Stem fasciated, a recessive mutation in sunflower (Helianthus annuus), alters plant morphology and auxin level

BACKGROUND AND AIMS: Plant lateral organs such as leaves arise from a group of initial cells within the flanks of the shoot apical meristem (SAM). Alterations in the initiation of lateral organs are often associated with changes in the dimension and arrangement of the SAM as well as with abnormal hormonal homeostasis. A mutation named stem fasciated (stf) that affects various aspects of plant development, including SAM shape and auxin level, was characterized in sunflower (Helianthus annuus). METHODS: F1, F2 and F3 generations were obtained through reciprocal crosses between stf and normal plants. For the genetic analysis, a chi2 test was used. Phenotypic observations were made in field-grown and potted plants. A histological analysis of SAM, hypocotyl, epicotyl, stem and root apical meristem was also conducted. To evaluate the level of endogenous indole-3-acetic acid (IAA), a capillary gas chromatography-mass spectrometry-selected ion monitoring analysis was performed. KEY RESULTS: stf is controlled by a single nuclear recessive gene. stf plants are characterized by a dramatically increased number of leaves and vascular bundles in the stem, as well as by a shortened plastochron and an altered phyllotaxis pattern. By histological analysis, it was demonstrated that the stf phenotype is related to an enlarged vegetative SAM. Microscopy analysis of the mutant's apex also revealed an abnormal enlargement of nuclei in both central and peripheral zones and a disorganized distribution of cells in the L2 layer of the central zone. The stf mutant showed a high endogenous free IAA level, whereas auxin perception appeared normal. CONCLUSIONS: The observed phenotype and the high level of auxin detected in stf plants suggest that the STF gene is necessary for the proper initiation of primordia and for the establishment of a phyllotactic pattern through control of both SAM arrangement and hormonal homeostasis.     

Derivatization does not influence antimicrobial and antifungal activities of applanoxidic acids and sterols from Ganoderma spp

Applanoxidic acids and sterols, isolated from Ganoderma spp., were acetylated and/or methylated. The antibacterial activity against Escherichia coli and Staphylococcus aureus and the antifungal activity against Candida albicans and Trichophyton mentagrophytes of the derivatives were investigated by a microdilution method, and compared with those of the natural products. Both natural and modified compounds exhibited comparable antibacterial and antifungal activities in a range of 1.0 to > 2.0 mg/ml minimal inhibitory concentration.     

Floristic gradients of herbaceous vegetation and P/N ratio in soil in a Mediterranean area

A broad range of herbaceous plant comunities in a Mediterranean Landscape in central Italy, running from heavily urbanized areas to semi-natural pastures, has been studied. These communities can be easily arranged along a gradient of ruderality. We inspected which of a series of soil parameters could better explain this gradient (pH, CaCO₃, granulometry, N, P, C/N, P/N). We show that (1) the single most important explanatory variable is P/N ratio of soil; (2) nitrogen and carbon pools in soil are related, in the set of communities studied, with another gradient of decreasingly frequent, predictable, moderate disturbance such as trampling. We discuss the meaning of these results. Nomenclature: Anzalone (1994, 1996).     

Evaluation of a high temperature immobilised enzyme reactor for production of non-reducing oligosaccharides

There is interest in the production of non-reducing carbohydrates due to their potential application in various industrial fields, particularly the food industry. In this paper, we describe the development of an immobilised cell bioprocess for the synthesis of non-reducing maltodextrins at high temperatures. The trehalosyl-dextrins-forming enzyme (TDFE) isolated from the thermoacidophilic archaeon Sulfolobus solfataricus (strain MT4), was recently expressed at high yields in Escherichia coli (strain Rb-791). Here, we evaluate different matrices, such as polyacrylamide gel, crude egg white, chitosan and calcium alginate for their effectiveness in immobilising whole recombinant E. coli cells subjected to prior thermal permeabilisation. Calcium-alginate based gels formed a solid biocatalyst with a good activity yield and the best enzymatic stability at the operating temperature (75°C). Therefore, these beads were used to pack a glass column reactor to perform the bioconversion of interest. Optimal operating parameters were defined in relation to the substrate stream flow-rate and the substrate-to-biocatalyst ratio. The production of trehalosylmaltotetraose from maltohexaose reached equilibrium with a constant of about 2.6 at 75°C. The bioreactor was exploited for production of trehalosylmaltodextrins from a commercial mixture of maltodextrins, achieving a productivity of 106.5 mg ml⁻¹ h⁻¹ (g biocatalyst)⁻¹ with ~40% conversion when using a 30% (w/v) solution.