731 



William Vidaver 



in the induction period during illumination in species of brown 

 and green marine algae and a freshwater green alga. This tran- 

 sient could not be observed in the response of the red alga 

 Porphyra . 



In those algae displaying the transient, oxygen must be evolved 

 as a response to light by a mechanism which is presumably insensi- 

 tive to inhibition by hydrostatic pressure of at least 15000 psi. 

 This response appears to differ kinetically from those usually 

 associated with enzymatic reactions^"' chap. 9)^ Variations of 

 temperature and pressure seem to have a greater effect on the 

 rates of those processes which proceed more slowly than the reac- 

 tions involved with the transient. By further slowing through 

 temperature extremes or the application of hydrostatic pressure, 

 it is possible to isolate (by the elimination of swamping) the 

 pre-a transient in algae that normally do not show it. 



:tions that utilize the products of the oxygen-evolving photo- 

 :tions. Reaction rate theory^^' '^"^P* ^^ predicts inhibition 



The high or low temperature requirement for induction of the 

 transient in some algae may result from rate changes in enzymatic 

 react] 



reactions. Reaction rate theory" 

 of enzymatic reactions as a consequence of temperature extremes. 

 Low or high temperature could induce the appearance of the tran- 

 sient by the reduction of the relatively high rates of the reac- 

 tions which consume the immediate photoproducts (other than molec- 

 ular oxygen). 



I 



The transient may result from the functioning of a primary 

 oxygen-evolving mechanism, since its lack of pressure sensitivity 

 suggests that it is not the result of enzymatic reactions. If - 

 this response is due to a photolytic water reaction, then it may f 

 be presumed that oxygen evolution in plants that show the tran- 

 sient is the result of rapid photochemical reactions, and does not 

 require the intervention of enzymatic transport systems. If it is 

 assumed that a very early response to light is the evolution of f 

 oxygen, and that oxygen evolution does not continue unless the 

 products formed during this process are consumed in some way (Hill 

 reaction), then it may be expected that only the transient would 

 appear in response to illumination. Hydrostatic pressure blocks k 

 the reactions by which the photoproducts seem to be utilized. 

 Consequently, the transient persists under pressure, while steady 

 rate oxygen evolution is inhibited. This response is analogous to 

 that of isolated chloroplasts lacking an added Hill oxidant which 

 show only a single, transient oxygen-production spike. These 

 chloroplasts require a certain dark interval before the maximum fj 

 transient rate may be regained'^^. Experiments not presented here * 

 indicate a similar, though shorter time course for maximum tran- 

 sient recovery in whole cells. 



