Stomata modulate the exchange of water and CO2between plant and atmosphere. Although stomatal density is known to affect CO2diffusion into the leaf and thus photosynthetic rate, the effect of stomatal density and patterning on CO2assimilation is not fully understood. We used wild types Col-0 and C24 and stomatal mutants sdd1-1 and tmm1 of Arabidopsis thaliana, differing in stomatal density and pattern, to study the effects of these variations on both stomatal and mesophyll conductance and CO2assimilation rate. Anatomical parameters of stomata, leaf temperature and carbon isotope discrimination were also assessed. Our results indicate that increased stomatal density enhanced stomatal conductance in sdd1-1 plants, with no effect on photosynthesis, due to both unchanged photosynthetic capacity and decreased mesophyll conductance. Clustering (abnormal patterning formed by clusters of two or more stomata) and a highly unequal distribution of stomata between the adaxial and abaxial leaf sides in tmm1 mutants also had no effect on photosynthesis. Except at very high stomatal densities, stomatal conductance and water loss were proportional to stomatal density. Stomatal formation in clusters reduced stomatal dynamics and their operational range as well as the efficiency of CO2transport.

• MeSH
• Arabidopsis genetics   metabolism   MeSH
• Photosynthesis genetics   physiology   MeSH
• Plants, Genetically Modified genetics   metabolism   MeSH
• Carbon Isotopes metabolism   MeSH
• Carbon Dioxide metabolism   MeSH
• Arabidopsis Proteins genetics   metabolism   MeSH
• Plant Stomata genetics   metabolism   MeSH
• Publication type
• Journal Article MeSH

The initiation of stomata, microscopic valves in the epidermis of higher plants that control of gas exchange, requires a co-ordinated sequence of asymmetric and symmetric divisions, which is under tight environmental and developmental control. Arabidopsis leaves grown under elevated photosynthetic photon flux density have a higher density of stomata. STOMAGEN encodes an epidermal patterning factor produced in the mesophyll, and our observations indicated that elevated photosynthetic irradiation stimulates STOMAGEN expression. Our analysis of gain and loss of function of STOMAGEN further detailed its function as a positive regulator of stomatal formation on both sides of the leaf, not only in terms of stomatal density across the leaf surface but also in terms of their stomatal index. STOMAGEN function was rate limiting for the light response of the stomatal lineage in the adaxial epidermis. Mutants in pathways that regulate stomatal spacing in the epidermis and have elevated stomatal density, such as stomatal density and distribution (sdd1) and too many mouth alleles, displayed elevated STOMAGEN expression, suggesting that STOMAGEN is either under the direct control of these pathways or is indirectly affected by stomatal patterning, suggestive of a feedback mechanism. These observations support a model in which changes in levels of light irradiation are perceived in the mesophyll and control the production of stomata in the epidermis by mesophyll-produced STOMAGEN, and whereby, conversely, stomatal patterning, either directly or indirectly, influences STOMAGEN levels.

• MeSH
• Arabidopsis genetics   growth & development   metabolism   radiation effects   MeSH
• Photosynthesis MeSH
• Plant Leaves growth & development   metabolism   radiation effects   MeSH
• Arabidopsis Proteins genetics   metabolism   MeSH
• Plant Stomata genetics   growth & development   metabolism   radiation effects   MeSH
• Gene Expression Regulation, Plant radiation effects   MeSH
• Signal Transduction MeSH
• Light MeSH
• Gene Expression Regulation, Developmental radiation effects   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH