ESTIMATION OF THE ANATOMICAL, STOMATAL AND BIOCHEMICAL-COMPONENTS OF DIFFERENCES IN PHOTOSYNTHESIS AND TRANSPIRATION OF WILD-TYPE AND TRANSGENIC (EXPRESSING YEAST-DERIVED INVERTASE TARGETED TO THE VACUOLE) TOBACCO-LEAVES

Photosynthesis and transpiration rates of transgenic (expressing yeast -derived invertase targeted to the vacuole) tobacco (Nicotiana tabacum L.) leaves were, respectively, 50 and 70% of those of a wild type at 20 degrees C, 350 cm(3) m(-3) CO2 concentration, 450 mu mol (photons) m(-2) s(-1) of light intensity, and 70% relative air humidity, These d ifferences could be attributed: (a) to changes in leaf anatomy and, co nsequently, to changes in gases diffusion between tile cells' surfaces and the atmosphere; (b) to different stomatal apertures, and, for the photosynthesis rate, (c) to the altered CO2 assimilation rate, Our ob jective was to estimate the relative contributions of these three sour ces of difference, Measurements on the wild-type and the transgenic le af cross-sections gave values for the cell area index (CAI, cell area surface per unit of leaf area surface) of 15.91 and 13.97, respectivel y. The two-dimensional model 2DLEAF for leaf gas exchange was used to estimate quantitatively anatomical, stomatal and biochemical component s of these differences, Transpiration rate was equal to 0.9 for the wi ld-type and to 0.63 mmol m(-2) s(-1) for the transgenic leaf: 24.0% of the difference (0.066 mmol m(-2) s(-1)) was caused by the greater cel l area surface in the wild-type leaf, and 66.0% was caused by a smalle r stomatal aperture in the transgenic leaf, Photosynthetic rate was 3. 10 and 1.55 mu mol m(-2) s(-1) for the wild-type and transgenic leaves , respectively. Only 10.3% of this difference (0.16 mu mol m(-2) s(-1) ) was caused by the difference in CAI, and the remaining 89.7% was cau sed by altered CO2 assimilation rate.