Senescent spotting or brown spot on bananas, is regarded as a form of programmed cell death (PCD). These spots appear in areas where stomata are present on the banana peel, there is no report describing the relationship between these spots and stomata on peel. This research aims to investigate whether senescent spotting in banana is involved in the PCD of stomata on peel. Three banana cultivars, ‘Khai-Kasetsart 2’ (KK2), ‘Dwarf Cavendish’ (CVD), and ‘Hom Thong’ (HT) bananas were examined for senescent spotting. KK2 banana exhibited more severe senescent spotting than CVD banana, while HT bananas did not display brown spot. Electrolyte leakage and DNA degradation increased before the spotting was observed in KK2 and CVD bananas. The peel structure revealed compact cells in CVD and HT bananas, whereas KK2 banana had a loose cell structure. Notably, KK2 banana had a high stomata density correlate with weight loss. Interestingly, the stomata type of KK2 banana was the same as CVD banana, being the typical type, while HT had a sunken type. The spotting zone of KK2 and CVD bananas revealed that stomata were more open than in the healthy zone. Additionally, the outer ground tissue of spotting zone flattened and collapsed, while the healthy zone did not exhibit this flattening and collapsing. Observations of cell morphology in the spotting zone of KK2 banana showed a detached plasma membrane, organelle destruction, and the presence of cell corpse with an absence of cytoplasm clearance. In conclusion, the result provides an evidence that stomata type on the banana peel involve in PCD, resulting in senescent spotting.

中文翻译：

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与香蕉衰老斑点的程序性细胞死亡相关的气孔类型和果皮结构

香蕉上的衰老斑或褐斑被认为是程序性细胞死亡 (PCD) 的一种形式。这些斑点出现在香蕉皮上有气孔的区域，但没有报道描述这些斑点与果皮上的气孔之间的关系。本研究旨在探讨香蕉的衰老斑是否与果皮气孔的 PCD 有关。对三个香蕉品种“Khai-Kasetsart 2”(KK2)、“Dwarf Cavendish”(CVD) 和“Hom Thong”(HT) 香蕉进行了衰老斑点检测。 KK2 香蕉比 CVD 香蕉表现出更严重的衰老斑点，而 HT 香蕉则没有表现出褐斑病。在 KK2 和 CVD 香蕉中观察到斑点之前，电解质泄漏和 DNA 降解增加。 CVD 和 HT 香蕉的果皮结构显示细胞紧密，而 KK2 香蕉的细胞结构松散。值得注意的是，KK2 香蕉具有与体重减轻相关的高气孔密度。有趣的是，KK2香蕉的气孔类型与CVD香蕉相同，为典型类型，而HT为凹陷型。 KK2 和 CVD 香蕉的斑点区显示气孔比健康区更开放。此外，斑点区域的外部地面组织变平和塌陷，而健康区域没有表现出这种变平和塌陷。对KK2香蕉点样区细胞形态的观察显示质膜脱落、细胞器破坏、存在细胞尸体且缺乏细胞质清除。总之，该结果提供了香蕉皮上的气孔类型参与PCD，导致衰老斑的证据。