Journal Article

Overproduction of Abscisic Acid in Tomato Increases Transpiration Efficiency and Root Hydraulic Conductivity and Influences Leaf Expansion

Thompson, Andrew J., Andrews, John, Mulholland, Barry J., Horridge, Jon S., Smillie, Ian R. A., Hilton, Howard W., McKee, John M. T., Farquhar, Graham D., Taylor, Ian B., Black, Colin R., Smeeton, Rachel C.

2007

Overview

Overexpression of genes that respond to drought stress is a seemingly attractive approach for improving drought resistance in crops. However, the consequences for both water-use efficiency and productivity must be considered if agronomic utility is sought. Here, we characterize two tomato (Solarium lycopersicum) lines (sp12 and sp5) that overexpress a gene encoding 9-cisepoxycarotenoid dioxygenase, the enzyme that catalyzes a key rate-limiting step in abscisic acid (ABA) biosynthesis. Both lines contained more ABA than the wild type, with sp5 accumulating more than sp12. Both had higher transpiration efficiency because of their lower stomatal conductance, as demonstrated by increases in δ¹³C and δ¹ɸO, and also by gravimetric and gas-exchange methods. They also had greater root hydraulic conductivity. Under well-watered glasshouse conditions, mature sp5 plants were found to have a shoot biomass equal to the wild type despite their lower assimilation rate per unit leaf area. These plants also had longer petioles, larger leaf area, increased specific leaf area, and reduced leaf epinasty. When exposed to root-zone water deficits, line sp12 showed an increase in xylem ABA concentration and a reduction in stomatal conductance to the same final levels as the wild type, but from a different basal level. Indeed, the main difference between the high ABA plants and the wild type was their performance under well- watered conditions: the former conserved soil water by limiting maximum stomatal conductance per unit leaf area, but also, at least in the case of sp5, developed a canopy more suited to light interception, maximizing assimilation per plant, possibly due to improved turgor or suppression of epinasty.

• Publisher: American Society of Plant Biologists,American Society of Plant Physiologists
• Subject: abscisic acid / Abscisic Acid - metabolism / Agronomy. Soil science and plant productions / Biological and medical sciences / Biomass / Biomass production / biosynthesis / canopy / crops / Disasters / Drought / drought tolerance / Economic plant physiology / Environmental Stress and Adaptation to Stress / enzymes / epinasty / Fundamental and applied biological sciences. Psychology / gas exchange / gene overexpression / genes / Genotypes / greenhouses / growth & development / Leaf area / Leaves / Lycopersicon esculentum / mature plants / metabolism / petioles / physiology / Plant growth / Plant Leaves / Plant Leaves - growth & development / Plant Leaves - physiology / Plant Roots / Plant Roots - physiology / Plants / root hydraulic conductivity / shoots / soil water / Solanum / Solanum lycopersicum / Solanum lycopersicum - metabolism / Solanum lycopersicum - physiology / stomatal conductance / tomatoes / Transpiration / turgor / Water / Water relations, transpiration, stomata / water stress / water use efficiency / Xylem