Growth responses of rice in ammonium-based nutrient solution with variable calcium supply

It is commonly known that calcium promotes NO₃ ^- uptake in many crop species. However, calcium enhancement of NH₄ ⁺ uptake by plants has received little attention. This study aimed to evaluate the effect of Ca supplements on NH₄ ⁺ uptake and plant growth in solution cultured rice. Supplemental Ca applied at vegetative and reproductive phases of plant ontogeny tended to stimulate NH₄ ⁺ absorption, and accordingly resulted in a better straw and grain yield. However, excessively supplied Ca (400 ppm) was detrimental to plant growth. Increases in straw and grain yield observed at Ca levels up to 300 ppm were linked to the Ca-enhanced activities of glutamine synthetase (GS), glutamate synthase (GOGAT), and ribulose 1, 5-bisphosphate carboxylase/oxygenase (Rubisco).     

Sucrose synthase in rice plants : growth-associated changes in tissue specific distributions

Different parts of the rice (Oryza sativa L.) plant at different growth stages were analyzed for sucrose synthase (SS) by enzyme activity assay and enzyme-linked immunosorbent assay directly on the extracts or on the eluates from a gel filtration column. On a dry matter basis, the amount of soluble protein and SS activity decreased significantly, but the amount of enzyme protein changed little in growing leaves. In the grain, the SS activity was the highest at the early ripening stage and decreased later, but the amount of SS protein increased with the increase in maturity. In the root, a low activity of SS was detectable only in the tillering but not in other stages. Immunoblotting of SS protein extracted from different parts of rice showed two bands. Elution patterns of crude extracts from a gel filtration column showed the presence of several types of SS protein. Among them, two to three types with larger elution volumes had the SS activity but others with smaller elution volumes (considered as the aggregated forms) had no activity. The SS purified from different parts of the plant showed similar but distinctly different electrophoretic mobilities in a native gel. It has been concluded that different isozymes are expressed in different tissues at different growth stages.     

The channel properties of possible gramicidin dimers

Extending previous work (Sung & Jordan, 1987 a, Biophys. J. 51, 661-672; 1988, Biophys. J.54, 519-526), we describe channel properties of five possible gramicidin dimers by studying dimerization energies and axial electrical potentials. Unlike the head-to-head dimer (the predominant channel former), both tail-to-tail and head-to-tail dimers with the same beta-helical monomer structure as the head-to-head dimer only form four intermonomer hydrogen bonds and are much less stable. Were channels formed from these dimers to be observed, their electrical potential profiles suggest that they should be cation selective, probably conduct less than the head-to-head dimer, have a central cation binding site, bind cations preferentially if crystallizable, and in the case of the head-to-tail dimer, rectify. Like the antiparallel double stranded helical dimer (a possible minor conducting pathway) the parallel double stranded helical dimer has 28 interstrand hydrogen bonds, but its hydrogen bond network is quite distorted and it is much less stable. If it formed, its electrical potential profile suggests that it would be cation selective, bind anions preferentially if crystallizable, rectify, and at high enough voltages, might exhibit a conductance greater than that of the antiparallel form.     

Modulation of calmodulin levels, calmodulin methylation, and calmodulin binding proteins during carrot cell growth and embryogenesis.

Carrot cell cultures were used to study the dynamics of calmodulin protein levels, calmodulin methylation, and calmodulin-binding proteins during plant growth and development. Comparisons of proliferating and nonproliferating wild carrot cells show that, while calmodulin protein levels does not vary significantly, substantial variation in post-translational methylation of calmodulin on lysine-115 is observed. Calmodulin methylation is low during the lag and early exponential stages, but increases substantially as exponential growth proceeds and becomes maximal in the postexponential phase. Unmethylated calmodulin quickly reappears within 12 h of reinoculation of cells into fresh media, suggesting that the process is regulated according to the cell growth state. Calmodulin and calmodulin-binding proteins were also analyzed during the formation and germination of domestic carrot embryos in culture. Neither calmodulin methylation nor calmodulin protein levels varied significantly during somatic embryogenesis. However, upon germination of embryos, the level of calmodulin protein doubled. By calmodulin overlay analysis, we have detected a major 54,000 M(r) calmodulin-binding protein that also increased during embryo germination. This protein was purified from carrot embryo extracts by calmodulin-Sepharose chromatography. Overall, the data suggest that calmodulin methylation is regulated depending upon the state of cell growth and that calmodulin and its target proteins are modulated during early plant development.     

Phosphatidylinositol-3-kinase is a non-tyrosine phosphorylated member of the insulin receptor signalling complex.

In rat HTC cells expressing a large number of human insulin receptors, insulin stimulated phosphatidylinositol-3-kinase (PI-3-kinase) activity. This activity was more effectively immunoprecipitated with anti-phosphotyrosine antibody (alpha-PY) than with anti-insulin receptor antibody (alpha-IR), suggesting that PI-3-kinase was not directly associated with the insulin receptor. alpha-PY immunoprecipitable PI-3 kinase activity, which was regulated by insulin, corresponded to a small pool of the total cellular PI-3-kinase activity. PI-3-kinase was not directly tyrosine phosphorylated by insulin treatment. A comparison of both catalytic activity and content of PI-3-kinase in alpha-PY immunoprecipitates indicated that after insulin treatment PI-3-kinase activity was enhanced by its association with tyrosine phosphorylated proteins. These studies suggest therefore that PI-3-kinase is a non-tyrosine phosphorylated member of the insulin receptor signalling complex.     

14,15N, 13C, 57Fe, and 1,2H Q-band ENDOR study of Fe-S proteins with clusters that have endogenous sulfur ligands.

The benefits of performing ENDOR experiments at higher microwave frequency are demonstrated in a Q-band (35 GHz) ENDOR investigation of a number of proteins with [nFe-mS] clusters, n = 2, 3, 4. Each protein displays several resonances in the frequency range of 0-20 MHz. In all instances, features are seen near v approximately 13 and 8 MHz that can be assigned, respectively, to "distant ENDOR" from 13C in natural-abundance (1.1%) and from 14N (the delta m1 = +/- 2 transitions); the nuclei involved in this phenomenon are remote from and have negligible hyperfine couplings to the cluster. In addition, a number of proteins show local 13C ENDOR signals with resolved hyperfine interactions; these are assigned to the beta carbons of cysteines bound to the cluster [A(13C) approximately 1.0 MHz]. Five proteins show resolved, local delta m1 = +/- 2 ENDOR signals from 14N with an isotropic hyperfine coupling, 0.4 less than or equal to A(14N) less than or equal to 1.0, similar to those seen in ESEEM studies; these most likely are associated with N-H...S hydrogen bonds to the cluster. Anabaena ferredoxin further shows a signal corresponding to A(14N) approximately 4 MHz. Quadrupole coupling constants are derived for both local and distant 14N signals. The interpretation of the data is supported by studies on 15N- and 13C-enriched ferredoxin (Fd) from Anabaena 7120, where the 15N signals can be clearly correlated with the corresponding 14N signals and where the 13C signals are strongly enhanced. Thus, the observation of 14N delta m1 = +/- 2 signals at Q-band provides a new technique for examining weak interactions with a cluster.(ABSTRACT TRUNCATED AT 250 WORDS)     

Interaction of nuclear factors with upstream sequences of a lipid body membrane protein gene from carrot.

To study the regulation of gene expression during embryo development, we isolated a gene, DC 59, expressed in embryos but not in mature carrot plants. Sequence and S1 analysis showed that the gene was composed of one exon encoding a polypeptide of 19 kilodaltons and was highly homologous to the lipid body membrane protein gene L3 from maize. The plant hormone abscisic acid regulated the accumulation of DC 59 mRNA. To understand the mechanism of embryo-specific and hormonal regulation of DC 59, 5' DNA fragments were incubated with nuclear proteins. Two adjacent regions (from -706 to -235) interacted with nuclear extracts from embryos, resulting in the formation of four complexes (C1, C2, C3, and C4). Factors involved in the formation of the C3 and C4 complexes could be competed with sequences upstream of DC 8, a gene that is coordinately expressed with DC 59 during embryo development. DNase I footprinting analysis revealed that nuclear extracts from embryos bound to four AT-rich sequences, and the protected motifs within fragment V were located in the highly homologous upstream regions of DC 59 and DC 8 genes.