Role of Changes in Cell Size in the Evolution of Wheat

Abstract

The objective of the present work was to examine to what extent increase in cell size has contributed to the parallel increases in leaf and grain size in the course of evolution in wheat. Eighteen lines were chosen to represent wild and cultivated wheats at the diploid and tetraploid levels, cultivated hexaploid wheats, and the two Aegilops species likely to have contributed the B and D genomes. All plants were grown at 21/16°C under natural light. The penultimate leaves and the basal grains from central spikelets were selected for comparison.

The projected area of separated mesophyll cells from leaves was 1.5–2 times larger in the cultivated tetraploid and hexaploid wheats than in the diploids, and correlated positively but weakly with leaf blade area (r = 0.50), and negatively with photosynthetic rate in Triticum species (r = -0.66).

Cell size in the endosperm bore no relation to cell size in the aleurone layer or mesophyll, or to grain volume. Aleurone cell size, however, correlated positively with both grain volume (r = 0.82) and mesophyll cell size (r = 0.79).

Increase in grain weight during evolution has not involved increase in either specific gravity of the mature grain or endosperm cell size. Presumably increase in endosperm cell number has been the major factor.

With increase in grain size during evolution there has been a fall in percentage nitrogen in the grain.