title: The effect of gibberellic acid on the response of leaf extension to low temperature.
abstract: The effect of cooling on leaf extension rate (LER) and on relative elemental growth rate (REGR) was measured in both gibberellic acid (GA)-responsive dwarf barley and in the same barley variety treated with GA. Seedlings were maintained at 20 degrees C while their leaf extension zone (LEZ) temperature was reduced either in steps to -6 degrees C in short-term cooling experiments, or to 10 degrees C for 48 h in long-term cooling experiments. Short-term cooling resulted in a biphasic response in LER, with a clear inflection point identified. Below this point, the activation energy for leaf extension becomes higher. The short-term response of LER to cooling was altered by the application of GA, which resulted in a lower base temperature (Tb), inflection point temperature and activation energy for leaf extension. Both GA-treated and untreated seedlings were less sensitive to cooling maintained for a prolonged period, with LER making a partial recover over the initial 5 h. Although long-term cooling reduced maximum REGR, it resulted in a longer LEZ and an increase in the length of mature interstomatal cells in GA-treated and untreated seedlings. These changes in overall physiology appear to enhance the ability of the leaves to continue expansion at suboptimal temperatures. In both GA-treated and cold-acclimated tissue, the occurrence of a longer LEZ was associated with a lower temperature sensitivity in LER.
authors.affiliation: School of Biological Science, University of Wales Bangor, Bangor, Gwynedd, LL57 2UW UK.
authors.forename: A D
authors.initials: AD
authors.lastname: Farrell
authors.forename: H J
authors.initials: HJ
authors.lastname: Ougham
authors.forename: A D
authors.initials: AD
authors.lastname: Tomos
mesh_terms: D003080:Cold Temperature; D005875:Gibberellins / Q000494:pharmacology*; D001467:Hordeum / Q000187:drug effects*; D018515:Plant Leaves / Q000187:drug effects* / Q000254:growth & development; D013997:Time Factors
chemical_list: D005875:Gibberellins; C007842:gibberellic acid