Effects of short-term osmotic stress on leaf hydraulic conductivity and ZmPIPs mRNA accumulation in maize seedlings

Plants maintain water balance by varying hydraulic properties, and plasma membrane intrinsic proteins (PIPs) may be involved in this process. Leaf xylem and root hydraulic conductivity and the mRNA contents of four highly expressed ZmPIP genes (ZmPIP1;1, ZmPIP1;2, ZmPIP2;2, and ZmPIP2;5) in maize (Zea mays) seedlings were investigated. Under well-watered conditions, leaf hydraulic conductivity (K-leaf) varied diurnally and was correlated with whole-plant hydraulic conductivity. Similar diurnal rhythms of leaf transpiration rate (E), K-leaf, and root hydraulic conductivity (K-root) in well-watered plants are important for maintaining whole-plant water balance. After 2 h of osmotic stress treatment induced by 10% polyethylene glycol 6000, the K-root of stressed plants decreased but K-leaf increased, compared with well-watered plants. The mRNA contents of four ZmPIPs were significantly up-regulated in the leaves of stressed plants, especially for ZmPIP1;2. Meanwhile, ZmPIP2;5 was significantly down-regulated in the roots of stressed plants. After 4 h of osmotic stress treatment, the E and leaf xylem water potentials of stressed plants unexpectedly increased. The increase in K-leaf and a partial recovery of K-root may have contributed to this process. The mRNA content of ZmPIP1;2 but not of the other three genes was up-regulated in roots at this time. In summary, the mRNA contents of these four ZmPIPs associated with K-leaf and K-root change in maize seedlings during short-term osmotic stress, especially for ZmPIP1;2 and ZmPIP2;5, which may help to further reveal the hydraulic resistance adjustment role of ZmPIPs.