Water stress induced alterations in ornithine aminotransferase of ragi (Eleusine coracana): protection by proline against heat inactivation and denaturation by urea and guanidinium chloride

Water stress resulted in a specific response leading to a large and significant increase (80-fold) in free proline content of ragi (Eleusine coracana) leaves and seedlings. L-Proline protected ornithine aminotransferase, an enzyme in the pathway for proline biosynthesis, isolated from normal and stressed ragi leaves against heat inactivation and denaturation by urea and guanidinium chloride. The protection of the stressed enzyme by L-proline was much more complete than that of the enzyme isolated from normal leaves. While L-ornithine, one of the substrates, protected the stressed enzyme against inactivation, it enhanced the rate of inactivation of the normal enzyme. α-Ketoglutarate protected both the normal and stressed enzyme against inactivation and denaturation. These results support the suggestion that ornithine aminotransferase has undergone a structural alteration during water stress. In view of the causal relationship between elevated temperature and water stress of plants under natural conditions, the protection afforded by proline against inactivation and denaturation of the enzyme from stressed leaves assumes significance. These results provide an explanation for a possible functional importance of proline accumulation during water stress

Alterations in the biosynthesis of proteins and nucleic acids in finger millet (Eleucine coracana) seedlings during water stress and the effect of proline on protein biosynthesis

The biosynthesis of DNA appeared to be unaffected in the water-stressed seedlings of finger millet (Eleucine coracana), but an increase in the synthesis de novo of RNA and proteins was observed during mild water stress. The polyribosome content was also increased in stressed finger millet seedlings. Proline, a solute which accumulates during water stress, enhanced the incorporation of radioactive precursors into proteins; caused an increase in translatability of finger millet messengers in vitro; and stabilized the polyribosomes isolated from normal seedlings. The results emphasize the role of proline in the adaptation of finger millet to the intermittent drought it experiences during cultivation

Alterations in the Biosynthesis of Proteins and Nucleic Acids in Finger Millet (Eleucine Coracana) Seedlings during Water Stress and the Effect of Proline on Protein Biosynthesis

The biosynthesis of DNA appeared to be unaffected in the water-stressed seedlings of finger millet (Eleucine coracana), but an increase in the synthesis de novo of RNA and proteins was observed during mild water stress. The polyribosome content was also increased in stressed finger millet seedlings. Proline, a solute which accumulates during water stress, enhanced the incorporation of radioactive precursors into proteins; caused an increase in translatability of finger millet messengers in vitro; and stabilized the polyribosomes isolated from normal seedlings. The results emphasize the role of proline in the adaptation of finger millet to the intermittent drought it experiences during cultivation

Water stress induced alterations in ornithine aminotransferase of ragi (Eleusine coracana): Protection by proline against heat inactivation and denaturation by urea and guanidinium chloride

Water stress resulted in a specific response leading to a large and significant increase (80-fold) in free proline content of ragi (Eleusine coracana) leaves and seedlings. L-Proline protected ornithine aminotransferase, an enzyme in the pathway for proline biosynthesis, isolated from normal and stressed ragi leaves against heat inactivation and denaturation by urea and guanidinium chloride. The protection of the stressed enzyme by L-proline was much more complete than that of the enzyme isolated from normal leaves. While L-ornithine, one of the substrates, protected the stressed enzyme against inactivation, it enhanced the rate of inactivation of the normal enzyme. α-Ketoglutarate protected both the normal and stressed enzyme against inactivation and denaturation. These results support the suggestion that ornithine aminotransferase has undergone a structural alteration during water stress. In view of the causal relationship between elevated temperature and water stress of plants under natural conditions, the protection afforded by proline against inactivation and denaturation of the enzyme from stressed leaves assumes significance. These results provide an explanation for a possible functional importance of proline accumulation during water stress

Alterations in the activities of the enzymes of proline metabolism in Ragi (Eleusine coracana) leaves during water stress

Free proline content in Ragi (Eleusine coracana) leaves increased markedly (6 to 85 fold) as the degree of water stress, created by polyethylene gylcol treatment, was prolonged There was also a marginal increase in soluble proteins in the stressed leaves as compared to that in the controls. Water stress stimulated the activities of ornithine aminotransferase and pyrroline-5-carboxylate reductase, the enzymes of proline biosynthesis and markedly inhibited the enzymes involved in proline degradation viz., proline oxidase and pyrroline-5-carboxylate dehydrogenase. These results suggest that increase in free proline content of Ragi leaves could be due to enhanced activities of the enzymes synthesizing proline but more importantly due to severe inhibition of the enzymes degrading proline. These observations establish for the first time, the pathway of proline metabolism in plants by way of detection of the activities of all the enzymes involved and also highlight the role of these enzymes in proline accumulation during water stress