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Phosphorylation of a stromal enzyme protein in maize (Zea mays) mesophyll chloroplasts.

ABSTRACT: When intact maize (Zea mays) mesophyll chloroplasts were illuminated in the presence of [32P]orthophosphate and subsequently subjected to sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, a major polypeptide species of Mr 100000 was found to be heavily labelled. This polypeptide was not found in maize mesophyll thylakoid or cytoplasmic fractions, but was localized solely in the chloroplast stroma. No phosphorylation of polypeptides in the 100000-Mr region was observed in the mesophyll chloroplasts from C3 species (where the primary product of CO2 fixation is a 3-carbon compound), suggesting that this polypeptide arises from a protein associated with C4 metabolism (where the first product of CO2 fixation is a 4-carbon compound). The 100kDa polypeptide was major component of the maize mesophyll chloroplast, comprising 10-15% of the total protein, which banded in an identical position to the apoprotein of the enzyme pyruvate, orthophosphate dikinase, which catalyses a reaction of the C4 cycle [Edwards & Walker (1983) C3, C4: Mechanisms, and Cellular and Environmental Regulation, of Photosynthesis, Blackwell Scientific Publications, Oxford and London]. Phosphorylation in the 100kDa species was prohibited by treatment of lysed chloroplasts with antibody to pyruvate, orthophosphate dikinase (EC 2.7.9.1). These data suggest that the phosphorylated polypeptide observed after sodium dodecyl sulphate/polyacrylamide-gel electrophoresis is the monomeric form of this enzyme. The 100kDa polypeptide was partially phosphorylated in darkness, but a significant increase in the degree of phosphorylation was found on illumination. This polypeptide was found to be dephosphorylated only slowly when the chloroplasts were returned to darkness. Maximum phosphorylation was observed in the presence of pyruvate or dihydroxyacetone phosphate, which also caused maximum activation of pyruvate, orthophosphate dikinase. Phosphorylation of the 100kDa polypeptide did not coincide with deactivation of pyruvate, orthophosphate dikinase, but maximum phosphorylation occurred under conditions that promoted maximum activity of the enzyme, at which time one phosphate group was associated with each enzyme molecule. Protein phosphorylation did not appear to arise from the reaction mechanism of the enzyme.

SUBMITTER: Foyer C

PROVIDER: S-EPMC1144166 | biostudies-other | 1984 Aug

REPOSITORIES: biostudies-other

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Project description:Maize (Zea mays L.) is an important source of carbohydrates and protein in the diet in sub-Saharan Africa. The objectives of this study were to (i) estimate general (GCA) and specific combining abilities (SCA) of 13 new quality protein maize (QPM) lines in a diallel under stress and non-stress conditions, (ii) compare observed and predicted performance of QPM hybrids, (iii) characterize genetic diversity among the 13 QPM lines using single nucleotide polymorphism (SNP) markers and assess the relationship between genetic distance and hybrid performance, and (iv) assess diversity and population structure in 116 new QPM inbred lines as compared to eight older tropical QPM lines and 15 non-QPM lines. The GCA and SCA effects were significant for most traits under optimal conditions, indicating that both additive and non-additive genetic effects were important for inheritance of the traits. Additive genetic effects appeared to govern inheritance of most traits under optimal conditions and across environments. Non-additive genetic effects were more important for inheritance of grain yield but additive effects controlled most agronomic traits under drought stress conditions. Inbred lines CKL08056, CKL07292, and CKL07001 had desirable GCA effects for grain yield across drought stress and non-stress conditions. Prediction efficiency for grain yield was highest under optimal conditions. The classification of 139 inbred lines with 95 SNPs generated six clusters, four of which contained 10 or fewer lines, and 16 lines of mixed co-ancestry. There was good agreement between Neighbor Joining dendrogram and Structure classification. The QPM lines used in the diallel were nearly uniformly spread throughout the dendrogram. There was no relationship between genetic distance and grain yield in either the optimal or stressed environments in this study. The genetic diversity in mid-altitude maize germplasm is ample, and the addition of the QPM germplasm did not increase it measurably.

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Phosphorylation of a stromal enzyme protein in maize (Zea mays) mesophyll chloroplasts.

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