The Geoelectric Effect in Plant Shoots: II. SENSITIVITY OF CONCENTRATION CHAIN ELECTRODES TO REORIENTATION

A concentration chain, static-drop electrode system has beenused by several investigators to measure the geoelectric effectin plant shoots. This paper describes investigations of theinherent sensitivity of this electrode system to reorientationwith respect to gravity. When the gelatine plug of the electrodeis made up with distilled water, and the contact solution is0.1 mM KCl, a potential difference develops immediately afterelectrodes in direct contact are rotated through 90° intothe vertical plane. A similar response is found when the contactsolution is 5 mM CaCl₂. Increasing the concentration of thecontact solution, or incorporating KCl, K₂SO₄, or ZnSO₄ intothe gelatine plug, drastically reduces the potential differencedeveloped after reorientation. The potential difference acrosselectrodes in direct contact decreases as the electrodes age.The potential difference measured with these electrodes acrossa decapitated, horizontally placed, hypocotyl of Helianthusarmuus also decreases as the electrodes age. The polarity ofthe charge is reversed as compared with that found when theelectrodes are in direct contact. The kinetic characteristicsof the geoelectric potential difference developed across a non-decapitated,horizontal coleoptile of Zea mays change as the electrodes age.With fresh electrodes the potential develops immediately afterreorientation and continues to increase with time. With 4-day-oldelectrodes, however, no potential difference develops until9 min after the moment of reorientation, but then it increaseswith time. The characteristics of the geoelectric potentialdifference developed with the aged concentration-chain, static-dropelectrodes are similar to those found with several other typesof electrodes which do not themselves have an inherent sensitivityto reorientation with respect to gravity. The results supportour earlier suggestion that the potential difference which apparentlydevelops with the static-drop electrode system, immediatelyafter a shoot is turned through 90° in reality developsin the electrode system itself and not in the plant tissue.The geoelectric effect which arises in the living plant shootbegins to develop approximately 10 min after reorientation.