l-Alanine induces programmed cell death in V. labrusca cell suspension cultures

Plant cell suspension cultures are reliable year-round sources of enzymes involved in secondary metabolite biosynthesis. Numerous studies have used V. vinifera cell suspension cultures as an experimental system for studying these processes, while those from Concord grape (V. labrusca L.) have been poorly exploited. V. vinifera cell suspension cultures have been shown to grow well with casein hydrolysate (CH), which is a good source of reduced nitrogen in many tissue culture systems. The present report shows that V. labrusca cell suspension cultures, in contrast to those of V. vinifera, could only be established in the absence of CH as a source of reduced nitrogen. CH contains 20 amino acids, among which, the single amino acid l-alanine activates a programmed cell death response in V. labrusca cells, as determined by terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling (TUNEL) assay and propidium iodide nuclei staining. Programmed cell death was accompanied by the coordinated activation of phenylalanine ammonia lyase (PAL), cinnamic acid 4-hydroxylase (C4H), and stilbene synthase (STS) gene expression, as well as by the accumulation of stilbenes and other phenolic compounds.