Measurement of photosynthesis as a way to assess phytotoxicity

Abstract

Toxic agents may affect photosynthesis either by altering the diffusion of CO₂ to the photosynthesizing cells or by altering the chloroplast activity for CO₂ fixation. Therefore, the effect of toxic chemicals can be assessed by measurement of the rate of CO₂ fixation. The effects on photosynthesis caused by altered CO₂ diffusion can be distinguished from those caused at the chloroplast level by evaluating the CO₂ concentration inside the leaf. If CO₂ concentrations remain constant or rise as photosynthesis declines, the inhibition must act on chloroplast activity. If the CO₂ concentrations decrease as photosynthesis declines, the inhibition may be caused by slower diffusion of CO₂into the leaf. The latter possibility would suggest a stomatal closure to be the most probable cause of the decline of photosynthesis.     

多环芳烃对卤虫无节幼体的光诱导毒性

以卤虫Ⅱ～Ⅲ龄无节幼体为实验材料,在实验室内研究4种多环芳烃的光诱导毒性,比较了在有紫外(UV)和无UV照射条件下多环芳烃对卤虫幼体的存活和几种生理生化指标的影响.结果表明:UV辐射(UVA:476 μw·cm-2;UVB:6.5 μW·cm-2)明显提高了菲、蒽、荧蒽和芘对卤虫幼体的毒性,其24 h LC50值分别是无UV照射条件下LC50值的1/139、1/182、1/102和1/88.UV照射诱导了荧蒽对卤虫幼体的氧化损伤,过氧化物酶(POD)对荧蒽的光诱导毒性较超氧化物歧化酶(SOD)敏感;卤虫幼体的丙二醛(MDA)和Na ·K -ATPase是衡量荧蒽光诱导毒性的较敏感参数.     

Comparative phototoxicity of nanoparticulate and bulk ZnO to a free-living nematode Caenorhabditis elegans: the importance of illumination mode and primary particle size

The present study evaluated phototoxicity of nanoparticulate ZnO and bulk-ZnO under natural sunlight (NSL) versus ambient artificial laboratory light (AALL) illumination to a free-living nematode Caenorhabditis elegans. Phototoxicity of nano-ZnO and bulk-ZnO was largely dependent on illumination method as 2-h exposure under NSL caused significantly greater mortality in C. elegans than under AALL. This phototoxicity was closely related to photocatalytic reactive oxygen species (ROS) generation by the ZnO particles as indicated by concomitant methylene blue photodegradation. Both materials caused mortality in C. elegans under AALL during 24-h exposure although neither degraded methylene blue, suggesting mechanisms of toxicity other than photocatalytic ROS generation were involved. Particle dissolution of ZnO did not appear to play an important role in the toxicity observed in this study. Nano-ZnO showed greater phototoxicity than bulk-ZnO despite their similar size of aggregates, suggesting primary particle size is more important than aggregate size in determining phototoxicity.     

UVR-induced toxicity of sludge and polycyclic aromatic hydrocarbons on seed germination and seedling growth of Triticum aestivum L.

The depletion of the ozone layer and enhancement of solar radiation may exert an adverse influence on the ecosystem. Phototoxicity of sludge and polycyclic aromatic hydrocarbons (PAHs) under ultraviolet radiation (UVR) to seedling was studied. Seeds of wheat (Triticum aestivum) were planted in sludge and PAHs (anthracene (An), benzo(a)pyrene (BaP) and pyrene (Py)) with and without UVR. Toxicity of sludge increased in the presence of UVR in wheat. UVB radiation was found to be more hazardous than UVA radiation. Results demonstrated that An, BaP and Py induced phototoxicity at various concentrations (1–10?µg/mL) under UVA (1.5?mW/cm²) or UVB (1.08?J/cm²) exposure. The pattern of phototoxicity was An?>?Py?>?BaP to shoot length, root length, and fresh weight; chlorophyll, protein content, enzyme activity of catalase and α-amylase were reduced while the activity of superoxide dismutase and starch was enhanced. Reduction in seedling growth and biochemical parameters may be related to less photosynthesis, less nutritional uptake, and distortion of root cap. Thus, the synergistic effect may be due to alterations in photosynthesis, phytohormones, or nutritional uptake.     

Photodynamic effects of 31 different phthalocyanines on a human keratinocyte cell line

Phthalocyanines (Pcs, colored macromolecular compounds with the ability to generate singlet oxygen) represent a promising group of photosensitizers due to their intense absorption in the red and UV portion of the spectrum which leads to their excitation. In order to characterize possible toxic effects associated with eventual practical use and application of these chemicals, we employed an in vitro cell culture model to evaluate cytotoxic effects of 31 different phthalocyanines using neutral red uptake assay. An immortalized human keratinocyte cell line HaCaT was exposed to the tested chemicals for 2 or 24 h, either with or without illumination in the last 60 min of the exposure period. After 2- or 24-h exposure without illumination, no cytotoxic effects or weak cytotoxic effects were induced by any Pc under the study and EC50 values could not be obtained within the tested concentration ranges (1.25–20 mg L⁻¹ or 0.625–10 mg L⁻¹). On the other hand, exposure to phthalocyanines under illumination induced a significant cytotoxic effect. The most pronounced cytotoxicity was elicited by Pcs previously shown to have high positive charge densities at peripheral parts of substituent groups, which is most likely the factor responsible for the binding of Pc to negatively charged membranes on the cell surface and thus guaranteeing the tight connection necessary for the singlet oxygen attack on the cell surface.