PLANT PHYSIOLOGY , Vol 101, Issue 2 553-560, Copyright © 1993 by American Society of Plant Biologists
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ENVIRONMENTAL AND STRESS PHYSIOLOGY |
Evidence for a Large and Sustained Glycolytic Flux to Lactate in Anoxic Roots of Some Members of the Halophytic Genus Limonium
J. Rivoal and A. D. Hanson
Institut de Recherche en Biologie Vegetale de I'Universite de Montreal, 4101 est rue Sherbrooke, Montreal, Quebec H1X 2B2, Canada
Soil salinity and anaerobiosis often occur together. This led us to
investigate the fermentative metabolism in roots of species from the
halophytic genus Limonium (Plumbaginaceae). Root segments from hypoxically
induced plants were incubated for 8 h under strict anoxia in the presence
of [U-14C]glucose. In three species (Limonium latifolium, L. nashii, and L.
humile), the pattern of 14C-labeled end products was typical of higher
plants, with a 14C flux to ethanol higher than that to lactate. However, in
four species (L. ramosissimum, L. gougetianum, L perezii, and L. sinuatum),
the rate of lactate fermentation was exceptionally high, and in the latter
two species the 14C flux to lactate exceeded that to ethanol. These two
species secreted most of the lactate produced into the medium. Calculations
indicated that the cytoplasm would have been lethally acidified had this
secretion not occurred. The effects of factors that might control lactate
fermentation or secretion (O2 partial pressure, pH, salt concentration)
were studied in two contrasting species: L. sinuatum and L. latifolium. In
both species, the lactate:ethanol ratio was higher under hypoxia (0.1-3 kPa
O2 partial pressure) than under strict anoxia. In L. sinuatum, this ratio
was slightly increased by increasing the pH of the medium from 5.5 to 7.5,
but salinity treatment had no effect. The potential contribution of lactate
fermentation to the overall carbon and energy metabolism of halophytes is
discussed.
