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Overexpressing OsPIP2;4 in the two rice cultivars Giza178 and IR64 resulted in contrasting cultivar-dependent physiological attributes under control and drought conditions in the field. In the T3 plants, PIP2;4 expression was significantly higher in the leaves and roots of Giza178 under control but only in the roots under drought condition and higher in the leaves and roots of IR64 under control but not under drought condition compared with that in the corresponding wild types. The transgene improved the plant growth in Giza178 under both growth conditions but had no significant effect in IR64 under either condition. The transgenic lines of Giza178 recovered their leaf relative water content faster than those of the wild type in the afternoon and showed improved gas exchange parameters, water use efficiency, and grain yield, as a result of improved root hydraulic conductivity (Lp r ) and xylem sap flow. No comparable responses were found in IR64 although Lp r and xylem sap flow were enhanced in the transgenic lines under the control condition only, suggesting that the positive effect of PIP2;4 on the well-watered leaves of IR64 was offset by the low root/shoot ratio and the inherent expression of other aquaporins. In the transgenic plants of IR64 under drought, PIP2;4 expression was not induced in the roots presumably due to an overriding post-transcription regulatory mechanisms, leading to the lack of changes in the Lp r and xylem sap flow and consequently, the plant growth, water relations, gas exchange, and grain yield were similar to the wild type. The data suggest that the outcome of overexpressing a single aquaporin gene depends on the plant architecture, internal responses to drought, and native expression of other aquaporins.

Nine-day-old wheat seedlings were treated with NaCl at 75, 150, and 225 mM for 15 days in the absence or presence of 5 mM glycine. NaCl particularly at 150 and 225 mM led to significant reductions in fresh and dry weights, chlorophylls, carotenoids, Ca(2+), K(+), and K(+)/Na(+) ratio. Contrarily, there were significant accumulations in Na(+), malondialdehyde (MDA), H2O2, soluble sugars, and proline concomitant with inhibitions in enzymatic and non-enzymatic antioxidants and in Rubisco. In the meantime, the transcript level of alternative oxidase (AOX) was highly upregulated by NaCl; the upregulation was greatest with the lowest concentration. However, the transcript level of H(+)/Na(+) antiporter exchanger (NHX1) was decreased by 75 and 150 mM NaCl but increased by 225 mM. Similarly, the transcript level of salt overly sensitive 1 (SOS1) was upregulated by only 225 mM. Nonetheless, the application of glycine mostly overcame the varied impacts of NaCl on growth, MDA, H2O2, pigments, metabolites, and elements. Moreover, glycine elevated enzymatic and non-enzymatic antioxidants to reach most likely the levels of the respective control. On the contrary, much induction was detected in Rubisco. The transcript levels of AOX, NHX1, and SOS1 were further upregulated; the upregulation of AOX was most pronounced with the highest NaCl concentration in the presence of glycine and only with 75 and 150 mM NaCl for NHX1 and SOS1. The increase in antioxidants concomitant with the decrease in MDA and H2O2 reveals that ROS scavenging system became more efficient in NaCl-treated wheat following glycine application, concluding that glycine could ameliorate wheat tolerance to salinity. Moreover, lowering Na(+) by glycine and mitigation of the decreased K(+)/Na(+) ratio synchronous with recovery in growth reduction and stimulation of AOX, NHX1 and SOS1 may emphasize the role of glycine in stimulating gene expression for raising wheat tolerance to NaCl.