Ikeuchi Momoko, Igarashi Hisako, Okada Kiyotaka, Tsukaya Hirokazu
Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Bunkyo-ku, Tokyo, 113-0033, Japan.
Planta. 2014 Jul;240(1):125-35. doi: 10.1007/s00425-014-2071-9. Epub 2014 Apr 10.
In compound leaves, leaflet primordia are initiated directionally along the lateral sides. Our understanding of the molecular basis of leaflet initiation has improved, but the regulatory mechanisms underlying spatio-temporal patterns remain unclear. In this study, we investigated the mechanisms of acropetal (from the base to the tip) progression of leaflet initiation in Eschscholzia californica. We established an ultraviolet-laser ablation system to manipulate compound-leaf development. Local ablation at the leaflet incipient site generated leaves with asymmetric morphology. In the majority of cases, leaflets that were initiated on the ablated sides shifted apically. Finite time-course observation revealed that the timing of leaflet initiation was delayed, but the distance from the leaf tip did not decrease. These results were suggestive of the local spacing mechanism in leaflet initiation, whereby the distance from the leaf tip and adjacent pre-existing leaflet determines the position of leaflet initiation. To understand how such a local patterning mechanism generates a global pattern of successive leaflet initiation, we assessed the growth rate gradient along the apical-basal axis. Our time-course analysis revealed differential growth rates along the apical-basal axis of the leaf, which can explain the acropetal progression of leaflet initiation. We propose that a leaflet is initiated at a site where the distances from pre-existing leaflets and the leaf tip are sufficient. Furthermore, the differential growth rate may be a developmental factor underlying the directionality of leaflet initiation.
在复叶中，小叶原基沿着叶的两侧定向起始。我们对小叶起始的分子基础的理解有所提高，但时空模式背后的调控机制仍不清楚。在本研究中，我们调查了加州罂粟小叶起始向顶（从基部到顶端）推进的机制。我们建立了一个紫外激光消融系统来操纵复叶发育。在小叶起始位点进行局部消融会产生形态不对称的叶片。在大多数情况下，在消融侧起始的小叶会向顶端移动。有限时间进程观察表明，小叶起始的时间延迟了，但与叶尖的距离并未减小。这些结果提示了小叶起始中的局部间隔机制，即与叶尖和相邻已存在小叶的距离决定了小叶起始的位置。为了理解这种局部模式形成机制如何产生连续小叶起始的全局模式，我们评估了沿顶 - 基轴的生长速率梯度。我们的时间进程分析揭示了沿叶顶 - 基轴的不同生长速率，这可以解释小叶起始的向顶推进。我们提出，小叶在与已存在小叶和叶尖的距离足够的位点起始。此外，不同的生长速率可能是小叶起始方向性的一个发育因素。
