Grass leaf elongation rate as a function of developmental stage and temperature: Morphological analysis and modelling

Elongation of successive leaves was measured following defoliation of tall fescue plants in controlled environments. Measurements were made under cons tant temperatures of 24 degrees C and 14 degrees C, and after temperature c hanges from 24 to 14 degrees C and vice versa. A morphological analysis of the growing leaf was made from the time it was 1 mm long until it was fully elongated. The time elapsed from initiation until the leaf was 1 mm long w as estimated. Young leaves less than 1.5 mm long elongated slowly at a cons tant leaf elongation rate (LER). By extrapolating this LER back to leaf ini tiation from the apex it was calculated that elongation lasted 42.5 d at 24 degrees C and 51 d at 14 degrees C. Lengths of the division zone (DZ) and the extension-only zone (E-OZ) increased to a maximum and then decreased du ring leaf development. Temperature change had an immediate effect on LER bu t the response varied depending on the direction of the temperature change. To describe these different features, an empirical model of DZ and E-OZ wa s designed. Its five parameters were optimized at constant temperature. The model was then used to simulate the LER of plants subjected to temperature changes. Instant and lasting effects of the initial temperature on mean LE R in plants transferred from 14 to 24 degrees C and vice versa were well si mulated. It was concluded that the major reason for differences was due to the growth stage (DZ and E-OZ lengths) at which the changes occurred at bot h temperatures. (C) 1999 Annals of Botany Company.