Function and transcript analysis of gibberellin-biosynthetic enzymes in wheat.

The enzymes gibberellin (GA) 20-oxidase and 3-oxidase are major sites of regulation in GA biosynthesis. We have characterised one member of each of the gene families encoding these enzymes that are highly expressed in elongating stems and in developing and germinating grains of wheat and are therefore likely to have prominent developmental roles in these tissues. We mapped the three homoeologues of the GA 20-oxidase gene TaGA20ox1 to chromosomes 5BL, 5DL and 4AL. TaGA20ox1 is expressed mainly in the nodes and ears of the elongating stem, and also in developing and germinating embryos. Expression in the nodes, ears and germinating embryos is predominantly from the A and D genomes. Each homoeologous cDNA encodes a functional enzyme that catalyses the multi-step conversions of GA12-GA9, and GA53-GA20. Time course and enzyme kinetic studies indicate that the initial oxidation steps from GA12 and GA53 to the free alcohol forms of GA15 and GA44, respectively, occur rapidly but that subsequent steps occur more slowly. The intermediate GA19 has an especially low affinity for the enzyme, consistent with its accumulation in wheat tissues. The three homoeologous cDNAs for the 3-oxidase gene TaGA3ox2 encode functional enzymes, one of which was shown to possess low levels of 2beta-hydroxylase, 2,3-desaturase, 2,3-epoxidase and even 13-hydroxylase activities in addition to 3beta-hydroxylase activity. In contrast to TaGA20ox1, TaGA3ox2 is expressed in internodes, as well as nodes and the ear of the elongating stem. It is also highly expressed in developing and germinated embryos.

Contrasting interactions between ethylene and abscisic acid in Rumex species differing in submergence tolerance.

Complete submergence of flooding-tolerant Rumex palustris plants strongly stimulates petiole elongation. This escape response is initiated by the accumulation of ethylene inside the submerged tissue. In contrast, petioles of flooding-intolerant Rumex acetosa do not increase their elongation rate under water even though ethylene also accumulates when they are submerged. Abscisic acid (ABA) was found to be a negative regulator of enhanced petiole growth in both species. In R. palustris, accumulated ethylene stimulated elongation by inhibiting biosynthesis of ABA via a reduction of RpNCED expression and enhancing degradation of ABA to phaseic acid. Externally applied ABA inhibited petiole elongation and prevented the upregulation of gibberellin A(1) normally found in submerged R. palustris. In R. acetosa submergence did not stimulate petiole elongation nor did it depress levels of ABA. However, if ABA concentrations in R. acetosa were first artificially reduced, submergence (but not ethylene) was then able to enhance petiole elongation strongly. This result suggests that in Rumex a decrease in ABA is a prerequisite for ethylene and other stimuli to promote elongation.

Modification of gibberellin biosynthesis in the grafted apple scion allows control of tree height independent of the rootstock.

The availability of short stature apple scions that required minimal applications of chemical growth retardants and could be used with a range of rootstocks would be of considerable benefit to fruit growers. We have suppressed the expression of a gene encoding the gibberellin (GA) biosynthetic enzyme GA 20-oxidase to reduce the levels of bioactive GAs in a scion variety, resulting in significant reductions in stem height. Application of GA3 reversed the effect. The scion remained dwarfed after grafting on to normally invigorating rootstocks, whilst control plants of the same cultivar displayed the expected vigour when grafted on to these rootstocks. This approach could be applicable to any perennial crop variety, allowing dwarf trees to be obtained on any available rootstock or on their own roots without the need for chemical growth retardant application. In effect, seedlings that are well suited to local conditions (drought, salinity) could be employed as tree rootstocks, as could existing rootstocks valued for characters other than vigour control, such as pest and disease resistance.

Synthesis and biological evaluation of pyrrolo[2,1-c][1,4]benzodiazepine (PBD) C8 cyclic amine conjugates.

We report examples of a series of novel pyrrolo[2,1-c][1,4]benzodiazepine (PBD) analogues 12-15 prepared from a common functionalized building block 11 that can be conveniently synthesized on a large scale and in optically pure form. Isoindoline analogue 15 is the most cytotoxic agent in this series, has the highest DNA-binding affinity, and shows significant activity in the in vivo hollow fibre assay.

3 beta,13-dihydroxylated C20 gibberellins from inflorescences of Rumex acetosa L.

Using full scan GC-MS a wide range of gibberellins (GAs) was identified in the young inflorescences of the dioecious species Rumex acetosa L., consistent with the ubiquitous early 13-hydroxylation pathway in both male and female plants. In addition, R. acetosa is the first species in which all three 3beta,13-dihydroxylated C(20)-GAs-GA(18), GA(38) and GA(23)-have been identified in the same organism, suggesting an early 3beta,13-dihydroxylation biosynthesis pathway in this species. Authentic GA(18), GA(38) and GA(23) were synthesized and their effects and that of GA(1), a GA common to both pathways, on the time to inflorescence emergence was investigated. GA(1) accelerated the emergence of inflorescences in both male and female plants. In addition some evidence for biological activity per se of the C(20)-GA(38) was obtained.

Synthesis of Sequence-Selective C8-Linked Pyrrolo[2,1-c][1,4]benzodiazepine DNA Interstrand Cross-Linking Agents.

An efficient convergent synthesis of a homologous series of C8-linked pyrrolobenzodiazepine dimers with remarkable DNA interstrand cross-linking activity and potent in vitro cytotoxicity is reported. The "amino thioacetal" cyclization procedure was used to produce the electrophilic DNA-interactive N10-C11 imine moiety during the final synthetic step. In order to construct the key A-ring fragments (9a-d), a versatile convergent approach has been developed to join two units of vanillic acid with alpha,omega-dihaloalkanes of varying length to provide the required bis(4-carboxy-2-methoxyphenoxy)alkanes while avoiding the formation of mixtures of monoalkylated and bisalkylated products.