Fluorescence emission spectra and thylakoid protein kinase activities of three higher plant mutants deficient in chlorophyll b

Abstract

The properties of three higher plant mutants having less than normal amounts of chlorophyll b were compared with their respective wild-types. These mutants included the chlorophyll- b-lacking U374 sweet clover ( Melilotus alba) and chlorina- f2 barley ( Hordeum vulgare) as well as the chlorophyll b-deficient CD3 wheat ( Triticum aestivum). Fluorescence emission spectra from leaves of the sweet-clover mutant at 77 K show great similarity to the previously published spectrum of the barley mutant; rather than the predominant long-wavelength emission at approx. 740 nm in the wild-type plants, an emission maximum at approx. 720 nm is observed. The wheat mutant, containing reduced but measurable amounts of chlorophyl b, had 77 K long-wavelength fluorescence emissions at both 720 and 740 nm. These data indicate that these PS-I-derived fluorescence emissions are strongly influenced by the presence of antennae components. When examined for the ability to perform a light-induced State 1-State 2 transition in vivo, none was detected in the U374 sweet clover, whereas the CD3 wheat was capable of this process. The phosphorylation of endogenous polypeptides in isolated thylakoid membranes was examined using [γ- 32P]ATP as substrate for the thylakoid protein kinase activities. All three mutants had higher thylakoid protein kinase activity than the respective normal plants on a chlorophyll basis. The response of the mutant and normal sweet clover thylakoid protein kinase activities to ATP concentration was essentially identical. In contrast, the thylakoid protein kinase activities in the barley and wheat mutants appeared to saturate at markedly lower ATP concentrations than in the respective normal plants. These data suggest that the chlorina- f2 and CD3 mutants may be lacking one of the thylakoid protein kinases normally present in wild-type plants and that mutants lacking chlorophyll b may be of at least two different types.