Enzymatic transformation of 5-aminolevulinic acid into chlorophyll a in chlorophyll b-less barley mutant

The chlorophyll b (Chl b)-less barley mutant chlorina 2807, genetically identical to the well-known mutant chlorina f2, is 30% deficient in chlorophyll a (Chi a). To elucidate the cause of Chi a deficiency, we measured the activity of the enzyme system involved in Chi a biosynthesis. Transformation of 5-aminolevulinic acid (5-ALA) into protochlorophyllide (Pchlide) and esterification of chlorophyllide (Chlide) to Chi a were studied. We measured the rate of Pchlide accumulation in darkness in etiolated leaves of mutant and wild-type plants preliminary illuminated for 1, 4 and 24 h and then treated with 5-ALA at a saturating concentration of 40 mM. The activity of this enzyme system increased during greening; however, the rate of the Pchlide accumulation in mutants was the same as in wild-type plants. Exogenous Chlides a and b were infiltrated into etiolated leaves of mutant and wild-type plants and Chi formation during dark incubation was followed. Both Chlides were esterified, although there was a tendency towards the more active esterification of Chlide a. Esterification capacity of mutant and wild-type plants were essentially similar. Thus, mutants have an undisturbed system of Chi a biosynthesis. Chi a deficiency is likely to be related to the absence of the proteins of the light-harvesting complexes that bind this Chl.