Si Yiru, Khanal Bishnu P, Schlüter Oliver K, Knoche Moritz
Fruit Science Section, Institute of Horticultural Production Systems, Leibniz University Hannover, Hannover, Germany.
Department of Horticultural Engineering, Leibniz Institute for Agricultural Engineering and Bioeconomy (ATB), Potsdam, Germany.
Front Plant Sci. 2021 Oct 21;12:730837. doi: 10.3389/fpls.2021.730837. eCollection 2021.
The pattern of cuticle deposition plays an important role in managing strain buildup in fruit cuticles. Cuticular strain is the primary trigger for numerous fruit-surface disorders in many fruit crop species. Recent evidence indicates a strain gradient may exist within the apple fruit cuticle. The outer layers of the cuticle are more strained and thus more susceptible to microcracking than the inner layers. A radial gradient in cuticle age is the most likely explanation. Our study aimed to establish whether (or not) deposition of new cutin in a developing apple fruit occurs on the inner surface of the cuticle, i.e., immediately abutting the outward-facing epidermal cell wall. Developing apples were fed with C oleic acid through the skin. Following a 14-d period for incorporation, the fruit was harvested and the cuticular membranes (CMs) isolated enzymatically. The CMs were then ablated to varying extents from the inner or the outer surfaces, using a cold atmospheric pressure plasma (CAPP). Afterwards, the ablated CMs were dewaxed and the C contents were determined by mass spectrometry. The incorporation of C in the cutin fraction was higher than in the wax fraction. The C content was highest in non-ablated, dewaxed CM (DCM) and decreased as ablation depth from the inner surface increased. There was no change in C content when ablation was carried out from the outer surface. As fruit development proceeded, more C label was found towards the middle of the DCM. These results offered direct evidence for deposition of cutin being on the inner surface of the cuticle, resulting in a radial gradient in cuticular age-the most recent deposition (youngest) being on the inner cuticle surface (abutting the epidermal cell wall) and the earliest deposition (oldest) being on the outer surface (abutting the atmosphere).
角质层沉积模式在控制果实角质层应变积累方面起着重要作用。角质层应变是许多水果作物品种中多种果实表面病害的主要诱因。最近的证据表明，苹果果实角质层内可能存在应变梯度。角质层外层比内层应变更大，因此更容易出现微裂纹。角质层年龄的径向梯度是最有可能的解释。我们的研究旨在确定发育中的苹果果实中，新角质的沉积是否发生在角质层的内表面，即紧邻向外的表皮细胞壁处。通过果皮给发育中的苹果饲喂油酸。经过14天的掺入期后，收获果实并酶法分离角质层膜（CMs）。然后使用冷大气压等离子体（CAPP）从内表面或外表面不同程度地烧蚀CMs。之后，将烧蚀后的CMs脱蜡，并通过质谱法测定碳含量。角质部分中碳的掺入量高于蜡质部分。未烧蚀、脱蜡的CM（DCM）中碳含量最高，且随着从内表面的烧蚀深度增加而降低。从外表面进行烧蚀时，碳含量没有变化。随着果实发育，在DCM中部发现更多的碳标记。这些结果为角质沉积在角质层内表面提供了直接证据，导致角质层年龄出现径向梯度——最新沉积（最年轻）在内角质层表面（紧邻表皮细胞壁），最早沉积（最老）在外表面（紧邻大气）。
