To evaluate the involvement of G-proteins in the signal transduction during stimulatory action of neurotransmitters, adrenalin and noradrenalin, on root exudation and the ivolvement of G-proteins in water transport in the root and creation of the root pressure, we tested the effects of guanosinethiodiphosphate, an inhibitor of GTP-binding capacity of G-proteins, and guanosinethiotriphosphate, a stimulator of this capacity. Experiments were performed with detached roots of 5–7-day-old maize (Zea mays L.) seedlings and the mittens produced from them due to the removal of the vascular cylinder. The latter are a convenient model to study the nature of the root pressure due to its strongly limited possibility to function as an osmometer during the early step of exudation. In the “mittens,” adrenalin and noradrenalin enhanced exudation, increased its temperature coefficient (Q10), root pressure, and its metabolic component much stronger than in detached roots with the vascular cylinder retained (conventionally named as “intact” roots). In control treatment (with water), guanosinethiodiphosphate retarded exudation on the average by 30% in intact roots and by 50% in mittens, simultaneously reducing Q10 from 3.0 to 1.7 in intact roots and from 4.0 to 1.3 in mittens. Guanosinethiotriphosphate exerted an opposite action: it stimulated exudation on the average by 30% in intact roots and by 60% in mittens; the Q10 value increased from 3.0 to 3.6 in intact roots and from 4.0 to 5.8 in mittens. These data indicate that G-proteins are involved in the control of water transport and creation of the root pressure (without any other treatments). Guanosinethiodiphosphate neutralized completely adrenalin-and noradrenalin-induced stimulation of exudation, resulting in the level substantially below the control one, especially in mittens. Guanosinethiotriphosphate enhanced stimulatory effects of both neurotransmitters, mainly in mittens, whereas its effect on intact roots was relatively weak, especially in experiments with noradrenalin. It should be emphasized that the mittens responded to both neurotransmitters and the regulators of G-protein activity much stronger than intact roots. The data obtained argue for the G-protein involvement in (1) transduction of adrenalin and noradrenalin signals stimulating root water-pumping activity and (2) the control of water transport and creation of the root pressure under normal conditions. Experiments with mittens indicate that this G-protein involvement could by mainly related to the functioning of the root cortex parenchymal cells and the formation of the metabolic component of the root pressure.
Russian Journal of Plant Physiology – Springer Journals
Published: Nov 7, 2007
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