Regulation of carbonic-anhydrase activity,inorganic-carbon uptake and photosynthetic biomass yield inChlamydomonas reinhardtii

The regulation of carbonic anhydrase by environmental conditions was determined forChlamydomonas reinhardtii. The depression of carbonic anhydrase in air-grown cells was pH-dependent. Growth of cells on air at acid pH, corresponding to 10 m CO₂ in solution, resulted in complete repression of carbonic-anhydrase activity. At pH 6.9, increasing the CO₂ concentration to 0.15% (v/v) in the gas phase, corresponding to 11 M in solution, was sufficient to completely repress carbonic-anhydrase activity. Photosynthesis and intracellular inorganic carbon were measured in air-grown and high-CO₂-grown cells using a silicone-oil centrifugation technique. With carbonic anhydrase repressed cells limited inorganic-carbon accumulation resulted from non-specific binding of CO₂. With air-grown cells, inorganic-carbon uptake at acid pH, i.e. 5.5, was linear up to 0.5 mM external inorganic-carbon concentration whereas at alkaline pH, i.e. 7.5, the accumulation ratio decreased with increase in external inorganic-carbon concentration. It is suggested that in air-grown cells at acid pH, CO₂ is the inorganic carbon species that crosses the plasmalemma. The conversion of CO₂ to HCO ₃ ^- by carbonic anhydrase in the cytosol results in inorganic-carbon accumulation and maintains the diffusion gradient for carbon dioxide across the cell boundary. However, this mechanism will not account for energy-dependent accumulation of inorganic carbon when there is little difference in pH between the exterior and cytosol.     

Nitrate reductase is not accumulated in chloroplast-ribosome-deficient mutants of higher plants

The activities of nitrite reductase (EC 1.7.7.1) are 60–70% of wild-type activity in pigment-deficient leaves of the chloroplast-ribosomedeficient mutants albostrians (Hordeum vulgare) and iojap (Zea mays). The activity and apoprotein of nitrate reductase (EC 1.6.6.1.) are lacking in the barley mutant. Only very low activities of nitrate reductase can be extracted from leaves of the maize mutant. The molybdenum cofactor of nitrate reductase and xanthine dehydrogenase (EC 1.2.3.2) is present in maize and barley mutant plants. However, it is not inducible by nitrate in pigment-deficient leaves of albostrians. From these results we conclude: (i) Nitrite reductase (a chloroplast enzyme) is synthesized in the cytoplasm and does not need the presence of nitrate reductase for the induction and maintenance if its activity. (ii) The loss or low activity of nitrate reductase is a consequence of the inability of the mutants to accumulate the apoprotein of this enzyme. (iii) The chloroplasts influence the accumulation (i.e. most probably the synthesis) of the nonchloroplast enzyme, nitrate reductase. The accumulation of nitrate reductase needs a chloroplast factor which is not provided by mutant plastids blocked at an early stage of their development.Abbreviations CRM cross-reacting material - Mo-co molybdenum cofactor - NiR nitrite reductase - NR nitrate reductase     

Duplicated chromosome segments in maize (Zea mays L.): further evidence from hexokinase isozymes

Summary The genetic control of hexokinase isozymes (ATP: d-hexose-6-phosphotransferase, E.C. 2.7.7.1, HEX) in maize (Zea mays L.) was studied by starch gel electrophoresis. Genetic analysis of a large number of inbred lines and crosses indicates that the major isozymes observed are encoded by two nuclear loci, designated Hex1 and Hex2. Five active allozymes and one null variant are associated with Hex1, while Hex2 has nine active alleles in addition to a null variant. Alleles at both loci govern the presence of single bands, with no intragenic or intergenic heteromers visible, suggesting that maize HEX's are active as monomers. Organelle preparations demonstrate that the products of both loci are cytosolic. All alleles, including the nulls, segregate normally in crosses. Vigorous and fertile plants were synthesized that were homozygous for null alleles at both loci, suggesting that other hexosephosphorylating enzymes exist in maize that are undetected with our assay conditions. Linkage analyses and crosses with B-A translocation stocks place Hex1 on the short arm of chromosome 3, 27 centimorgans from Pgd2 (phosphogluconate dehydrogenase) and Hex2 on the long arm of chromosome 6, approximately 45 centimorgans from Pgd1. It is suggested that the parallel linkages among these two pairs of duplicated genes reflects an evolutionary history involving chromosome segment duplication or polyploidy.Paper No. 10170 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, NC     

Dry matter and nitrogen accumulation and partitioning in selected soybean genotypes of different derivation

Summary Experiments were conducted to determine if changes in the accumulation and partitioning of dry matter (DM) and nitrogen (N) in soybean [Glycine max (L.) Merr.] were associated with agronomic improvements and to assess the degree of genetic variation present for these traits. Fifteen maturity group II soybean genotypes including three ancestral cultivars, three modern cultivars, and nine agronomically superior plant introductions (PI's) were grown in replicated tests at four locations in the eastern U.S. The DM and N of stems, pod walls, and seeds were determined at maturity, and the apparent harvest indices (HI) and the apparent nitrogen harvest indices (NHI) were calculated. Pod DM partitioning was calculated as the ratio of seed DM to total pod DM and pod N partitioning was the ratio of seed N to total pod N. The mean DM accumulation of the modern cultivars was significantly greater than that of the ancestral cultivars and PI's. The apparent HI and the pod DM partitioning of both the modern and ancestral cultivars were significantly higher than that of the PI's. The three modern cultivars demonstrated the highest N accumulation. As a group, the modern cultivars consistently showed maximal accumulation and partitioning of DM and N suggesting that these physiological traits are associated with agronomic improvement. No individual PI was found to possess DM or N accumulation or partitioning which significantly exceeded the best modern cultivar or ancestral cultivar, indicating that genotypes with accumulation or partitioning characteristics which exceed available germplasm may be difficult to identify. Seed yield was correlated (P<0.05) with both DM (r=0.61) and N (r=0.57) accumulation.     

Restitution of polarity in statocytes from centrifuged roots*

Abstract The structural polarity of statocytes from cress roots is changed by centrifugation. Upon low- dose centrifugation (3000 g min), the extent of stratification depends on statocyte position, i.e., central statocytes are affected more than lateral ones. Upon higher doses of centrifugation (60,000 and 360,000 g min), a uniform density gradient is established in all statocytes. If, after centrifugation, the roots are exposed to gravity again, the endoplasmic reticulum (ER) cisternae are relocated parallel to the periclinal cell walls within a few minutes; this relocation is independent of the direction of gravity in relation to the root axis, and independent of the previously applied centrifugation dose. This supports the notion that polarity is determined genetically. Cytochalasin B treatment, before and during centrifugation, totally inhibits the relocation of ER. After removing the drug by rinsing the roots, the statocytes restore cell polarity and relocate ER. These results indicate that relocation of ER cisternae may be mediated by microfilaments. When centrifuged roots are exposed to 1 g in the horizontal position, the latent period of gravitropism increases by 8–10 min relative to controls, regardless of the previously applied centrifugation doses. The kinetics of curvature are virtually identical. Since the increase in the latent period coincides with the time needed for most statocytes to restore the distal cell pole, it is evident that perception of gravity is correlated to the integrity of the distal cell pole.     

Interaction of a bovine thymic peptide extract with vasoactive intestinal peptide (VIP) receptors

Bovine t hymic peptide extract (1–100 g/ml) is shown to completely inhibit the binding of [¹²⁵I]VIP to rat blood mononuclear cells, lymphoid cells of spleen, and liver plasma membranes. In the three models, the bovine thymic peptide extract inhibits [¹²⁵I]VIP binding with a potency that is 4000–7000 times lower than that of the native VIP, on a weight basis. In rat liver plasma membranes, the bovine thymic peptide extract stimulates adenylate cyclase with a maximal efficiency that is similar to that of VIP. At maximal doses, VIP and thymic peptide extract do not exert an additive effect on adenylate cyclase, suggesting that the activation of the enzyme by the bovine thymic peptide extract occurs through VIP receptors. Finally, no VIP-like immunoreactivity was detected in the thymic peptide extract using an antiserum raised against mammalian VIP. All these data suggest the presence in the bovine thymic peptide extract of a new substance which behaves as a VIP agonist in rat.     

Phenolic acid effects on peanut growth and oil production

Plants of peanut (Arachis hypogaea L. var. PG No. 1) were given two foliar sprays of phenolic compounds (H-acid, 1, 2, 4-acid, resorcinol and RD-Brown) at 100 and 200 ppm, 35 and 50 days after sowing. In treated plants, shelling %, yield (kg/ha), number of gynophores per plant and number of pods per plant were significantly greater than in the control. Oil content of kernels also showed a significant increase with all the phenolic compounds applied. These compounds increased the linoleic acid concentration so improving nutritional quality. The number of gynophores was significantly correlated with the number of pods per plant and yield per hectare. The effect of phenolic compounds on growth and development was independent of their structural configuration.     

Stimulation of acid invertase activity by indol-3yl-acetic acid in tissues undergoing cell expansion

The soluble acid invertase activity of young, excised P. vulgaris internodal segments fell when they were incubated in water, and their elongation ceased within 6–7 h. IAA (10 M) promoted segment elongation and stimulated an increase in the specific activity of acid invertase to a level greater than that originally present. The rate of segment elongation in the presence of IAA was closely and positively correlated with the specific activity of the enzyme. Optimum concentration of IAA for both elongation and stimulation of invertase activity was 10 M. Concurrent protein synthesis was necessary for these responses to IAA. Segments cut from mature, fully-elongated internodes did not responsd to IAA.Inclusion of Ca²⁺, vanadate or mannitol in the incubation medium abolished IAA-induced segment elongation but did not inhibit the stimulation of acid invertase activity by IAA. Auxin-induced elongation and acid invertase activity were both substantially increased in the presence of up to 25 mM D-glucose or up to 50 mM sucrose. Inclusion of either sugar in the medium considerably increased tissue hexose concentrations. Under some circumstances cell growth and invertase synthesis may compete for available hexose substrate.It is concluded that IAA-induced promotion of acid invertase in P. vulgaris internodal segments is not simply an indirect consequence of removal of end-product (hexose) during IAA-induced cell growth and that a more direct action of IAA on enzyme turnover is involved.     

Effects of in vivo ultrasound hyperthermia on natural killer cell cytotoxicity in the hamster

The effects of in vivo ultrasound irradiation of the spleen on immunological functions were assessed with an in vitro natural killer (NK) cell cytotoxic assay. Anesthetized hamsters were exposed to 1 MHz ultrasound at intensity levels currently being used clinically for therapeutic diathermy and hyperthermia (1-5 W/cm2, for 500 sec with constant beam scanning). Hyperthermic levels in the spleen ranged from 38-43 degrees C. Significant depression of natural killer (NK) cell activity was seen 4 h after spleen irradiation as compared to sham irradiated and normal animals. A return towards normal levels was observed in experimental groups at 24 h after exposure. Sham and normal animals were not significantly different in NK activity, indicating no significant stress-related immunosuppressive effects due to handling. Differential leukocyte counts taken for each exposure condition showed significant lymphopenia at 4, 8, and 16 h after exposure, near normal levels at 24 h, and complete recovery by 48 h. The number of circulating mononuclear cells at 4 h showed a dose-related suppression as the exposure intensities were increased.