Starting as small, densely packed boxes, leaf mesophyll cells expand to form an intricate mesh of interconnected cells and air spaces, the organization of which dictates the internal surface area of the leaf for light capture and gas exchange during photosynthesis. Despite their importance, little is known about the basic patterns of mesophyll cell division, and how they contribute to cell and intercellular space organization. To address this, we tracked divisions within individual cell lineages in three dimensions over time in Arabidopsis spongy mesophyll. We found that early on, successive cell division planes switch their orientation such that each new cell wall intersects the previous at a right angle, creating a new multi-cell junction (the intersection of three or more cells). These junctions then open to create intercellular spaces. During subsequent enlargement of the spaces, the division planes of the surrounding cells show an increasing tendency to tilt in the direction of their adjacent intercellular spaces. This disrupts the alternating pattern, and by extension, halts the initiation of new multi-cell junctions and intercellular spaces, but allows the expansion of existing spaces. Both division patterns are specified before mitosis by the orientation of interphase cortical microtubules, which gradually narrow to form a preprophase band in the same orientation to establish the future plane of cell division. In the absence of the microtubule-associated protein CLASP, the early alternating division plane and microtubule patterns are compromised, whereas space-oriented divisions are exacerbated. This results in large distortions of the topological relations between cells and intercellular spaces, as well as changes in their relative abundance. Our data reveal the existence of two competing cell division mechanisms that are balanced by CLASP to specify the distribution of cells and intercellular spaces in spongy mesophyll tissue.

从小而密集的盒子开始，叶肉细胞膨胀形成相互连接的细胞和空气空间的错综复杂的网状结构，其组织决定了叶片的内表面积，用于光合作用期间的光捕获和气体交换。尽管它们很重要，但人们对叶肉细胞分裂的基本模式以及它们如何促进细胞和细胞间空间组织知之甚少。为了解决这个问题，我们在拟南芥中随着时间的推移在三个维度上跟踪单个细胞谱系内的分裂海绵状的叶肉。我们发现，在早期，连续的细胞分裂平面会改变它们的方向，使得每个新的细胞壁都以直角与前一个细胞壁相交，从而形成一个新的多细胞连接（三个或更多细胞的交叉点）。然后这些连接打开以创建细胞间空间。在随后的空间扩大过程中，周围细胞的分裂平面显示出向其相邻细胞间空间方向倾斜的趋势。这破坏了交替模式，并且通过扩展，停止了新的多细胞连接和细胞间空间的启动，但允许现有空间的扩展。两种分裂模式都是在有丝分裂前由间期皮质微管的方向指定的，逐渐变窄，形成同向的前期带，建立未来的细胞分裂平面。在没有微管相关蛋白 CLASP 的情况下，早期的交替分裂平面和微管模式受到损害，而面向空间的分裂加剧。这导致细胞和细胞间空间之间的拓扑关系发生巨大扭曲，以及它们的相对丰度发生变化。我们的数据揭示了两种相互竞争的细胞分裂机制的存在，它们由 CLASP 平衡，以指定海绵状叶肉组织中细胞和细胞间隙的分布。而面向空间的分裂则加剧了。这导致细胞和细胞间空间之间的拓扑关系发生巨大扭曲，以及它们的相对丰度发生变化。我们的数据揭示了两种相互竞争的细胞分裂机制的存在，它们由 CLASP 平衡，以指定海绵状叶肉组织中细胞和细胞间隙的分布。而面向空间的分裂则加剧了。这导致细胞和细胞间空间之间的拓扑关系发生巨大扭曲，以及它们的相对丰度发生变化。我们的数据揭示了两种相互竞争的细胞分裂机制的存在，它们由 CLASP 平衡，以指定海绵状叶肉组织中细胞和细胞间隙的分布。