Relations between specific leaf surface and gas exchanges in Triticum genotypes.

Specific surface (surface area per gram of material), photosynthetic rate and water vapor conductance of the flag leaf of four Triticum aestivum, one Triticum spelta and one Triticum dicoccum cultivars, grown in a greenhouse, were studied in order to establish the correlation among them in normal watered condition and under drought stress. The specific surface values obtained in our experiments by physical adsorption of nitrogen (temperature 77.3 K), ranged from 2.9 to 6.0 m2 g-1 and were higher than values obtained by conventional geometric methods based on optical microscopy. Differences were attributed to the ability of the technique to measure the roughness of the cellular wall of the mesophyll cells through which gas exchange take place. The measure of photosynthetic rate ranged from 5.0 to 29.3 µmol CO2 m-2 s-1, and the water vapor conductance ranged between 74.3 and 457.3 mmol H2O m-2 s-1. Significative statistical differences were found among cultivars in specific surface, photosynthetic rate and water vapor conductance, for both treatments. Although, a positive correlation was found among photosynthetic rate and water vapor conductance, no correlation was found between specific surface and photosynthetic rate or water vapor conductance.

Key words: Triticum, specific surface of leaves, photosynthetic rate, leaf conductance. Lycopersicon spp.