Dr. sc. Dietmar Funck

Dept. of Plant Physiology and Biochemistry, Konstanz

University, Konstanz, Germany

Proline in plants – protection or toxicity

In plants, biosynthesis and degradation of proline are

strictly compartmented to the cytosol and the

mitochondria, respectively. Biosynthesis is upregulated

by water deficiency, but feedback inhibition by proline

occurs at the transcriptional and posttranslational level.

Degradation is induced by proline, but inhibited by

water stress. Proline was classified as a compatible

solute that increases the osmolarity, stabilises

biological macromolecules, scavenges reactive oxygen

species (ROS) and might serve as a C and N storage

rapidly available after release from stress. However,

external proline application induced HR-like symptoms

including ROS formation and cell death. Most likely

accumulation of P5C/GSA, the degradation

intermediate, is inducing cellular damage or programmed

cell death after external proline application. This

hypothesis was further substantiated by the analysis of

mutant Arabidopsis lines that are unable to degrade

P5C/GSA. Accumulation of proline during pathogen

defence and specific upregulation of proline metabolic

enzymes at infection sites suggest a participation of

proline derived signals in HR-based resistance.