Alcoholic fermentation and malate metabolism in rice germinating at low oxygen concentrations
Avadhani, PN and Greenway, H and Lefroy, R and Prior, LD, Alcoholic fermentation and malate metabolism in rice germinating at low oxygen concentrations, Australian Journal of Plant Physiology, 5, (1) pp. 15-25. ISSN 0310-7841 (1978) [Refereed Article]
Germinating rice was exposed, in the dark, to low or zero O2 concentrations for 4-5 days by:
(1) submergence under 4-5 cm of stagnant solution (3 ppm 02); (2) exposure to a N2 atmosphere;.
or (3) submergence under solutions flushed with N2.
These treatments completely inhibited root growth. Elongation of coleoptiles was stimulated
in the stagnant solutions, but not in the N2 treatments.
In most experiments, low O2 concentrations resulted in twofold to eightfold increases of malate
concentrations in the shoots. Absence of 0, during exposure to Hi4C03-, for 30-60 min, inhibited
C02 dark fixation. This inhibition was considerably smaller when seedlings had been raised in N2
rather than in air. Under aerobic conditions during fixation, excised shoots from seedlings raised
in N2 fixed more C02 than shoots from seedlings raised in air.
Malate always contained 70% or more of the total fixed 14C, irrespective of the 0, regime during
germination and during I4CO2 fixation.
Ethanol in stagnant solutions was shown to be formed by the rice seedlings, rather than by
bacteria. Ethanol formation during one single day was 20-30-fold greater than the highest recorded
amounts of malate in the seedlings. Alcoholic fermentation also responded quickly to changes in
aeration regimes, indicating it was an important adaptive factor.
Another likely adaptive feature was the high K+ concentration in shoots, even of seedlings
grown in the complete absence of 0,. It is suggested that these high K+ concentrations have a
function in maintaining turgor required for the rapid extension growth of the coleoptiles under
low 0, concentrations.