The Growth Rate of Successive Leaves of Wheat Plants in Relation to Sugar and Protein Concentrations in the Extension Zone

Publisher Website
Google Scholar
Abstract
The growing part of a wheat leaf (the extension zone) is loocated at the leaf base and following from this it was proposed that the absolute leaf extension rate (Ler) can be partitioned into two components: the length of the extension zone (Lez) and the relative extension rate of that extension zone (Rez). Rez is an appropriate measure of the efficiency of leaf growth for comparing different leaves. This model of a wheat leaf was then used to investigate whether differences in growth rates between successive leaves on wheat plants were due to differences in hexose sugar or protein concentrations within the extension zone. Measurements were done in an irrigated field crop supplied with 0, 3, 10, or 30 kg N ha−1 per week. The mean values of Ler at 15 °C increased with leaf number and with nitrogen supply as did values for Lez. In contrast Rez at 15 °C declined from 0.9 d−1 for the first leaves to 0.3 d−1 for the flag leaf. Nitrogen supply had little effect on Rez. A separate measure of the efficiency of leaf growth, the responsiveness of Ler to temperature (measured as the slope of the temperature response curve), also decreased with leaf number by the same order as Rez and was similarly unaffected by nitrogen supply. The protein concentrations in the extension zones of the first leaves were around 40 mg g−1 fr. wt. and this declined to approximately 20 mg g−1 fr. wt for leaves emerging after tillers emerged and remained low thereafter. Protein concentrations were not correlated with the external supply of nitrogen. Hexose sugar concentrations followed a reverse pattern of increasing in the later order leaves and these also increased as nitrogen supply decreased. Both Rez and the responsiveness of Ler to temperature were positively correlated with the protein concentration, the relationship in each case being described by a rectangular hyperbola equation (P < 0.01), and negatively correlated with hexose concentrations. It was concluded that internal competition between growing points for reduced nitrogen caused the observed effects. However, differences in protein concentrations may not simply reflect differences in enzyme concentrations; rather these differences may indicate changes in some other character such as cell numbers.

This publication has 2 references indexed in Scilit: