Leaf Extension inZea mays

Abstract

Leaf extension rates of young maize plants were measured in the field. Large diurnal fluctua tions of air temperature from about 5-35 °C caused extension rates to vary from 0-4 mm h_1 3-6 mm Ir1. When the temperature of the shoot apical meristem was kept at 30-34 °C, extension rates remained constant, despite diurnal fluctuations of air temperature. Leaf water potentials ( 35 °C, whereas minimum night tem peratures were sometimes less than 5 °C. Since optimum air temperature for the growth of the variety of maize used in these experiments has been shown to be about 31 °C (Blacklow, 1972), it was important to determine rates of leaf extension in response to diurnal fluctuations of temperature. Also, as one of the wider aims of the research programme was to provide input to a model to predict the growth of maize, it was necessary to determine which organs were most sensitive to temperature, particularly in the early vegetative stage. 1 Present address: Department of Botany, University of Aberdeen, St. Machar Drive, Aberdeen AB9 2UD. This content downloaded from 207.46.13.184 on Fri, 29 Jul 2016 05:46:57 UTC All use subject to http://about.jstor.org/terms 1086 Watts—Leaf Extension in Zea mays Studies in controlled environments have indicated that leaf extension in maize stops at relatively high values of i/> (Boyer, 1970; Acevedo, Hsiao, and Henderson, 1971). In contrast, field studies have shown that leaf extension of maize may continue at much lower values of f (Cary and Wright, 1971). In order to investigate these apparent differences in response, measurements of if were made in both the field and in controlled-environment cabinets, and related to leaf extension. MATERIALS AND METHODS Field measurements Maize seeds (United 108) were sown sequentially throughout the growing season so that plants at the 4th to 7th leaf stage (i.e. with their shoot apical meristems just above the soil surface), were available for measurements over the period June to August. On selected days, leaf extension was measured continuously with an auxanometer as described by Kleinendorst and Brouwer (1970). As the leaf elongated the output was recorded on a Hewlett Packard chart recorder and hourly rates of leaf elongation were calculated. Temperature measurements were made with copper-constantan thermocouples connected to a Leeds and Northrup 12-point Speedomax recorder. Air temperature was measured by a shielded thermocouple at 30 cm height. For some measurements of leaf extension the tempera ture of the shoot apical meristem was controlled by clamping a split copper block around the base of the plant when the meristem was just above the soil surface (Pig. 1). A thermoelectric module (Cambion Model 3952-01), operating on the Peltier principle, was attached to the side of the copper block and the whole unit was enclosed in a block of expanded polystyrene for Supporting rod S N. pu]]ey fixed to shaft i 7 lof potentiometer Tripod 50 g weight Q Fine wire / -Tip of youngest emerged leaf To temperature-control unit