Pyruvate Kinase Activity of Wheat Plants Grown under Potassium Deficient Conditions

ABSTRACrWhen seven crop species were grown under identical environmental conditions, decreased sink:source ratio led to a decreased photosynthetic rate within 1 to 3 days in Cucumis sativus L., Gossypium hirsutum L., and Rapwaaus sativus L, but not in Capsicum annuum L., Solanum melongena L., Phaseolus vulgaris L., or Ricinus communis L. The decrease was not associated with stomatal closure. In cotton and cucumber, sink removal led to an increase in starch and sugar content, in glucose 6-phosphate and fructose 6-phosphate pools, and in the proportion of '4C detected in sugar phosphates and UDPglucose following '4CO2 supply.When mannose was supplied to leaf discs to sequester cytoplasmic inoranic phosphate, promotion of starch synthesis, and inhibition of C02 fixation, were observed in control discs, but not in discs from treated plants. Phosphate (Ricinus communis L.) were grown in 2-L cylindrical plastic containers filled with vermiculite. Plants were thinned to one plant per pot shortly after emergence and irrigated twice a week with deionized water and once a week with half-strength Hoagland solution. Excess water and solution were drained through the bottom ofthe container. All species were grown in a chamber maintained at 25C, at a quantum flux density of 450 ,umol m-2 s-' (400-700 nm) and a 13 h/l l h light/dark photoperiod.Experiments with cotton were conducted about 10 d after the appearance of the first flower (11-12 weeks after emergence). Bean plants were used at the stage of the fully expanded first trifoliate leaf (22-25 d after emergence).One experiment with cotton ( Fig. 1) was conducted on field grown plants, Cotton was planted on May 25 in rows 1 m apart and thinned to 10 plants/m2 after emergence. Following light sprinkling to ensure emergence, a trickle irrigation system was installed. Laterals were located next to plant rows and emitters were 40 cm apart. The plants were irrigated once a day and the quantity of water supplied was based on evaporation from a Class A pan. Nutrients containing urea, H3PO4 and KCI at N:P:K ratio of 4:1:2 were predissolved in the irrigation water at a concentration of 80 g x m-3. Plants were used for this experiment on August 12, when there were about 10 bolls or flowers per plant.The sink removed in the case of the growth-chamber grown cotton was the developing first boll, and measurements were conducted on the mature leaf adjacent to this boll peduncle. In the field-grown cotton, various numbers of boils or flowers were removed, and measurements were conducted on four leaves of different ages along the plant axis. The extracts of these were combined. In the case ofbean plants, the sink removed included the young developing second trifoliate leaf and developing buds. The first trifoliate leaf was considered as the source leaf.CO2 fixation rate was measured in 1.5 cm2 circular areas of attached leaves according to a procedure described earlier (12).

Section: Resultsmentioning

confidence: 90%

Effect of Altered Sink: Source Ratio on Photosynthetic Metabolism of Source Leaves

Plaut¹,

Mayoral²,

Reinhold³

1987

“…Zea mays L. cv. Kou 6 was germinated and grown for 6 or 7 days in darkness at 25 C in a sand bed supplemented with the standard medium described previously (19).…”

Section: Methodsmentioning

confidence: 99%

“…Zea mays L. cv. Kou 6 was germinated and grown for 6 or 7 days in darkness at 25 C in a sand bed supplemented with the standard medium described previously (19).Greening Experiments. Greening experiments were conducted at 25 to 27 C. The etiolated seedlings or the detached leaves were irradiated with white lamps (300 w National RF and 150 w Toki RF).…”

mentioning

confidence: 99%

Light Induction of Phosphoenolpyruvate Carboxylase in Etiolated Maize Leaf Tissue

Hayakawa

Matsunaga²,

Sugiyama³

1981

Self Cite

An antibody for phosphoenolpyruvate carboxylase was used to isolate and to quantitate the enzyme from greening maize (cv. KOU 6) leaves. The increase in enzyme activity during greening was due to de novo synthesis, which was paralleled by increases in enzyme protein and incorporation of leucine. The light-induced activity was due to one specific isoenzyme. The action spectrum for enzyme synthesis had red and blue peaks.Phosphoenolpyruvate carboxylase [orthophosphate:oxaloacetate carboxylase (phosphorylating), EC 4.1.1.311 activity increases during greening of C4 plants (4,6,10,20). This increase of activity in maize can be prevented by inhibitors of protein synthesis (6,10). This effect may be indirect e.g. due to modification of the enzyme. It has been suggested by the use of density labeling techniques that, shortly after the initiation of greening, the properties of the carboxylase from sugar cane are subjected to modification in the absence of protein synthesis (4). Whether the carboxylase is synthesized or modified during greening is important in cellular control of the enzyme and development of the C4 pathway.We report here that the increase of PEP4 carboxylase activity during the greening of maize leaf tissue is due to de novo synthesis. We also report the effects of light quality on the induction of activity and of illumination on PEP carboxylase isoenzymes. MATERIALS AND METHODSPlant Materials. Zea mays L. cv. Kou 6 was germinated and grown for 6 or 7 days in darkness at 25 C in a sand bed supplemented with the standard medium described previously (19).Greening Experiments. Greening experiments were conducted at 25 to 27 C. The etiolated seedlings or the detached leaves were irradiated with white lamps (300 w National RF and 150 w Toki RF). To study the wavelength effects on light induction of the enzyme, the seedlings were irradiated first by a white fluorescence lamp (1.0 ,uw For larger scale preparations, extraction of PEP carboxylase was carried out using a chilled Omni Mixer. Ten or 16 g primary leaves were blended four times for 30 s each time in 4 volumes 0.2 M Tris-HCl (pH 7.5) containing 10 mm 2-mercaptoethanol, 0.7% sodium ascorbate, and 1.5 g insoluble PVP. The homogenate was filtered through two layers of muslin and centrifuged at 35,000g for 15 min. The 30 to 60% saturated ammonium sulfate fraction was taken, dissolved in a few ml 50 mm Tris-HCl (pH 7.0) containing 100 ,LM EDTA and 10 mm 2-mercaptoethanol, and desalted by passing through a column of Sephadex G-25 equilibrated with the same buffer. All procedures were conducted at 4 C.Preparation of Antibody and Its Purification. Two rabbits (New Zealand White) were immunized over 1 month by injecting PEP carboxylase from mature green maize leaves and purified according to the method reported previously (22). Injections were made subcutaneously using incomplete adjuvant of Freund. During the course of immunization, a total of 3.5 mg PEP carboxylase was administered to each rabbit. IgG was purified by ammonium sulfate fractionation ...

“…The activation of the enzyme by mono-and divalent cations in relation to plant nutrition has been studied (14,(26)(27)(28)39), but the work to date (26,28,31) indicates that the higher plant enzyme does not show sigmoid kinetics towards PEP and is not activated by FDP. However, since neither of these properties is common to all pyruvate kinases, it was decided to re-examine the higher plant enzyme.…”

Section: Introductionmentioning

confidence: 99%

Pyruvate Kinase, a Possible Regulatory Enzyme in Higher Plants

Duggleby¹,

Dennis²

1973

A number of plant species were examined for the presence of pyruvate kinase (pyruvate-ATP phosphotransferase, EC 2.7.1.40), and of a phosphatase activity which hydrolyzes phosphoenolpyruvate. Of those examined, only cotton (Gossypium sp. L.) seeds were found to be sufficiently free of the phosphatase to permit a kinetic study of pyruvate kinase. (2,7,18,19,34,36) and organisms (10,17,21,32,36,38,41) appears to be a regulatory enzyme. It usually shows a sigmoid saturation curve towards PEP3 and is activated by FDP in eucaryotes and by AMP in procaryotes. However, some workers have described pyruvate kinases which do not fit these generalizations (3,6,30,42).The kinetic properties of pyruvate kinase from higher plants have not been examined in detail. The activation of the enzyme by mono-and divalent cations in relation to plant nutrition has been studied (14,(26)(27)(28)39), but the work to date (26,28,31) indicates that the higher plant enzyme does not show sigmoid kinetics towards PEP and is not activated by FDP. However, since neither of these properties is common to all pyruvate kinases, it was decided to re-examine the higher plant enzyme.