Mixed linkage glucan (MLG) and the Péclet effect
The genotypes varied in their physiological and isotopic response to growth light intensity. The genotypes (cslf6-1 , cslf6-2 ), which are transposon insertion lines created in a Nipponbare background, did not always have the same phenotype (Upadhyaya et al. 2006; Vega-Sánchez et al. 2012). They were similar in most anatomical features and biochemical properties (Vega-Sánchez et al. 2012; Ellsworth et al. 2018). However, genotype cslf6-1 had lower values than cslf6-2 in several physiological traits such as gs , E , and both A max and J max on a per gram basis (Ellsworth et al.2018) and L v in this study. Because all plants were grown in the same physical space and under the same conditions such as temperature and relative humidity, variation in these traits across genotypes can be either attributed to pleiotropic effects on the cell wall or background effects as seen by the differences between Nipponbare and the isogenic WT siblings of these different lines (Vega-Sánchez et al. 2012).
The genotypic response of Δ18OLW to growth light intensity can be explained within the Péclet effect theory by the corresponding response in stomatal density (Sd). Multiple studies have shown that Sd and stomatal size influence Δ18OLW by modifying E andL , and that differences in Sd were sufficient to drive species-level differences in Δ18OLWbetween mangrove and nearby freshwater species and acrossArabidopsis stomatal density lines (Rosado et al. 2013; Sternberg & Manganiello 2014; Larcher et al. 2015; Liang et al. 2018). In this study, lower L v in cslf6-1 was likely due to an interaction between a genotype-driven reduction in E related to Sd and an increased mesophyll and xylem water exchange due to lower water flow, which reduced the mixing length between enriched mesophyll water and unenriched water in the xylem (Farquhar & Gan 2003; Gan et al. 2003). Therefore, changes in Sd regulated the relative differences in Δ18OLW, but Sd alone did not predict the magnitude of Δ18OLW(Rosado et al. 2013; Larcher et al. 2015). Conversely and similar to Sternberg and Manganiello (2014), higher Δ18Oe at high light in wildtype and cslf6-2 did not result in higher Δ18OLW because increased advective flow (E ) and longer mixing length (L v) between xylem and mesophyll reduced back diffusion and the impact of Δ18Oe on Δ18OLW. The fact that the partial volume of the veins along with Sd, L v, andE co-varied with Δ18OLWsuggests that Δ18OLW was significantly influenced by the entire water transport path through the leaf and, consequently, may trace anatomical, physical, and physiological factors affecting water movement.