The functional role of the photosynthetic apparatus in the recovery of Brassica napus plants from pre-emergent metazachlor exposure

Metazachlor is a chloroacetamide herbicide, frequently used in Brassica napus cultivations around the world. Its primary target is the inhibition of very long chain fatty acid biosynthesis. This study included a morphological and physiological screening of hydroponically grown B. napus, exposed to a concentration range of 0, 0.25, 0.50, 0.75 and 1.0kg metazachlor per hectare. The results indicate that within a month after application, growth and development of B. napus are severely affected by low metazachlor doses. At intermediate metazachlor concentrations, loss of phosphorous and potassium from the plant tissues suggests destabilisation of cellular membranes, which may be a direct consequence of metazachlor application. This membrane instability could be indirectly linked with alterations of electron transport and a reduction of carbon assimilation. At increased metazachlor doses of 0.75kga.i.ha(-1), pigment concentrations are strongly reduced. However, chlorophyll fluorescence parameters seem to remain unaffected at metazachlor doses up to 0.75kga.i.ha(-1). At a metazachlor concentration of 1.0kga.i.ha(-1), negative effects are observed on all tested parameters, resulting in limited survival. The results indicate photosynthesis is assured at intermediate metazachlor concentrations for the cost of growth and development. It is clear that photosynthesis plays a key role in the survival strategy of young plants to overcome initially induced chemical stress.

Morphological, genetic and functional variability of a T-cell hybridoma line

The variability in the morphology, modal number of chromosomes, TCR expression and functional reactivity of a CII-specific T-cell hybridoma at continuous subcultivation have been investigated. As the number of passages increased, besides the oval semiadherent cells (normal phenotype), fibroblast-like cells (transformed phenotype) were also observed. The two cell subpopulations differed in their karyotype characteristic, as well as in their functional reactivity. The cell population with a normal phenotype was characterized by a tetramodal number of chromosomes (30, 40, 48 and 70) and trisomies of chromosomes 6 and 14, while the cell population with a transformed phenotype was characterized by a trimodal number of chromosomes (11, 68 and 74) and trisomy of chromosome 12. A nullisomy of sex chromosomes was established in both types of cells. In the initial passages of subcultivation, 73.04% of the cells with a normal morphological phenotype expressed TCR-CD3 complexes on their surface and possessed high functional reactivity. After a two-week subcultivation, the values of these indices went down considerably: 46.11% of the cells expressed functional TCR-CD3 complexes, as a result of which their functional reactivity decreased. Only 2.71% of the cells with a transformed morphological phenotype expressed functional TCR-CD3 complexes on their surface. In these cells, a total loss of reactivity towards the specific antigens was established. The achieved results show that at continuous subcultivation the T-cell hybridomas are unstable, and with the increase in the number of passages there appear chromosome rearrangements, leading to loss of their functional reactivity.

Protein extracts for nutritional purposes from fragile strains of Saccharomyces cerevisiae: reduction of the nucleic acid content and applicability of the protein extracts

92% of the cellular proteins from the osmotically fragile strain Sacch. cerevisiae 211 (MATa srbl srb2 tsl) were extracted by one passage in a high pressure disintegrator at 650 atm. After isoelectric precipitation, 60.1% of the proteins were isolated. The protein extract was rich in proteins (60-70%) but also contained 12-13% nucleic acids and 13-14% carbohydrates. Mild conditions were created for simultaneous reduction of nucleic acids and carbohydrates in the lysate prior to precipitation of proteins. Under these conditions the amount of nucleic acids in the protein extract was reduced to 2%, and that of the carbohydrates to 5.7%. As a result of the whole procedure on a pilot scale, 11 culture of Sacch. cerevisiae 211 grown in molasses based nutritional medium yielded 1 g protein extract. The applicability of this protein extract for nutritional purposes was demonstrated by determination of its amino acid composition, acute toxicity tests with Tetrahymena pyriformis and short-term animal nutrition tests. The results showed that the protein extract is a suitable source of SCP for nutritional purposes.

Protein extracts for nutritional purposes from fragile strains of Saccharomyces cerevisiae: construction of strains and conditions for lysis

A superfragile strain, Saccharomyces cerevisiae 211, carrying three nonallelic nuclear determinants of cell lysis by osmotic shock was isolated from the haploid progeny of a cross between two laboratory fragile strains VY 1160 and SY 15. The strain Sacch. cerevisiae 211 is prototrophic, grows well in both laboratory and industrial media, only when supplemented with osmotic stabilizers. The average protein content of its biomass after growth in a molasses-based nutritional medium is 48.7%. In laboratory conditions this strain releases about 60% of its cellular proteins by spontaneous lysis in water. However, on a pilot scale the protein yield decreases to about 25%. After a single disintegration step at 650 atm, practically all of the cellular protein--91.5%, is extracted without any additional chemical treatment. This result cannot be reached in any of the wild type strains tested even after triple treatment at 650 atm.