Regulation of cellular manganese and manganese transport rates in the unicellular alga Chlamydomonas1

Abstract

The cellular accumulation and uptake kinetics of manganese by Chlamya'omonas sp. were studied in model chelate buffer systems. Cellular manganese concentrations and uptake rates were related to the computed free manganese ion concentration and were independent of the total or chelated manganese concentration.Cellular manganese was constant at about 1 mmol liter-' of cellular volume at free manganese ion concentrations of 1 O-7.b-l O-6.3 mol liter-l and decreased below this range. Manganese uptake rates followed saturation kinetics and V,,,, but not KS (1 Om7.0 mol liter-l), varied with the fret manganese ion concentration in the growth medium. V.,, appeared to be under negative feedback control and increased with decreasing manganese ion concentration.

Response of the marine diatom Thalassiosira weissflogii to iron stress1

“…PQ and prnax for cells growing at fi = 0.02 h-l). These results, together with those of Sunda and Huntsman (1985) on manganese indicate that algae have developed the same type of homeostatic physiological mechanisms to regulate cellular trace element concentrations as those for regulation of major nutrients (McCarthy 198 1); could it be that all these elements are equally limiting in the marine environment (Brand et al 1983;Morel and Hudson 1984)?…”

“…This tends to rule out the free ferric ion as a regulator of iron transport because one would expect a more rapid response. Rather, it seems that cellular iron quotas are controlled by the cell's ability to vary pmax, through negative feedback regulation as has been suggested for manganese (Sunda and Huntsman 1985).…”

“…Sunda and Huntsman (1985) found that a similar response of short term uptake rate to nutrient stress controls cellular man-ganese quotas and transport in a Chlamydomonas species under manganese limitation.…”

Manganese oxidation in pH and O2 microenvironments produced by phytoplankton1,2

“…Phytoplankton are very efficient at taking up and accumulating Mn(II), which is required as a cofactor in the water-splitting, O,-evolving enzyme in photosystem II (Sauer 1980). It has been shcown that algae directly transport and accumulate Mn(I1) intracellularly to concentrations three or four orders of magnitude greater than those found in the environment (Larch 1977;Sunda and Huntsman 1985), thus directly removing biologically available Mn(U) from solution. It has also been hypothesized that phytoplankton indirectly remove Mn(I1) by oxi- dizing it to Mn(IV), a reaction effected by changing the pH and Eh of the aquatic environment (Huntsman and Sunda 1980;Tipping et al 1985).…”

Manganese content records seasonal upwelling in Lake Tanganyika mussels

“…These conditions favor the reduction and the dissolution of the Mn-oxides or Mn 2+ bounded to biological debris. (4) By contrast, an increase of biological activity concomitant with a supply of Mn d in surface waters likely enhances the production of Mn-rich particles, while green algae can efficiently take up and concentrate Mn 2+ intracellularly (Sunda and Huntsman, 1985). (5) Moreover, photosynthetic activity in dense algal population generates high pH (>9) which, in turn, favors oxides or carbonates precipitations in organicrich microenvironments (Richardson et al, 1988).…”