Department of Forest Genetics and Plant Physiology, Umeå Plant Science Centre (UPSC), Swedish University of Agricultural Sciences, Umeå, 901 83, Sweden.
Department of Computational and Systems Biology, John Innes Centre, Norwich Research Park, Colney Lane, Norwich, NR4 7UH, UK.
New Phytol. 2021 Oct;232(2):673-691. doi: 10.1111/nph.17468. Epub 2021 Jun 16.
Xylem fibers are highly elongated cells that are key constituents of wood, play major physiological roles in plants, comprise an important terrestrial carbon reservoir, and thus have enormous ecological and economic importance. As they develop, from fusiform initials, their bodies remain the same length while their tips elongate and intrude into intercellular spaces. To elucidate mechanisms of tip elongation, we studied the cell wall along the length of isolated, elongating aspen xylem fibers and used computer simulations to predict the forces driving the intercellular space formation required for their growth. We found pectin matrix epitopes (JIM5, LM7) concentrated at the tips where cellulose microfibrils have transverse orientation, and xyloglucan epitopes (CCRC-M89, CCRC-M58) in fiber bodies where microfibrils are disordered. These features are accompanied by changes in cell wall thickness, indicating that while the cell wall elongates strictly at the tips, it is deposited all over fibers. Computer modeling revealed that the intercellular space formation needed for intrusive growth may only require targeted release of cell adhesion, which allows turgor pressure in neighboring fiber cells to 'round' the cells creating spaces. These characteristics show that xylem fibers' elongation involves a distinct mechanism that combines features of both diffuse and tip growth.
木质部纤维是高度伸长的细胞，是木材的主要组成部分，在植物中发挥主要的生理作用，构成重要的陆地碳储存库，因此具有巨大的生态和经济重要性。随着它们从纺锤形原始细胞的发育，它们的身体保持相同的长度，而它们的尖端伸长并侵入细胞间隙。为了阐明尖端伸长的机制，我们研究了分离的、伸长的山杨木质部纤维的细胞壁，并使用计算机模拟预测了驱动细胞间空间形成所需的力，这些空间的形成是其生长所必需的。我们发现果胶基质表位（JIM5、LM7）集中在纤维素微纤维具有横向取向的尖端，而木葡聚糖表位（CCRC-M89、CCRC-M58）位于微纤维无序的纤维体中。这些特征伴随着细胞壁厚度的变化，表明虽然细胞壁在尖端严格伸长，但它在纤维上沉积。计算机模拟表明，侵入性生长所需的细胞间隙形成可能只需要有针对性地释放细胞黏附，这允许相邻纤维细胞的膨压将细胞“变圆”，形成空间。这些特征表明，木质部纤维的伸长涉及一种独特的机制，它结合了弥散生长和尖端生长的特征。
