Matschi Susanne, Vasquez Miguel F, Bourgault Richard, Steinbach Paul, Chamness James, Kaczmar Nicholas, Gore Michael A, Molina Isabel, Smith Laurie G
Section of Cell and Developmental Biology University of California San Diego La Jolla CA USA.
Present address: Department Biochemistry of Plant Interactions Leibniz Institute of Plant Biochemistry Weinberg 3 Halle (Saale) Germany.
Plant Direct. 2020 Oct 30;4(10):e00282. doi: 10.1002/pld3.282. eCollection 2020 Oct.
The hydrophobic cuticle of plant shoots serves as an important interaction interface with the environment. It consists of the lipid polymer cutin, embedded with and covered by waxes, and provides protection against stresses including desiccation, UV radiation, and pathogen attack. Bulliform cells form in longitudinal strips on the adaxial leaf surface, and have been implicated in the leaf rolling response observed in drought-stressed grass leaves. In this study, we show that bulliform cells of the adult maize leaf epidermis have a specialized cuticle, and we investigate its function along with that of bulliform cells themselves. Bulliform cells displayed increased shrinkage compared to other epidermal cell types during dehydration of the leaf, providing a potential mechanism to facilitate leaf rolling. Analysis of natural variation was used to relate bulliform strip patterning to leaf rolling rate, providing further evidence of a role for bulliform cells in leaf rolling. Bulliform cell cuticles showed a distinct ultrastructure with increased cuticle thickness compared to other leaf epidermal cells. Comparisons of cuticular conductance between adaxial and abaxial leaf surfaces, and between bulliform-enriched mutants versus wild-type siblings, showed a correlation between elevated water loss rates and presence or increased density of bulliform cells, suggesting that bulliform cuticles are more water-permeable. Biochemical analysis revealed altered cutin composition and increased cutin monomer content in bulliform-enriched tissues. In particular, our findings suggest that an increase in 9,10-epoxy-18-hydroxyoctadecanoic acid content, and a lower proportion of ferulate, are characteristics of bulliform cuticles. We hypothesize that elevated water permeability of the bulliform cell cuticle contributes to the differential shrinkage of these cells during leaf dehydration, thereby facilitating the function of bulliform cells in stress-induced leaf rolling observed in grasses.
植物茎尖的疏水角质层是与环境相互作用的重要界面。它由脂质聚合物角质组成，角质中嵌入并覆盖着蜡质，能提供抵御包括干燥、紫外线辐射和病原体侵袭在内的各种胁迫的保护。泡状细胞在叶片近轴表面纵向排列成条带状，与干旱胁迫下草叶中观察到的叶片卷曲反应有关。在本研究中，我们发现成年玉米叶片表皮的泡状细胞具有特殊的角质层，并对其功能以及泡状细胞自身的功能进行了研究。与叶片脱水过程中的其他表皮细胞类型相比，泡状细胞表现出更大程度的收缩，这为促进叶片卷曲提供了一种潜在机制。通过对自然变异的分析，将泡状细胞条带模式与叶片卷曲速率联系起来，进一步证明了泡状细胞在叶片卷曲中的作用。与其他叶片表皮细胞相比，泡状细胞角质层呈现出独特的超微结构，角质层厚度增加。对叶片近轴和远轴表面之间以及富含泡状细胞的突变体与野生型同胞之间的角质层导度进行比较，结果表明水分流失率升高与泡状细胞的存在或密度增加之间存在相关性，这表明泡状细胞角质层的透水性更强。生化分析显示，富含泡状细胞的组织中角质成分发生改变，角质单体含量增加。特别是，我们的研究结果表明，9,10 - 环氧 - 18 - 羟基十八烷酸含量增加以及阿魏酸比例降低是泡状细胞角质层的特征。我们推测，泡状细胞角质层透水性的提高有助于这些细胞在叶片脱水过程中产生差异收缩，从而促进泡状细胞在禾本科植物应激诱导的叶片卷曲中的功能。
