Somssich Marc, Vandenbussche Filip, Ivakov Alexander, Funke Norma, Ruprecht Colin, Vissenberg Kris, VanDer Straeten Dominique, Persson Staffan, Suslov Dmitry
School of Biosciences, University of Melbourne, Parkville, Melbourne, VIC, Australia.
Laboratory of Functional Plant Biology, Department of Biology, Ghent University, K.L. Ledeganckstraat 35, Gent 9000, Belgium.
Plant Cell Physiol. 2021 Sep 24;62(4):678-692. doi: 10.1093/pcp/pcab024.
The force of gravity is a constant environmental factor. Plant shoots respond to gravity through negative gravitropism and gravity resistance. These responses are essential for plants to direct the growth of aerial organs away from the soil surface after germination and to keep an upright posture above ground. We took advantage of the effect of brassinosteroids (BRs) on the two types of graviresponses in Arabidopsis thaliana hypocotyls to disentangle functions of cell wall polymers during etiolated shoot growth. The ability of etiolated Arabidopsis seedlings to grow upward was suppressed in the presence of 24-epibrassinolide (EBL) but enhanced in the presence of brassinazole (BRZ), an inhibitor of BR biosynthesis. These effects were accompanied by changes in cell wall mechanics and composition. Cell wall biochemical analyses, confocal microscopy of the cellulose-specific pontamine S4B dye and cellular growth analyses revealed that the EBL and BRZ treatments correlated with changes in cellulose fibre organization, cell expansion at the hypocotyl base and mannan content. Indeed, a longitudinal reorientation of cellulose fibres and growth inhibition at the base of hypocotyls supported their upright posture whereas the presence of mannans reduced gravitropic bending. The negative effect of mannans on gravitropism is a new function for this class of hemicelluloses. We also found that EBL interferes with upright growth of hypocotyls through their uneven thickening at the base.
重力是一个恒定的环境因素。植物地上部分通过负向重力性和抗重力性对重力做出反应。这些反应对于植物在萌发后引导地上器官的生长远离土壤表面并在地面上保持直立姿态至关重要。我们利用油菜素类固醇（BRs）对拟南芥下胚轴中两种重力反应的影响，来阐明黄化苗生长过程中细胞壁聚合物的功能。在24-表油菜素内酯（EBL）存在的情况下，黄化拟南芥幼苗向上生长的能力受到抑制，但在油菜素唑（BRZ，一种BR生物合成抑制剂）存在的情况下增强。这些影响伴随着细胞壁力学和组成的变化。细胞壁生化分析、纤维素特异性滂胺S4B染料的共聚焦显微镜观察以及细胞生长分析表明，EBL和BRZ处理与纤维素纤维组织、下胚轴基部细胞扩张和甘露聚糖含量的变化相关。事实上，纤维素纤维的纵向重新定向以及下胚轴基部的生长抑制支持了它们的直立姿态，而甘露聚糖的存在减少了向重力性弯曲。甘露聚糖对向重力性的负面影响是这类半纤维素的一个新功能。我们还发现，EBL通过下胚轴基部的不均匀增厚干扰其直立生长。
