Enhancement of ethylene biosynthesis and germination with thidiazuron and some selected auxins in Striga asiatica seeds

Witchweed [ Striga asiatica (L.) Kuntze], an economically important parasitic weed on several poaceous crops, is difficult to control. In nature, germination and subsequent morphogenesis of Striga are cued to specific host-derived chemical signals. Seeds (approximately 2.4 mg) treated with thidiazuron (TDZ) or the auxins 2,4-dichlorophenoxy-acetic acid (2,4-D), 1-naphthalene acetic acid (NAA), or 2-(4-chloro- o -tolyloxy) propionic acid (MCPP) produced little ethylene (66-138 nl l⁻¹). Combinations of TDZ with the auxins increased ethylene production by 4- to 18-fold. Ethylene production was strongly inhibited (86–92%) by aminoethoxyvinylglycine (AVG), inhibitor of 1-aminocyclopropane-1-carboxylic acid (ACC) synthase. Ethylene evolved from seeds treated with TDZ in combination with 2,4-D increased after a lag period and was promoted by a pretreatment in 2,4-D. TDZ or any of the auxins, at the rates tested, effected negligible to low levels of germination (0 to 16%), whereas mixtures of TDZ with the above auxins stimulated 38 to 84% germination. Test solutions containing TDZ and indole-3-acetic acid (IAA) were, however, less effective. TDZ/auxin-induced germination was inhibited by AVG and the ethylene action inhibitor silver thiosulfate (STS). The inhibitory effect of the former was reversed by treatment with ACC. In vitro studies revealed negligible germination (< 1%) on control medium. Seeds germinating on media containing TDZ alone developed into seedlings with distinct shoots and rudimentary roots. Seeds germinating on media containing 2,4-D, irrespective of TDZ concentration, were induced to form calli. The results are consistent with a model in which both germination and subsequent morphogenesis in Striga are associated with exogenous and endogenous phytohormones.     

Reverse splicing of the Tetrahymena IVS: evidence for multiple reaction sites in the 23S rRNA.

Group I introns in rRNA genes are clustered in highly conserved regions that include tRNA and mRNA binding sites. This pattern is consistent with insertion of group I introns by direct interaction with exposed regions of rRNA. Integration of the Tetrahymena group I intron (or intervening sequence, IVS) into large subunit rRNA via reverse splicing was investigated using E. coli 23S rRNA as a model substrate. The results show that sequences homologous to the splice junction in Tetrahymena are the preferred site of integration, but that many other sequences in the 23S rRNA provide secondary targets. Like the original splice junction, many new reaction sites are in regions of stable secondary structure. Reaction at the natural splice junction is observed in 50S subunits and to a lesser extent in 70S ribosomes. These results support the feasibility of intron transposition to new sites in rRNA genes via reverse splicing.     

Invertases of carnation petals. Partial purification, characterization and changes in activity during petal growth

Carnation ( Dianthus caryophyllus L. cv. White Sim) petals contained two distinct invertases (EC 3.2.1.26) based on chromatographic behavior on DEAE-cellulose. Both are soluble in 20 m M sodium phosphate buffer (pH 6.5) and exhibit acid pH optimum of 5.5. Extraction of a cell wall preparation from petals with 1 M NaCl released little additional activity. Furthermore, only traces of activity remained associated with the NaCl-extracted cell wall preparation. One of the soluble invertases, representing over 75% of the total activity, was partially purified by (NH₄)₂SO₄ fractionation and sequential chromatography over diethylaminoethyl-cellulose, concanavalin-A sepharose and polyacrylamide P-200. The enzyme was purified 38-fold with a recovery of 12%. It had an apparent native molecular weight of 215 kDa. The partially purified invertase is a β-fructofuranosidase (EC 3.2.1.26) based on its specificity for sucrose. The K_m for sucrose was 3.3 m M . Accumulation of reducing sugars and increased invertase activity during expansive petal growth indicates that sucrose is the major source of carbon for petal growth.     

Dynamics of Biological Macromolecules: Not a Simple Slaving by Hydration Water

We studied the dynamics of hydrated tRNA using neutron and dielectric spectroscopy techniques. A comparison of our results with earlier data reveals that the dynamics of hydrated tRNA is slower and varies more strongly with temperature than the dynamics of hydrated proteins. At the same time, tRNA appears to have faster dynamics than DNA. We demonstrate that a similar difference appears in the dynamics of hydration water for these biomolecules. The results and analysis contradict the traditional view of slaved dynamics, which assumes that the dynamics of biological macromolecules just follows the dynamics of hydration water. Our results demonstrate that the dynamics of biological macromolecules and their hydration water depends strongly on the chemical and three-dimensional structures of the biomolecules. We conclude that the whole concept of slaving dynamics should be reconsidered, and that the mutual influence of biomolecules and their hydration water must be taken into account.     

Changes in protein and mRNA populations during the senescence of carnation petals

Developmental changes in polypeptide and mRNA popultions in carnation ( Dianthus caryophyllus L. cv. White Sim) petals were investigated during the senescence of harvested flowers. Total proteins were extracted from flower petals at various stages of senescence and subjected to separation by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Analysis of the Coomassie blue stained gels revealed polypeptides with apparent molecular weights of 76, 62, 35.5 and 24 kDa which increased, while those with molecular weights of 70.5, 67.5, 46.5 and 31 kDa decreased during petal senescence. Changes in mRNA populations were investigated by translating poly (A)⁺RNA, isolated from carnation petals, in vitro using the rabbit reticulocyte lysate system. Polypeptides synthesized in vitro were separated by one- and two-dimensional gel electrophoresis and visualized by fluorography. Three classes of mRNA's were associated with the senescence of carnation petals. The majority of the mRNA's were constitutive at all stages of senescence. Another class of mRNA's increased with the climacteric rise in ethylene production, which accompanied the onset of senescence. Their translation products were 81, 58, 42, 38 and 35 kDa. In addition, several mRNA's appeared to decrease in abundance during the course of petal senescence. These results indicate that senescence of carnation flower petals is associated with changes in gene expression.