Studies on the Photoactivation of the Water-Oxidizing Enzyme

Abstract

ABSTRACFIn weak yet optimal light intensity, complete photoactivation of the water-oxidizing enzyme in NH20H-extracted wheat (Triticum aativwn, var Analysis ofthe interrelationship between 02 evolving capacity, PSII polypeptides, and abundances and/or stability of the Mn complex have been made using specific algal mutants (6,33,47) and Triton derived 02 evolving membranes (6, 26, 37 (9-11, 22, 39, 40). This process has been defined (42) as a multiquantum process driven by PSII quantum events leading to Mn ligation into the inactive apo-S-State complex with the conversion of the inactive complex into an active water oxidizing S-State complex.This multiquantum process has been observed with Mn-deficient algae made Mn-sufficient (9), NH20H extracted algae (10), dark grown Chlorella capable of synthesis in darkness of the pigments of photosynthesis, PSI and PSII trapping centers and electron transport components (1 1), wheat leaves greened under widely spaced flash regimes leading to the synthesis of the pigments of photosynthesis, PSI and PSII trapping centers and electron transport components but not the active water oxidizing S-State complex (22), and Tris-extracted spinach chloroplasts reactivated by DCIPH23 washings (56).Additionally, light requirements for the appearance of V02 have been noted for Mn-deficient higher plants made , spruce needles greened in darkness (38), some cold sensitive higher plants following cold stress regimes (31, 34), Trisacetone extracted spinach chloroplasts (57), and intact chloroplasts from wheat leaves greened under widely spaced flashes (39,40

Studies on the Photoactivation of the Water-Oxidizing Enzyme

“…These results coupled with previous observations (4) imply that quantitative/qualitative differences exist in thylakoid polypeptides synthesized in light versus dark; moreover, they suggest that such differences relate to the complete recovery of photoinhibited PSII traps in light but not in dark (4). CAP, but not CH, abolishes the photoinduced recovery (4).…”

“…Thus these results (Fig. 2) and the results of Figure 5 showing the absence of modification of the 32 kD QB protein contrast with those obtained by photoinhibition of Chlamydomonas cells (25) and isolated pea thylakoids (32) (4). Second, a PSII artificial electron donor diminishes the slow rise-time by -4-fold (4).…”

“…Our data show that recovery from weak light photoinhibition of NH20H extracted leaves is dependent upon slow, light-induced 70S protein synthesis (4 from being related to recovery of P511 from photoinhibition. We therefore conclude that the photoinduced synthesis of only peak 2 ( Fig.…”

“…CAP, but not CH, abolishes the photoinduced recovery (4). We therefore surmised that any quantitative/qualitative differences in thylakoid polypeptides synthesized in light versus dark are causally related to recovery from photoinhibition and that these polypeptides are encoded by chloroplast DNA.…”

“…Thus, both proteins may be susceptible to attack by a single protease. We offer the scheme of Figure 11 to explain our conclusions from studies on the disassembly of the S-state complex, the photoinhibition of the oxidant side of PSII traps, the photoinduced recovery of PSII trap function via processes requiring 70S synthesis of a -~34 kD (D2) polypeptide, and the reassembly of the S-state complex via photoactivation (3,4,6) by NH20H or Tris inactivation of the S-state water oxidizing enzyme. We observe solubilization of -4 Mn, 1 to 2 specifically bound Ca2+/PSII units (see, however, Refs.…”