Brüggenwirth Martin, Knoche Moritz
Institute for Horticultural Production Systems, Leibniz-University Hannover, Herrenhäuser Straße 2, 30419, Hannover, Germany.
Planta. 2017 Apr;245(4):765-777. doi: 10.1007/s00425-016-2639-7. Epub 2016 Dec 23.
Cell wall swelling, fracture mode (along the middle lamellae vs. across cell walls), stiffness, and pressure at fracture of the sweet cherry fruit skin are closely related. Skin cracking is a common phenomenon in many crops bearing fleshy fruit. The objectives were to investigate relationships between the mode of fracture, the extent of cell wall swelling, and the mechanical properties of the fruit skin using sweet cherry (Prunus avium) as a model. Cracking was induced by incubating whole fruit in deionised water or by fracturing exocarp segments (ESs) in biaxial tensile tests. The fracture mode of epidermal cells was investigated by light microscopy. In biaxial tensile tests, the anticlinal cell walls of the ES fractured predominantly across the cell walls (rather than along) and showed no cell wall swelling. In contrast, fruit incubated in water fractured predominantly along the anticlinal epidermal cell walls and the cell walls were swollen. Swelling of cell walls also occurred when ESs were incubated in malic acid, in hypertonic solutions of sucrose, or in water. Compared to the untreated controls, these treatments resulted in more frequent fractures along the cell walls, lower pressures at fracture (p ), and lower moduli of elasticity (E, i.e., less stiff). Conversely, compared to the untreated controls, incubating the ES in CaCl and in high concentrations of ethanol resulted in thinner cell walls, in less frequent fractures along the cell walls, higher E and p . Our study demonstrates that fracture mode, stiffness, and pressure at fracture are closely related to cell wall swelling. A number of other factors, including cultivar, ripening stage, turgor, CaCl, and malic acid, exert their effects only indirectly, i.e., by affecting cell wall swelling.
甜樱桃果实表皮的细胞壁肿胀、断裂模式（沿中层薄片还是穿过细胞壁）、硬度以及断裂时的压力密切相关。果皮开裂是许多肉质果实作物中的常见现象。本研究以甜樱桃（Prunus avium）为模型，旨在探究断裂模式、细胞壁肿胀程度与果实表皮机械性能之间的关系。通过将整个果实浸泡在去离子水中或在双轴拉伸试验中对果皮切片（ESs）进行断裂来诱导开裂。通过光学显微镜研究表皮细胞的断裂模式。在双轴拉伸试验中，ESs的垂周细胞壁主要是穿过细胞壁断裂（而非沿细胞壁断裂），且未出现细胞壁肿胀。相比之下，浸泡在水中的果实主要沿垂周表皮细胞壁断裂，且细胞壁发生了肿胀。当ESs浸泡在苹果酸、高渗蔗糖溶液或水中时，细胞壁也会发生肿胀。与未处理的对照相比，这些处理导致沿细胞壁的断裂更频繁、断裂时的压力更低（p）以及弹性模量更低（E，即更软）。相反，与未处理的对照相比，将ESs浸泡在CaCl和高浓度乙醇中会导致细胞壁更薄、沿细胞壁的断裂更不频繁、E和p更高。我们的研究表明，断裂模式、硬度和断裂时的压力与细胞壁肿胀密切相关。许多其他因素，包括品种、成熟阶段、膨压、CaCl和苹果酸，仅通过影响细胞壁肿胀间接发挥作用。
