Effect of Temperature on the Fatty Acid Composition and Yield of Evening Primrose (Oenothera lamarckiana) Seeds

The oil content and yield of evening primrose (Oenothera lamarckianaL.) seeds decreased significantly at high temperatures (32 ?C)compared with lower ones (25 ?C and below), under controlledgrowing conditions. Moreover, the fatty acid composition ofthe seed oils was also affected by the temperature regime. Higheroleic acid levels and lower linoleic and -linolenic acid (GLA)levels were characteristic of the seeds developed at highertemperatures. The opposite trend was observed at lower temperatures.In field experiments, seeds of O. lamarckiana plants sown inautumn contained lower oleic acid levels, and higher linoleicacid and GLA levels than seeds of spring plantings. This effectwas also demonstrated for seeds developed on the same stem inflorescenceunder increasing temperatures during the season in the field.Changes in fatty acid composition during various stages of seeddevelopment were observed. Key words: Evening primrose, oil, fatty acids, Oenothera spp., gamma linolenic acid     

Indices of water deficit in susceptible and resistant cucumbers in response to infection by cucumber mosaic virus

Indices of water deficit were determined under conditions of non-limited water supply in cucumber mosaic virus (CMV)-infected seedlings of the susceptible cv. Bet Alpha. An increase in the concentration of soluble solids, decrease of water and osmotic potentials, and increase of proline concentration were found in the CMV-infected cotyledons. In the cv. Shimshon, which is resistant to CMV, virus infection caused only a slight change in the concentration of the soluble solids and in the osmotic potential; water potential and proline content were not affected. Concomitantly, infectivity of cotyledons by CMV was much lower in the tolerant cv. Shimshon than in the susceptible cv. Bet Alpha. The possible association of water deficit with virus-induced growth retardation is discussed.     

Heterothallism in Saccharomyces cerevisiae isolates from nature: effect of HO locus on the mode of reproduction

Understanding the evolution of sex and recombination, key factors in the evolution of life, is a major challenge in biology. Studies of reproduction strategies of natural populations are important to complement the theoretical and experimental models. Fungi with both sexual and asexual life cycles are an interesting system for understanding the evolution of sex. In a study of natural populations of yeast Saccharomyces cerevisiae , we found that the isolates are heterothallic, meaning their mating type is stable, while the general belief is that natural S. cerevisiae strains are homothallic (can undergo mating-type switching). Mating-type switching is a gene-conversion process initiated by a site-specific endonuclease HO; this process can be followed by mother–daughter mating. Heterothallic yeast can mate with unrelated haploids (amphimixis), or undergo mating between spores from the same tetrad (intratetrad mating, or automixis), but cannot undergo mother–daughter mating as homothallic yeasts can. Sequence analysis of HO gene in a panel of natural S. cerevisiae isolates revealed multiple mutations. Good correspondence was found in the comparison of population structure characterized using 19 microsatellite markers spread over eight chromosomes and the HO sequence. Experiments that tested whether the mating-type switching pathway upstream and downstream of HO is functional, together with the detected HO mutations, strongly suggest that loss of function of HO is the cause of heterothallism. Furthermore, our results support the hypothesis that clonal reproduction and intratetrad mating may predominate in natural yeast populations, while mother–daughter mating might not be as significant as was considered.