The Role of Sugars, Hexokinase, and Sucrose Synthase in the Determination of Hypoxically Induced Tolerance to Anoxia in Tomato Roots

Abstract

Hypoxic pretreatment of tomato (Lycopersiron esculentum M.)roots induced an acclimation to anoxia. Survival in the absence of oxygen was improved from 10 h to more than 36 h if externa1 sucrose was present. The energy charge value of anoxic tissues increased during the course of hypoxic acclimation, indicating an improvement of energy metabolism. In acclimated roots ethanol was produced immediately after transfer to anoxia and little lactic acid accumulated in the tissues. In nonacclimated roots significant ethanol synthesis occurred after a 1-h lag period, during which time large amounts of lactic acid accumulated in the tissues. Severa1 enzyme activities, including that of alcohol dehydrogenase, lactate dehydrogenase, pyruvate decarboxylase, and sucrose synthase, increased during the hypoxic pretreatment. In contrast to maize, hexokinase activities did not increase and phosphorylation of hexoses was strongly inhibited during anoxia in both kinds of tomato roots. Sucrose, but not glucose or fructose, was able to sustain glycolytic flux via the sucrose synthase pathway and allowed anoxic tolerance of acclimated roots. These results are discussed in relation to cytosolic acidosis and the ability of tomato roots to survive anoxia.

Hypoxic Induction of Anoxia Tolerance in Rice Coleoptiles

“…These results are also consistent with the results found in roots of several plants Qohnson et al, 1989;Waters et al, 1991;Andrews et al, 1994;Germain et al, 1997;Kato-Noguchi, 2000a) , suggesting that the mechanism in hypoxic acclimation to anoxia implicated in their roots may act in rice coleoptiles.…”

“…Thus, the H-PT coleoptiles of the rice seedlings maintained greater level of ATP than the N-PT coleoptiles under anoxic stress. A greater level of A TP was found to be a significant contributory factor to the plant survival under the stress conditions (Raymond et al, 1985;Menegus et al, 1991;Germain et al, 1997).…”

“…The tolerance improved by H-PT was associated with greater concentration of A TP and with sustained levels of glycolysis and ethanolic fermentation (Drew, 1997). The increase in the tolerance was paralleled by an increase in alcohol dehydrogenase (ADH) and pyruvate decarboxylase (PDC) activities (Andrews et al, 1994;Germain et al, 1997;. Furthermore, the importance of ethanolic fermentation in the anaerobic responses has been demonstrated by the studies on the ADH null mutants, which show reduced anoxia tolerance in several plant species Qohnson et al, 1994;Matsumura et al, 1995;.…”

“…Hypoxic pretreatment (H-PT) greatly improved the viability of several plant species during a subsequent period of severe hypoxia or anoxia Qohnson et al, 1989;Waters et al, 1991;Andrews et al, 1994;Germain et al, 1997;Kato-Noguchi 2000a). The tolerance improved by H-PT was associated with greater concentration of A TP and with sustained levels of glycolysis and ethanolic fermentation (Drew, 1997).…”

Reactive Oxygen Species-Driven Transcription in Arabidopsis under Oxygen Deprivation

“…Suc feeding enhances transcription of HSPs (Loreti et al, 2005) that, acting as chaperones, may prevent aggregation, denaturation, misfolding, and degradation of proteins important for plant survival. Indeed, exogenous sugar strongly enhances low-O 2 tolerance in a variety of plant species (Vartapetian and Andreeva, 1986;Perata et al, 1992;Germain et al, 1997;Loreti et al, 2005).…”