Abstract
The hypothesis that aquaporins and carbonic anhydrase (CA) are involved in the regulation of stomatal (g s) and mesophyll (g m) conductance to CO2 was tested in a short-term water-stress and recovery experiment in 5-year-old olive plants (Olea europaea) growing outdoors. The evolution of leaf gas exchange, chlorophyll fluorescence, and plant water status, and a quantitative analysis of photosynthesis limitations, were followed during water stress and recovery. These variables were correlated with gene expression of the aquaporins OePIP1.1 and OePIP2.1, and stromal CA. At mild stress and at the beginning of the recovery period, stomatal limitations prevailed, while the decline in g m accounted for up to 60% of photosynthesis limitations under severe water stress. However, g m was restored to control values shortly after rewatering, facilitating the recovery of the photosynthetic rate. CA was downregulated during water stress and upregulated after recovery. The use of structural equation modelling allowed us to conclude that both OePIP1.1 and OePIP2.1 expression could explain most of the variations observed for g s and g m. CA expression also had a small but significant effect on g m in olive under water-stress conditions.
Highlights
Water stress is considered the main environmental factor limiting photosynthesis, plant growth, and yield worldwide, especially in semi-arid areas, where Olea europaea is well adapted (Boyer, 1982; Lawlor, 1995; Flexas et al, 2004)
The main objective of this study was to provide a step forward in the putative role played by AQPs and carbonic anhydrase (CA) in the regulation of gm under water stress
This study supports the hypothesis that the regulation of gm is regulated mainly by AQPs and that both OePIP1.1 and OePIP2.1 are likely to interact to exert a significant effect on gm
Summary
Water stress is considered the main environmental factor limiting photosynthesis, plant growth, and yield worldwide, especially in semi-arid areas, where Olea europaea is well adapted (Boyer, 1982; Lawlor, 1995; Flexas et al, 2004). Et al, 2002, 2004; Centritto et al, 2003; Galmés et al, 2007a; Warren, 2008a; Peeva and Cornic, 2009) in many species, several authors have suggested a possible co-regulation of gsc and gm (Centritto et al, 2003; Flexas et al, 2002, 2012) Such co-regulation depends on the species and the prevailing conditions, such as the combination of drought with VPD (Perez-Martin et al, 2009) or with radiation (Flexas et al, 2009; Galle et al, 2009). The main limiting factor for photosynthesis during water stress or recovery can vary depending on species (Galmés et al, 2007a; Ennahli and Earl, 2005), the intensity of previous stress (Flexas et al, 2009), light and temperature (Galle et al, 2009), plant age (Varone et al, 2012), and the application of successive drought and recovery cycles (Galle et al, 2011)
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