Der Chlorophyllgehalt, die PEP- und RuDP-Carboxylase Aktivitäten während der Blattentwicklung einer ergrünenden Chlorophyllmutante und einer normalen Linie von Zea mays L.

Abstract

The second leaves of virescent (FS 1 Pe 8AB) and normal green seedlings (F2) of flint maize (Zea mays L.) were studied from the time of their appearance to the onset of senescence. The activities of phosphopyruvate (PEP) carboxylase and ribulose-1,S-diphosphate (RuDP) carboxylase and the content of chlorophyll were measured, the ratio of chlorophyll alb was determined and the dry weight of the plant ascertained. The highest level of chlorophyll was observed in normal leaves shortly after full leaf extension; the pigment had, however, already been present at relatively high concentrations soon after leaf appearance. Mutant leaves contained comparatively little chlorophyll at this stage, but they accumulated this pigment as rapidly as did normal leaves during the three subsequent weeks and evidenced a normal chlorophyll content at the end of this period. The ratio of chlorophyll alb was low in young mutant leaves, but increased up to the normal level as these leaves aged. The activities of PEP carboxylase and RuDP carboxylase on a fresh weight basis were highest in normal young leaves and decreased rapidly subsequent to full expansion. The rate of loss of activity slowed with the ageing of the leaves. The corresponding activities in virescent seedlings were low immediately following leaf appearence; they then increased rapidly until full leaf expansion had been achieved and reached levels corresponding to those attained in the development in normal leaves RuDP carboxylase rather sooner than PEP carboxylase. When the activity of PEP carboxylase was related to the chlorophyll concentration differences between mutant and normal leaves became no longer apparent, thus indicating a dependence of enzyme activity and pigment level on the state of plastide differentiation. This degree of conformity was not demonstrated for RuDP carboxylase on a chlorophyll basis. No differences were observed in the life span of virescent and normal leaves. The pigment level and the enzyme activities indicated a synchronisation of development in the ageing