A mechanism for the establishment of polar cell morphology based on the cytoskeleton-derived forces exerted on the cell boundary

A mechanism for the establishment of polar cell morphology is presented, based on the internal forces that the cytoskeletal structures exert on the cell boundary. Cell shapes are determined by postulating that they correspond to the minimum of the total energy of the system, which is the sum of the bending energy of the cell boundary and the potential energies of the involved forces. Axisymmetrical cell shapes are considered, and it is assumed that the cytoskeletal structures exert an extensional axial force and are involved in controlling the area of the cell boundary. The dependence of cell shapes on the axial force is presented for different values of this area. The results show that, at increasing axial force, the cell undergoes a discontinuous transition from an oval shape, exhibiting an equatorial mirror symmetry into a polar shape. The proposed mechanism is related to previously documented specific effects of microtubule- and actin-modifying drugs on polar shapes of developing isolated retinal photoreceptor cells. Received: 28 January 1998 / Revised version: 25 July 1998 / Accepted: 29 July 1998     

Production of fertile tobacco pollen from microspores in suspension culture and its storage for in situ pollination

Summary A simple procedure is described for the in vitro production of tobacco (Nicotiana tabacum L.) pollen from microspores isolated just before entering mitosis. During a 3-day culture period in a liquid medium containing pyrimidine nucleosides these microspores develop into young pollen grains to the stage of starch deposition. Pollen maturation and transition to dormancy is achieved during a further 2- to 3-day culture period in the same medium stepwise supplemented by a concentrated solution of sucrose and l-proline. Upon transfer of the pollen to a simple germination medium containing sucrose and boric acid, up to 40% of the grains were observed to produce relatively long tubes. The in vitro-matured pollen grains can be stored at-20° C either suspended in 1.17 M sucrose and 100 mM l-proline or separated from the medium on filter paper discs. The stored pollen germinated both in vitro and on the stigma, the pollen tubes grew through the style into the ovary and pollination produced up to 300 viable seeds per pod. The procedure is of interest for pollen developmental studies and various fields of pollen manipulation, such as in vitro pollen selection.     

Bemisia tabaci (Gennadius) population density and pupal size are dependent on rootstock and nitrogen in hydroponic tomato crop

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Free radical–scavenging activity and DNA damaging potential of auxins IAA and 2‐methyl‐IAA evaluated in human neutrophils by the alkaline comet assay

Auxins, of which indole‐3‐acetic acid (IAA) is the most widespread representative, are plant hormones. In addition to plants, IAA also naturally occurs in humans in micromolar concentrations. In the presence of peroxidase, indolic auxins are converted to cytotoxic oxidation products and have thus been proposed for use in gene‐directed enzyme/prodrug tumor therapy. Since data on the genotoxicity of IAA and its derivatives are not consistent, here we investigate the early DNA damaging effects (2‐h treatment) of the auxins, IAA, and 2‐methyl‐indole‐3‐acetic acid (2‐Me‐IAA) by the alkaline comet assay and compare them with their free radical–scavenging activity measured by the 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) assay. Human neutrophils are chosen as the test system since they possess inherent peroxidase activity. The results of the comet assay indicate an increase in DNA damage in a dose‐dependent manner up to 1.00 mM of both auxins. Generally, IAA applied in the same concentration had greater potential to damage DNA in human neutrophils than did 2‐Me‐IAA. The genotoxicities of the two examined auxins are negatively correlated with their antioxidant activities, as measured by the DPPH assay; 2‐Me‐IAA showed a higher antioxidant capacity than did IAA. We assume that differences in the molecular structure of the tested auxins contributed to differences in their metabolism, in particular, with respect to interactions with peroxidases and other oxidative enzymes in neutrophils. However, the exact mechanisms have to be elucidated in future studies. © 2010 Wiley Periodicals, Inc. J Biochem Mol Toxicol 24:165–173, 2010; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/jbt.20323     

Rhizobacteria associated with Miscanthus x giganteus improve metal accumulation and plant growth in the flotation tailings

Plant and Soil - Flotation tailings represent an extremely unfriendly substrate for plant colonization due to toxic metal concentrations and marked macronutrient deficiencies. The perennial grass...     

Blue mould decay of stored onion bulbs caused by Penicillium polonicum,P. glabrum and P. expansum

Onion bulbs (Allium cepa L.) can be stored for up to 12 months to ensure their availability all year, but one of the limiting factors is decay caused by blue mould fungi. Postharvest development of blue mould is not only economically important, but also poses a health hazard due to mycotoxin contamination. Onion bulbs of different yellow and red cultivars with blue mould symptoms were collected from three storage facilities in Serbia. Pathogenic isolates were identified and characterized based on their molecular (partial β‐tubulin gene), morphological (micro‐ and macromorphology, and colony growth) and biochemical properties (analyses of indole metabolites via Ehrlich test). Three Penicillium species were identified: P. polonicum, P. glabrum and P. expansum. Virulence on inoculated onion bulbs varied significantly within isolates of P. glabrum, but the most virulent isolate of P. polonicum and P. glabrum did not differ, nor did they differ from an isolate of P. expansum. Variability in virulence of individual P. glabrum isolates corresponded to differences in their molecular and macromorphological characters. P. glabrum and P. expansum were identified for the first time as causal agents of onion bulb decay in Serbia. Data from this investigation provide insight into diversity of economically important and possibly toxigenic blue mould fungi which brings attention to their presence in storage facilities and therefore the necessity of the application of prevention measures.     

A review of the West Palaearctic aphidiines (Hymenoptera: Braconidae: Aphidiinae) parasitic on Uroleucon spp., with the description of a new species

A review of aphidiine wasps (Hymenoptera: Braconidae) parasitizing the Uroleucon species in the West Palaearctic is presented. Eleven species are keyed and illustrated. In addition, a new hymenopteran parasitoid species: Praon nonveilleri n. sp. from Uroleucon inulicola (Hille Ris Lambers) infesting Inula ensifolia L., is described. The new species is diagnosed and illustrated. It belongs to the “dorsale-yomenaé” species group and was collected from the Djetinja canyon in Serbia and Montenegro. The aphidiines presented in this work were identified from 97 aphid taxons occurring on 236 plant taxons. Furthermore, 361 original parasitoid – host aphid – host plant associations of the species mentioned in the key are presented. Finally, phylogenetic relationships inside the “dorsale-yomenae” species group and related species were reconstructed using cladistic distance methods.     

The growth form of the inducing microorganism and chitin addition affect mycolytic enzyme production byTrichoderma harzianum

The effect of the growth form of the inducing microorganism on specificTrichoderma harzianum mycolytic enzyme production was studied. The pelleted form ofRhizopus nigricans gave a better product concerning protoplast formation ability. The maximum yield of protoplasts from the target fungusCochliobolus lunatus was 1×10⁸ ml^–1. Analysis of individual specific enzyme activities inTrichoderma mycolytic enzyme preparations confirms the importance of high chitinase and low protease activity for high protoplast yields. Supplementation of the production medium with chitin increased the chitinase activity in theTrichoderma exoenzyme mixture.