Using the fucosylation mutant sensitive-to-freezing8 (sfr8) to explore the influence of plant cell wall on transpiration

Cell walls have a specialised structure and function in guard cells that surround and control the openness of the stomata, microscopic pores allowing CO2 uptake and water loss. The Arabidopsis thaliana senstive-to-freezing8 (sfr8) mutant loses water more quickly than wildtype and has severely reduced levels of cellular fucose, affecting multiple aspects of cell wall, including xyloglucan, pectin, proteins and mechanical strength. The defective cell wall components of sfr8 may result in a higher transpiration rate. This study aims to discover how the sfr8 cell wall mutation influences transpiration. Arabidopsis mutants affected in different aspects of cell wall were measured for their transpiration rate and stomatal conductance, the rate of stomatal gas exchange. Mutants in fucosylation, pectin abundance, xyloglucan and mechanical stress all had transpiration or stomatal conductance during dehydration stress similar to wildtype. Only one mutant other than sfr8 had transpiration and stomatal conductance significantly higher than wildtype during drought stress and changing CO2 concentration; the pectin modification mutant, reduced wall acetylation2 (rwa2). Further measures of stomatal structure and function were taken. sfr8 had significantly different stomatal development to wildtype and limited stomatal dynamics, whereas, rwa2 had stomatal size, density and aperture equivalent to wildtype. Mutants were tested for drought tolerance and surprisingly, sfr8 had a better survival rate than wildtype, which may be attributed to the altered stomatal development. The results of this study and supporting literature indicate that pectin crosslinking, but not all pectin modification, affects transpiration, stomatal behaviour and drought tolerance. The higher transpiration rate of rwa2 is probably due to cuticle damage. Moreover, sfr8 had the highest transpiration of all tested mutants suggesting that other factors may influence sfr8 transpiration, which are explored. Understanding the mechanistic basis of genes, like SFR8, that affect stomatal characteristics and drought tolerance will become increasingly important as drought becomes more prevalent.