Intraspecific variation in the response of rice (Oryza sativa) to increased CO2– photosynthetic, biomass and reproductive characteristics

Two rice ( Oryza sativa L.) cultivars of contrasting morphologies, IR-36 and Fujiyama-5, were exposed to ambient (360 μl l⁻¹) and ambient plus 300 μl l⁻¹ CO₂ from time of emergence until ca 50% grain fill at the Duke University Phytotron, Durham, North Carolina. Exposure to increased CO₂ resulted in about a 50% increase in the photosynthetic rate for both cultivars and photosynthetic enhancement was still evident after 3 months of exposure to a high CO₂ environment. The photosynthetic response at 5% CO₂ and the response of CO₂ assimilation (A) to internal CO₂ (C_i) suggest a reallocation of biochemical resources from RuBP carboxylation to RuBP regeneration. Increases in total plant biomass at elevated CO₂ were approximately the same in both cultivars, although differences in allocation patterns were noted in root/shoot ratio. Differences in reproductive characteristics were also observed between cultivars at an elevated CO₂ environment with a significant increase in harvest index for IR-36 but not for Fujiyama-5. Changes in carbon allocation in reproduction between these two cultivars suggest that lines of rice could be identified that would maximize reproductive output in a future high CO₂ environment.     

Dark inhibition of ribulose-1,5-bisphosphate carboxylase/oxygenase in legumes: A biosystematic study

2-carboxyarabinitol 1-phosphate (CA 1-P) is a naturally occurring inhibitor of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). Members of the Fabaceae exhibit a particularly wide range in the extent of CA 1-P accumulation during darkness and include Phaseolus vulgaris, whose dark/light regulation of Rubisco activity is principally achieved by synthesis/degradation of CA 1-P. An extensive survey of the degree of dark inhibition of Rubisco was undertaken for the subfamily Papilionoideae to elucidate evolutionary patterns in the occurrence of this regulatory mechanism. Seventy-five species from 21 tribes were examined. Dark inhibition of Rubisco was found in ancestral tribes such as the Sophoreae, but was substantially reduced or absent in representative species of three more recently evolved tribes, Cicereae, Hedysareae and Vicieae. We conclude that regulation of Rubisco by CA 1-P is neither of recent origin nor of restricted distribution among the Papilionoideae. On the contrary, it becomes lost or less pronounced only in a minority of the more evolutionarily advanced species in this important subfamily.     

Pulse-modulated photoacoustic measurements reveal strong gas-uptake component at high CO2-concentrations

The effect of high CO₂-concentration on photoacoustic signals from tobacco leaves is studied by means of a recently developed pulse modulation method which provides simultaneous information on photothermal and photobaric components in the millisecond time domain. High CO₂-concentrations are found to induce large gas-uptake signals. Simultaneous measurements of chlorophyll fluorescence suggest that the uptake signals are correlated with energy-dependent fluorescence quenching. Very similar CO₂-concentration dependencies are found in the absence and presence of methylviologen, which is known to catalyze O₂-reduction, and in the presence of glyceraldehyde, which blocks Calvin cycle and photorespiration. It is suggested that the CO₂-enhanced uptake signal is likely to reflect O₂-uptake in the Mehler reaction. However, it is not ruled out that also rapid CO₂-solubilisation or CO₂-binding caused by light-induced stroma alkalisation are involved. Strong uptake is also induced when the CO₂-concentration in the closed photoacoustic chamber increases due to dark-respiration. The consequences of these findings with respect to the interpretation of photoacoustic data (e.g., low-light effect) and to the regulatory role of O₂-dependent electron flow are discussed.     

Protein analysis during the ontogeny of normal and male sterile stamenless-2 mutant stamens of tomato (Lycopersicon esculentum Mill.)

The levels and synthesis of proteins during the ontogeny of normal and male sterile stamenless-2 (sl-2/sl-2) mutant stamens of tomato (Lycopersicon esculentum) were examined. The mutant stamens contained low levels of soluble protein which were related to reduction in protein synthesis. The mutant stamens, however, possessed many polypeptides similar to the normal and synthesized a 53-kd polypeptide at stages when there are abnormalities in tapetum development. The mutant stamens also possessed a 23-kd and some low molecular weight polypeptides that were considered as degradative proteins. Normal stamens exhibited the synthesis of many polypeptides not found in the mutant, from microspore mother cell to the preanthesis stages. In addition, at the time of pollen maturation there was a greater synthesis of several polypeptides, particularly those of 42 and 37 kd. Although the causative mechanisms of male sterility in the sl-2/sl-2 mutant are not known, the synthesis, and the lack, of specific polypeptides reported here appears to be associated with pollen degeneration.This work was supported by an operating grant from the Natural Sciences and Engineering Research Council of Canada to V.K.S.     

Long-term expression of gene introduction into normal human T-lymphocytes by retroviral-mediated gene transfer

Human T-lymphocytes are long lived, easily accessible, mature, and capable of proliferation. They are theoretically a suitable target for retroviral mediated gene transfer. To test this hypothesis, normal human T-cells obtained from bone marrow and peripheral blood were stimulated with phytohemagglutinin (PHA) and infected 24 h later with the retroviral vector N2 which carries the bacterial neo gene. T-lymphocytes were propagated in culture for up to 14 weeks with interleukin-2 (IL-2). Analysis by whole cell RNA dot/blot using a single stranded RNA probe demonstrated persistent expression of the neo gene. Preliminary functional studies revealed that both helper and suppressor functions were preserved in the infected cells in culture. These results demonstrate that normal T-cells are capable of long-term expression of genes introduced by retroviral mediated gene transfer and are potential target cells for somatic gene therapy.     

On the origin of mitochondria: a reexamination of the molecular structure and kinetic properties of pyruvate dehydrogenase complex from brewer''s yeast

45Ca2+ incorporated in response to glucose was selectively mobilized from the beta-cell-rich pancreatic islets of ob/ob-mice after raising the intracellular Na+ by removal of K+ or addition of ouabain or veratridine. Also studies of insulin release indicated opposite effects of glucose and Na+ on the intracellular sequestration of calcium. The fact that glucose inhibits insulin release induced by raised intracellular Na+ indicates that this sugar can lower the cytoplasmic [Ca2+]. The concept of a dual action of glucose on the cytoplasmic [Ca2+]. The concept of a dual action of glucose on the cytoplasmic [Ca2+] might well explain previous observations of an inhibitory component in the glucose action on the 45Ca2+ efflux.     

Genetic analysis of X-linked mutagen-sensitive mutants of Drosophila melanogaster

Mutants at 2 new loci which control mutagen-sensitivity are described. Mutants at both loci are female-sterile and are hypersensitive to killing by MMS; neither increases the frequency of sex-linked recessive lethals. A screen of previously described female-sterile and meotic mutants has revealed that a number of these are also sensitive to mutagens. In addition, several new mutants have been identified on the basis of sensitivity to either HN2 or MMS. An anlysis of complementation data suggests that all of the X-linked genes controlling sensitivity to MMS may now have been identified. Among the new mei-41 alleles are mutants which show verly little meiotic nondisjunction or loss. Cytogenetic mapping of previously known mutants is also described. The mutants mus(1)104^D1 and mei-41^D5 are located in th eregion 14B13±?14D1,2 on the polytene chromosome map, and they map very close to each other genetically. Cytogenetically mus(1)101^D1 is between salivary chromosome bands 12A6,7 and 12D3, mus(1)103^D1 is between bands 12A1,2 and 12A6,7, and mus(1)-109^A1 is in section 8F3-9A2.     

Ellipticines and human liver microsomes: Spectral interaction with cytochrome P-450 and hydroxylation. Inhibition of aryl hydrocarbon metabolism and mutagenicity

Some pharmacological properties of ellipticine (E) and its derivatives linked to their interaction with cytochrome P-450 have been investigated with human liver microsomes. 9-Hydroxyellipticine (9-OHE) interacts with human liver cytochrome P-450 exhibiting a type II spectrum (λ_max: 428 nm, K_s = 1.1 μM). After incubation with human liver microsomes the E was converted to 9-OHE; 7-hydroxyellipticine was not produced. The cytotoxic effect of this biotransformation has been evaluated on leukemic L1210 cells, in vitro, and found to be equal to those elicited by liver microsomes of control or phenobarbital (PB) pretreated rats. Moreover, 9-OHE and 9-fluoroellipticine (9-FE) strongly inhibit the benzo[a]pyrene hydroxylase (AHH) activity of human liver microsomes (I₅₀ = 2.6 μM and 1.6 μM, respectively) as well as the mutagenesis induced by the polycyclic aromatic hydrocarbon 2-acetylaminofluorene (AAF); 1 μg/plate of each of these compounds is able to inhibit by more than 50% the mutagenicity of 5 μg/plate AAF.