Regulation of Seed Germination and the Role of Aquaporins under Abiotic Stress

Aquaporins play a major role in governing the movement of water between neighboring cells during seed germination and are major players in response to abiotic stress conditions that affect water availability. Seeds of pea (Pisum sativum L. cv. Arkel) were used for studying cell growth, expression and function of aquaporins during seed imbibition, radicle emergence and growth.Water channel functioning checked by inhibitory test with mercuric chloride showed closed water channels prior to growth initiation. Addition of mercury scavenging agents dithiothreitol and β-mercaptoethanol along with the HgCl2 overcame the observed inhibitory effects in terms of moisture content. The presence of aquaporin inhibitors (HgCl2 and ZnCl2) and NaCl reduced seedling growth. Here we studied expression of a plasma membrane intrinsic protein (PsPIP1;2) and a tonoplast intrinsic protein (PsTIP1;1) by using the semi quantitative RT-PCR in the germinated seedlings exposed to different abiotic stresses. Treatment with NaCl, HgCl2 and ZnCl2 differentially regulated gene expression in radicle, cotyledon and plumule. NaCl and Hg, upregulated expression of PsPIP1;2 and PsTIP1;1 in radicle and expression of PsTIP1;1 was significantly upregulated in radicle and suppressed in cotyledon by Zn. A possible role for aquaporins in germinating seeds and seedling response to abiotic stresses is discussed.