Proline (Pro) catabolism involves the consecutive activity of Pro dehydrogenase (ProDH) and P5C dehydrogenase (P5CDH), which generate D1-pyrroline 5 carboxilate (P5C) and glutamate, respectively. Both enzymes have mitochondrial localization. ProDH gene expression is induced by exogenous Pro as well as by the attack of avirulent pathogen. Some of these conditions also alter P5CDH gene expression. In addition, P5CDH transcript levels are regulated by SRO5-P5CDH natural siRNA, induced by oxidative stress and salinity. Uncoupled ProDH and P5CDH activities may generate accumulation of P5C, a proposed inducer of apoptosis in animals. P5C is a highly unstable metabolite which quantification in plant tissues has severe limitations. We evaluated if in tissues triggering cell death, ProDH, P5CDH, and SRO5 transcript levels are compatible with P5C accumulation.
