Polyamines induce rapid biosynthesis of nitric oxide (NO) in Arabidopsis thaliana seedlings.

In this study, we examined the regulation by putrescine, spermidine and spermine of nitric oxide (NO) biosynthesis in Arabidopsis thaliana seedlings. Using a fluorimetric method employing the cell-impermeable NO-binding dye diaminorhodamine-4M (DAR-4M), we observed that the polyamines (PAs) spermidine and spermine greatly increased NO release in the seedlings, whereas arginine and putrescine had little or no effect. Spermine, the most active PA, stimulated NO release with no apparent lag phase. The response was quenched by addition of 2-aminoethyl-2-thiopseudourea (AET), an inhibitor of the animal nitric oxide synthase (NOS) and plant NO biosynthesis, and by 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-1-oxy-3-oxide (PTIO), an NO scavenger. By fluorescence microscopy, using the cell-permeable NO-binding dye diaminorhodamine-4M acetoxymethyl ester (DAR-4M AM), we observed that PAs induced NO biosynthesis in specific tissues in Arabidopsis seedlings. Spermine and spermidine increased NO biosynthesis in the elongation zone of the Arabidopsis root tip and in primary leaves, especially in the veins and trichomes, while in cotyledons little or no effect of PAs beyond the endogenous levels of NO-induced fluorescence was observed. We conclude that PAs induce NO biosynthesis in plants.

During stationary phase, Beijerinckia derxii shows nitrogenase activity concomitant with the release and accumulation of nitrogenated substances.

Beijerinckia derxii, a free-living nitrogen-fixing bacterium, maintained an increasing nitrogenase specific activity during the stationary growth phase. To verify the destination of the nitrogen fixed during this phase, intra and extracellular nitrogenated contents were analyzed. Organic nitrogen and amino acids were detected in the supernatant of the cultures. An increase in intracellular content of both nitrogen and protein occurred. Cytoplasmic granules indicated the presence of arginine. The ability of a non-diazotrophic bacterium (E. coli) to use B. derxii proteins as a source of nitrogen was observed concomitantly with E. coli growth. There is a suggestion that B. derxii contributes to the environment by both releasing nitrogenated substances and accumulating substances capable of being consumed after its death.