Simulating the optical properties of phytoplankton cells using a two-layered spherical geometry

Effective use of ocean colour and other bio-optical observations is dependent upon an ability to understand and characterise the angular scattering properties of phytoplankton populations. The two-layered sphere appears to offer the simplest heterogeneous geometry capable of simulating the observed angular scattering of phytoplankton cells. A study is made of the twolayered spherical model for the simulation of the inherent optical properties of algal populations, with a particular focus on backscattering as causal to ocean colour. Homogenous and two-layered volume-equivalent single particle models are used to examine the effects of varying cellular geometry, chloroplast volume, and complex refractive index on optical efficiency factors. A morphology with a chloroplast layer surrounding the cytoplasm is shown to be optimal for algal cell simulation. Appropriate chloroplast volume and refractive index ranges, and means of determining complex refractive indices for cellular chloroplast and cytoplasm material, are discussed with regard to available literature. The approach is expanded to polydispersed populations using equivalent size distribution models: to demonstrate variability in simulated inherent optical properties for phytoplankton assemblages of changing dominant cell size and functional type. Finally, a preliminary validation is conducted of inherent optical properties determined for natural phytoplankton populations with the two-layered model, using the reflectance approximation. The study demonstrates the validity of the two-layered geometry and refractive index structure, and indicates that the combined use of equivalent size distributions with the heterogeneous geometry can be used to establish a quantitative formulation between single particle optics, size and assemblage-specific inherent optical properties, and ocean colour.

Amperometric Titration Largely Overestimates Chloride Concentrations in Chloroplast Extracts

Determination of chloride contents in aqueously isolated chloroplasts from spinach by amperometric titration indicated chloride concentrations of 60 to 100 mmol 1-1 (based on a chloroplast volume of 25 μl mg-1 chlorophyll). However, when analyzed by anion chromatography, chloride contents in chloroplasts were much lower (1-8 mmol 1-1). In leaf extracts chloride concentrations obtained with both methods were rather similar. Boiling of chloroplast extracts prior to chloride titration reduced indicated chloride contents by a factor of three or four, but did not change results obtained with anion chromatography. It is concluded that chloroplasts contain large amounts of silver complexing agents giving rise to a drastic overestima­tion of chloroplast chloride concentrations when measured by amperometric titration. Boiling and centrifugation of extracts apparently precipitates these compounds only insufficiently.

Phytotoxic Action of Paraquat on the Photosynthetic Apparatus

Treatment of microalgae (Bumilleriopsis) with paraquat (1,1-dimethyl-4,4-dipyridylium dichloride) under culture conditions in the light for 20 or 160 h leads to light-induced oxygen uptake and more or less severe chlorophyll bleaching, which is accompanied by formation of malondial-dehyde. The ratio of chlorophyll to packed chloroplast volume remains about the same as that of the control, presumably indicating destruction of membranes concurrently with pigments. Unre­lated to retardation of growth, degree of bleaching or to the formation of malondialdehyde quite a uniform degree of inactivation (≈ 50%) of partial redox reactions is observed in the region of photosystem II and I except for the terminal part of photosystem I (pigment 700 → NADP+) . The action of paraquat in the cell centers primarily on the photosynthetic membrane system and redox chain.

Initial Light Effects on Chloroplast Ultrastructure in Soybeans

Light induced changes in chloroplast volume and thylakoid membranes have been documented in a few plants by light and electron microscopy, as well as with the use of a Coulter counter. We wish to demonstrate that significant structural changes occur in soybean chloroplasts mediated both by genetically dictated levels of photosynthetic pigments, and by light intensity and duration as examined by TEM and an electronic image analyzer.A comparison was made of a field variety (Harasoy) with strain T219 soybeans which genetically segregate into three phenotypes: dark green (DG), light green (LG), and a lethal yellow (LY). All plants in mineral nutrient media were maintained under 12 hr. photoperiods for six weeks prior to sampling. LY plants were grafted to DG at 3-5 days postgermination. Interveinal leaf discs were stamped from sixth node trifoliate leaves prior to illumination and fixed for TEM as were samples at varying time intervals up to 1 hr.