Stomatal aperture can compensate altered stomatal density in Arabidopsis thaliana at growth light conditions

Abstract

Stomatal density of transgenic Arabidopsis thaliana plants over-expressing the SDD1 (stomatal density and distribution) gene was reduced to 40% and in the sdd1-1 mutant increased to 300% of the wild type. CO2 assimilation rate and stomatal conductance of over-expressers and the sdd1-1 mutant were unchanged compared with wild types when measured under the light conditions the plants were exposed to during growth. Lower stomatal density was compensated for by increased stomatal aperture and conversely, increased stomatal density was compensated for by reduced stomatal aperture. At high light intensities the assimilation rates and stomatal conductance of SDD1 over-expressers were reduced to 80% of those in wild type plants. Areas beneath stomata and patches lacking stomata were analysed separately. In areas without stomata, maximum fluorescence yield (Fv / Fm) and quantum yield of photosystem II (Φ PSII) were significantly lower than in areas beneath stomata. In areas beneath stomata, Fv / Fm and Φ PSII were identical to levels measured in wild type leaves. At high light intensities over-expressers showed decreased photochemical quenching (qP) compared with wild types. However, the decrease of qP was significantly stronger in areas without stomata than in mesophyll areas beneath stomata. At high CO2 partial pressures and high light intensities CO2 assimilation rates of SDD1 over-expressers did not reach wild type levels. These results indicate that photosynthesis in SDD1 over-expressers was reduced because of limiting CO2 in areas furthest from stomata at high light.

Stomatal Size, Speed, and Responsiveness Impact on Photosynthesis and Water Use Efficiency

“…These findings indicated that increased stomatal aperture compensated for the lower stomatal density in the SDD1 plants while reduced aperture in the sdd1-1 plants offset the greater number of stomata. However, at high light intensities, low g s in the SDD1 overexpressors and restricted CO 2 diffusion limited A to 80% of the wild type (Büssis et al, 2006). These findings exemplify the role of both the physical and functional stomatal features in determining g s and that manipulation of physical attributes may be counterbalanced by modifications in function.…”

“…Transgenic plants overexpressing SDD1 have a 40% reduction in stomatal densities compared with the wild type (Von Groll et al, 2002). In a comparative study, Büssis et al (2006) showed no difference in g s or assimilation rate when measured under growth photosynthetically active photon flux density (PPFD) conditions (180 mmol m 22 s 21 ) between the overexpressing SDD1 plants, the sdd1-1 mutants, and wild-type controls. These findings indicated that increased stomatal aperture compensated for the lower stomatal density in the SDD1 plants while reduced aperture in the sdd1-1 plants offset the greater number of stomata.…”

“…An interesting observation in the Büssis et al (2006) study was the high-resolution chlorophyll fluorescence imaging that revealed two distinct areas of mesophyll in the SDD1 plants: one where mesophyll lay above stomata and the other where stomata were absent. Measurements of maximum and actual photosynthetic efficiency were identical to the wild type in areas with stomata; however, leaf areas without stomata showed lower maximum and actual photosynthetic efficiency, illustrating that stomatal patterning determined CO 2 concentration and photosynthesis across the leaf lamina and that lateral fluxes of gas could not compensate for reduced vertical diffusion as a result of reduced stomatal numbers (Büssis et al, 2006). This work agrees with reports that suggest that lateral fluxes can limit photosynthesis (Morison et al, 2005) but depend on species and leaf anatomy (Lawson and Morison, 2006).…”

“…It is possible to increase or decrease the gaseous conductance of the ensemble of stomata per unit of leaf area (g s ) through the manipulation of stomatal densities (Büssis et al, 2006). In addition, there is potential to alter the stomatal response or sensitivity to environmental signals through the manipulation of guard cell characteristics that affect stomatal mechanics (e.g.…”

SHORTROOT-Mediated Increase in Stomatal Density Has No Impact on Photosynthetic Efficiency

“…7). Studies with stomatal density and distribution (sdd1-1) mutants in Arabidopsis also showed that stomatal density cannot be correlated directly with g s , because increased numbers can be compensated for by decreased functional stomatal aperture (Büssis et al, 2006;Lawson and Blatt, 2014). This compensation mechanism appears to be environmentally dependent, in that no difference in g s or assimilation rates were detected when the wild type, sdd-1 mutants with increased stomatal density, and SDD1 overexpression lines with a 40% reduction in stomatal number were compared under light conditions of 180 mmol m 22 s 21 PPFD (Berger and Altmann, 2000;Von Groll et al, 2002).…”