ESTIMATION OF THE ANATOMICAL, STOMATAL, AND BIOCHEMICAL COMPONENTS OF DIFFERENCES IN PHOTOSYNTHESIS AND TRANSPIRATION OF WILD AND TRANSGENIC TOBACCO LEAVES

Authors: PACHEPSKY, LUDMILA - DUKE UNIVERSITY, NC; Acock, Basil; FISAHN, JOACHIM - MAX PLANK INS., GERMANY

Submitted to: Annals of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/21/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Through genetic engineering, it is now possible to take genes from one species and have them operate in another species. This has great potential for developing new crop plants with desirable characteristics. However, the results of introducing new genes are straightforward in relatively few cases. Usually we do not know how the genes produce the observed effects. This paper describes the use of a mathematical model of a leaf to understand changes caused by introducing genes into a tobacco plant. The genes were taken from yeast and they reduced leaf photosynthesis and transpiration rates by 50% and 70%, respectively. The two-dimensional model 2DLEAF was used to quantitatively separate the anatomical, stomatal, and biochemical components of these differences. The sizes and distributions of cells in the original and altered leaves were measured on leaf cross-sections and entered into the model. From measured rates of photosynthesis and transpiration, the model was used to estimate first the size of the small pores (stomatal aperture) in each leaf, then the biochemical activity of the photosynthetic cells. 24% of the difference in transpiration between the leaves was caused by the greater cell area surface in the original leaf, and 66% was caused by the smaller stomatal aperture in the altered leaf. 10% of the difference in photosynthesis rate between the leaves was caused by the greater cell area surface in the original leaf, and the remaining 90% was caused by altered biochemical activity. This demonstrates that models can help us understand gene action, so that we can take full advantage of genetic engineering to develop new crops for feeding the increasing world population.

Technical Abstract: Photosynthesis and transpiration rates of transgenic (yeast derived acid invertase overexpressed in vacuole) tobacco (Nicotiana tabacum L.) leaves were, respectively, 50 and 70% of those of a wild type at 20 degrees C, 350 ppm CO2 concentration, 45 mol (photons) m-2 s-1 of light intensity, and 70% relative air humidity. These differences could be attributed (a) to changes in leaf anatomy and, consequently, to changes in gases diffusion between the cells' surfaces and the atmosphere, (b) to different stomatal apertures, and, for the photosynthesis rate, (c) to the altered biochemical activity of photosynthetic cells. Our objective was to estimate the relative contributions of these three sources of differences. Measurements on the wild type and the transgenic leaf cross-sections showed that the cell area indices (CAI, cell area surface per unit of leaf area surface) had values equal to 15.91 and 13.97, respectively. The two-dimensional model 2DLEAF for leaf gas exchange was used to quantitatively estimate anatomical, stomatal, and biochemical components of these differences. Transpiration rate was equal to 0.9 for the wild 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 cell area surface in the wild-type leaf, and 66.0% was caused by a smaller stomatal aperture in the transgenic leaf. Photosynthesis rate was 3.10 and 1.55 mmol m-2 s-1 for the wild-type and transgenic leaves, respectively. 10.3% of this difference (0.16 mmol m-2 s-1) was caused by the difference in CAI, and the remaining 89.7% was caused by altered biochemical activity.