Nuclear, Virescent Mutants of Zea mays L. with High Levels of Chlorophyll (a/b) Light-Harvesting Complex during Thylakoid Assembly

Abstract

We have found nuclear, recessive mutants in Zea mays L where assembly of the major chlorophyll (a/b) light-harvesting complex (LHC) was not delayed relative to most other thylakoid protein complexes during thylakoid biogenesis. This contrasts with the normal development of maize chloroplasts (NR Baker, R Leech 1977 Plant Physiol 60: 640-644). All four mutants examined were allelic and virescent, and displayed visibly higher yields of leaf Chl fluorescence during greening. Fully greened mutants had normal leaf Chl fluorescence yield and normal levels of LHC, and grew to maturity under field conditions. Therefore, delayed LHC assembly is not an oblipte feature of thylakoid differentiation.Assigning the molecular basis for the mutation should provide information concerning reguation of LHC assembly. Several possibilities are discussed. The pleiotropic mutant phenotype is not attributable to defects in thylakoid glycerolipid synthesis. Thylakoids isolated from greening mutant leaf sections had elevated glycerolipid/Chl ratios. In addition, both the molar distribution and acyl composition of four major glycerolipids were normal for developing mutant thylakoids.Biogenesis ofphotosynthetic membranes in eucaryotes follows a programmed differentiation that allows efficient conversion of absorbed light to biochemical energy. The observed sequence is similar for differentiating thylakoids ofgreen algae (1) and higher plant etioplasts (2) and for thylakoids of developing protochloroplasts of several monocots including maize (4). PSI activity and PSI-dependent phosphorylation of ADP can be detected before PSII reaction center activity which, in turn, is followed by appearance of the water splitting activity. Insertion of the LHC2 into thylakoids lags behind the electron transport chain and may continue for some time after the redox carriers have achieved final activities (4, 16). It is unknown at what level(s)

A Putative Chloroplast Thylakoid Metalloprotease VIRESCENT3 Regulates Chloroplast Development in Arabidopsis thaliana

“…Virescence is quite prevalent in higher plants and has long fascinated plant biologists. Early work has identified virescent mutants from many plant species including maize, cotton, tobacco, peanut, and bean, and genetic analyses have shown that both nuclear and chloroplast mutations can be responsible for the virescent phenotype (5)(6)(7)(8)(9).…”

The Phenotype of a Virescent Chloroplast Mutation in Tobacco Is Associated with the Absence of a 37.5 kD Thylakoid Polypeptide

“…Kyle and Zalik (18) examined thylakoid proteins in the virescent barley and found that during greening ofetiolated mutant plants, greening-specific proteins (presumably including cab protein) appeared later in development than in the wild type. Polacco et al (22) analyzed the v424 nuclear virescent maize mutant and reported that thylakoid proteins coded for by the chloroplast genome were present in decreased amounts, while the amount of the nuclear-encoded cab protein was similar to that in the control strain. No thylakoid polypeptides were missing in the v-424 mutant.…”