Expression of Δ1-pyrroline-5-carboxylate dehydrogenase and proline/arginine homeostasis in Solanum tuberosum

Polyclonal antibodies raised in mouse against purified potato Δ1‐pyrroline‐5‐carboxylate dehydrogenase (P5C‐DH, EC 1.5.1.12), which catalyses the last step in the catabolism of both proline and arginine, were used to investigate the expression of this enzyme. Distribution of P5C‐DH in potato (Solanum tuberosum L. cv. Desiree) organs was studied at different stages during plant development. Variations in enzyme level were determined in axenically grown plantlets following the addition of exogenous proline, and in cell suspension cultures under hyperosmotic stress and after its relief. Free proline and arginine levels were also quantified, and compared to those of the enzyme. Results were consistent with a developmental, but not with an environmental, control of P5C‐DH expression. The possible involvement of specific isozymes in proline and arginine oxidation is discussed.