Department of Biosciences, Durham University, South Road, Durham, UK.
Department of Physics, University of Oxford, Parks Road, Oxford, UK.
J Exp Bot. 2023 Apr 18;74(8):2680-2691. doi: 10.1093/jxb/erad039.
The Arabidopsis sensitive-to-freezing8 (sfr8) mutant exhibits reduced cell wall (CW) fucose levels and compromised freezing tolerance. To examine whether CW fucosylation also affects the response to desiccation, we tested the effect of leaf excision in sfr8 and the allelic mutant mur1-1. Leaf water loss was strikingly higher than in the wild type in these, but not other, fucosylation mutants. We hypothesized that reduced fucosylation in guard cell (GC) walls might limit stomatal closure through altering mechanical properties. Multifrequency atomic force microscopy (AFM) measurements revealed a reduced elastic modulus (E'), representing reduced stiffness, in sfr8 GC walls. Interestingly, however, we discovered a compensatory mechanism whereby a concomitant reduction in the storage modulus (E'') maintained a wild-type viscoelastic time response (tau) in sfr8. Stomata in intact leaf discs of sfr8 responded normally to a closure stimulus, abscisic acid, suggesting that the time response may relate more to closure properties than stiffness does. sfr8 stomatal pore complexes were larger than those of the wild type, and GCs lacked a fully developed cuticular ledge, both potential contributors to the greater leaf water loss in sfr8. We present data that indicate that fucosylation-dependent dimerization of the CW pectic domain rhamnogalacturonan-II may be essential for normal cuticular ledge development and leaf water retention.
拟南芥抗冻 8 突变体（sfr8）表现出细胞壁（CW）岩藻糖水平降低和抗冻能力受损。为了研究 CW 岩藻糖基化是否也会影响对干燥的响应，我们测试了 sfr8 和等位突变体 mur1-1 中叶片切除的效果。与野生型相比，这些突变体而非其他岩藻糖基化突变体的叶片水分丧失显著更高。我们假设，保卫细胞（GC）壁中岩藻糖基化的减少可能会通过改变机械性能来限制气孔关闭。多频原子力显微镜（AFM）测量显示，sfr8 GC 壁的弹性模量（E'）降低，代表刚性降低。然而，有趣的是，我们发现了一种补偿机制，其中储存模量（E''）的同时降低维持了 sfr8 中野生型粘弹性时间响应（tau）。sfr8 完整叶圆盘中的气孔对关闭刺激，即脱落酸，正常响应，表明时间响应可能与关闭特性而不是刚性更相关。sfr8 的气孔孔径复合体大于野生型，GC 缺乏完全发育的角质边缘，这两者都可能导致 sfr8 叶片水分丧失增加。我们提供的数据表明，CW 果胶域鼠李半乳糖醛酸 II 的岩藻糖基化依赖性二聚化可能对正常角质边缘发育和叶片水分保持至关重要。
