Mesophyll Cell Surface Area Research Articles

Effects of light and temperature on leaf anatomy and photosynthesis in Fragaria vesca.

Fragaria vesca, the woodland strawberry, was grown under a series of controlled environments including variations in light intensity, average temperatures, and temperature amplitude around a constant mean. Observations on CO2 exchange capacities, leaf anatomy, and cell ultrastructure were made for each treatment to determine relationships between these variables. With increasing light intensity, leaf thickness, leaf density, and mesophyll cell surface area and volume per leaf surface area increased. Net photosynthesis (NPS) per leaf weight decreased with increasing light pretreatment while NPS per area increased from low to medium intensity, then decreased at the highest intensity. Depression of photosynthesis at the highest light pretreatment may have been due to massive starch accumulation in the chloroplasts associated with the sodium vapor lamps used. Correlation of all anatomical variables was highly significant with dark respiration and NPS per dry weight but insignificant for NPS per leaf area. In the variable temperature treatments, photosynthetic acclimation occurred with a shift in optimum temperature for NPS in the direction of prevailing growth temperature. Absolute rates were highest at moderate pretreatment temperatures and were reduced by extreme growth temperatures. Thick leaves with low density mesophyll became thinner and more dense with increasing growth temperature corresponding to an increase in maximum net photosynthetic rates. Leaves became thicker and more dense at the highest temperatures, but with an increase in cell damage and indications of changes in metabolic pathways. Highest correlations for gas exchange rates were with specific leaf weight (weight per area). Correlation with other anatomical variables were scattered or insignificant. It was concluded that adaptation to a range of environmental conditions cannot be consistently attributed to changes in mesophyll cell volume or surface area.

Relation between Mesophyll Surface Area, Photosynthetic Rate, and Illumination Level during Development for Leaves of Plectranthus parviflorus Henckel

The influence of illumination level during leaf development on the mesophyll cell surface area per unit leaf area (A(mes)/A), CO(2) resistances, and the photosynthetic rate was determined for leaves of Plectranthus parviflorus Henckel. The relative importance of A(mes)/A versus CO(2) resistances in accounting for observed changes in photosynthesis was quantitatively evaluated using equations based on analogies to electrical circuits.When the illumination during development was raised from 900 to 42,000 lux, the leaves more than tripled in thickness as the mesophyll cells increased in size and frequency, which caused A(mes)/A to go from 11 to 50. The net rate of photosynthesis at light saturation concomitantly increased 4-fold, reflecting a corresponding decrease in the total resistance for CO(2) movement per unit leaf area. However, the CO(2) resistance per unit area of mesophyll cells remained about 580 seconds per centimeter for leaves grown under 900 to 42,000 lux. Thus, for P. parviflorus, the increased photosynthetic rate for leaves developing under higher illuminations resulted from a higher A(mes)/A, not from changes in the CO(2) resistances within individual mesophyll cells, expressed per unit area of cell surface. Results are discussed in terms of previously observed increases in thickness, internal leaf area, and photosynthetic rates for sun versus shade leaves on various plant species.