Light-influenced extracellular accumulation of b (pathogenesis-related) proteins in Nicotiana green tissue induced by various chemicals or prolonged floating on water

Abstract

The extracellular accumulation of b (pathogenesis-related) proteins in Nicotiana tabacum cv. Xanthi-nc and cv. Samsun and in Nicotiana sylvestris was studied by floating leaf disks on solutions (50 μM – 5 mM) of putative inducers at pH 4 to 8 for 72 h. Intercellular fluid b proteins were detected only in green tissue, and optimal conditions required specific light regimes. Amino acids, organic acids, sugars, nucleotides, amines, vitamins, hormones, metals, and several other chemicals were compared with acetylsalicylate at 0.3 mM for the presence of b proteins in intercellular fluid extracts analyzed by native polyacrylamide gel electrophoresis. Several protein and non-protein amino acids and some of their derivatives were inducers in addition to thiamine, thiamine derivatives, and a few other chemicals at concentrations ranging from 200 μM to 5 mM. Various ways of introducing inducers into tissue (floating, injection, infiltration, root uptake) allowed b protein accumulation. Stimulation of b protein accumulation was observed when osmotica (sucrose at 200 mM) were added to inducers. Chelating agents, spermidine, lysine, and hydroquinone could inhibit b protein accumulation induced by L-serine, thiamine, L-α-aminoisobutyrate, and silver nitrate. Results with inducing chemicals and with prolonged floating of tissue on water, which was also conducive to b protein accumulation, support the hypothesis that b protein accumulation is a green tissue generalized response to various forms of prolonged stress.