Elicitors are compounds stimulating any type of plant defense. This broader definition of elicitors includes both substances of pathogen origin (exogenous elicitors and compounds released from plants by the action of the pathogen (endogenous elicitors). Also elicitors could be used as enhancers of plant-secondary-metabolite synthesis and could play an important role in biosynthetic pathways to enhanced production of commercially important compounds. The increased production, through elicitation, of the secondary metabolites from plant cell cultures has opened up a new area of research, which could have important economical benefits for bio industry.

A multidisciplinary study was carried out to analyse the chromosome doubling process during the early stages of in vitro maize microspore embryogenesis. The main stages (microspore derivatives) that were formed in the course of the culture were analysed. Chromosome number was determined from squashed cells, and DNA content was measured by cytometry. In parallel, an ultrastructural analysis of the microspore derivatives demonstrated the occurrence of a nuclear fusion process. It seems likely that nuclear fusion ensures chromosome doubling at early stages of induced microspore embryogenesis. It occurs precisely at the 5/7 day stage in the embryonic domain and probably leads to polyploidy in the endosperm domain of the microspore derivatives. As a conclusion a scheme summarises the results and proposes an interpretation of the sequence of chromosome doubling events during early maize microspore embryogenesis. Understanding of this process will be important for future efforts to increase the percentage of homozygous plants for crop improvement.

Understanding the origin and evolution of sex chromosomes requires studying recently evolved X-Y chromosome systems such as those in some flowering plants. We describe Y chromosome deletion mutants of Silene latifolia, a dioecious plant with heteromorphic sex chromosomes. The combination of results from new and previously described deletions with histological descriptions of their stamen development defects indicates the presence of two distinct Y regions containing loci with indispensable roles in male reproduction. We determined their positions relative to the two main sex determination functions (female suppressing and the other male promoting). A region proximal to the centromere on the Y p arm containing the putative stamen promoting sex determination locus includes additional early stamen developmental factors. A medial region of the Y q arm carries late pollen fertility factors. Cytological analysis of meiotic X-Y pairing in one of the male-sterile mutants indicates that the Y carries sequences or functions specifically affecting sex chromosome pairing.

Around 200 BC, the Nordic tribes devised rune symbols to represent the forces of nature. Among these symbols were X-GEBA, the rune of love and sexuality, and Y-FEOH, the rune of success. It was believed that by picking the right rune, the wearer could harness the power the rune represented. Hazard or deep intuition? It turns out that in biology, X and Y symbols define sexual fates and reproduction success.Sex determination systems based on heteromorphic X and Y sex chromosomes are particularly interesting to study from both a developmental and an evolutionary perspective. There are many parallels between the sex determination systems, as well as the organization of sex chromosomes, in different species, even between animals and plants.Two main systems of chromosomal sex determination, XY and X:A (autosomal chromosome) ratio, apparently have evolved many times. Mammals, for example, have the XY system, with a dominant (active) Y chromosome containing the key sex determination function(s), whereas Drosophila melanogaster has an X:A system, where the ratio of X:A chromosomes determines sex by an X chromosome counting system, the Y chromosome being largely dispensable (Hodgkin, 1992).Dioecy is a widespread condition in flowering plants, despite their recent evolutionary origin: 6% of the 240,000 angiosperm species are dioecious and 7% of 13,000 genera of angiosperms include dioecious species, suggesting that it has arisen many times during flowering plant evolution (Renner and Ricklefs, 1995). Dioecy is correlated with perennial climbing growth, wind, or water pollination and has a preponderance in tropical flora. Model species with a chromosomal sex determination are white campion (Silene latifolia; XY system), hop (Humulus lupulus; X:A system), and sorrel species (Rumex spp.) which include both XY-like and X:A systems (Figs. 1 and 2).Plant sex determination has been recently and extensively covered (Ainsworth et al., 1998); therefore, we will mainly concentrate on the contribution of this very particular group of plants to the universal question of sex chromosome evolution.

Lung cancer is a serious health problem, since it is one of the leading causes for death worldwide. Molecular–cytogenetic studies could provide reliable data about genetic alterations which could be related to disease pathogenesis and be used for better prognosis and treatment strategies. We performed whole genome oligonucleotide microarray-based comparative genomic hybridization in 10 samples of non-small cell lung cancer. Trisomies were discovered for chromosomes 1, 13, 18 and 20. Chromosome arms 5p, 7p, 11q, 20q and Хq were affected by genetic gains, and 1p, 5q, 10q and 15q, by genetic losses. Microstructural (<5 Mbp) genomic aberrations were revealed: gains in regions 7p (containing the epidermal growth factor receptor gene) and 12p (containing KRAS) and losses in 3p26 and 4q34. Based on high amplitude of alterations and small overlapping regions, new potential oncogenes may be suggested: NBPF4 (1p13.3); ETV1, AGR3 and TSPAN13 (7p21.3-7p21.1); SOX5 and FGFR1OP2 (12p12.1-12p11.22); GPC6 (13q32.1). Significant genetic losses were assumed to contain potential tumour-suppressor genes: DPYD (1p21.3); CLDN22, CLDN24, ING2, CASP3, SORBS2 (4q34.2-q35.1); DEFB (8p23.1). Our results complement the picture of genomic characterization of non-small cell lung cancer.

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The barley chromosomal mutant T-35, in which only one pair of satellite chromosomes is apparent, was analyzed using a range of cytological and molecular techniques. Using conventional Feulgen staining, Giemsa and silver banding, in situ hybridization, and Southern blot analysis, unequivocal cytological and molecular evidence was obtained that T-35 is a homozygous deletion of rRNA genes residing in the nucleolus organizer region (NOR) of chromosome 6. According to the criteria of arm ratio and Giemsa-banding pattern of this chromosome, the deletion involved the whole NOR, one of the breakpoints being localized in the short arm proximally to the NOR-associated heterochromatic band, the other probably in the satellite of the chromosome. As a result of this deletion, an increased activity of the rRNA genes (as indicated by the size of the silver bands) on the other NOR-bearing chromosome (chromosome 7) was observed. The possible reasons for this phenomenon are discussed.

The transcriptional activity of NORs in a new structural mutant of barley (PK-88-4) was studied based on the positive reaction of NORs of metaphase chromosomes with AgNO3 and the number and size of silver-stained nucleoli in somatic interphase cells and meiocytes. PK-88-4 proved to contain a pericentric inversion that split NOR 7 into two unequal parts residing in the opposite arms of the reconstructed chromosome 7(5). This chromosomal rearrangement enables testing of intrachromosomal suppression of NORs and provides insight into the mechanisms of intraspecific nucleolar dominance. Both parts of the split NOR proved to be transcriptionally active, and are not subject to intrachromosomal nucleolar dominance. Thus, translocation-induced intraspecific nucleolar dominance is probably the result of interaction of NOR6 and NOR7 or other genetic factors located on the NOR-bearing chromosomes 6(6H) and 7(5H).