Hence, in response to blue light, PHOT2 promotes the development of cylindrical palisade cells along a predetermined axis in a tissue-autonomous manner.
光是植物用来改变其生长和发育的重要环境信息源。叶片中的栅栏薄壁组织细胞对蓝光做出反应，形成圆柱状；然而，这种反应的光感觉机制尚未阐明。在这项研究中，我们分析了光受体缺失突变体中的栅栏细胞反应。首先，我们发现两种不同的光感觉机制以不同的比例共同作用，这取决于光的强度。在较低强度的蓝光下观察到的一种反应仅由蓝光受体光受体 2（PHOT2）介导。另一种反应则以光受体非依赖的方式在更高强度的光下被激发。为了确定 PHOT2 在组织中感知光刺激以调节反应的位置，在 phot1 phot2 突变体背景下，用组织特异性启动子控制 GFP 标记的 PHOT2（P2G）的表达。结果表明，P2G 在叶肉中的表达，而不是在表皮中，促进了栅栏薄壁组织细胞的发育。此外，与 GFP 融合的 PHOT2 的组成型激活 C 端激酶片段（P2CG）在没有光提供的定向提示的情况下，促进了圆柱状栅栏薄壁组织细胞向正确方向的发育。因此，对蓝光的响应，PHOT2 以组织自主的方式沿预定的轴促进圆柱状栅栏薄壁组织细胞的发育。
