PHOTOINHIBITION OF PHOTOSYNTHESIS IN NATURAL WATERS*

Abstract— A quantitative analysis of the wavelength-dependent influence of solar irradiance on natural phytoplankton photosynthesis has been made. The effect on productivity due to several different UV radiation regimes has been measured. In the course of this analysis, it has been shown that the biological weighting function for photoinhibition of chloroplasts (Jones and Kok, 1966) allows the calculation of a biologically effective dose which is consistent with the measured photoinhibition in natural phytoplankton populations. The ecological implications of a change in available UV radiation, possibly due to anthropogenic altering of the ozone layer, are explored and it is found that the present static bottle ^l4C technique of measuring in situ phytoplankton productivity does not lend itself to assessing accurately the potential ecological consequences of possible increased MUV (middle ultraviolet radiation in the 280–340 nm region) on phytoplankton populations. A small change in MUV has a relatively minor effect on photoinhibition dose rates whereas it has a large potential effect on DNA dose rates.     

Benzolactams. II. Synthesis of tetrahydrobenz[d]indeno-[1,2-b]azepines and their 12-Oxo derivatives

Aromatic methoxy and/or methylenedioxy substituted 7-methyltetrahydrobenz[d]indeno[1,2-b]-azepines 7 and their 12-oxo derivatives 8 were efficiently synthesized by the general method consisting of two types of intramolecular dehydrative cyclizations, as follows. N-Methyl-N-β-phenethylacetamides 1 were cyanomethylated in the two-step process of chloromethylation and treatment of the resultant benzyl chlorides with sodium cyanide. The condensation of the benzyl cyanides 2 with the appropriate benzaldehydes, followed by reduction of the benzylidene function, gave α,β-diphenylpropionitriles 3 . Successively, hydrolysis to the amino acids 4 and the thermal cyclization converted 3 to the benzylbenzazepinones 5 , which were also prepared by benzylation of the benzazepinones 6 smoothly by heating of 5 with phosphoryl chloride to afford the title azepines 7 . Further, these tetracyclic enamines 7 underwent autoxidation to the corresponding 12-oxo derivatives 8 , on exposure to oxygen in the presence of Triton B.     

ULTRAVIOLET RADIATION IN ANTARCTICA: INHIBITION OF PRIMARY PRODUCTION

With the seasonal formation of the ozone hole over Antarctica, there is much concern regarding the effects of increased solar UV-B radiation (280–320 nm) on the marine ecosystem in the Southern Ocean. In situ incubations of natural phytoplankton assemblages in antarctic waters indicate that under normal ozone conditions UV-B radiation is responsible for a loss of approximately 4.9% of primary production in the euphotic zone, whereas UV radiation with wavelengths between 320 and 360 nm causes a loss of approximately 6.2%. When combined with data on the action spectrum for photoinhibition by UV radiation, our data suggest that the enhanced fluence of UV-B radiation under a well-developed ozone hole (150 Dobson units) would decrease daily primary productivity by an additional amount of 3.8%. Calculations that take into consideration the extent and duration of low stratospheric ozone concentrations during September to November indicate that the decrease in total annual primary production in antarctic waters due to enhanced UV-B radiation would be 0.20%.