The coalescence of protein storage vacuoles (PSVs) is one of the most prominent cellular changes occurring in cereal aleurone cells during germination. This structural change is highly coupled with the functional transition of this organelle from a storage compartment to a lytic section. Gibberellic acid (GA) promotes this process, whereas abscisic acid (ABA) prevents it. Previously, we demonstrated that ABA-inducible HvTIP3;1 plays a decisive role in ABA-mediated prevention of PSV fusion. In this follow-up study, we examined whether the aquaporin activity of tonoplast intrinsic protein (TIP) is related to its preventive effect on PSV fusion using various functional mutants. The defective forms of aquaporin (HvTIP3;1m and HvTIP3;1ΔNPA-GFPs for HvTIP3;1, and HvTIP1;2m for HvTIP1;2) were found to be less effective than the usual form in delaying the PSV fusion process occurring in GA-treated cells. In contrast, overexpression of HvTIP3;1m reduced the preventive effect of ABA on PSV fusion. Upon inhibition of aquaporin activity using mercury, PSV fusion occurred to a greater extent in ABA-treated barley protoplasts. These data suggest that the aquaporin activity of TIP is involved in the deterrent effect of TIP on PSV coalescence. TIP3-GFP barley transgenic seeds showed prolonged expression of the TIP3;1 transcript. Moreover, PSV fusion progressed at a much slower rate compared to wild type. Additionally, the degradation of storage proteins was not as efficient, suggesting that a metamorphic transition of PSVs to lytic organelles is closely correlated with the disappearance of HvTIPs and the PSV fusion process.

中文翻译：

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大麦液泡膜内源蛋白的水通道蛋白活性与糊粉细胞中蛋白质储存液泡聚结的延迟有关

蛋白质储存液泡 (PSV) 的聚结是发芽期间谷物糊粉细胞中发生的最显着的细胞变化之一。这种结构变化与该细胞器从储存室到裂解部分的功能转变高度相关。赤霉酸 (GA) 促进了这一过程，而脱落酸 (ABA) 则阻止了这一过程。此前，我们证明了 ABA 诱导型 HvTIP3;1 在 ABA 介导的 PSV 融合预防中起决定性作用。在这项后续研究中，我们检查了液泡膜内在蛋白 (TIP) 的水通道蛋白活性是否与其使用各种功能突变体对 PSV 融合的预防作用有关。缺陷形式的水通道蛋白（HvTIP3；1m 和 HvTIP3；HvTIP3 的 1ΔNPA-GFP；1 和 HvTIP1；HvTIP1 的 2m；2) 发现在延迟 GA 处理的细胞中发生的 PSV 融合过程方面不如通常的形式有效。相反，HvTIP3;1m 的过表达降低了 ABA 对 PSV 融合的预防作用。在使用汞抑制水通道蛋白活性后，在 ABA 处理的大麦原生质体中发生更大程度的 PSV 融合。这些数据表明，TIP 的水通道蛋白活性与 TIP 对 PSV 聚结的威慑作用有关。TIP3-GFP 大麦转基因种子显示 TIP3;1 转录物的延长表达。此外，与野生型相比，PSV 融合的进展速度要慢得多。此外，储存蛋白的降解效率不高，这表明 PSV 向裂解细胞器的变形转变与 HvTIP 的消失和 PSV 融合过程密切相关。