A comparative study of melting and non-melting flesh peach cultivars reveals that during fruit ripening endo-polygalacturonase (endo-PG) is mainly involved in pericarp textural changes, not in firmness reduction
A comparative study of melting and non-melting flesh peach cultivars reveals that during fruit ripening endo-polygalacturonase (endo-PG) is mainly involved in pericarp textural changes, not in firmness reduction
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DOI：
10.1093/jxb/err109
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发表时间：
2011-07-01
影响因子：
6.9
通讯作者：
Citterio, S.
中科院分区：
文献类型：
--
作者：
Ghiani, A.;Onelli, E.;Citterio, S.
桃子软化通常归因于细胞壁的分解，其中内聚半乳糖醛酸酶（endo-PG）催化的果胶解聚发挥着核心作用。在这项研究中，通过比较果皮形态和内切-PG在连续成熟阶段的融化（MF）和非融化果肉（NMF）果实中的表达和定位，测试了内切PG的功能对于实现融化果肉质地至关重要但对于降低果实硬度并不重要的假设。对 MF Bolero、Springbelle 和 Springcrest 以及 NMF Oro-A 和 Jonia 品种进行了分析。 MF 和 NMF 果实都留在树上成熟，硬度达到 < 10 牛顿 (N)。果皮组织的图像分析显示，在软化过程中，细胞膨胀度的丧失是所有 MF 和 NMF 果实的中果皮细胞所共有的过程，并且在硬度小于 20 N 的桃子中清晰可见。相比之下，细胞粘附力的丧失是在成熟 MF 果实果皮中独有的特征。在这种成熟的果实中，大量的内切-PG亚型被高度表达，并且酶定位于中间片层。因此，成熟 MF 桃果皮的特征是宽阔的质外体空间。相比之下，在任何 NMF 水果或未成熟的 MF 桃子中均未观察到细胞粘附丧失。因此，在未成熟的 NMF 果实中未检测到内切 PG，而在成熟的 NMF 和未成熟的 MF 桃子中则发现很少且表达较差的酶亚型。在该果实中，表达较差的内切-PG 主要位于细胞质和内部初生细胞壁内的囊泡中。总体而言，结果表明需要内切PG功能才能实现融化的果肉质地，其特点是宽的质外体空间和部分萎缩的中果皮细胞。相反，鉴于 NMF 桃子的软化能力（达到 5-10 N），endo-PG 活性对果实硬度的降低没有关键影响。与番茄一样，共质体/质外体水状态的变化似乎是桃果实调节其硬度的主要过程。
Peach softening is usually attributed to the dismantling of the cell wall in which endo-polygalacturonase (endo-PG)-catalysed depolymerization of pectins plays a central role. In this study, the hypothesis that the function of endo-PG is critical for achieving a melting flesh fruit texture but not for reducing fruit firmness was tested by comparing pericarp morphology and endo-PG expression and localization in melting (MF) and non-melting flesh (NMF) fruit at successive stages of ripening. MF Bolero, Springbelle, and Springcrest, and NMF Oro-A and Jonia cultivars were analysed. Both MF and NMF fruit were left to ripen on the tree and reached a firmness of < 10 Newtons (N). The image analysis of pericarp tissues revealed that during softening the loss of cell turgidity was a process common to mesocarp cells of all MF and NMF fruit and was clearly visible in peaches with a firmness of less than similar to 20 N. In contrast, the loss of cell adhesion was a feature exclusively observed in ripe MF fruit pericarp. In this ripe fruit, large numbers of endo-PG isoforms were highly expressed and the enzyme localization corresponded to the middle lamella. As a consequence, wide apoplastic spaces characterized the pericarp of ripe MF peaches. In contrast, no loss of cell adhesion was observed in any NMF fruit or in unripe MF peaches. Accordingly, no endo-PG was detected in unripe NMF fruit, whereas few and poorly expressed enzyme isoforms were revealed in ripe NMF and in unripe MF peaches. In this fruit, the poorly expressed endo-PG localized mainly in vesicles within the cytoplasm and inner primary cell wall. On the whole the results suggested that endo-PG function was needed to achieve melting flesh texture, which was characterized by wide apoplastic spaces and partially deflated mesocarp cells. Conversely, endo-PG activity had no critical influence on the reduction of fruit firmness given the capacity of NMF peaches to soften, reaching values of 5-10 N. As in tomato, the change of symplast/apoplast water status seems to be the main process through which peach fruit regulates its firmness.