Involvement of Singlet Oxygen in 5-Aminolevulinic Acid-Induced Photodynamic Damage of Cucumber (Cucumis sativus L.) Chloroplasts

Abstract

Cucumber (Cucumis sativus L., cv Poinsette) plants were sprayed with 20 millimolar 5-aminolevulinic acid and then incubated in the dark for 14 hours. The intact chloroplasts were isolated from the above plants in the dark and were exposed to weak light (250 micromoles per square meter per second). Within 30 minutes, photosystem 11 activity was reduced by 50%. The singlet oxygen (102) scavengers, histidine and sodium azide (NaN3) significantly protected against the damage caused to photosystem II. The hydroxyl radical scavenger formate failed to protect the thylakoid membranes. The production of 102 monitored as N,N-dimethyl p-nitrosoaniline bleaching increased as a function of light exposure time of treated chloroplasts and was abolished by the 102 quencher, NaN3. Membrane lipid peroxidation monitored as malondialdehyde production was also significantly reduced when chloroplasts were illuminated in the presence of NaN3 and histidine. Protochlorophyllide was the most abundant pigment accumulated in intact chloroplasts isolated from 5-aminolevulinic acid-treated plants and was probably acting as type 11 photosensitizer.

The Regulation of Enzymes Involved in Chlorophyll Biosynthesis

“…Presumably by binding to pPORA, Pchlide triggers the actual translocation step (Reinbothe et al, 1995a and unpublished results). This could reduce the risk of free excited pigment molecules interacting with molecular oxygen during illumination to form oxygen radicals and singlet oxygen which could cause damage of the plastid compartment (Tripathy and Chakraborty, 1991 ;Chakraborty and Tripathy, 1992). The fact that the mature PORA enzyme remains stable in the light after its in vitro import into etioplasts and etiochloroplasts isolated from 30-min-illuminated barley seedlings (Reinbothe et al, 1995e) seems to be consistent with such an idea.…”

Comparative Proteomics Analysis of Differentially Expressed Proteins in Chickpea Extracellular Matrix during Dehydration Stress

“…The supernatant was taken for determination of photosynthetic pigments: chlorophyll a (mg/g) ϭ ((12.7 ϫ A 663 Ϫ 2.69 ϫ A 645 ) v/w), chlorophyll b (mg/g) ϭ ((22.9 ϫ A 645 Ϫ 4.68 ϫ A 663 ) v/w), and carotenoid (mg/g) ϭ (((1000 ϫ A 470 ) Ϫ (3.27 ϫ chlorophyll a ϩ 1.04 ϫ chlorophyll b))/227 v/w). The experiments were done in triplicates using corrected tissue weights calculated for actual moisture content of the tissue at the respective time points (22).…”

“…Oxidized MDA was calculated according to the following formula: MDA (g/mg) ϭ ((A 532 Ϫ A 600 ) ϫ volume ϫ 100)/(155 ϫ total protein (mg)). The experiments were carried out in triplicates using corrected weights calculated for actual moisture content of the seedlings at each time point (22).…”

Antioxidant and free radical scavenging activity of Pithecellobium dulce (Roxb.) Benth wood bark and leaves

“…[23,24] Singlet oxygen was generated by a reaction between NaOCl and H 2 O 2 , and the bleaching of RNO was monitored at 440 nm. The reaction mixture contained 45 mM phosphate buffer (pH 7.1), 50 mM NaOCl, 50 mM H 2 O 2 , 50 mM histidine, 10 μM RNO and various concentrations (0.0-200.0 μg/ml) of sample in a final volume of 2 ml.…”