Plant Physiology Preview
Published on February 2, 2007; 10.1104/pp.106.093559
OPEN ACCESS ARTICLE
Received November 22, 2006
Accepted January 24, 2007
Over-Production of Abscisic Acid in Solanum Lycopersicum L. Increases Transpiration Efficiency and Root Hydraulic Conductivity and Influences Leaf Expansion
Andrew J. Thompson *, John Andrews , Barry J. Mulholland , John M. T. McKee , Howard W. Hilton , Jon S. Horridge , Graham D. Farquhar , Rachel C. Smeeton , Ian R. A. Smillie , Colin R. Black , and Ian B. Taylor
Warwick HRI, Wellesbourne, University of Warwick, Warwickshire, CV35 9EF, UK; Environmental Biology Group, Research School of Biological Sciences, Australian National University, GPO Box 475, Canberra ACT 2601, Australia; Department of Plant Sciences, School of BioSciences, University of Nottingham, Sutton Bonington Campus, Loughborough, Leicestershire LE12 5RD, UK
* Corresponding author; email: a.j.thompson{at}warwick.ac.uk.
Over-expression 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 lines, sp12 and sp5, that over-express a gene encoding 9-cis-epoxycarotenoid dioxygenase, the enzyme that catalyzes a key rate-limiting step in abscisic acid (ABA) biosynthesis. Both lines contained more ABA than the wild-type (WT), with sp5 accumulating more than sp12. Both had higher transpiration efficiency because of their lower stomatal conductance, as demonstrated by increases in  13C and 18O, 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 WT 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 WT, but from a different basal level. Indeed, the main difference between the high ABA plants and WT 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.
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