AtPIP2;5 Aquaporin Affects Mesophyll Conductance to CO<sub>2</sub> and Stomatal Density in Nicotiana tabacum Leaves
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The plasma membrane intrinsic protein AtPIP2;5 aquaporin is known for accelerating water flow into plant cells; however, its role in CO2 transport in leaf mesophyll cells (as a ‘cooporin’) is not well understood. We investigated parameters of leaf water loss and CO2 uptake in transgenic tobacco (Nicotiana tabacum cv. Xanthi) leaves expressing the AtPIP2;5 gene from Arabidopsis thaliana (AtPIP2;5) and in wild-type (WT) tobacco. The control and transgenic plants were subjected to osmotically induced drought stress and a recovery period. Transpiration and photosynthesis rates (E, AN), stomatal and mesophyll conductance to CO2 (gs, gm), water use efficiency (WUE) and stomatal density (SD) were measured using gas exchange and stable isotope techniques. AtPIP2;5 expression in well-watered plants did not change AN and gs but increased gm by 42% compared to WT (p≤0.05). After 7 days of drought, gm decreased to 50% of its original value in PIP2;5 plants while remaining almost unchanged in the controls. AN also decreased significantly in stressed PIP2;5 plants compared to WT, while gs did not differ between genotypes. gm did not respond to 7 days of recovery in PIP2;5 and WT. However, in the transgenic plants, we found significant increases in SD and SI compared to WT. Instantaneous WUE was lower in transgenics than in WT. Our results suggest that AtPIP2;5 expressed in tobacco is also involved in CO2 transport in mesophyll cells during photosynthetic CO2 fixation. However, its facilitating role may turn into inhibition of CO2 flux during drought stress, persisting even after recovery.
Abstract
The plasma membrane intrinsic protein AtPIP2;5 aquaporin is known for accelerating water flow into plant cells; however, its role in CO2 transport in leaf mesophyll cells (as a ‘cooporin’) is not well understood. We investigated parameters of leaf water loss and CO2 uptake in transgenic tobacco (Nicotiana tabacum cv. Xanthi) leaves expressing the AtPIP2;5 gene from Arabidopsis thaliana (AtPIP2;5) and in wild-type (WT) tobacco. The control and transgenic plants were subjected to osmotically induced drought stress and a recovery period. Transpiration and photosynthesis rates (E, AN), stomatal and mesophyll conductance to CO2 (gs, gm), water use efficiency (WUE) and stomatal density (SD) were measured using gas exchange and stable isotope techniques. AtPIP2;5 expression in well-watered plants did not change AN and gs but increased gm by 42% compared to WT (p≤0.05). After 7 days of drought, gm decreased to 50% of its original value in PIP2;5 plants while remaining almost unchanged in the controls. AN also decreased significantly in stressed PIP2;5 plants compared to WT, while gs did not differ between genotypes. gm did not respond to 7 days of recovery in PIP2;5 and WT. However, in the transgenic plants, we found significant increases in SD and SI compared to WT. Instantaneous WUE was lower in transgenics than in WT. Our results suggest that AtPIP2;5 expressed in tobacco is also involved in CO2 transport in mesophyll cells during photosynthetic CO2 fixation. However, its facilitating role may turn into inhibition of CO2 flux during drought stress, persisting even after recovery.