Effect of hydropriming on germination and aquaporin gene expression in rice

Water uptake, modulated by aquaporins, is closely correlated with germination. This study aimed to evaluate the roles of aquaporins during germination by comparing the water uptake and aquaporin gene expression profiles of rice seeds showing differential priming-induced progress in germination. We focused on the expression of all 33 aquaporins in rice (Oryza sativa L.) seeds during germination. For priming, rice seeds were submerged in tap water at 30 degrees C for 12 h and dried to obtain the initial seed water content. The germination rate, seed water content, and aquaporin gene expression in primed and non-primed (control) seeds after imbibition were measured. Priming promoted the germination rate but did not increase water uptake during the early germination period (0-24 h after imbibition). Thereafter, the expression levels of various aquaporin isoforms, such as OsPIP1s, PIP2s, and TIPs, in both the primed and control seeds increased abruptly, which was clearly antecedent in the primed seeds. The antecedent aquaporin gene abundance in the primed seeds in the post-germination phase may contribute to the development of cells and/or tissues in the germinating seeds, by modulating an increase in water permeability. In contrast, the mRNA levels of OsTIP3;1 decreased immediately after imbibition. OsTIP3;1 was strongly present in the aleurone layer, probably stored during ripening, suggesting a distinct role in developing seeds, but not in germination. Summarily, though our results suggested that the improvement in germination speed by priming may not be caused by aquaporins, we identified aquaporins that immediately started to increase water absorption during/after germination.

Automated summary

Aquaporins play important roles in rice seed germination by modulating water uptake to promote seed development. Priming improved germination rate but did not increase water uptake in the early germination phase. Aquaporin gene expression levels increased abruptly in both primed and control seeds after germination, with a clear antecedence in primed seeds.