PLANT PHYSIOLOGY , Vol 113, Issue 4 1395-1404, Copyright © 1997 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
The Determination of Relative Elemental Growth Rate Profiles from Segmental Growth Rates (A Methodological Evaluation)
W. S. Peters and N. Bernstein
Institute of Soils and Water, The Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel
Relative elemental growth rate (REGR) profiles describe spatial patterns of
growth intensity; they are indispensable for causal growth analyses.
Published methods of REGR profile determination from marking experiments
fall in two classes: the profile is either described by a series of
segmental growth rates, or calculated as the slope of a function describing
the displacement velocities of points along the organ. The latter technique
is usually considered superior for theoretical reasons, but to our
knowledge, no comparative methodological study of the two approaches is
currently available. We formulated a model REGR profile that resembles
those reported from primary roots. We established the displacement velocity
profile and derived growth trajectories, which enabled us to perform
hypothetical marking experiments on the model with varying spacing of marks
and durations of measurement. REGR profiles were determined from these data
by alternative methods, and results were compared to the original profile.
We find that with our model plotting of segmental relative growth rates
versus segment position provides exact REGR profile estimations, if the
initial segment length is less than 10% of the length of the whole growing
zone, and if less than 20% of the growing zone is displaced past its
boundary during the measurement. Based on our analysis, we discuss
systematic errors that occur in marking experiments.
