Development of an epiphyte indicator of nutrient enrichment: A critical evaluation of observational and experimental studies

An extensive review of the literature describing epiphytes on submerged aquatic vegetation (SAV), especially seagrasses, was conducted in order to evaluate the evidence for response of epiphyte metrics to increased nutrients. Evidence from field observational studies, together with laboratory and field mesocosm experiments, was assembled from the literature and evaluated for a hypothesized positive response to nutrient addition. There was general consistency in the results to confirm that elevated nutrients tended to increase the load of epiphytes on the surface of SAV, in the absence of other limiting factors. In spite of multiple sources of uncontrolled variation, positive relationships of epiphyte load to nutrient concentration or load (either nitrogen or phosphorus) often were observed along strong anthropogenic or natural nutrient gradients in coastal regions. Such response patterns may only be evident for parts of the year. Results from both mesocosm and field experiments also generally support the increase of epiphytes with increased nutrients, although outcomes from field experiments tended to be more variable. Relatively few studies with nutrient addition in mesocosms have been done with tropical or subtropical species, and more such controlled experiments would be helpful. Experimental duration influenced results, with more positive responses of epiphytes to nutrients at shorter durations in mesocosm experiments versus more positive responses at longer durations in field experiments. In the field, response of epiphyte biomass to nutrient additions was independent of climate zone. Mesograzer activity was a critical covariate for epiphyte response under experimental nutrient elevation, but the epiphyte response was highly dependent on factors such as grazer identity and density, as well as nutrient and ambient light levels. The balance of evidence suggests that epiphytes on SAV will be a useful indicator of persistent nutrient enhancement in many situations. Careful selection of appropriate temporal and spatial constraints for data collection, and concurrent evaluation of confounding factors will help increase the signal to noise ratio for this indicator.     

The isolation,characterization and application in the Triticeae of a set of wheat RFLP probes identifying each homoeologous chromosome arm

Summary To investigate the use of RFLP analysis in the Triticeae, a set of low copy number probes has been isolated from a wheat cDNA library. The probes identify each of the 14 homoeologous chromosome arms of wheat as determined by analysis of DNA fragments hybridizing to the probes in aneuploid lines of Chinese Spring. These probes can be used in RFLP analyses both for the assignment of homoeology of alien chromosomes or arms added to wheat, and for the determination of chromosome dosage in wheat aneuploids. Different chromosomes from various Triticeae species can therefore be followed in a wheat genetic background using a single technique. The potential uses of the set in facilitating the transfer of alien segments into wheat are outlined.     

Optimal seasonal timing of univoltine and bivoltine insects

This study examines the optimal seasonal timing of the life cycle for univoltine and bivoltine insects, assuming that resource availability has a peak in the middle of a year and is symmetric around it. Results show that if the growth rate increases in proporrion to the bodyweight, bivoltine life cannot be optimal. If the growth rate is a power function of the bodyweight with a power smaller than unity, a symmetric bivoltine solution can be the optimal provided that the resource availability has a plateau in the middle of the season. If the resource availability has a sharp peak, the optimal pattern is an asymmetric bivoltine solution in which the larval periods of two generations differ in length. The bivoltine life cycle is more likely to be superior to the univoltine one if: growth is fast, suitable growing season is long, biomass loss during nonlarval stages is small, and egg size is small.     

Highly asymmetric intergeneric nuclear hybrids between Nicotiana and Petunia: evidence for recombinogenic and translocation events in somatic hybrid plants after “gamma”-fusion

Summary Extremely asymmetric nuclear hybrids have been obtained via protoplast fusion in an intergeneric combination. Irradiated (cobalt⁶⁰,100 krad) kanamycinresistant Petunia hybrida mesophyll protoplasts were chemically fused with wild-type mesophyll protoplasts of Nicotiana plumbaginifolia. Eighty-six hybrid colonies were selected on kanamycin-containing medium, and twenty-four of these could be induced to regenerate numerous shoots. Cytological analysis of the regenerants showed the presence of a few chromosome fragments in some lines, and even a metacentric chromosome in yet another line. Besides additional chromosome fragments some lines only possessed typical Nicotiana chromosomes, and this at the diploid (2n = 2X = 20) as well as the tetraploid (2n = 2X = 40) level. Biochemical analysis showed that all regenerants had neomycin phosphotransferase activity (NPTII), which suggests that intergenomic recombination and or translocation events took place at least in those lines where no additional chromosome fragments could be detected. The presence of the NPTII gene was shown by Southern hybridization. All regenerants tested were fertile, and the segregation ratios for the kanamycin gene (for self and backcross pollinations to the recipient partner) for some of the regenerants correspond with Mendelian rules for a monogenic dominant marker. Most of the regenerants showed abnormal segregation ratios; in this case, no correlation could be made between segregation ratio and chromosome composition.Our results demonstrate the existence of intergenomic recombination and translocations evens in nuclear somatic hybrid plants obtained via gamma-fusion.     

Selection of monosomic addition plants in offspring families using repetitive DNA probes in Beta L.

The distribution of two repetitive DNA probes Sat-121 and PB6-4, specific for the section Procumbentes of the genus Beta, was tested in 16 B. patellaris monosomic addition families using a dot-blot hybridization procedure. All monosomic additions were accurately distinguished from diploid sib plants with both DNA probes. The probe PB6-4, with the strongest signal after hybridization, was selected for rapid screening of an extensive number of putative monosomic additions in B. patellaris or B. procumbens addition families using a squash-blot hybridization procedure. The probe PB6-4 detected 118 monosomic additions in 640 plants (18.4%) in eight different B. procumbens addition families. The addition family with chromosome 4 of B. procumbens was semi-lethal and could not be tested. The distribution of PB6-4 in B. patellaris addition families was confirmed in 63 addition families using the squash-blot procedure. In 4580 plants of these addition families, 628 individual monosomic additions (13.7%) were found. The relationship of the morphological characteristics of monosomic addition plants to the results of the squash-blot hybridization (plants with signal) using probe PB6-4 is quite rigorous but not complete. The correlation between plants with a signal and chromosome number (2n=19) is complete. These results indicate that sequences present on PB6-4 are probably present on all chromosomes of B. patellaris and B. procumbens. The possibility of utilizing the sequence information of Sat-121 for a PCR-based assay to screen for putative monosomic addition plants was also investigated as an alternative to chromosome counting. The DNA-amplification profiles using the primers REP and REP.INV clearly distinguished monosomic addition plants from their diploid sibs.     

Intergeneric transfer of a partial genome and direct production of monosomic addition plants by microprotoplast fusion

Results are reported on the transfer of single, specific chromosomes carrying kanamycin resistance (Kan^R) and -glucuronidase (GUS) traits from a transformed donor line of potato (Solanum tuberosum) to a recipient line of the tomato species Lycopersicon peruvianum through microprotoplast fusion. Polyethylene glycol-induced mass fusion between donor potato microprotoplasts containing one or a few chromosomes and normal recipient diploid L. peruvianum protoplasts gave several Kan^R calli. A high frequency of plants regenerated from Kan^R calli expressed both Kan^R and GUS, and contained one or two copies of npt-II and a single copy of gus. Genomic in situ hybridization showed that several microprotoplast hybrid plants had one single potato donor chromosome carrying npt-II and gus genes and the complete chromosome complement of the recipient L. peruvianum (monosomic additions). Several monosomic-addition hybrid plants could be regenerated within the short time of 3 months and they were phenotypically normal, resembling the recipient line. These results suggest that the transfer of single chromosomes is tolerated better than is the transfer of the whole donor genome. The unique advantages of microprotoplast fusion are discussed: these include the direct production of monosomic addition lines for the transfer and introgression of economically important traits in sexually-incongruent species, the construction of chromosome-specific DNA libaries, high-resolution physical mapping and the identification of alien chromosome domains related to gene expression.     

Molecular genetic characterization of plant somatic hybrids

An efficient and easy method for genetic characterization of plant somatic hybrids is proposed. In a first qualitative approach, four somatic hybrids and their parental species (Nicotiana tabacum andN. plumbaginifolia) were characterized by DNA fingerprinting and Random Amplification of Polymorphic DNA (RAPD). After this, a quantitative estimation of the degree of parental contribution to the hybrids was carried out by means of a slot-blot analysis. Both qualitative methods, showed one hybrid identical toN. tabacum, two almost identical toN. plumbaginifolia, and a fourth similar to this parental species, but with someN. tabacum admixture. The quantitative method, for the same hybrids, gave 83%, 7%, 7%, and 37%N. tabacum DNA contribution, respectively.     

Transfer of resistance to potato leafroll virus, potato virus Y and potato virus X from Solarium brevidens to S. tuberosum through symmetric and designed asymmetric somatic hybridisation

Resistance to potato leafroll virus (PLRV), potato virus Y (PVY^o) and potato virus X (PVX) was studied in symmetric and asymmetric somatic hybrids produced by electrofusion between Solanum brevidens (2n=2×=24) and dihaploid S. tuberosum (2n=2×=24), and also in regenerants (B-hybrids) derived through protoplast culture from a single somatic hybrid (chromosome number 48). All of the somatic hybrids between 5. brevidens and the two dihaploid lines of potato cv. Pito were extremely resistant to PLRV and PVY^oand moderately resistant to PVX, irrespective of their chromosome number and ploidy level (tetraploid or hexaploid). Most (56%) of the asymmetric hybrids of irradiated S. brevidens and the dihaploid line of potato cv. Pentland Crown (PDH40) had high titres of PVY^osimilar to those of PDH40, whereas the rest of the hybrids had PVY^otitres less than a tenth of those in PDH40. Three B-hybrids had a highly reduced chromosome number (27, 30 and 34), but were however as resistant to PLRV, PVY^oand PVX as 5. brevidens. Two asymmetric hybrids and one B-hybrid were extremely resistant to PLRV but susceptible to both PVY and PVX. The results suggested that resistance to PLRV in 5. brevidens is controlled by a gene or genes different from those controlling resistance to PVY and PVX, and the gene(s) for resistance to PVY and PVX are linked in S. brevidens.     

非同位素PCR－单链构象多态性技术的建立和应用

ＰＣＲ－单链构象多态性技术问世以来,成为研究基因突变的工具,特别是在分子肿瘤学研究中,广泛应用于癌基因,抑癌基因突变的研究,常规ＰＣＲ－ＳＳＣＰ采用同位素标记ＰＣＲ产物,测序板电泳分离突变,在操作和费用上有种种局限,文章建立了一种非同位素ＰＣＲ－ＳＳＣＰ技术;通过不对称ＰＣＲ获得单链,普通ＰＡＧＥ分离,经银染检出突变,用这种方法,还研究了四株鼻咽癌细胞株ＣＮＥ１,ＣＮＥ２,ＨＫ１和ＳＵＮＥ１中肿瘤