## 3 Results
### Enzyme Activity  
Before the drought stress treatment, the activity of Rubisco in the NT plants was 120 nmol min\({}^{-1}\) mg\({}^{-1}\), and it diminished (\(p\leq 0.05\)) when drought stress was applied (Figure 3a). After four days of drought, the Rubisco in the NT plants had lower activity, which was 70% lower compared to day zero, and remained unchanged (\(p\geq 0.05\)) for the rest of the experiment (Figure 3a). In the 35S and rd-1B transgenic lines, the Rubisco activity in non-stressed plants was 40 nmol min\({}^{-1}\) mg\({}^{-1}\), and this increased (\(p\leq 0.05\)) from day two of the drought treatment (Figure 3a). Rubisco showed a similar performance in both the 35S and rd-1B lines, as it remained unchanged (\(p\geq 0.05\)) from day four until day eight of stress (Figure 3a). However, the Rubisco activity was 13% lower in the 35S plants than in the rd-1B line at the end of the drought treatment (Figure 3a). Figure 3: Effect of drought stress on enzymes involved in Calvin cycle and sugar 3.5 synthesis: (**a**) Rubisco activity; (**b**) fructose biphosphatase (FBPase); (**c**) sucrose phosphate synthase (SPS). Values are mean \(\pm\) SE (\(n=3\)). Letters indicate significant differences during days of drought (\(p\leq 0.05\)). The transgenic rd-1C line had the highest (\(p\leq 0.05\)) Rubisco activity among all the lines throughout the experiment (Figure 3a). Before the drought treatments, the activity of Rubisco in the rd-1C plants was 148 nmol min\({}^{-1}\) mg\({}^{-1}\), and it diminished (\(p\leq 0.05\)) on the second day of drought (Figure 3a). On day four, the Rubisco activity in the rd-1C line increased (\(p\leq 0.05\)) to its original value and was maintained until the end of the stress (Figure 3a). The FBPase activity was higher (\(p\leq 0.05\)) in the NT wheat plants before drought compared to the transgenic lines (Figure 3b). Two days after starting the drought treatment, the activity of FBPase in the NT plants diminished (\(p\leq 0.05\)), and it reached its lowest (\(p\leq 0.05\)) activity on the sixth day, which was half the value compared to day zero (Figure 3b). Transgenic plants from the 35S line showed less FBPase activity than the NT and other transgenic lines (Figure 3b). The FBPase activity in the 35S plants was 130 nmol min\({}^{-1}\) mg\({}^{-1}\) and showed no changes (\(p\geq 0.05\)) from day zero to day six of the treatment (Figure 3b). On the eighth day of drought, the 35S plants had higher FBPase activity (\(p\leq 0.05\)) (Figure 3b). The FBPase activity in non-stressed rd-1B plants was 210 nmol min\({}^{-1}\) mg\({}^{-1}\), and it diminished (\(p\leq 0.05\)) on the second day of drought (Figure 3b). The activity of FBPase increased (\(p\leq 0.05\)) from day four to day six in the rd-1B plants, and on the eighth day of drought, it went back to its initial activity (Figure 3b). In the rd-1C transgenic plants, the FBPase activity gradually decreased throughout the drought treatment (Figure 3b). The NT plants had a higher (\(p\leq 0.05\)) SPS activity than the transgenic lines (Figure 3c). After being reduced (\(p\leq 0.05\)) on day two of drought, the SPS activity in the NT plants recovered its initial activity on day four (\(p\leq 0.05\)) and declined again on the sixth day of drought until the end of the experiment (Figure 3c). The activity of SPS in the transgenic 35S plants was 21 nmol min\({}^{-1}\) mg\({}^{-1}\) at day zero, and this declined from day two to day four of drought. The SPS activity had an increase (\(p\leq 0.05\)) in the 35S plants on the sixth day of stress and declined again on day eight (Figure 3c). In the rd-1B plants, the activity of SPS was 17 nmol min\({}^{-1}\) mg\({}^{-1}\) on day zero, and it decreased (\(p\leq 0.05\)) almost three-fold by day two of the treatment (Figure 3c). No significant changes were observed in the SPS activity in the rd-1B plants on days four and six of drought (Figure 3c). By the end of the drought stress treatment, the SPS activity was the same (\(p\geq 0.05\)) for the transgenic lines rd-1B and 35S and NT plants (Figure 3c).