Spectrophotometric characteristics of chlorophylls a and b and their pheophytins in ethanol.

Studies on Nitrogen‐fixing Blue‐green Algae

Chlorophylls are the green pigments in plants some of which, and perhaps all, participate in photosynthesis. An understanding of their nature, genesis, transformation, and function in plants requires that they and their near chemical relatives be recognized qualitatively and oftentimes be determined quantitatively. In addition to the use of analytical procedures for the identification and determination of the chlorophylls as participants in plant physiological processes, these methods may be used in various other fields of science and technology some of which are genetics, plant nutrition, certain aspects of pure chemistry, crop production of land and sea, medicine, pharmaceuticals, food technology, and paleontology.

Chlorophylls: Analysis in Plant Materials

The refractive index of phytoplankton is calculated from its metabolite composition. The mean index of the algal dry mass, relative to the index of water, seems to vary from 1.146 for green algae to 1.167 for coccolithophonds. This difference of 0.021 reduces to 0.007 and 0.003 when the partial water volumes of the algae are 0.6 and 0.8, respectively. The most important factor for the variation of the refractive index is the algal water content. If a reasonable average range of the partial water volume is 0.6 ± 0.2, the corresponding range of the refractive index relative to sea water becomes 1.06 ±0.04. This result is in excellent agreement with estimates based on optical measure- ments of pure algal cultures. The normal dispersion of the refractive index is negligible, but anoma- lous dispersion in the vicinity of strong absorption bands may be of importance for the light scattering properties of small phytoplankton.

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Refractive index of phytoplankton derived from its metabolite composition

Photosynthesis by phytoplankton cells in aquatic environments contributes to more than 40% of the global primary production (Behrenfeld et al., 2006). Within the euphotic zone (down to 1% of surface photosynthetically active radiation [PAR]), cells are exposed not only to PAR (400-700 nm) but also to UV radiation (UVR; 280-400 nm) that can penetrate to considerable depths (Hargreaves, 2003). In contrast to PAR, which is energizing to photosynthesis, UVR is usually regarded as a stressor (Hader, 2003) and suggested to affect CO2-concentrating mechanisms in phytoplankton (Beardall et al., 2002). Solar UVR is known to reduce photosynthetic rates (Steemann Nielsen, 1964; Helbling et al., 2003), and damage cellular components such as D1 proteins (Sass et al., 1997) and DNA molecules (Buma et al., 2003). It can also decrease the growth (Villafane et al., 2003) and alter the rate of nutrient uptake (Fauchot et al., 2000) and the fatty acid composition (Goes et al., 1994) of phytoplankton. Recently, it has been found that natural levels of UVR can alter the morphology of the cyanobacterium Arthrospira (Spirulina) platensis (Wu et al., 2005b). On the other hand, positive effects of UVR, especially of UV- A (315-400 nm), have also been reported. UV- A enhances carbon fixation of phytoplankton under reduced (Nilawati et al., 1997; Barbieri et al., 2002) or fast-fluctuating (Helbling et al., 2003) solar irradiance and allows photorepair of UV- B-induced DNA damage (Buma et al., 2003). Furthermore, the presence of UV-A resulted in higher biomass production of A. platensis as compared to that under PAR alone (Wu et al., 2005a). Energy of UVR absorbed by the diatom Pseudo-nitzschia multiseries was found to cause fluorescence (Orellana et al., 2004). In addition, fluorescent pigments in corals and their algal symbiont are known to absorb UVR and play positive roles for the symbiotic photosynthesis and photoprotection (Schlichter et al., 1986; Salih et al., 2000). However, despite the positive effects that solar UVR may have on aquatic photosynthetic organisms, there is no direct evidence to what extent and howUVR per se is utilized by phytoplankton. In addition, estimations of aquatic biological production have been carried out in incubations considering only PAR (i. e. using UV-opaque vials made of glass or polycarbonate; Donk et al., 2001) without UVR being considered (Hein and Sand-Jensen, 1997; Schippers and Lurling, 2004). Here, we have found that UVR can act as an additional source of energy for photosynthesis in tropical marine phytoplankton, though it occasionally causes photoinhibition at high PAR levels. While UVR is usually thought of as damaging, our results indicate that UVR can enhance primary production of phytoplankton. Therefore, oceanic carbon fixation estimates may be underestimated by a large percentage if UVR is not taken into account.

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Solar UV Radiation Drives CO2 Fixation in Marine Phytoplankton: A Double-Edged Sword

1. Solutions of chlorophyll a were prepared in thirteen solvents and of chlorophyll b in five solvents by direct elution from sucrose adsorption columns. 2. Absorption spectra for each solvent are reported as measured spectrophoto-electrically in the visible region. 3. Spectra for the ultraviolet region to 2650 A were determined for solutions in ethyl ether. 4. A preparation of dried chlorophyll a was made which retained excellent spectroscopic properties. 5. The application of Kundt's rule to chlorophyll solutions is discussed, as well as certain relations of spectroscopic properties and solvents to analytical applications.

F. P. Zscheile

Papers

Effects of Solvent Upon Absorption Spectra of Chlorophylls A and B; Their Ultraviolet Absorption Spectra in Ether Solution