Abstract Calcium plays an important role in the regulation of fruit firmness, but the mechanism behind this remains poorly understood. In this study, we investigated the firmness of the fruit pulp in the peduncle, calyx, and equatorial parts of Fuji apples. The pulp protoplasts of the three parts were obtained by enzymatic hydrolysis. The patch clamp technique was used to measure the Ca2+ current on the protoplast membranes of the three parts. The firmness was significantly different among the three fruit parts. The equatorial part, which had the lowest firmness, had the highest Ca2+ efflux, while the lowest Ca2+ efflux was measured near the calyx, which had the highest firmness. Supplementation of potassium fertilizer to apple trees promoted fruit firmness and reduced Ca2+ efflux from pulp cells. Spraying 10 mg/L auxin directly onto young fruit increased the firmness and reduced cell Ca2+ efflux. These results indicated that Ca2+ efflux is correlated with fruit firmness. Because fruit softening is a natural phenomenon during fruit ripening, we conclude that the reduction in cellular Ca2+ efflux can maintain cell viability and increase the firmness of apple fruit pulp.

中文翻译：

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Ca2+ 外流与苹果硬度呈负相关

摘要 钙在调节果实硬度方面起着重要作用，但其背后的机制仍知之甚少。在这项研究中，我们调查了富士苹果的花序梗、花萼和赤道部分果肉的硬度。三部分的纸浆原生质体均通过酶解法获得。膜片钳技术用于测量三部分原生质体膜上的Ca2+电流。三个果实部分的硬度差异显着。硬度最低的赤道部分具有​​最高的 Ca2+ 流出量，而在花萼附近测量到的 Ca2+ 流出量最低，其硬度最高。向苹果树补充钾肥可促进果实硬度并减少果肉细胞中的 Ca2+ 外流。将 10 mg/L 的生长素直接喷洒在幼果上会增加果实的硬度并减少细胞 Ca2+ 外流。这些结果表明 Ca2+ 流出与果实硬度相关。由于果实软化是果实成熟过程中的一种自然现象，我们得出结论，细胞 Ca2+ 外流的减少可以维持细胞活力并增加苹果果肉的硬度。