Contribution of ornithine aminotransferase to proline accumulation in NaCl‐treated radish cotyledons

Abstract

Light‐grown cotyledons of radish (Raphanus sativus L. cv National) subjected to increasing NaCI concentrations displayed a dose‐dependent accumulation of proline at the beginning of their differentiation. Neither erythromycin nor DCMU significantly affected the salt‐induced proline accumulation, which suggests that plastids may not be involved in proline synthesis. Gabaculine has been shown previously to be a powerful and irreversible inhibitor of ornithine aminotransferase [Hervieu et al. (1993) Phyto‐chemistry 34, 231–234]. This inhibitor applied in vivo at a very low concentration (1 mmol m−3) reduced considerably the salt‐induced proline accumulation of radish cotyledons. These results indicate that the ornithine pathway contributes, via an increase of ornithine aminotransferase activity, to proline synthesis, as well as the glutamate pathway, in salt‐treated cotyledons. The use of transcription and translation inhibitors revealed that the salt‐induced increase in ornithine aminotransferase activity may proceed via an activation of the translation of preformed mRNAs. The pre‐existing ornithine aminotransferase mRNAs in radish seeds may be an important adaptation to NaCI, leading to proline accumulation at the beginning of seedling growth.

Proline Metabolism and Its Implications for Plant-Environment Interaction

“…Studies showing decreased proline accumulation in the presence of the OAT inhibitor gabaculine (Hervieu et al, 1995;Yang and Kao, 1999) seemed to support the idea of OAT having a significant role in proline synthesis, although it is still clearly secondary to proline synthesis from glutamate by P5CS1. In addition, overexpression of OAT resulted in enhanced proline accumulation (Roosens et al, 2002;Wu et al, 2003).…”

Differential responses of the enzymes involved in proline biosynthesis and degradation in drought tolerant and sensitive cotton genotypes during drought stress and recovery

“…Plants also synthesize proline from ornithine by ornithine amino transferase (OAT, Delauney and Verma 1993). Although some studies showed increased OAT activity under salt or drought stress conditions (Hervieu et al 1995;Roosens et al 2002); most studies indicated that under these conditions the free proline increase appears to be mainly due to the activity of the enzymes of the glutamate pathway (Roosens et al 1999). Our results agree with these later conclusions, given that in our experiment the OAT activity did not vary in its activity during entire period of stress and recovery (Fig.…”

Biochemical characterization, homology modeling and docking studies of ornithine δ-aminotransferase—an important enzyme in proline biosynthesis of plants

“…Over-expression of an Arabidopsis d-OAT gene in rice conferred both salt and drought stress tolerance [34]. The contribution of d-OAT to proline biosynthesis during salt stress and following its withdrawal is not clear and its role is actively debated [10]. Though the relative contributions of glutamate and ornithine pathways for the production of proline (by estimating the transcript levels of P5CS and OAT) under salt stress were reported earlier [7,12], the activities of the respective enzymes were not reported under identical conditions.…”