Tokyo Metropolitan University, Minami-Osawa 1-1, Tokyo 192-0397, Japan.
J Plant Res. 2010 May;123(3):381-90. doi: 10.1007/s10265-009-0284-y. Epub 2009 Dec 2.
Chloroplast photorelocation movement is important for plants to perform efficient photosynthesis. Phototropins were identified as blue-light receptors for chloroplast movement in Arabidopsis thaliana and in the fern Adiantum capillus-veneris, whereas neochrome functions as a dual red/blue light receptor in the latter. However, the signal transduction pathways involved in chloroplast movement remain to be clarified. To investigate the kinetic properties of signalling from these photoreceptors to the chloroplasts, we deduced the speed of signal transfer using Adiantum capillus-veneris gametophytes. When a region of dark-adapted gametophyte cells was subjected to microbeam irradiation, chloroplasts moved towards the irradiated area even in subsequent darkness. We therefore recorded the movement and calculated the speeds of signal transfer by time-lapse imaging. Movement speeds under red or blue light were similar, e.g., about 1.0 microm min(-1) in prothallial cells. However, speeds varied according to cell polarity in protonemal cells. The speed of signal transfer from the protonemal apex to the base was approximately 0.7 microm min(-1), but roughly 2.3 microm min(-1) in the opposite direction. The speed of signal transfer in Arabidopsis thaliana mesophyll cells was approximately 0.8 microm min(-1) by comparison. Surprisingly, chloroplasts located farthest away from the microbeam were found to move faster than those in close proximity to the site of irradiation both in Adiantum capillus-veneris and A. thaliana.
叶绿体的光定位运动对于植物进行高效光合作用非常重要。在拟南芥和蕨类植物铁线蕨中，光敏色素被鉴定为叶绿体运动的蓝光受体，而新色素则在后者中充当红/蓝光双受体。然而，参与叶绿体运动的信号转导途径仍有待阐明。为了研究这些光受体向叶绿体传递信号的动力学特性，我们使用铁线蕨配子体推断了信号传递的速度。当暗适应的配子体细胞的一个区域受到微束照射时，叶绿体即使在随后的黑暗中也会向照射区域移动。因此，我们通过延时成像记录了运动并计算了信号传递的速度。红光或蓝光下的运动速度相似，例如在原叶体细胞中约为 1.0 µm min(-1)。然而，在原丝体细胞中，速度会根据细胞极性而变化。从原丝体顶端到基部的信号传递速度约为 0.7 µm min(-1)，但在相反方向上约为 2.3 µm min(-1)。相比之下，拟南芥叶肉细胞中的信号传递速度约为 0.8 µm min(-1)。令人惊讶的是，在铁线蕨和拟南芥中，与微束距离最远的叶绿体被发现比靠近照射部位的叶绿体运动得更快。
