PHOTOSYNTHETIC DIFFERENCES AMONG LYCOPERSICON SPECIES AND TRITICUM-AESTIVUM CULTIVARS

Leaf photosynthesis rate (A) and water use efficiency expressed as A/g(s) (g(s), stomatal conductance) are controlled by stomatal properties and leaf internal anatomical and biochemical/physiological characteristics. Two germplasm entries were selected from each of the genera Triticum and Lycopersicon with contrasting drought resistance. Both drought resistant entries (L. pennellii and T. aestivum cv. TAM W-101) had the greater A/g(s) within each pair. Of the two entries with high A/g(s) L. pennellii had lower A and TAM-101 had higher A than the respective counterpart with low A/g(s) (L. esculentum and T. aestivum cv. Sturdy, respectively). Comparison of photosynthetic stomatal supply capacities and mesophyll biochemical demand capacities suggested that differences in mean A and A/g(s) in contrasting tomato species were dependent on the lower mean g(s) of L. pennellii than L. esculentum, because in leaves with equal g(s) the balance between stomatal supply and mesophyll demand was identical. In wheat leaves operating at identical g(s), however, TAM W-101 had greater mesophyll capacity than Sturdy. Lower A and A/g(s) of Sturdy than TAM W-101 was correlated with lower carboxylation efficiency and lower light and CO2 saturated A, factors associated with the photosynthetic biochemistry of mesophyll tissue. At identical g(s), the balance between mesophyll and stomatal capacities and limitations of TAM W-101 was the same as for the two tomato species. This suggested that for these three entries (L. esculentum, L. pennellii, and TAM W-101), the differences in A and A/g(s) resulted from differences in the mean and range of g(s). Sturdy was unique by having low A and low A/g(s), a result of poor mesophyll capacity compared to the other entries.