ANOXIA TOLERANCE IN TOBACCO ROOTS - EFFECT OF OVEREXPRESSION OF PYRUVATE DECARBOXYLASE

Plant survival during flooding relies on ethanolic fermentation for en ergy production. The available literature indicates that the first enz yme of the ethanolic fermentation pathway, pyruvate decarboxylase (PDC ), is expressed at very low levels and is likely to be rate-limiting d uring oxygen deprivation. The authors expressed high levels of bacteri al PDC in tobacco to study the modulation of PDC activity in vivo, and assess its impact on the physiology of ethanolic fermentation and sur vival under oxygen stress. In contrast to leaves, wild-type normoxic r oots contained considerable PDC activity, and overexpression of the ba cterial PDC caused only a moderate increase in acetaldehyde and ethano l production under anoxia compared to wild type roots. No significant lactate production could be measured at any time, making it unlikely t hat lactate-induced acidification (LDH/PDC pH-stat) triggers the onset of ethanol synthesis. Instead, the authors favour a model in which th e flux through the pathway is regulated by substrate availability The increased ethanolic flux in the transgenics compared to the wild-type did not enhance anoxia tolerance. On the contrary, rapid utilisation o f carbohydrate reserves enhanced premature cell death in the transgeni cs while replenishment of carbohydrates improved survival under anoxia .