Cloning of cDNA for pyruvate, Pi dikinase from maize leaves

mentioning

confidence: 57%

Photocontrol of Sorghum Leaf Phosphoenolpyruvate Carboxylase

Thomas

Crétin²,

Kéryer³

et al. 1987

“…Either maize seed or wheat leaf PPDK is inactivated at a rate similar to that of maize leaf PPDK when placed in an inactivating mixture containing the regulatory protein which catalyzes light-mediated activation and inactivation ofPPDK activity (10). In both wheat and maize, the seed PPDK subunit is synthesized on cytoplasmic ribosomes as a 94 kD polypeptide (3), while in maize leaves (3,16) and in wheat leaves (3), it is synthesized as a 110 kD polypeptide which includes a 16 kD 'leader' that permits the polypeptide to be taken up by chloroplasts and processed to give the mature 94 kD polypeptide (4).…”

mentioning

confidence: 99%

Appearance and Accumulation of C₄ Carbon Pathway Enzymes in Developing Wheat Leaves

Aoyagi¹,

Bassham²

1986

Soluble protein has been extracted from sections of wheat leaves, from base to tip, and the content of several key enzymes of photosynthetic carbon assimilation in each section has been determined by the protein blot method. In the first leaf, ribulose 1,5-bisphosphate carboxylase (RuBPC) (EC 4.1.1.39) in the basal 0 to 1 centimeter section is about 12% the level in the tip section, whereas phosphoenolpyruvate carboxylase (EC 4.1.1.31) is present in small amounts in the basal section and does not change much in the tip. Pyruvate orthophosphate dikinase (PPDK) (EC 2.7.9.1) first appears in the 4 to 6 centimeter section and increases gradually with development to 10-fold in the tip. Malic enzyme, NADP-dependent (EC 1.3.137) also appears in the 4 to 6 centimeter section but remains low to the tip.Fixation of '4C02 by wheat leaf base sections resulted in 42% of total incorporation into malate and aspartate, indicating j ¶-carboxylation, whereas in the tip section these labeled compounds were only 8% of the total. Although the amount of PPDK in wheat leaves is only 1 to 3% of that in maize leaves, this C3 PPDK may have a limited role in photosynthesis leading to formation of C4 compounds. The possibility of a further role, similar to that in C4 plants, but for intracellular carbon transport in wheat leaves is discussed. The presence of malic dehydrogenase, NADP- (23).The enzyme activities required for C4 metabolism are generally present in C3 species, although the amount may be much less and the physical properties of the enzymes may be different.

“…The 1 10 kD polypeptide synthesized with maize leaf poly(A)RNA has been assumed to have a 16 kD 'leader' which facilitates entry into the chloroplasts, where it would be processed to give 94 kD WC GC SO.5 S1 S2. 5 Stages of differentiation PPDK polypeptide (12). This 110 kD polypeptide can be taken up and processed by isolated spinach chloroplasts (3).…”

mentioning

confidence: 99%

“…Regulation of the synthesis of PPDK in callus differs from regulation in leaftissue. In leaves, the synthesis of PPDK mRNA (12) and of PPDK polypeptides (14) are regulated quantitatively by light illumination whereas the level ofPPDK in callus seems to be independent of light. Moreover, although the concentration of PPDK in the callus tissue is much less than in leaves, the apparent Km (pyruvate) is only about one-third as large (Table I).…”

mentioning

confidence: 99%

Appearance and Accumulation of C₄ Carbon Pathway Enzymes in Developing Maize Leaves and Differentiating Maize A188 Callus

Aoyagi

Bassham²

1986

ABSTRACIRegenerating maize A188 tissue cultures were examined for the presence of enzymes involved in C4 photosynthesis, for cell morphology, and for '4C labeling kinetics to study the implementation of this pathway during plant development. For comparison, sections of maize seedling leaves were examined. Protein blot analysis using antibodies to leaf enzymes showed a different profile of these enzymes during the early stages of shoot regeneration from callus from the closely-coordinated profile observed in seedling leaves. Pyruvate orthophosphate dikinase (PPDK) (EC 2.7.9.1) and phosphoenolpyruvate carboxylase (PEPC) (EC 4.1.1.31) were found in nonchlorophyllous callus while ribulose 1,5-bisphosphate carboxylase (RuBPC, EC 4.1.139) and malic enzyme, NADP-specific (ME-NADP) (EC 1.3.1.37) were not detectable until later.Enzyme activity assays showed the presence of ME-NADP as well as PEPC and PPDK in nonchlorophyllous callus. However, the activities of ME-NADP and PEPC had properties similar to those of the enzymes from C3 leaves and from etiolated C4 leaf tissues, but differing from the corresponding enzymes in the mature leaf.Immunoprecipitation of in vitro translation products of poly(A)RNA extracted from embryoid-forming callus showed both the 110 kilodalton precursor to chloroplast PPDK and the 94 kilodalton polypeptide. Therefore, the chloroplast tye of PPDK mRNA is present prior to the appearance of leaf morphology.Analysis of the labeled products of 4C02 fixation by nonchlorophylIous calli indicated ,-carboxylation to give acids of the tricarboxylic acid cycle, but no incorporation into phosphoglycerate. With greening of the callus, some incorporation into phosphoglycerate and sugar phosphates occurred, and this increased in shoots as they developed, although with older shoots the increase in B-carboxylation products was even greater. Analysis of enzyme levels in young leaf sections by protein blot and of '4C-labeling patterms in the present study are in general agreement with enzyme activity determinations of previous studies, providing additional information about PPDK levels, and supporting the model proposed for developing young leaves.These results suggest that maize leaves begin to express C4 enzymes during ontogeny through several stages from greening and cell differentiation as seen in the callus and then shoot formation, and finally acquire capacity for full C4 photosynthesis during leaf development concomitant with the development of Kranz anatomy and accumulation of large amounts of enzymes involved in carbon metabolism.