S-RNAse-based self-incompatibility (SI) in petunia (Petunia hybrida L.) is a self-/non-self-recognition system underlying the pistil rejection of self-pollen. Using different methods, including a TUNEL assay, we have recently shown that programmed cell death (PCD) is a factor of the SI in petunia. Here, we show that the growth of self-incompatible pollen tubes in the style tissues during 4 h after pollination is accompanied by five-sixfold increase in a caspase-like protease (CLP) activity. Exogenous cytokinin (CK) inhibits the pollen tube growth and stimulates the CLP activity in compatible pollen tubes. The actin depolymerization with latrunculin B induces a sharp drop in the CLP activity in self-incompatible pollen tubes and its increase in compatible pollen tubes. Altogether, our results suggest that a CLP is involved in the SI-induced PCD and that CK is a putative activator of the CLP. We assume that CK provokes acidification of the cytosol and thus promotes the activation of a CLP. Thus, our results suggest that CK and CLP are involved in the S-RNAse-based SI-induced PCD in petunia. Potential relations between these components in PCD signaling are discussed.

中文翻译：

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半胱天冬酶样蛋白酶和植物激素细胞分裂素作为基于 S-RNA 酶的自交不亲和性诱导的矮牵牛 PCD 的决定因素。

矮牵牛 (Petunia hybrida L.) 中基于 S-RNA 酶的自交不亲和 (SI) 是一种自我/非自我识别系统，是自身花粉雌蕊排斥的基础。使用不同的方法，包括 TUNEL 检测，我们最近表明程序性细胞死亡 (PCD) 是矮牵牛 SI 的一个因素。在这里，我们表明在授粉后 4 小时内，花柱组织中自相不相容的花粉管的生长伴随着半胱天冬酶样蛋白酶 (CLP) 活性的五六倍增加。外源性细胞分裂素 (CK) 抑制花粉管生长并刺激相容花粉管中的 CLP 活性。与 latrunculin B 的肌动蛋白解聚导致自不相容花粉管中 CLP 活性急剧下降，而在相容花粉管中增加。共，我们的结果表明 CLP 参与了 SI 诱导的 PCD，而 CK 是 CLP 的推定激活剂。我们假设 CK 会引起细胞质酸化，从而促进 CLP 的激活。因此，我们的结果表明 CK 和 CLP 参与了矮牵牛中基于 S-RNAse 的 SI 诱导的 PCD。讨论了 PCD 信令中这些组件之间的潜在关系。