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 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).