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L Sodek

Publications and source records attributed to L Sodek.

9 recordsLinked to original sources
PubMed2005

Aerenchyma formation and recovery from hypoxia of the flooded root system of nodulated soybean.

BACKGROUND AND AIMS: Flooding results in hypoxia of the root system to which N2 fixation of nodulated roots can be especially sensitive. Morphological adaptions, such as aerenchyma formation, can facilitate the diffusion of oxygen to the hypoxic tissues. Using soybean, the aim of the study was to characterize the morphological response of the nodulated root system to flooding and obtain evidence for the recovery of N metabolism. METHODS: Sections from submerged tissues were observed by light microscopy, while sap bleeding from the xylem was analysed for nitrogenous components. KEY RESULTS: Flooding resulted in the rapid formation of adventitious roots and aerenchyma between the stem (immediately above the water line), roots and nodules. In the submerged stem, taproot, lateral roots and adventitious roots, lysigenous aerenchyma arose initially in the cortex and was gradually substituted by secondary aerenchyma arising from cells derived from the pericycle. Nodules developed aerenchyma from cells originating in the phellogen but nodules situated at depths greater than 7-8 cm showed little or no aerenchyma formation. As a result of aerenchyma formation, porosity of the taproot increased substantially between the 4th and 7th days of flooding, coinciding with the recovery of certain nitrogenous products of N metabolism of roots and nodules transported in the xylem. Thus, on the first day of flooding there was a sharp decline in xylem ureides and glutamine (products of N2 fixation), together with a sharp rise in alanine (product of anaerobic metabolism). Between days 7 and 10, recovery of ureides and glutamine to near initial levels was recorded while recovery of alanine was partial. CONCLUSIONS: N metabolism of the nodulated soybean root system can recover at least partially during a prolonged period of flooding, a process associated with aerenchyma formation.

Nitrogen Fixation↗
PubMed2000

Enzymatic characterization of a novel phospholipase A2 from Crotalus durissus cascavella rattlesnake (Maracambóia) venom.

The PLA2 and crotapotin subunits of crotoxin from Crotalus durissus cascavella venom were purified by a combination of HPLC molecular exclusion (Protein Pack 300SW column) and reverse-phase HPLC (RP-HPLC). Tricine SDS-PAGE showed that the PLA2 and crotapotins migrated as single bands with estimated molecular masses of 15 and 9 kDa, respectively. The amino acid composition of the PLA2 showed the presence of 14 half-cysteines and a high content of basic residues (Lys, Arg, His), whereas the crotapotins were rich in hydrophobic, negatively charged residues and half-cysteines. The PLA2 showed allosteric behavior, with maximal activity at pH 8.3 and 35-40 degrees C. The C. d. cascavella PLA2 required Ca2+ for activity, but was inhibited by Cu2+ and Zn2+ and by Cu2+ and Mg2+ in the presence and absence of Ca2+, respectively. Crotapotin (F3) and heparin inhibited the catalytic activity of the PLA2 by acting as allosteric inhibitors.

Allosteric Regulation↗
PubMed1997

The enzymology of lysine catabolism in rice seeds--isolation, characterization, and regulatory properties of a lysine 2-oxoglutarate reductase/saccharopine dehydrogenase bifunctional polypeptide.

In plant, the catabolism of lysine has only been studied in some detail in maize. The enzymes lysine 2-oxoglutarate reductase (also known as lysine alpha-ketoglutarate reductase; LOR) and saccharopine dehydrogenase (SDH), which convert lysine into saccharopine, and saccharopine into glutamic acid and 2-aminoadipate 6-semialdehyde, respectively, were isolated from immature rice seeds and partially purified through a three-step purification procedure involving ammonium sulphate precipitation, and anion-exchange and gel-filtration chromatographies, leading to a final yield of 30% for LOR and 24% for SDH. The molecular masses estimated by gel-filtration chromatography on a Sephacryl S200 column and by native non-denaturing PAGE using Ferguson plots were 203 kDa for both enzymes by gel-filtration and 202 kDa for both enzymes by native non-denaturing PAGE. A second band of LOR and SDH activities on native gels was observed for both enzymes with an estimated molecular mass of 396 kDa, which indicated a multimeric structure. Kinetic studies were consistent with an ordered sequence mechanism for LOR, where 2-oxoglutarate is the first substrate and saccharopine is the last product. The results observed for the LOR/SDH activity ratios during purification, the copurification in all three steps, the molecular masses, the relative mobilities on native non-denaturing gels and the pI estimated for LOR and SDH suggest the existence of a bifunctional polypeptide containing LOR and SDH activities.

Kinetics↗
PubMed1982

Lysine-ketoglutarate reductase activity in developing maize endosperm.

Lysine-ketoglutarate reductase activity was detected and characterized in the developing endosperm of maize (Zea mays L.). The enzyme showed specificity for its substrates: lysine, alpha-ketoglutarate, and NADPH. Formation of the reaction product saccharopine was demonstrated. The pH optimum of the enzyme was close to 7, and the K(m) for lysine and alpha-ketoglutarate were 5.2 and 1.8 millimolar, respectively.

Journal Article↗
PubMed1980

Distribution and Properties of a Potassium-dependent Asparaginase Isolated from Developing Seeds of Pisum sativum and Other Plants.

Asparaginase (EC 3.5.1.1) was isolated from the developing seed of Pisum sativum. The enzyme is dependent upon the presence of K(+) for activity, although Na(+) and Rb(+) may substitute to a lesser extent. Maximum activity was obtained at K(+) concentrations above 20 millimolar. Potassium ions protected the enzyme against heat denaturation. The enzyme has a molecular weight of 68,300.Asparaginase activity developed initially in the testa, with maximum activity (3.6 micromoles per hour per seed) being present 13 days after flowering. Maximum activity (1.2 micromoles per hour per seed) did not develop in the cotyledon until 21 days after flowering. Glutamine synthetase and glutamate dehydrogenase were also present in the testae and cotyledons but maximum activity developed later than that of asparaginase.Potassium-dependent asparaginase activity was also detected in the developing seeds of Vicia faba, Phaseolus multiflorus, Zea mays, Hordeum vulgare, and two Lupinus varieties. No stimulation of activity was detected with the enzyme isolated from Lupinus polyphyllus, which has previously been shown to contain a K(+)-independent enzyme.

Journal Article↗
PubMed1977

Glutamate synthase: a possible role in nitrogen metabolism of the developing maize endosperm.

Glutamate synthase activity was demonstrated in the developing endosperm of maize (Zea mays L.). The enzyme shows specificity for glutamine and alpha-ketoglutarate as amino donor and acceptor, respectively. Both NADH and NADPH function as electron donors although lower activities were often, but not always, obtained with NADPH. The apparent K(m) values for glutamine, alpha-ketoglutarate, and NADH were 1.35 mm, 0.57 mm, and 7 mum, respectively.The pattern of activity during endosperm development revealed a well defined peak coinciding with the period of most active N accumulation. Activity in general was related to the rates of accumulation throughout development. Maximum glutamate synthase activity was the order of 56 nmoles of glutamate formed per minute per endosperm compared with a rate of N accumulation of 9.5 nmoles per minute.It is suggested that glutamate synthase plays a key role in the N nutrition of the maize endosperm providing a means whereby N transported in the form of glutamine is made available for the synthesis of other seed protein amino acids via transaminase reactions. Transaminase activity involving glutamate, the product of the glutamate synthase reaction, was also demonstrated.

Journal Article↗