Department of Chemistry and Biomolecular Sciences, Macquarie University, Sydney, New South Wales 2109, Australia.
Plant Physiol. 2010 Mar;152(3):1459-70. doi: 10.1104/pp.109.149864. Epub 2010 Jan 8.
Bran from bread wheat (Triticum aestivum 'Babbler') grain is composed of many outer layers of dead maternal tissues that overlie living aleurone cells. The dead cell layers function as a barrier resistant to degradation, whereas the aleurone layer is involved in mobilizing organic substrates in the endosperm during germination. We microdissected three defined bran fractions, outer layers (epidermis and hypodermis), intermediate fraction (cross cells, tube cells, testa, and nucellar tissue), and inner layer (aleurone cells), and used proteomics to identify their individual protein complements. All proteins of the outer layers were enzymes, whose function is to provide direct protection against pathogens or improve tissue strength. The more complex proteome of the intermediate layers suggests a greater diversity of function, including the inhibition of enzymes secreted by pathogens. The inner layer contains proteins involved in metabolism, as would be expected from live aleurone cells, but this layer also includes defense enzymes and inhibitors as well as 7S globulin (specific to this layer). Using immunofluorescence microscopy, oxalate oxidase was localized predominantly to the outer layers, xylanase inhibitor protein I to the xylan-rich nucellar layer of the intermediate fraction and pathogenesis-related protein 4 mainly to the aleurone. Activities of the water-extractable enzymes oxalate oxidase, peroxidase, and polyphenol oxidase were highest in the outer layers, whereas chitinase activity was found only in assays of whole grains. We conclude that the differential protein complements of each bran layer in wheat provide distinct lines of defense in protecting the embryo and nutrient-rich endosperm.
来自面包小麦（Triticum aestivum‘Babbler’）麦粒的麸皮由许多覆盖活糊粉层细胞的死亡母体组织的外层组成。死亡的细胞层作为一种抵抗降解的屏障，而糊粉层则参与在萌发过程中动员胚乳中的有机底物。我们从小麦的三个不同麸皮层（外层、中间层和内层）中进行了显微解剖，分别为外层（表皮和下皮层）、中间层（横细胞、管细胞、种皮和珠心组织）和内层（糊粉层），并使用蛋白质组学来鉴定它们各自的蛋白质组成。外层的所有蛋白质都是酶，其功能是提供直接的保护，防止病原体侵害或增强组织强度。中间层更复杂的蛋白质组表明其具有更大的功能多样性，包括抑制病原体分泌的酶。内层含有参与代谢的蛋白质，这与活糊粉层细胞相符，但该层还包含防御酶和抑制剂以及 7S 球蛋白（仅存在于这一层）。通过免疫荧光显微镜，发现草酸盐氧化酶主要定位于外层，木聚糖酶抑制剂蛋白 I 定位于中间层富含木聚糖的珠心层，而病程相关蛋白 4 主要定位于糊粉层。在水提取物中，草酸盐氧化酶、过氧化物酶和多酚氧化酶的活性在最外层最高，而几丁质酶活性仅在整个谷物的测定中发现。我们得出的结论是，小麦每个麸皮层的差异蛋白质组成提供了不同的防御线，以保护胚胎和富含营养的胚乳。
