Abstract
Survival and mortality of plants in response to severe drought may be related to carbon starvation, but little is known about how plasma membrane intrinsic proteins may help alleviate the drought-induced damage. Here, we determined the roles of plasmalemma aquaporin gene in improving plant water status, maintaining carbon accumulation, and thereby enhancing drought tolerance. Seven StPIP1 transformed potato (Solanum tuberosum L.) lines (namely T1, T2…T7) were compared with non-transgenic control plant at molecule and whole-plant levels. The relative expression of StPIP1 gene was found in leaves, stems and roots, with the most abundant expression being in the roots. The transgenic lines T6 and T7 had the highest StPIP1 expression, averaging 7.2 times that of the control and the greatest differences occurred 48 h after mannitol osmotic stress treatment. Using an evaluation index to quantifying the degree of drought tolerance, we found that the StPIP1 transgenic lines T6 and T7 had the highest drought tolerance, averaging 8.5 times that of the control. Measured at 30 days in drought stress treatment, the control plant decreased net photosynthetic rate by 33 and 56%, respectively, under moderate and severe stresses; also decreased stomatal conductance by 39 and 65%; and lowered transpiration rate by 49 and 69%, compared to the no-stress treatment, whereas the transgenic lines T6 and T7 maintained a relatively stable level with slight decreases in these properties. The constitutive overexpression of StPIP1 in potato improved plant water use efficiency and increased nonstructural carbohydrate concentration, which helped alleviate carbon starvation and minimized the loss of biomass and tuber yield due to drought stress. We conclude that the expression of StPIPs improves overall water relations in the plant and helps maintain photosynthesis and stomatal conductance; these help minimize carbon starvation and enhance the whole plant tolerance to drought stress.
Highlights
The shortage of fresh water is one of the most severe constraints in crop productivity in arid and semiarid areas (Toenniessen et al, 2003; Chai et al, 2016)
The plasmid pStPIP1 containing the StPIP1 gene was constructed and both StPIP1 and neomycin phosphotransferase II (Npt II) genes were verified with PCR amplification (Figure S1)
Our study demonstrated the strong roles the StPIP1 gene plays in alleviating drought tolerance, reflected by various biophysicochemical properties of the transgenic lines, including antioxidant enzyme activities, nonstructural carbohydrates, photosynthesis efficiency, stomatal conductance, and transpiration rate
Summary
The shortage of fresh water is one of the most severe constraints in crop productivity in arid and semiarid areas (Toenniessen et al, 2003; Chai et al, 2016). Aquaporins (AQPs) are integral membrane proteins that serve as channels in the transfer of water, and in some cases, small solutes across the membrane These proteins respond to water availability in a timely manner (Ding et al, 2015) and the exploration of the AQP responses to drought will help improve plant water use efficiency (Hu et al, 2012; Moshelion et al, 2015). All four types of AQPs display highly conserved structures wherein six membrane-spanning alpha helices are linked by five short loops with their N- and C-termini toward the cytosol Two of these loops contain highly conserved asparagineproline-alanine motifs, which play an important role in the formation of water-selective channels (Chaumont et al, 2001). The efficiency of water transport in plant tissues relies on plasma membrane intrinsic proteins (Zhou et al, 2007)
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