PtrWRKY75-overexpressing transgenic poplar showed improved drought tolerance under short-term drought stress
To explore the differences in stress tolerance between OE lines and WT plants, a drought treatment was applied by withholding watering for 7 days. As expected, the leaves of the WT plants were wilted after 7 days of drought, whereas those of the OE lines remained turgid (Figure 5A). During the drought treatment, the net photosynthesis rate,G s, and transpiration rate of WT and OE poplars were measured (Figure 5B–D). The photosynthesis rate of WT plants decreased significantly, with almost no photosynthetic activity recorded on day 7 of the drought treatment, whereas the net photosynthesis rate of the OE lines decreased significantly in the first 4 days and then slowed down, and remained at a certain level at day 7 (Figure 5B). The G s and transpiration rate in WT and OE lines decreased under drought treatment, but the decline in OE lines was slower than that in WT (Figure 5C, D). In addition, the OE lines maintained a higher leaf relative water content (RWC) than the WT plants under drought (Figure 5E). Leaf water loss, an important parameter for evaluating plant tolerance to water deficit stress, was also examined in the WT and OE lines. The WT plants lost water faster than did the OE lines under dehydration conditions (Figure 5F). Electrical conductivity can reflect the extent of damage to the plasma membrane. After short-term drought stress, the relative electrical conductance (REC) of both WT and the OE lines increased, but to a higher level in WT than in the OE lines, indicating that the leaves of WT suffered greater membrane damage (Figure 5G). Together, these results showed that the OE lines were more tolerant than were WT plants to short-term drought stress.