Hydroxyl free radical production by the reaction of N-methyl-N'-nitro-N-nitrosoguanidine with hydrogen peroxide without exposure to light.

We examined hydroxyl free radical (.OH) production in the mixture of H2O2 and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) without exposure to light using the electron spin resonance spin-trapping technique. When the mixtures were protected from exposure to light, .OH was formed at pH 6.5 and above; it was not formed at pH 5.0 and below, consistent with our previous report. The amount of .OH trapped depended on the concentrations of MNNG and H2O2 and the pH. Nitrite ion was also detected colorimetrically at pH 6.5 and above, but not detected at pH 5.0 and below in the mixtures without exposure to light. Moreover, its production depended on the concentrations of MNNG and H2O2 and the pH. The formation of N-methyl-N'-nitroguanidine in the mixture at pH 7.8 was confirmed by thin-layer chromatography and melting point. These results suggest that nucleophilic attack by H2O2 on the nitroso nitrogen of MNNG results in the formation of N-methyl-N'-nitroguanidine and peroxynitrous acid, which degrades homolytically to yield .OH and nitrogen dioxide, resulting in the production of nitrite ion, at pH 6.5 and above without exposure to light.     

Plasma membrane-anchored chloroplasts are necessary for the gravisensing system of Ceratopteris richardii prothalli

Journal of Plant Research - The prothalli of the fern Ceratopteris richardii exhibit negative gravitropism when grown in darkness. However, no sedimentable organelles or substances have been...     

A hypergravity environment increases chloroplast size,photosynthesis, and plant growth in the moss Physcomitrella patens

The physiological and anatomical responses of bryophytes to altered gravity conditions will provide crucial information for estimating how plant physiological traits have evolved to adapt to significant increases in the effects of gravity in land plant history. We quantified changes in plant growth and photosynthesis in the model plant of mosses, Physcomitrella patens, grown under a hypergravity environment for 25 days or 8 weeks using a custom-built centrifuge equipped with a lighting system. This is the first study to examine the response of bryophytes to hypergravity conditions. Canopy-based plant growth was significantly increased at 10×g, and was strongly affected by increases in plant numbers. Rhizoid lengths for individual gametophores were significantly increased at 10×g. Chloroplast diameters (major axis) and thicknesses (minor axis) in the leaves of P. patens were also increased at 10×g. The area-based photosynthesis rate of P. patens was also enhanced at 10×g. Increases in shoot numbers and chloroplast sizes may elevate the area-based photosynthesis rate under hypergravity conditions. We observed a decrease in leaf cell wall thickness under hypergravity conditions, which is in contrast to previous findings obtained using angiosperms. Since mosses including P. patens live in dense populations, an increase in canopy-based plant numbers may be effective to enhance the toughness of the population, and, thus, represents an effective adaptation strategy to a hypergravity environment for P. patens.

     

Involvement of Carboxyl Groups of the PSII Reaction Center Proteins in Photoactivation of the Apo-Water-Oxidizing Complex

Involvement of residues of acidic amino acids in photo-ligationof manganese into the apo-water-oxidizing complex was investigatedby use of l-ethyl-3-[3-(dimethylami-no)propyl]carbodiimide (EDC),a water-soluble carboxyl modifier. Treatment of Mn-depletedPSII membranes by EDC in the presence of nucleophiles induceda loss of photoactivation capability in the Mn complex and partialloss of capability of photooxidation of Mn²⁺, but little decreasein the DCIP photoreduction supported by diphen-ylcarbazide.The inhibition of diphenylcarbazide-photo-oxidation by submicromolarMn²⁺, indicative of the intactness of high-affinity Mn-bindingsites, was apparently abolished by EDC treatment. From aminoacid quantitation analysis of Dl and D2 proteins and CP47 ofthe chemically-modified membranes, approximately three carboxylgroups of the D1 protein were found to be chemically-modifiedwith EDC after removal of the functional Mn. These results suggestthat acidic amino acids on the D1 protein are involved in photoactivationof the apo-water-oxidizing complex and probably in ligationof Mn to the water-oxidizing complex. (Received October 21, 1996; Accepted March 3, 1997)