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Hydrogen sulfide can exist in oxic waters in the form of a dissolved gas, dissociated ions, dissolved metal sulfide complexes, and particulate metal sulfides. The sum of the dissolved species is termed total dissolved sulfide (TDS). In addition to the hydrolysis of carbonyl sulfide, it has been speculated that phytoplankton may produce TDS. We present results from preliminary culture studies which demonstrate that phytoplankton produce TDS and particulate acid‐volatile sulfide (pAVS). The phylogenetic order of TDS + pAVS production (per unit cell volume) for the oceanic species examined is Synechococcus sp. > Emiliania ≈ Pyramimonas obovata > Thalassiosira oceanica. Moreover, TDS and pAVS production increases when the concentrations of uncomplexed trace metals in culture media are also increased, suggesting metal detoxification via the formation of metal sulfide complexes.

Seasonal changes in the concentrations of Cd and phosphate (P) in the macroalga Macrocystis pyrifera have been studied in Otago Harbour, a shallow marine embayment. Both components showed the same seasonal cycle, with concentration maxima during the austral winter (June-July) and summer periods (December-February) when growth of M. pyrifera was minimal. During these periods, cells contained significant quantities of electron-dense polyphosphate bodies (PPBs). Culture experiments showed that Cd uptake from seawater media was greatly enhanced when PPBs were induced to form. With 0.44 pmol Cd kg-l in the medium, cultures forming PPBs contained 40-50 times as much Cd in excess of controls as those grown at the same Cd concentration in which PPBs were not formed. With 44 pmol kg-l in the medium, PPB-forming cultures took up about twice as much Cd as those not forming PPBs. The incorporation of Cd into cellular PPBs may be an important mechanism for the uptake of this element even at natural Cd concentrations.

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Tetraamide hosts not only complex para‐benzoquinone to form 1, they also activate the guest towards electrochemical reduction. The structure and redox properties of this system bear close similarity to those of the quinone binding domains of photosynthetic reaction centers.