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K Sauer

Publications and source records attributed to K Sauer.

At least 127 records · Page 7Linked to original sources
PubMed1973

Chlorophyll Formation in Greening Bean Leaves during the Early Stages.

In the evolution of the absorption spectrum of etiolated bean leaves (Phaseolus vulgaris L.) following illumination, a rapid photoconversion of 50% or more of the active protochlorophyllide at room temperature is followed by a shift of the chlorophyll(ide) absorption maximum: C(678)--> -->C(684)-->C(672 nm). Kinetic studies at 2 C and the absence of an isosbestic point provide evidence for an intermediate between C(678) and C(684). A dramatically different evolution is observed following the photoconversion of only 5 to 30% of the active protochlorophyllide at room temperature. C(672) appears within 30 seconds, and no subsequent dark shift occurs during the following 90 minutes. At 0 C, conversion of 5% of the active protochlorophyllide produces a new species, C(676), which converts progressively to C(672) within 10 minutes. We interpret the results in terms of two photochemical steps operating in series for the complete conversion of active protochlorophyllide. Furthermore, there appears to be competition between an irreversible, terminal dark shift and the second light reaction. We propose a scheme based on dimers of protochlorophyllide reduced stepwise to dimers of chlorophyllide in two successive light reactions. The intermediate mixed protochlorophyllide-chlorophyllide dimer absorbs at 676 nm and displays a much faster dissociation to monomers than does the chlorophyllide-chlorophyllide dimer.

Journal Article↗
PubMed1971

The sites of photoconversion of protochlorophyllide to chlorophyllide in barley seedlings.

The photoreduction of protochlorophyllide a to chlorophyllide a in intact 6-day-old seedlings of etiolated barley (Hordeum vulgare) exhibits a small initial phase, followed by an induction period of about 1 hour before a rapid phase of additional chlorophyll formation begins. Cycloheximide, an inhibitor of protein synthesis, has no effect on the initial phase of conversion of preformed protochlorophyllide, but it either abolishes or severely inhibits the subsequent phase of rapid chlorophyll synthesis within 45 minutes of its application to the seedlings. An analysis of the biphasic inhibition process suggests that the lifetime of the enzyme controlling protochlorophyllide synthesis (probably delta-amino-levulinic acid synthetase) is not longer than 10 minutes.The rapid phase of chlorophyll formation can be effected by a series of brief (15 second) pulses of light spaced at least 5 minutes apart. When longer dark intervals are used, no increase is observed in the yield of chlorophyll per pulse. We interpret the findings to indicate that the photoconversion takes place at distinct enzymatic sites whose concentration does not increase during a period of 4 hours following the initial illumination. The sites can be used repeatedly with a turnover time determined by the removal of the product chlorophyllide and the synthesis and placement of a new protochlorophyllide molecule.

Journal Article↗