Phenotypic plasticity in response to drought stress: Comparisons of domesticated tomato and a wild relative

Phenotypic plasticity is the ability of an organism to undergo reversible behavioral, morphological or physiological changes in response to environmental conditions. Phenotypic plasticity enables plants to cope with uncertain environmental conditions, such as drought. A primary plastic trait is the rate of stomatal response to changes in ambient conditions, which determines the amount of water lost via transpiration, as well as levels of CO2 absorption, growth and productivity. Here, we examined the differences between domesticated and wild tomato species and their responses to drought stress. We found that the domesticated tomato had a higher transpiration rate and higher stomatal conductance (gs). The domesticated tomato also had greater biomass and greater leaf area under drought conditions, as compared to the wild tomato. Despite the domesticated tomatos higher transpiration rate and higher gs, there was no difference between the photosynthetic rates of the two lines. Moreover, the wild tomato had a higher maximum rate of rubisco activity, which might explain its greater molecular and whole canopy water-use efficiency. The domesticated tomatos higher transpiration rate and greater leaf area led to its earlier exposure to drought stress, as compared to the wild tomato, which maintained higher levels of soil water, enabling it to maintain steady rates of whole-canopy stomatal conductance (gsc) for extended periods. The wild tomato was also more sensitive to the soil water availability and lowered its maximum transpiration rate at a higher soil-water-content level. Our results suggest that the domestication process of tomatoes favored morphological/anatomical performance traits over physiological efficiency.