Uptake and Metabolism of Sulfate by Chlorella. I. Sulfate Accumulation and Active Sulfate

Abstract

The uptake and metabolismii of sulfur has enjoyed relatively little attention as compared with other elements known to be essential for plant nutrition. Considerable information has been developed on the metabolism of sulfur by nmicroorganisms, but in chlorophyllaceous plants relatively little is known regarding the mechanisms of sulfur reduction and incorporation into organic forms following its absorption as the inorganic sulfate ioIn (15).The formation of "active" sulfate by animal and plant cells has recently become a subject of some interest, and several workers have shown the existence of systems capable of activating sulfate by combining the latter with nucleosides in a number of compounds which serve to facilitate the transfer and further reduction of sulfate (8., 12, 13, 17, 18). In most cases this work has involved in vitro study of systems isolated from animal or yeast cells, but Sadenosylmethionine has recently been identified in acid extracts of Chlorella cells fed S35O`and enzymatic evidence for the existence of other "active" sulfates obtained (12).Recent work in this laboratory (16) has shown that 2,4-dichlorophenoxyacetic acid has no detectable effect on the total uptake of sulfate by Chlorella at 10 C, but has a very pronounced effect on the uptake of this ion at 25°C. This indication of an auxin effect on sulfur metabolism has incited additional study of this problem. The present work is concerned with the mechanismii of sulfate uptake by Chlorella and the possible role of "active" sulfate in this process. MATERIALS AND AMETHODSThe material used for these studies was Chlorella

Transport of Selenate and Selenite into Astragalus Roots

“…Tlle ioni accumulates against a concenitratioin gradient, and its entry is sensitive to respiratory and competitive inhibitors. In these nmanv features, accumulation of selenate is comparable to that of sulfate for which active transport has been reported in the roots (2, 7) and leaves (4, 5) of higher plants as well as in algae (6,18).…”

Photophosphorylation In Vivo

“…Regarding the high dependence of sulfate influx on temperature (100, 187) and the great difference between the observed and the calculated electrochemical gradients (187) an active uptake of the sul fate ion must be supposed. In some organisms the influx of sulfate is stimulated by light, dependent on external sulfate concentration (100,125,242,267) in others (e.g. Chara australis and Ch.…”

Studies of Sulfate Utilization by Algae. 4. Properties of a Cell-Free Sulfate-Reducing System From Chlorella

“…We have previously shown that the produtcts formed from sulfate by intact Chlor ella cells are: cysteine, glutathione, homocysteine, .S-adeno'syl methionine, and adenosine-3'->phosphate-5'-phosphosutlfate (PAPS) (11,13,14). Some of these compotunds were also identified sutbsequiently by others (3,17).…”

“…The formation of PAPS from suilfate by thliis species of Chilorella has already been mentionied (11,17). TPNH has also been implicated in sulfate-redutciing, systemis from yeast (6,18 The uindialyzed extracts show a brief lag followed by essentially liinear kinetics from aboutt 1 hour to 12 houirs but beyond this time the activity progressively dimini,shes (fig 1).…”