Received April 27, 2006
Returned for revision May 9, 2006
Accepted May 31, 2006
Long-term submergence-induced elongation in Rumex palustris requires ABA-dependent biosynthesis of GA1
Joris J. Benschop , Jordi Bou , Anton J.M. Peeters , Niels Wagemaker , Kerstin Gühl , Dennis Ward , Peter Hedden , Thomas Moritz , and Laurentius A.C.J. Voesenek *
Plant Ecophysiology, Institute of Environmental Biology, Utrecht University, Sorbonnelaan 16, 3584 CA Utrecht, the Netherlands
* Corresponding author; email: l.a.c.j.voesenek{at}bio.uu.nl.
Rumex palustris (polygonceae) responds to complete submergence with enhanced elongation of its youngest petioles. This process requires the presence of gibberellin (GA) and is associated with an increase in the concentration of GA1 in elongating petioles. We have examined how GA biosynthesis was regulated in submerged plants. Therefore, cDNAs encoding GA-biosynthetic enzymes GA 20-oxidase (GA20ox) and GA 3-oxidase (GA3ox,) and the GA-deactivating enzyme GA 2-oxidase (GA2ox) were cloned from R. palustris and the kinetics of transcription of the corresponding genes was determined during a 24 h submergence period. The submergence-induced elongation response could be separated in several phases: (i) during the first phase of 4 h petiole elongation was insensitive to GA, (ii) from 4-6 h onwards growth was limited by GA and (iii) from 15 h onwards underwater elongation was dependent, but not limited by GA. Submergence induced an increase of GA1 concentration, as well as enhanced transcript levels of RpGA3ox1. Exogenous abscisic acid (ABA) repressed the transcript levels of RpGA20ox1 and RpGA3ox1 and thus inhibited the submergence-induced increase in GA1. ABA had no effect on the tissue responsiveness to GA.
