Growth kinetics of Marquis wheat. V. Morphogenic dependence

Abstract

The rate coefficients of the exponential period of growth of the vegetative organs of Marquis wheat were changed and made biphasic by the morphogenesis of the stem apex from the vegetative to the flowering state. The rate coefficient of stem elongation was lower in the initial or vegetative phase than later, and it was initially insensitive to temperature up to 20 °C but temperature sensitive in the final or flowering phase from 10 °C to 30 °C. In contrast the growth coefficients of plant, shoots, and roots computed from measurements of dry weight were higher in the first phase than in the second phase and increased with temperature to a maximum at 20 °C in both phases. The differences were attributed to the less autotrophic nature and initially more limited growth of the stem. The raised stem-growth coefficient in the flowering phase was compensated by slowed growth of its shoot. Tillers grew most rapidly, successive tillers more so, and accounted for the previously observed dominant growth of "stems" as stems plus leaf sheaths. The change of slope within the exponential plots was not noticed in previous work at 25 °C and it portends higher maximal coefficients for vegetative (initial phase) plant growth than those previously estimated from the entire exponential period. However, under optimal conditions the growth coefficient of the whole plant seems to be internally limited to about half that of one or another organ.