The Dual Effect Of No In Stomatal Movement And Its Biological Significance

The studies have established that NO function as signaling molecules mediates reponses to abiotic and biotic stress,which regulated many process of development,physiology and metabolism in plant. Unique morphology character and physiology action of guard cell make it unique signal transduction tool that provide an elegant system to dissect an intricate network of signaling pathways,so there are increasingly concerns about NO is involved in signaling transduction of stomatal movement.A large number of evidences have showed that NO donors can induce the clousure of stoma of Arabidopsis thaliana, Commelina communis,Vicia faba.L and wheat,and NO is also involved in the the signal transduction of JA, ABA,SA,ethylene,dark-ness, UV-B and CO₂ induced stomatal closure as a signaling molecule.However,studies have also shown that NO can induce stomatal opening. In addition, the relationship concerning NO and reactive oxygen species, some studies show that the NO-induced stomatal closure is regulated to the inducing of the generation of reactive oxygen species H₂O₂ in stomatal movement;Researches in plant senescence shows that NO can be direct or indirect play a role of removalling of reactive oxygen species by working with them.Second,previous studies also showed that,the same environmental factors,such as osmotic stress and UV radiation, have different effects on stomatal movement in the same plants or different plants under different physiological conditions. However, for a long time for the results of the study led to the causes of inconsistency are still not clear.The present experiments,using epidermal strip bioassay of vicia faba L.,laser-scanning confocal microscopy, we mainly investigate NO donors of different concentrations and different types have impact on stomatal movement under different physiological conditions and the relationship of NO and H₂O₂ in the guard cells,revealing the relationship between the dual effect of NO on stomatal movement and exogenous NO concentration,and the effects on intracellular levels of NO and H₂O₂ by the treatments of different concentrations of exogenous NO;Second,this article has studied the different effects on stomatal movement of guard cells by different intensity of UV-B radiation,and the relationship with endogenous NO and H₂O₂ concentration, to show that the reason of different effects of the same environmental factors on stomatal movement. The main results were followed:1. Both SNP and GSNO at low and high concentration ranges could not only induce the closure of opened-stomata under light, but also reduce the aperture of closed-stomata under darkness, H₂O₂ or ABA; Both SNP and GSNO at middle range of concentrations had no obvious effect on the aperture of opened-stomata under light, but induce the opening of closed-stomata under darkness, H₂O₂ or ABA. The recovery experiment further showed that widespread, non-specific damage to guard cells was caused by the high range of NO donors, but not by low and middle ranges of NO donors, because the high range-closed stomata was not reopened under a subsequent light recovery, but the low and middle range-closed or opened stomata could be reopened or reclosed by a subsequent light or dark recovery respectively. These results indicated that NO can induce not only stomatal closure, but also stomatal opening, which depend on the endogenous NO concentration.2. The results of measuring the level of NO and H₂O₂, using laser scanning confocal microscopy show that,SNP and GSNO at low and high concentration ranges could induce the fluorescence intensity of gurad cells under light,and had a certain degree of promotion on the fluorescence intensity of gurad cells under darkness, H₂O₂ or ABA.SNP and GSNO at middle range of concentrationshad no obvious effect on the fluorescence intensity of gurad cells under light,but it could decrease the fluorescence intensity of gurad cells under darkness, H₂O₂ or ABA. The results show that the different effects of stomatal movement treated by different concentrations of exogenous NO is related to the different NO and H₂O₂ levels in guard cells. At the same time,the results also suggest that low concentrations of NO can induce reactive oxygen species,and higher concentrations of NO may be directly related to the reactive oxygen species play a role in removal of reactive oxygen species.3.0.8 W/m² UV-B radiation could induce the closure of opened-stomata under light, 0.2 W/m² of UV-B radiation could induce the opening of closed-stomata under darkness. The result shows that the UV-B radiation has dual effect on the movement of stoma.4.0.8 W/m² UV-B radiation can induce the increase of NO and H₂O₂ level in isolated epidermal strips, 0.2 W/m² UV-B radiation can induce the decrease of NO and H₂O₂ level in isolated epidermal strips. The result shows that dual effect of the UV-B radiation is related to the endogenous NO and H₂O₂ in guard cells.