Short‐term responses of phloem transport to mechanical perturbation

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Abstract
Jaeger, C. H., Goeschl, J. D., Magnuson, C. E., Fares, Y. and Strain, B. R. 1988. Short‐term responses of phloem transport to mechanical perturbation. ‐ Physiol. Plant. 72: 588–594.Phloem transport was monitored using a continuous stream of11CO2‐labelled air administered to one leaf while gamma detectors measured11C activity at intervals along the stem. The effect of gentle, non‐injurious mechanical perturbation on phloem transport was tested in cotton (Gossypium hirsutumL. cv. Stoneville 213). Mechanical stimuli such as shaking, localized vibration and gentle massage were applied while the plants were at isotope equilibrium. Localized phloem blockages were observed within 1–2 min of the stimuli. The blockages lasted from 6–55 min and full recovery of transport required 20–175 min. The effect of preconditioning to mechanical perturbation on phloem transport was tested in bush beans (Phaseolus vulgarisL. cv. Cherokee Bush). Preconditioning of a bean seedling to gentle stem massage resulted in a shorter blockage response and quicker transport recovery period when the seedling was massaged during a11C tracer experiment compared to a control seedling. These results indicate that measurements of phloem transport on recently disturbed plants will probably show depressed phloem transport velocities. Measurements should be made after at least a 24‐h disturbance‐free recovery period.