Plant Science Letters最新文献

Methyl viologen-dependent nitrite reductase (EC 1.7.7.1) (NiR) was purified about 1780-fold with a yield of 3.5% from etiolated bean shoots with a procedure involving ammonium sulfate precipitation, DEAE-cellulose chromatography, Butyl-Toyopearl chromatography, ferredoxin-Sepharose affinity chromatography and Ultrogel AcA44 gel filtration. The purified enzyme was apparently homogeneous as shown by polyacrylamide disc gel electrophoresis with a specific activity of 53.4 units/mg protein. The molecular weight of the enzyme was estimated to be 100 kilodaltons by gel filtration. Subunit analysis by sodium dodecyl sulfate polyacrylamide gel electrophoresis yielded two protein bands with a large subunit molecular weight of 64 kilodaltons and a small subunit molecular weight of 35 kilodaltons. The purified enzyme could be stored at −20°C for several weeks without any loss of activity in the presence of 10% glycerol and 10 mM ß-mercaptoethanol.

The polypeptide composition of chloroplast envelopes from wild-type Arabidopsis was compared with that of a mutant (CS1562) deficient in chloroplast dicarboxylate transport activity. An abundant 42 kilodalton (kd) protein in the envelopes from wild-type is low or absent in envelopes from the mutant. It is suggested that this polypeptide may be a component of the dicarboxylate transporter.

We demonstrate continued nitrogenase activity in isolated bacteroids of Rhizobium strain ANU289 from nodules of siratro (Macroptilium atropurpureum) and the non-legume Parasponia rigida for periods up to 240 min with maximum activities maintained at 52 nmol ethylene produced h⁻¹ mg⁻¹ protein. Both legume and non-legume bacteroids showed a broader oxygen tolerance in the presence of the nodule supernatant. Isolated Parasponia-derived bacteroids exhibited an optimum nitrogenase activity at about 0.1% O₂ in the gas phase, while siratro bacteroids had a slightly higher O₂ optimum. These findings illustrate that (i) Rhizobium bacteroids isolated from a non-legume host are highly oxygen-sensitive for their nitrogenase activity, (ii) the Parasponia nodule supernatant increases the oxygen tolerance of the bacteroids.

Cells of the green alga Golenkinia, pre-cultured so that the contribution of any nitrogen source other than delta-aminolevulinic acid (ALA) to endogenous nitrogen reserves is minimal or absent, are capable of sustained growth on ALA as the sole source of nitrogen in either light or dark. Yield is proportional to ALA concentration up to 10 mM; higher concentrations are increasingly inhibitory. This optimal concentration supports cell numbers, growth rates and chlorophyll levels equal to those found using the same concentration of nitrate. These findings support the suggestion that ALA is not committed to porphyrin synthesis and indicate that conclusions regarding regulation of chlorophyll synthesis based on long-term addition of ALA to systems sensitive to carbon/nitrogen levels in the medium be reconsidered.

The effect of far-red light on the appearance of the radish ribulose 1,5-bisphosphate carboxylase, its subunits and the mRNA for the small subunit has been studied. The immunological analysis of the accumulation of holoenzyme and small subunit showed that there was no pool of free small subunit either in the etiolated seedlings or in the far-red light illuminated seedlings. The precursor to the small subunit has been identified by immunoprecipitation of the in vitro translation products directed by poly(A)-containing RNA of radish cotyledons. The irradiation of radish cotyledons with far-red light led to the apparent increase of the level of the translatable mRNA for the small subunit.

A laboratory study was carried out using field grown peach (Prunus persica) and prune (P. domestica) flowers. The object was to find out why prune flowers are more freeze tolerant than peach flowers. After the flowers are fully open, it was found that the ovaries may still supercool, even with ice crystals present in the flower stem. The mechanics involved were explored with a computer model of the simultaneous heat, water and solute flow in the flower and stem tissue during freezing. Water flow toward growing ice crystals may cause a discontinuity in the liquid phase between the flower stem and the ovary, creating a barrier to nucleation. It was concluded that the prune flowers survive lower temperatures than the peach because the water in their ovaries is more apt to supercool, particularly when the dew point of the air is not reached.

A γ gliadin cDNA clone has been sequenced. The clone encodes 251 amino acid residues beginning with a 19 residue signal peptide. The putative processed amino terminus is characteristic of a γ gliadin. Fourteen imperfect repeats of a heptapeptide occur near the amino terminus. Data from hybrid selected translation suggest that the cDNA contains $\text{sol3}\text{4}$ of the mRNA coding region. These results provide the first description of the amino terminus of a γ gliadin precursor.

Wheat embryos were allowed to germinate under the imposition of a stress factor in the nature of a suboptimal germination temperature. The protein synthetic activities of cell-free systems prepared from embryos isolated from seed lots of wheat having high viability but differing in vigour were related to the vigour of the seed lot. Reduced messenger RNA levels in low vigour embryos could account, in part, for the reduced rate of protein synthesis observed in vivo during germination at a suboptimal temperature. In addition, a lesion at the level of ribosomal activity also appeared in low vigour embryos during the early germination period, but this lesion, which resulted in a reduction in the rate of protein synthesis in vitro, was not caused by any gross breakdown of ribosomal RNA. A second lesion affecting the aminoacyl-tRNA synthetase activity in low vigour embryos was also detected, but no differences in the activities of elongation factors 1 and 2 in high and low vigour embryos could be detected under these suboptimal germination conditions.

Plasma membrane ATPase partially purified from radish seedlings (Raphanus sativum L.) (2.4–3.5 μmol P_i min⁻¹ mg⁻¹ protein) has been reconstituted in proteoliposomes by the cholate-dialysis technique. Proteoliposomes are able to acidify their internal volume in the presence of Mg:ATP. Mg:ATP-dependent proton pumping is prevented by N,N′-dicyclohexylcarbodiimide (DCCD) and by vanadate at the same concentrations which are effective on the phosphohydrolyzing activity of the plasma membrane ATPase.

We hybridized a 887 bp chloroplast DNA fragment from Chlamydomonas carrying part of the large subunit (LSU) gene of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) to DNA extracted from various Euglena strains. The hybridization patterns observed with several restriction enzyme analyses of Euglena chloroplast DNA are in agreement with the known localization of the Euglena LSU gene (Stiegler et al., Nucleic Acids Res., 10 (1982) 3427). We obtained hybrids with DNA from four wild-type strains and six mutants in which we had characterized RuBisCO. No hybrid was observed with DNA from mutants Y₃BUD, W₃BUL and W₃₄ZUD in which no RuBisCO was detected, suggesting that the LSU gene is either strongly modified or absent in these mutants.