HortScience 33:471 (1998)
Tomatoes remember being brushed
Thomas Björkman and Lauren C. Garner
Department of Horticultural Sciences, New York State Agricultural Experiment
Station, Cornell University, Geneva, NY 14456-0462
ABSTRACT Tomato seedlings grown in close proximity elongate rapidly
in a shade-avoidance response. A daily touch stimulus can eliminate the
extra growth associated with shade avoidance. Experiments to determine
how the touch stimulus is integrated were performed on tomato seedlings
grown in plug trays 22 mm apart, starting when 2 fully expanded leaves
overlapped between plants to induce the shade-avoidance response. The standard
touch stimulus was applied by brushing the surface of the canopy 10 times
each morning with a piece of Styrofoam sheet. This treatment reduced the
daily growth rate from 7.7 to 5.8 mm/day, but quadrupling the dose further
reduced growth only slightly (J. Amer. Soc. Hortic. Sci. 121:894). The
ability of the plants to sum individual stimuli was tested by varying the
interval between the individual strokes. Intervals of 0.01, 0.1, 1 and
10 min all produced the same growth response. Thus the individual strokes
were perceived as a single stimulus. Had they been perceived as separate
stimuli, long intervals would have increased the response. There was no
refractory period of insensitivity following the stimulus; that would have
reduced the response at longer intervals. The height reduction was directly
proportional to the number of days that the treatment was applied, indicating
that each day of treatment reduced the growth rate for only one day (from
5.9 mm/day to 2.7 mm/day). Thus brief stimuli are integrated during the
day and expressed as a reduction of growth the next diurnal cycle..
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