Photosynthetic action spectra and adaptation to spectral light distribution in a benthic cyanobacterial mat

We studied adaptation to spectral light distribution in undisturbed benthic communities of cyanobacterial mats growing in hypersaline ponds at Guerrero Negro, Baja California, Mexico. Microscale measurements of oxygen photosynthesis and action spectra were performed with microelectrodes; spectral radiance was measured with fiber-optic microprobes. The spatial resolution of all measurements was 0.1 mm, and the spectral resolution was 10 to 15 nm. Light attenuation spectra showed absorption predominantly by chlorophyll a (Chl a) (430 and 670 nm), phycocyanin (620 nm), and carotenoids (440 to 500 nm). Blue light (450 nm) was attenuated 10-fold more strongly than red light (600 nm). The action spectra of the surface film of diatoms accordingly showed activity over the whole spectrum, with maxima for Chl a and carotenoids. The underlying dense Microcoleus population showed almost exclusively activity dependent upon light harvesting by phycobilins at 550 to 660 nm. Maximum activity was at 580 and 650 nm, indicating absorption by phycoerythrin and phycocyanin as well as by allophycocyanin. Very little Chl a-dependent activity could be detected in the cyanobacterial action spectrum, even with additional 600-nm light to excite photosystem II. The depth distribution of photosynthesis showed detectable activity down to a depth of 0.8 to 2.5 mm, where the downwelling radiant flux at 600 nm was reduced to 0.2 to 0.6% of the surface flux.     

Water Balance in Cucumis Plants, Measured by Nuclear Magnetic Resonance, I

In this paper we demonstrate the study of plant water balanceby the non-invasive measurement of tissue water content andwater flow using proton nuclear magnetic resonance (NMR). Sapvelocity and flux were measured independently in the presenceof an excess of stationary tissue water. The instrumentationdescribed allows automated and unattended measurement of flow-and water content-variables in a well-defined region of theplant over periods of several days, with a time resolution betweensuccessive measurements of c. 5 s. Using this apparatus theeffect of changes in light intensity (day/night rhythm) andrelative humidity on stem tissue water content as well as onthe velocity and flux of xylem sap in the stem were investigatedin a cucumber plant. The results are in agreement with predictionsfrom a simple model for plant water balance, which is basedon water potential, flow rate and resistance to flow. As longas only transpiration is varied, flow rate and water content(or potential) are affected in opposite ways as demonstratedin this paper. In contrast, the model predicts that changesin uptake (resulting from changes in, for example, root resistance)will induce changes in water content and flow in the same direction.An experimental verification of this prediction is given ina subsequent paper, where, in addition, the NMR results arecompared to those obtained with a dendrometer. Key words: Water balance model, Cucumis sativus L., flow, water content, NMR, water balance measurement     

Carbon isotopic fractionation in heterotrophic microbial metabolism.

Differences in the natural-abundance carbon stable isotopic compositions between products from aerobic cultures of Escherichia coli K-12 were measured. Respired CO2 was 3.4% depleted in 13C relative to the glucose used as the carbon source, whereas the acetate was 12.3% enriched in 13C. The acetate 13C enrichment was solely in the carboxyl group. Even though the total cellular carbon was only 0.6% depleted in 13C, intracellular components exhibited a significant isotopic heterogeneity. The protein and lipid fractions were -1.1 and -2.7%, respectively. Aspartic and glutamic acids were -1.6 and +2.7%, respectively, yet citrate was isotopically identical to the glucose. Probable sites of carbon isotopic fractionation include the enzyme, phosphotransacetylase, and the Krebs cycle.     

TASTE GROUP THRESHOLDS AND SENSORY EVALUATION OF SPANISH WINE VINEGARS

Wine vinegar is a product obtained from wine acidification which contains at least 5% by wt. of acetic acid, in general without any additives or colorings.
Aspects studied in this work include: the determination of the taste group thresholds (geometric mean of the individual best-estimate thresholds "BET") of two different acids (citric and acetic acids) in aqueous solution and spanish vinegars produced from table and sherry wines. The results obtained suggest that wine vinegar can be considered something more than just an acidulant agent.
In order to evaluate differences among wine vinegars, discriminant tests for twenty-five spanish vinegars (sherry, table and flavored vinegars) were applied. Six of the twelve attributes freely chosen by assessors allowed grouping of the spanish wine vinegars according to their sensory aspects.     

Arginine deprivation in KB cells: I. Effect on cell cycle progress

When exponentially growing KB cells were deprived of arginine, cell multiplication ceased after 12 h but viability was maintained throughout the experimental period (42-48 h). Although tritiated thymidine ([(3)H]TdR) incorporation into acid-insoluble material declined to 5 percent of the initial rate, the fraction of cells engaged in DNA synthesis, determined by autoradiography, remained constant throughout the starvation period and approximately equal to the synthesizing fraction in exponentially growing controls (40 percent). Continous [(3)H]TdR-labeling indicated that 80 percent of the arginine-starved cells incorporated (3)H at some time during a 48-h deprivation period. Thus, some cells ceased DNA synthesis, whereas some initially nonsynthesizing cells initiated DNA synthesis during starvation. Flow microfluorometric profiles of distribution of cellular DNA contents at the end of the starvation period indicated that essentially no cells had a 4c or G2 complement. If arginine was restored after 30 h of starvation, cultures resumed active, largely asynchronous division after a 16-h lag. Autoradiographs of metaphase figures from cultures continuously labeled with [(3)H]TdR after restoration indicated that all cells in the culture underwent DNA synthesis before dividing. It was concluded that the majority of cells in arginine-starved cultures are arrested in neither a normal G1 nor G2. It is proposed that for an exponential culture, i.e. from most positions in the cell cycle, inhibition of cell growth after arginine with withdrawal centers on the ability of cells to complete replication of their DNA.     

The modification of a common wheat-Thinopyrum distichum translocated chromosome with a locus homoeoallelic to Lr19

Summary The Chinese Spring ph1b and ph2b mutants, as well as the nulli 5B tetra 5D stock were utilized in an attempt to effect homoeologous chromatin exchange between the Indis chromosome translocation [derived from Thinopyrum distichum (Thunb.) Löve] and chromosome arm 7DL of common wheat. A homoeoallele of Lr19 and linked genes for yellow flour-pigmentation were utilized as markers. Seven selections with recombinations involving the foreign, translocated segment were recovered. Four of these had white endosperms and were leaf-rust resistant. The remaining lines were leaf-rust resistant and had levels of endosperm pigmentation intermediate to those of Indis and Chinese Spring. The recombined translocation segments coding for white endosperm are no longer associated with chromosome 7D. The original translocated segment may, therefore, not be fully homoeologous to 7DL. The recombinants with white endosperm also lack the stem-rust resitance gene Sr25, but retained the segregation distorter locus, Sd-1. However, it seems as though an enhancer locus (or loci) of Sd-1 had been lost.     

Studies on the primary sequence requirements for PKC-alpha, -beta 1 and -gamma peptide substrates.

The substrate specificity of purified PKC-alpha, -beta and -gamma has been investigated. A series of synthetic peptides based upon the sequence surrounding serine-7 in glycogen synthase were generated and used to determine the basic residue requirements of these PKC isotypes. While PKC-alpha and -beta are indistinguishable in their phosphorylation of these peptides, PKC-gamma shows a distinct specificity profile for these synthetic substrates.     

Purification and characterisation of bovine brain protein kinase C isotypes alpha, beta and gamma

Several polyclonal antisera specific for each of the protein kinase C isotypes alpha, beta 1, beta 2 and gamma have been generated and used to monitor the purification and subsequent separation of these polypeptides. A simple protocol has been developed for the efficient co-purification of these isotypes from bovine brain. The separation of the alpha, beta 1, beta 2 and gamma isotypes has been monitored using the antibodies and pools containing pure alpha, beta 1, and gamma forms have been produced. These isotypes have been characterised for activator dependence and substrate specificity. The results indicate that while the isotypes have similar requirements for magnesium, calcium, ATP and phosphatidylserine, they differ in their dependence on phorbol esters and diacylglycerols. The isotypes also differ in their range of substrate specificities. The implications of these results are discussed.