Effects of water stress and constitutive expression of a drought induced chitinase gene on water-use efficiency and carbon isotope composition of strawberry

Recombinant DNA technology and tracer technique are being widely used for different purposes. Plant genetic transformation is a common practice for increasing crop tolerance to biotic and abiotic stresses and stable isotopes is a good tool to track the effects of environmental stresses on crop productivity. In this research, the effect of water stress on plant carbon isotopic composition (δ13C) and water use efficiency (WUE), as indicators of physiological processes and environmental factors, were evaluated for transgenic strawberry (Fragaria x ananassa) plants continuously expressing a chitinase gene and non-transgenic plants. To implement water stress, strawberry plants were grown in pots and were assigned to three different soil water contents (SWC) of well-watered, moderately-watered and water-stressed. Treatments were implemented for two months, in a growth chamber. At the final stage of the experiment, leaves were randomly collected from each experimental unit. After oven-drying and powdering, subsamples of 4 to 5 mg of plant materials were combusted under vacuum, using Vycor tubes containing cupric oxide and silver wire. Combustion took place at 520 degrees C for 5 hrs to produce carbon dioxide. Carbon isotope composition (δ13C) was measured relative to Vienna Pee Dee Belmnite (VPDB). Both SWC and the expression of chitinase gene in transgenic strawberry plants significantly affected δ13C and WUE (p < 0.001). Highly significant (p < 0.01), but negative correlations were found between δ13C and plant dry matter components, such as lead dry matter (r = -0.92; p = 0.009) and total dry matter (r = -0.92; p = 0.008). High correlations were found between δ13C and water use per plant (r = -0.93; p = 0.006), and between δ13C and leaf area per plant (r = -0.93; p = 0.006)