Antioxidant enzymes regulate reactive oxygen species during pod elongation in Pisum sativum and Brassica chinensis.

Previous research has focused on the involvement of reactive oxygen species (ROS) in cell wall loosening and cell extension in plant vegetative growth, but few studies have investigated ROS functions specifically in plant reproductive organs. In this study, ROS levels and antioxidant enzyme activities were assessed in Pisum sativum and Brassica chinensis pods at five developmental stages. In juvenile pods, the high levels of O2.- and .OH indicates that they had functions in cell wall loosening and cell elongation. In later developmental stages, high levels of .OH were also related to increases in cell wall thickness in lignified tissues. Throughout pod development, most of the O2.- was detected on plasma membranes of parenchyma cells and outer epidermis cells of the mesocarp, while most of the H2O2 was detected on plasma membranes of most cells throughout the mesocarp. This suggests that these sites are presumably the locations of ROS generation. The antioxidant enzymes superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) apparently contributed to ROS accumulation in pod wall tissues. Furthermore, specifically SOD and POD were found to be associated with pod growth through the regulation of ROS generation and transformation. Throughout pod development, O2.- decreases were associated with increased SOD activity, while changes in H2O2 accumulation were associated with changes in CAT and POD activities. Additionally, high POD activity may contribute to the generation of(.)OH in the early development of pods. It is concluded that the ROS are produced in different sites of plasma membranes with the regulation of antioxidant enzymes, and that substantial ROS generation and accumulation are evident in cell elongation and cell wall loosening in pod wall cells.

Lead and cadmium induced alterations of cellular functions in leaves of Alocasia macrorrhiza L. Schott.

Alocasia macrorrhiza is a fast growing and propagating herbaceous species commonly found in South China. To determine its physiological responses to Pb and Cd stresses, the biochemical, histochemical and cytochemical changes under PbAC2 and CdCl2 phytotoxicity were detected using leaf discs as an experimental model. After leaf discs were infiltrated in different concentrations of PbAC2 and CdCl2 solutions (0, 50, 100, 150, 200 microM) for 72 h, the formation of reactive oxygen species (H2O2 and O2-) in plant tissue were found to be exaggerated together with elevated OH concentration and cell death. Changes in chlorophyll fluorescence (Fv/Fm, PhiPSII, qP and NPQ) imaging colours/areas of leaf discs indicated decreased photosystem II functions by both heavy metal treatments and positive reactions of antioxidants under Pb2+ stress. Results showed that fluorescent detection of hydroxylated terephthlate using terephthalic acid as OH trap is a simple, yet valuable and specific method for monitoring OH generation in plant tissue under heavy metal stresses. As compared with Cd2+, Pb2+ was found to be less toxic, indicating that A. macrorrhiza tissue might have a potential tolerance to Pb.

Light acclimation and HSO(3) (-) damage on photosynthetic apparatus of three subtropical forest species.

The effects of long-term (33 months) sun/shade acclimation and short-term (within 10 h) HSO(3) (-) treatment on leaf photosynthetic apparatus were investigated in three subtropical forest plants, Pinus massoniana, Schima superba, and Acmena acuminatissima. After 33 months' growth in two light environments (100 and 12% sunlight), rapid light curves (RLC), chlorophyll fluorescence imaging and chloroplast ultrastructures of three tested species were changed to different degrees. When leaf sections were immersed in 50 mM NaHSO(3) for 10 h, all the RLCs were lowered; chlorophyll fluorescence imaging was inclined to present warmer colors and imaging areas were decreased. However, changes in chloroplast ultrastructures differed from three species. Our results showed that the photosynthetic apparatus of a dominant species, A. acuminatissima, in the late succession stage of a subtropical forest in South China, was less sensitive to NaHSO(3) under both growing light intensities. Conversely, the chloroplasts of P. massoniana, the pioneer heliophyte species, were most susceptible to NaHSO(3). It is deduced that, SO(2) pollution may become as a factor to accelerate the succession of subtropical forest.

Stress-induced alteration of chlorophyll fluorescence polarization and spectrum in leaves of Alocasia macrorrhiza L. Schott.

The value of intrinsic chlorophyll fluorescence polarization, and the intensity in emission spectrum were investigated in leaf segments of Alocasia macrorrhiza under several stress conditions including different temperatures (25-50 degrees C), various concentrations of NaCl (0-250 mM), methyl viologen (MV, 0-25 microM), SDS (0-1.0%) and NaHSO(3) (0-80 microM). Fluorescence emission spectrum of leaves at wavelength regions of 500-800 nm was monitored by excitation at 436 nm. The value of fluorescence polarization (P value), as result of energy transfer and mutual orientation between chlorophyll molecules, was determined by excitation at 436 nm and emission at 685 nm. The results showed that elevated temperature and concentrations of salt (NaCl), photooxidant (MV), surfactant (SDS) and simulated SO(2) (NaHSO(3)) treatments all induced a reduction of fluorescence polarization to various degrees. However, alteration of the fluorescence spectrum and emission intensity of F(685) and F(731) depended on the individual treatment. Increase in temperature and concentration of NaHSO(3) enhanced fluorescence intensity mainly at F(685), while an increase in MV concentration led to a decrease at both F(685) and F(731). On the contrary, NaCl and SDS did not cause remarkable change in fluorescence spectrum. Among different treatments, the negative correlation between polarization and fluorescence intensity was found with NaHSO(3) treatments only. We concluded that P value being measured with intrinsic chlorophyll fluorescence as probe in leaves is a susceptible indicator responding to changes in environmental conditions. The alteration of P value and fluorescence intensity might not always be shown a functional relation pattern. The possible reasons of differed response to various treatments were discussed.

The anti-photooxidation of anthocyanins-rich leaves of a purple rice cultivar.

In the leaf of rice (Oryza sativa L.) cultivar Yunnan purple rice, the anthocyanins with an obvious absorption peak at 530nm were distributed in the cells of upper and lower epidermis, bulliform tissue and bristle. The maximal photosynthetic oxygen evolution rate and chlorophyll content in flag leaves were 28% and 23%, respectively, more than the common green leaf rice cultivar Chijiaoruanzhan. Higher chlorophyll content is probably one of the physiological adaptations for enhancing light harvesting capacity of the antenna in photosystems in this cyanic leaves species. Upon the photooxidation of leaf segments mediated by methyl viologen in weak light for 3 days, the distinct bleaching of anthocyanins in purple rice was associated with the reduction of scavenging ability to DPPH * free radical ability and the increase in membrane leakage rate. But almost no changes in contents of flavonoids and total phenolics were observed. Chlorophyll fluorescence parameters Fv/Fo, qP and phi(PSII) decreased with the increase in NPQ and DES of xanthophylls cycle after photooxidation treatment. Green rice leaves showed more decrease in DPPH * scavenging rate and more increase in cell membrane leakage rate but showed a trace of anthocyanins during photooxidation. It is suggested that anthocyanin may be a beneficial and primary antioxidant in sun cyanic rice leaves against oxidative stress induced by environmental adversity. And photooxidation could induce different changing patterns of anthocyanins between the tested purple and green rice leaves.

The antioxidative function of lutein: electron spin resonance studies and chemical detection.

In the present study, both electron spin resonance (ESR) and chemical detection confirmed that lutein [extracted from alfalfa (Medicago sativa L.)], the most abundant xanthophyll in thylakoids of chloroplasts, could serve as an antioxidant to scavenge reactive oxygen species (ROS) in vitro. Lutein exhibited a greater capacity for scavenging hydroxyl (OH·) and superoxide (O2·-) radicals than ß-carotene at the same concentration, whereas the opposite trend was observed in the capacity for scavenging singlet oxygen (1O2). The capacity of lutein for scavenging ROS from high to low is OH· > O2·- > 1O2. We hypothesise that lutein plays an important photoprotective role in scavenging O2·- and OH· under severe stress. This hypothesis is consistent with our previous report that the lut2 (lutein-deficient) Arabidopsis mutant is more susceptible to damage than the npq1 (lutein-replete but violaxanthin de-epoxidase-deficient) Arabidopsis mutant under severe stress during exposure to high light intensity at low temperature (Peng and Gilmore 2003).

Thermostability of photosynthesis in two new chlorophyll b-less rice mutants.

Leaves of the two new chlorophyll b-less rice mutants VG28-1, VG30-5 and the wild type rice cv. Zhonghua 11 were subjected to temperatures 28, 36, 40, 44 and 48 degrees C in the dark for 30 min or gradually elevated temperature from 30 degrees C to 80 degrees C at 0.5 degrees C/min. The thermostability of photosynthetic apparatus was estimated by the changes in chlorophyll fluorescence parameters, photosynthetic rate and pigment content, chloroplast ultrastructure and tissue location of H2O2 accumulation. There were different patterns of F(o)-temperature curves between the Chl b-less mutants and the wild type plant, and the temperature of F(o) rising threshold was shifted 3 degrees C lower in the Chl b-less mutants (48 degrees C) than in the wild type (51 degrees C). At temperature up to about 45 degrees C, chloroplasts were swollen and thylakoid grana became misty accompanied with the complete loss of photosynthetic oxygen evolution in the two Chl b-less mutants, but chloroplast ultrastructure in the wild type showed no obvious alteration. After 55 degrees C exposure, the disordered thylakoid and significant H2O2 accumulation in leaves were found in the two Chl b-less mutants, whereas in the wild type plant, less H2O2 was accumulated and the swollen thylakoid still maintained a certain extent of stacking. A large extent of the changes in qP, NPQ and Fv/Fm was consistent with the Pn decreasing rate in the Chl b-less mutants during high temperature treatment as compared with the wild type. The results indicated that the Chl b-less mutants showed a tendency for higher thermosensitivity, and loss of Chl b in LHC II could lead to less thermostability of PSII structure and function. Heat damage to photosynthetic apparatus might be partially attributed to the internal oxidative stress produced at severely high temperature.