© 1991 Heron Publishing—Victoria, Canada
Control of growth of juvenile leaves of Eucalyptus globulus: effects of leaf age
J. C. Metcalfe (1), W. J. Davies (1, 2) and J. S. Pereira (3)
1. Institute of Environmental and Biological Sciences, University of Lancaster, Lancaster LA1 4YQ, United Kingdom / 2. Author to whom reprint requests should be addressed / 3. Department of Forestry, Instituto Superior de Agronomia, P-1399 Lisboa Codex, Portugal / Received July 7, 1990
Summary
Biophysical variables influencing the expansion of plant cells (yield threshold, cell wall extensibility and turgor) were
measured in individual Eucalyptus globulus leaves from the time of emergence until cessation of growth. Leaf water relations variables and growth rates were determined
as relative humidity was changed on an hourly basis. Yield threshold and cell wall extensibility were estimated from plots
of leaf growth rate versus turgor. Cell wall extensibility was also measured by the Instron technique, and yield threshold
was determined experimentally both by stress relaxation in a psychrometer chamber and by incubation in a range of polyethylene
glycol solutions.
Once emerging leaves reached approximately 5 cm2 in size, increases in leaf area were rapid throughout the expansive phase and varied little between light and dark periods.
Both leaf growth rate and turgor were sensitive to changes in humidity, and in the longer term, both yield threshold and cell
wall extensibility changed as the leaf aged. Rapidly expanding leaves had a very low yield threshold and
high cell wall extensibility, whereas mature leaves had low cell wall extensibility. Yield threshold increased with leaf age.
