Active enzyme sedimentation of pig heart fumarase.

Active band sedimentation studies of pig heart fumarase indicate that the enzyme is predominantly tetrameric at enzyme concentrations between 0.0125 and 0.25 mg/ml and at a fumarate concentration of 2.5 mM. At enzyme concentrations of 0.25--1.0 mg/ml and fumarate concentrations known to activate and inhibit the enzyme, the sedimentation band of fumarase becomes disperse and indicates the presence of polymers greater than tetramers.

Detailed restriction enzyme map of crown gall-suppressive IncW plasmid pSa, showing ends of deletion causing chloramphenicol sensitivity.

Detailed restriction enzyme maps of the antibiotic resistance plasmid pSa and of a chloramphenicol-sensitive spontaneous deletion mutant of pSa were constructed. The smaller plasmid contained one set of three restriction enzyme sites that appeared at both ends of the deleted region in the intact plasmid. The frequency of loss of chloramphenicol resistance was 1% after eight logs of growth and was dependent on the recA gene function of Escherichia coli. A previously published map lacks an 11-kilobase-pair SstII fragment present on this map.

Are the in vitro effects of disalicylidenepropanediamine mediated by salicylaldehyde?

Disalicylidenepropanediamine (DSPD) has been used widely to investigate photosynthesis using in vitro systems. Evidence is presented which shows that DSPD hydrolyzes rapidly in aqueous solution at pH 7.8 to salicylaldehyde and 1,3-diaminopropane. The effects attributed to DSPD could have been caused by salicylaldehyde.

Assay for Helminthosporium maydis Toxin-binding Activity in Plants.

A relatively rapid and sensitive assay is described for assessing the binding of Helminthosporium maydis Race T(14) C-toxins I and II to plant components. The technique is a modification of the one of Haddad and Birge (J. Biol. Chem. 250: 299-303, 1975), and utilizes dextran-coated charcoal as an adsorbent for the unreacted toxin and employs a Millipore filter to isolate the protein-toxin complex.Extracts from susceptible corn line W64A Tms possess a protein primarily localized in the cytosol which is relatively heat-insensitive, ficin- and papain-sensitive, and binds toxins I and II at half-saturation in the order of 0.1 mm. The toxin-binding activities of the extracts of various corn lines and other species are not correlated to resistance or susceptibility to H. maydis Race T, nor to sensitivity to the toxins. These findings are discussed relative to the function of the binding protein and cellular sensitivity to the toxins.

The relationship between carbon dioxide fixation and chlorophyll a fluorescence during induction of photosynthesis in maize leaves at different temperatures and carbon dioxide concentrations.

The rate of CO2 fixation (Fc) and 680 nm chlorophyll fluorescence emission (F680) were measured simultaneously during induction of photosynthesis in Zea mays L. leaves under varying experimental conditions in order to assess the validity of fluorescence as an indicator of in vivo photosynthetic carbon assimilation. Z. mays leaves showed typical 'Kautsky' fluorescence induction curves consisting of a fast rise in emission (O to P) followed by a slow quenching via a major transient (S-M) to a steady-state (T). After an initial lag, net CO2 assimilation commenced at a point corresponding to the onset of the S-M transient on the F680 induction curve. Subsequently, Fc and F680 always arrived at a steady-state simultaneously. Decreasing the dark-adaption period increased the rate of induction of both parameters. Alteration of leaf temperature produced anti-parallel changes in induction characteristics of Fc and F680. Reducing the CO2 level to below that required for saturation of photosynthesis also produced anti-parallel changes during induction, however, at CO2 concentrations tenfold greater than the atmospheric level the rate of F680 quenching from P to T was appreciably reduced without a similar change in the induction of Fc. Removal of CO2 at steady-state produced only a small increase in F680 and a correspondingly small decrease in F680 occurred when CO2 was re-introduced. The complex relationship between chlorophyll fluorescence and carbon assimilation in vivo is discussed and the applicability of fluorescence as an indicator of carbon assimilation is considered.

The role of carbon dioxide and oxygen in determining chlorophyll fluorescence quenching during leaf development.

Chlorophyll fluorescence emission at 680 nm (F680) and the rate of CO2 fixation were measured simultaneously in sections along the length of wheat and maize leaves. These leaves possess a basal meristem and show a gradation in development towards the leaf tip. The redox state of the primary electron acceptor, Q, of photosystem II was estimated using a non-invasive method. Distal mature leaf sections displayed typical F680 induction curves which were generally anti-parallel with CO2 fixation and during which Q became gradually oxidised. In leaf-base sections net assimilation of CO2 was not detectable, F680 quenched slowly and monotonously without displaying any of the oscillations typical of mature tissue and Q remained relatively reduced. Sections cut from mid-regions of the leaf showed intermediate characteristics. There were no major differences between the wheat and maize leaf in the parameters measured. The results support the hypothesis that generation of the transthylakoid proton gradient and associated ATP production is not a major limitation to photosynthesis during leaf development in either C3 or C4 plants. Removal of CO2 from the mature leaf sections caused little change in steady-state F680 and produced about 50% reduction of Q. When O2 was then removed, F680 rose sharply and Q became almost totally reduced. In immature tissue unable to assimilate CO2, removal of O2 alone caused a similar large rise in F680 and reduction of Q whilst removal of CO2 had negligible effects on F680 and the redox state of Q. It is concluded that in leaf tissue unable to assimilate CO2, either because CO2 is absent or the tissue is immature, O2 acts as an electron acceptor and maintains Q in a partially oxidised state. The important implication that O2 may have a role in the prevention of photoinhibition of the photochemical apparatus in the developing leaf is discussed.

Studies on the limitations to photosynthesis in leaves of the atrazine-resistant mutant ofSenecio vulgaris L.

In leaves of an atrazine-resistant mutant ofSenecio vulgaris the quantum efficiency of CO2 assimilation was reduced by 21% compared to the atrazine-susceptible wild type, and at a light level twice that required to saturate photosynthesis in the wild type the CO2 fixation rate in the mutant was decreased by 15%. In leaves at steady-state photosynthesis there was a measurable increase in the reduction state of the photosystem II (PSII) primary quinone acceptor,Q A. Although this would lead to a decreased rate of PSII electron transport and may thus explain the decrease in quantum efficiency, this cannot account for the fall in the maximum rate of CO2 fixation. The atrazine-resistant mutant showed an appreciably longer photosynthetic induction time which indicates an effect on carbon metabolism; however, the response of CO2-fixation rate to intercellular CO2 concentration revealed no differences in carboxylation efficiency. There were also no differences in the ability to perform a State 1-State 2 transition between the atrazine-resistant and susceptible biotypes and no difference in the profiles of phosphorylated thylakoid polypeptides. It is concluded that the alteration of the redox equilibrium between PSII quinone electron acceptors in the atrazine-resistant biotype limits appreciably the photosynthetic efficiency in non-saturating light. Additionally, there is a further, as yet unidentified, limitation which decreases photosynthesis in the resistant mutant under light-saturating conditions.