Role of oxygen fixation in hydroxyproline biosynthesis by etiolated seedlings

Oxygen fixation into hydroxyproline in etiolated maize seedlings : verification by tandem mass spectrometry

Etiolated maize (Zea mays L.) seedlings were grown in the dark for 5 days in an atmosphere enriched with 10.0 atom% (18)O(2). Hydroxyproline was isolated from root and shoot tissues, purified, and methylated. It was not possible to determine (18)O incorporation into hydroxyproline by conventional mass spectrometry because the final product was not sufficiently pure. The final product was analyzed successfully by tandem mass spectrometry. The (18)O content of the hydroxyl oxygen atom was 10 +/- 0.7 atom%. This result demonstrates that the hydroxyl oxygen atom in hydroxyproline was derived exclusively from molecular oxygen.

Reversal of hydroxyproline-induced inhibition of elongation of Avena coleoptiles

Hydroxy-l-proline-induced inhibition of elongation of Avena coleoptile segments was measured in water and in indole-3-acetic acid. This inhibition was completely reversed by l-proline.Time-sequence experiments revealed that some time had to elapse, or some elongation had to occur, prior to the onset of hydroxyproline inhibition. The presence of sucrose supported the rate of auxin-induced elongation throughout a 24-hour period, and enhanced the effectiveness of hydroxyproline as an inhibitor of elongation.The application of adenosine triphosphate effectively counteracted the hydroxy-proline-induced inhibition of elongation; completely in water, and partially in indole-3-acetic acid. Optimal ATP concentrations were between 0.25 and 0.75 mm. Similarly, guanine-HCL, l-glutamic acid, and l-ornithine-HCL were capable of reversing the hydroxyproline inhibition. Other compounds that were tested but which proved to be less effective are tabulated.It is suggested that hydroxyproline may exert its inhibitory effect on the protein and/or RNA synthesis necessary for elongation of the oat coleoptile by interference with the metabolism of adenosine triphosphate or other high energy compounds.