Chromenes and benzofurans of the asteraceae,their chemistry and biological significance

Chromenes (benzopyrans) and benzofurans are characteristic natural products of certain tribes of the Asteraceae. This review highlights recent findings     

GC-MS of perdeuteriomethylated flavonoid aglycones

GC-MS of perdeuteriomethylated flavonoid aglycones, singly and in mixtures, yields information about both the aglycone types and their substitution patterns. Fragmentation patterns of flavonoid aglycones are discussed. Acid hydrolysis of perdeuteriomethylated flavonoid glycosides, singly and in mixtures, followed by ethylation with diazoethane provides derivatives suitable for GC-MS; the introduced ethyl groups permit identification of the position of attachment of sugars in flavonoid O-glycosides.     

Growth capacity in response to auxin of coleoptile segments of normal and dwarf rice strains

Auxin-induced growth, epidermal cell length, cellular osmotic potential, and cell wall composition of coleoptile segments excised from one normal and two dwarf rice strains were studied 2, 3, 4, and 5 days after soaking. The auxin-induced growth was higher at the early stages of coleoptile growth and decreased with age, being always higher in normal than in the two dwarf strains. A good correlation between auxin-induced growth and auxin-induced decrease in the minimum stress-relaxation time has been found, suggesting that the different growth capacity in response to auxin among the three different strains is due to differences in the structure of their cell walls. In fact, cell wall analysis revealed that (1) the relative -cellulose content of the cell walls was higher in the two dwarf strains than in the normal one, and (2) the auxin-induced decrease in noncellulosic glucose was high, compared with dwarf strains, in the normal strain, which showed the higher auxin-induced growth, showing a highly significant correlation between the decrease in noncellulosic glucose and the growth in response to auxin. Thus, the different growth between normal and dwarf strains might be attributed to their different capacity to degrade -glucan of their cell walls.     

Are diatom diversity indices reliable monitoring metrics?

A biological survey was carried out in 640 stations spread over the Loire-Bretagne National Network (France) between 1996 and 2000. Epilithic diatom inventories were obtained following standard methods. A total of 934 diatom taxa were identified. Common diversity indices (species richness, Shannon’s diversity, equitability, dominance, etc.) were calculated and compared against abiotic factors verify their reliability as biomonitoring metrics. Sampling stations were classified according to their trophic status (TP concentration). Several theoretical predictions about the relationship between community structural parameters and limnological variables were tested. In general, diversity indices exhibited poor linear correlations with environmental factors indicating ecological status. No clear patterns were found concerning species accumulation curves, occurrence-abundance, frequency-abundance and frequency distribution of diatom taxa between different trophic levels, although assemblages from stations with lower TP levels were characterized by relatively high dominances of certain taxa, mainly Achnanthidium minutissimum. In the light of these findings, the use of diatom diversity indices in biological quality surveillance protocols in continental waters is discouraged. Results are compared and discussed with similar studies.     

Exogenous and endogenous growth regulators on apogamy in Dryopteris affinis (Lowe) Fraser-Jenkins sp. affinis

This work showed for the first time the relationship between the effect of exogenous auxins and gibberellins on apogamy in Dryopteris affinis (Lowe) Fraser-Jenkins sp. affinis and its endogenous contents during early apogamic events. The addition of NAA (0.53 and 5.37 μM) or GA₃ 2.8 μM to an MS solid medium significantly increased apogamous sporophyte formation. BA induced brown callus that regenerated sporophytes in a hormone-free medium. The endogenous contents of GA₁, GA₃, GA₄, GA₇, GA₉ and IAA were determined by GC–MS in gametophytes cultured on MS solid medium, before and during early stages of apogamous embryo development. The accumulation of both GA₉ and IAA before embryo development was evident as high levels of GA₄ in the earliest analysed stage of embryo development and high levels of GA₃ in elongating shoots were found. The role of gibberellins on apogamy was also supported by data showing a decrease in the percentage of gametophytes developing embryos because of the addition of flurprimidol to the culture medium.     

Genome size variation and morphological differentiation within Ranunculus parnassifolius group (Ranunculaceae) from calcareous screes in the Northwest of Spain

Ranunculus parnassifolius is an orophilous plant distributed throughout Central and Southwestern Europe (Alps, Pyrenees and Cantabrian Mountains). Its evolutionary history and taxonomy are often complicated, having been little studied before now. The purpose of this article is to present flow cytometry measurements and multivariate morphometric analyses to ascertain cytotype distribution patterns and the morphological differentiation of R. parnassifolius s.l. from calcareous screes in the Northwest of Spain. DNA ploidy level and morphometric analysis were determined for plants of R. parnassifolius s.l. using flow cytometry (112 individuals) and multivariate analysis (152 individuals). Specimens were collected in eight localities in the Northwest of the Iberian Peninsula. Different sample preservation methods (fresh, frozen, and herbarium specimens) were employed as well as the use of various buffers and internal standards, in order to test the reproducibility of DNA flow cytometry. Three ploidy levels were detected in the study area (diploid, tetraploid, and pentaploid), and mixed-cytotype populations were also found. The mean nuclear DNA content of the R. parnassifolius group ranged from 7.43 ± 0.185 to 7.63 ± 0.339 pg/2C in diploids and from 15.09 ± 0.161 to 15.85 ± 0.587 pg/2C in tetraploids. The analysis of the monoploid genome sizes (1Cx) did not reveal a clear difference among cytotypes. These results suggest low intraspecific variation, at least among the populations studied. In addition, a comparison of different DNA reference standards was conducted. A new value for the chicken genome size was used as internal reference standard (2C = 3.14 ± 0.155 pg), with similar results found using both animal and plant standards (Pisum sativum and Solanum lycopersicum). Finally, herbarium vouchers and frozen tissue were proved to be suitable for DNA ploidy level measurements. This study provided a first assessment of C values in the R. parnassifolius group using flow cytometry. The weak morphological distinction of the cytotypes and the existence of mixed-cytotype populations in the Northwest of Spain are reported here for the first time. The different distribution pattern of the two cytotypes is discussed.     

Genetics of resistance to the pink stem borer (Sesamia nonagrioides) in maize (Zea mays)

Our knowledge of the genetics of resistance to the pink stem borer ( Sesamia nonagrioides ) in maize ( Zea mays ) is restricted to a few crosses among maize inbreds. The objectives of this study were to enlarge our understanding of the genetics of traits related to damage by pink stem borer and yield under infestation and to use generation means analyses to compare per se and testcross performance for detecting epistatic effects. All generations, either per se or crossed to testers, were evaluated in a 10 × 10 triple lattice design under artificial infestation with S. nonagrioides in 2005 and 2006. Most traits fit an additive–dominance model; but evidence for epistasis for resistance and yield under infestation was shown. Epistasis, in general, did not appear to play an important role in the inheritance of yield under pink stem borer infestation. However, the epistasis contribution to maize yield performance could be important in some outstanding crosses such as EP42 × A637. Testcross generation means revealed epistatic effects undetected by the generation means analysis, but neither method was able to eliminate dominance effects that could prevail over epistatic effects.