CHARACTERISTICS OF RESPIRATORY METABOLISM IN PEA LEAVES DURING HYPOBARIC HYPOXIA

We investigated reactions of respiratory metabolism in green leaves of pea (Pisum sativum L.) under light in the presence of increasing hypo baric hypoxia. The nature of responses is shown to depend in significa nt measure on the time of influence. Six-hour 20-fold rarefaction of a tmospheric air leading to reduction of gas partial pressure (to 1.148 kPa for O2 and to 0.0016 kPa for CO2) switched glycolysis over to ferm entation, did not inhibit the Krebs cycle, and stimulated photosynthet ic activity. Under conditions of 12-h exposure, functional activity of chloroplasts was suppressed and significant reorganization of respira tory metabolism occurred. The rate of noncyclic photophosphorylation w as sharply lowered, activity of glyceraldehyde phosphate dehydrogenase decreased, and content of sugars and amino acids declined. On the oth er hand, increases occurred in the activities of glucose-6-phosphate d ehydrogenase, pyruvate kinase, malic enzyme, isocitrate dehydrogenase, and alcohol dehydrogenase. Eighteen-hour hypoxia led to increase of t he respiratory rate, a burst of photosynthetic activity attaining the control level being observed here. A tendency towards fading of metabo lic processes was detected after 24 h of influence. Compensatory respo nses based on the interrelationship of photosynthesis and respiration are actuated under conditions of total hypobaric anoxia, where the who le plant is enclosed in the pressure chamber.