Comparison of Light-dependent Oxygen Uptake, Protochlorophyll(ide)-650 Photoconversion, and Chlorophyll Disappearance in Wheat Etioplasts

Red light exposures given to dark-grown wheat seedlings (Triticum aestivum L.) prior to etioplast isolation reduced the ability of these organelles to consume O(2). The same preharvest red light exposures also decreased protochlorophyll(ide) content of etioplasts. In addition, regeneration of both O(2) uptake rates as well as protochlorophyll(ide) levels followed a parallel time course. These similarities suggested that photoconversion of protochlorophyll(ide)-650 to chlorophyll(ide) may mediate some process with O(2) as the electron acceptor. This process appears to involve photooxidation of nonphotoconvertible protochlorophyll(ide) as well as of newly formed chlorophyll(ide). This hypothesis is further supported by the observations that: (a) the in vitro light induced O(2) uptake phenomenon was observed in solubilized protochlorophyll(ide) holochrome preparations; and (b) photoinduced O(2) uptake was reduced to zero rate by light exposure time equivalent to that required for chlorophyll(ide) and nonphotoconvertible protochlorophyll(ide) destruction.