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 Pisum sativum (argentum mutant) epidermal leaf strips and also upon intact pea foliage. NO-related trials included a novel technique enabling chlorophyll fluorescence determination at subcellular sites, biophysical 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 the 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 statistically significant increase. This effect was accompanied by a marked increase of MGDG-monolayer surface tension and also by a SNAP concentration-dependent decrease of LOX activity. A further observation was that the superoxide free radical, like the NO free radical, also induced similar microviscosity changes of the MGDG chloroplast membrane galactolipid However, the combination of the two radicals, to purportedly form the peroxynitrite (HOONO) adduct, was not additive. Results are discussed in light of a combined biophysical and biochemical effect on the pi component of the C=C double bonds in chloroplast membrane galactolipids. Such bonding inter alin may lower efficiency of photosynthetic electron transport and so doing may be a contributing factor to the multifaceted endogenous stress or exogenous pollution syndrome.