Cool temperature acclimation: Evidence for anatomical constraints on photosynthesis

Some of the anatomical and biochemical responses observed when plants acclimate to cool temperatures are similar to responses seen during high light acclimation. This study aimed to assess whether similar anatomical limitations as implicated in acclimation to high growth light intensities may also be involved in acclimation to low growth temperatures, and may consequently have the potential to constrain photosynthesis under cool growth temperature in plant lines not adapted to growth at low temperature. I investigated two anatomical parameters (vein density and specific leaf weight) that can limit photosynthetic acclimation to high light conditions and compared the response of these parameters with the response of maximal photosynthetic capacity during cool temperature acclimation. Two cold temperature-adapted plant species or ecotopes ( Mimulus lewisii, Arabidopsis thaliana ecotype Sweden) upregulated photosynthetic capacity when grown in cool conditions, whereas closely related warm temperature-adapted plants lines (Mimulus cardinalis, Arabidopsis thaliana ecotype Italy) did not. Furthermore, specific leaf weight (leaf dry weight/area) was positively associated with photosynthetic capacity changes, which suggests that leaf thickness and underlying mesophyll structure may be major limiting factors during cool temperature photosynthetic acclimation. No evidence for a capacity to alter foliar vein density was found for any of the above species, although additional investigation is needed to fully exclude export capacity limitation as a factor during cool temperature photosynthetic acclimation.