Overexpression of PIP1;2 increases mesophyll conductance

Groszmann M, Skinner S, Von Caemmerer S and Evans JR

ARC Centre of Excellence for Translational Photosynthesis, Australian National University.

Aquaporins in plants are encoded by multigene families. Plasma membrane intrinsic proteins (PIPs) have been categorised into two groups, but this is not clearly associated with their function. Due to easy methodology, many have been functionally assayed for their ability to alter membrane permeability to water. However, determining CO2 permeability is difficult and while some aquaporins have been shown to increase membrane permeability to CO2 in yeast or Xenopus oocytes, in planta demonstrations are limited. We have been using Arabidopsis to investigate AQP function. We generated Arabidopsis lines overexpressing each plasma membrane intrinsic protein to facilitate in planta characterisation of CO2 permeability. Following initial screening for enhanced growth, several lines of PIP1;2, PIP1;3 and PIP 1;4 were chosen for more detailed characterisation using combined gas exchange and carbon isotope measurements to determine mesophyll conductance. Overexpression of PIP1;2 increased mesophyll conductance and was associated with a decrease in the draw-down in CO2 between intercellular airspaces and sites of carboxylation within chloroplasts. Overexpression of PIP1;4 also increased mesophyll conductance, but as this was associated with increased photosynthetic capacity, further anatomical characterisation is needed to identify the reason. There was no significant effect from overexpressing PIP1;3.