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Abstract
Metabolic responses to auxin. VII. Effects on glycolysis. — The detection of changes the of level of respiratory substrates could provide an indication on the site of action of auxin. The effects of indoleacetic acid on the contents in several glycolysis intermediates in isolated segments from the growing part of the third internode of etiolated pea seadlings were thus investigated.
Hexose phosphates, triose phosphates, phospho-enol-pyruvate, pyruvate and ethanol were determined enzymatically in the neutralized perchloric extracts from groups of segments incubated for 3 hours in the presence or in the absence of 5 × 10 −5 M indoleacetic acid. No significant difference appeared between the results on the perchloric extracts and those obtained after fractionation with barium and alcohol, according to Umbreit et al.
Acetaldehyde was measured as by Klotz. Pyruvate was determined also as a phenyl-hydrazone, according to Cavallini and Frontali; the same method was used for the determination of α-ketoglutarare and of an unknown compound, showing a chromatographic behavior similar to that of an uronic acid.
Auxin induced a modest but significant increase of hexose-6-phosphates (16%) and of fructose di-phosphate (38%). For glucose-1-phosphate and triose phosphates — present at very low concentration — no significant changes could be detected, α-ketoglutarate level appeared unchanged. The compound behaving as an uronic acid increased, in the auxin treated segments, by more than 100%.
A very definite response to auxin appeared at the level of pyruvate. acetaldehyde and alcohol. Pyruvate quite reproducibly increased by 60%, and acetaldehyde production was more than doubled. In contrast, alcohol decreased by about 40%.
These results are discussed in relation to the previous data on the effects of auxin on the oxidative metabolism, and, particularly, to the findings of an increased rate of CO-sensitive respiration and of the rise of the ATP, TPNH and red. glutathione levels in the auxin treated pea internode segments.