The Transient Inhibition of Phloem Translocation in Phaseolus vulgaris by Abrupt Temperature Drops, Vibration, and Electric Shock

Bean plants (Phaseolus vulgaris L. cv. Fardenlosa Shiny) approximately 3 weeks old were labelled with carbon-11 via their most basal compound leaves; and the transient inhibitions to stem translocation caused by (i) abrupt drops in temperature, (ii) vibration, or (iii) electric shock were studied. The duration of the inhibition caused by abrupt drops in temperature was found to decrease steadily with increasing temperature and to be absent above 40 °C, and the same was true of inhibitions caused by electric shock; however, translocation seemed relatively insensitive to temperatures as high as 55 °C. This inhibition, which could be observed in both intact stems and those with the epidermis removed, was abolished in the latter by presoaking in lanthanum-containing solutions although it was not sensibly affected by EGTA solutions or by calcium ionophores. Certain combinations of closely spaced stimuli (e.g. temperature-temperature or electroshock-vibration) caused the response to fatigue while others (e.g. electroshock-temperature) seemed not to. More detailed investigation of the electric shock inhibition showed (i) that it varied only slightly with electrode separation, (ii) that its duration was independent of shock polarity, but increased with shock duration to a plateau which was achieved at about 2 s, and (iii) that its duration increased steadily from a threshold at a shock intensity of about ½ V mm−1.