Accession differences in LWC most likely result from the effect of mesophyll cell wall thickness on leaf density and not differences in water potential as plants in experiment 3 were not water stressed (Garnier and Laurent 1994; Evans et al. 1994). Leaf anatomical traits such as leaf and cell wall thickness, surface area of mesophyll cells exposed to internal air spaces, and the location of chloroplasts within those cells was initially shown to correlate with g m several decades ago (von Caemmerer

and Evans 1991; Evans et al. 1994). In particular, selleck chemicals llc mesophyll cell wall thickness was shown to negatively affect g m. Therefore, high LWC accessions should have thinner mesophyll cell walls resulting in high g m and more negative

δ13C (Evans et al. 1994), which is consistent with our data. These ideas have been revisited recently and the importance of the cell wall properties (thickness and water content) and the coverage of air exposed surfaces of mesophyll cells by chloroplasts is receiving more attention (Evans et al. 2009; Tholen and Zhu 2011; Tosens et al. 2012). Direct measurement of leaf thickness and density may explain some of the variation in g m and δ13C among plants with similar LWC values (Fig. 6). Alternatively, variation in COO-porin content or activity could be responsible for the g m and δ13C variation in plants with LWC. Recent studies have found a significant role for chloroplast ABT199 membrane CO2 transporting aquaporins

(COO-porin) has been demonstrated and provides a clearly heritable mechanism for both rapid and sustained adjustment of g m (Flexas et al. 2006; Uehlein et al. 2008, 2012; Heckwolf et al. 2011). We have found strong correlations between LWC, A, and g s, so focusing on plants with this website similar LWC should limit the influence of those factors on variation in δ13C and increase the relative influence of g m from cell wall properties or COO-porin content or activity on δ13C variation. Fig. 6 Relationship between leaf water content (LWC) and leaf carbon isotope composition (δ13C) among 39 accessions of Arabidopsis thaliana. Open and filled symbols represent spring and winter accession means, respectively. Line represents linear regression; r 2 and P values are given The ABI4 transcription factor causes changes in leaf anatomy and mesophyll conductance To further test for a causal effect of leaf anatomy on gas exchange (experiment 4 in Table 1), we used abi4, a mutant of locus AT2G40220, which is an AP2/ERF transcription factor (TF). ABI4 is closely related to the DREB2 TFs and the mutant was initially described as ABA insensitive based on a germination screen (Finkelstein 1994). Subsequent work has shown that the transcript is expressed in seedlings (Soderman et al. 2000) and fully developed rosette leaves (Finkelstein et al. 1998).