EFFECT OF STRESS NITRIC-OXIDE (NO) - INTERACTION BETWEEN CHLOROPHYLL FLUORESCENCE, GALACTOLIPID FLUIDITY AND LIPOXYGENASE ACTIVITY

In an endeavor to ascertain the effect of nitric oxide (NO) applied at ambient concentrations, which as formerly found are stress-inducing, experiments were carried out on stomatal guard cell chloroplasts of Pi sum sativum (argentum mutant) epidermal leaf strips and also upon inta ct pea foliage. NO-related trials included a novel technique enabling chlorophyll fluorescence determination at subcellular sites, biophysic al monitoring of surface tension of simulated chloroplast galactolipid monolayers - monogalactosyldiacylglycerol (MGDG), and comparison with palmitoyllinoleylphosphatidylcholine (PLPC), as well as lipoxygenase (LOX; EC 1.13.11.12) assay of foliage of intact plants treated with th e NO-generating agent - S-nitroso-N acetylpenicillamine (SNAP). It was found that at a very early stage, red chlorophyll fluorescence in the 690 nm region of guard cell chloroplasts manifested a highly statisti cally significant increase. This effect was accompanied by a marked in crease of MGDG-monolayer surface tension and also by a SNAP concentrat ion-dependent decrease of LOX activity. A further observation was that the superoxide free radical, like the NO free radical, also induced s imilar microviscosity changes of the MGDG chloroplast membrane galacto lipid However, the combination of the two radicals, to purportedly for m the peroxynitrite (HOONO) adduct, was not additive. Results are disc ussed in light of a combined biophysical and biochemical effect on the pi component of the C=C double bonds in chloroplast membrane galactol ipids. Such bonding inter alin may lower efficiency of photosynthetic electron transport and so doing may be a contributing factor to the mu ltifaceted endogenous stress or exogenous pollution syndrome.