Effect of O2 on the Kinetics of the Flash-Induced 518 nm Absorbance Change in Vivo

The kinetics of the flash induced 518 nm absorbance change (A₅₁₈)in lettuce leaves were found to be dependent on O₂ concentration.(1) Either a lower O₂ partial pressure or the addition of weakred background illumination accelerated the decay of (A₅₁₈)while far-red background light induced a transient acceleration.(2) In the presence of background red light the accelerateddecay could be restored to the original dark level by the additionof O₂. A linear relationship was found between the intensityof red background light and the O₂ pressure required for thisrestoration. (3) The O₂ dependence of (A₅₁₈) decay halftimewas biphasic, the sensitive phase saturating at 0.3 atmospheresO₂ independent of input light energy while the O₂ concentrationneeded to saturate the second phase increased with increasinginput light energy (increasing flash frequency). (4) Treatmentwith N, N'-dicyclohexylcarbodiimide (DCCD) or KCN eliminatedall O₂ and background light effects and DCMU treatment inhibitedall but the sensitive phase of the O₂ dependence on (A₅₁₈) decayhalftime. (5) The extent of the lag phase in the dark recoveryof (A₅₁₈) normally present after preillumination induced accelerationof decay was decreased with added O₂ or KCN. (6) It was concludedthat O₂ competes directly with background red light inducedelectron transport to PS I acceptors to influence the (A₅₁₈)decay. A possible mechanism involving the O₂ sensitive ferredoxin-thioredoxin-reductaseactivation of chloroplast coupling factor 1 ATP-hydrolase activitywas discussed. (Received December 17, 1982; Accepted April 28, 1983)