Alkaloid biosynthesis in Papaver sp. cells in culture and during organogenesis

In vitro cell cultures of two Papaver species, P. somniferum and P. bracteatum initiated from mature seeds were screened for their ability to produce alkaloids. Protocols for callus induction, somatic embryogenesis and organogenesis were established. The alkaloid contents were analysed by high-performance-liquid chromatography, thin-layer chromatography and spectrophotometric assays. Undifferentiated callus produced small amounts of sanguinarine, which increased with the degree of tissue differentiation. Embryogenic calli were maintained in culture for more than 2 years, retaining a high regeneration capability. Thin-layer chromatography analysis revealed variations in alkaloid spectrum between parallel cell lines. The morphinan alkaloid, thebaine, was found to be accumulated exclusively in morphogenous strains of P. bracteatum, and morphine was the major alkaloid in the spectrum of P. somniferum dedifferentiated callus. Regenerant plants synthesized thebaine and sanguinarine at the same level as juvenile plants grown from P. bracteatum seeds. We revealed differences in the ability to produce different types of alkaloids: seed-derived plants were able to accumulate thebaine while undifferentiated primary cell cultures produced only sanguinarine. The production of either sanguinarine and morphinan alkaloids are found in regenerants showing that both metabolic pathways were active in young plantlets.     

The species and chromosomal distribution of the centromeric alpha-satellite I sequence from sheep in the tribe Caprini and other Bovidae

The evolution of chromosomes in species in the family Bovidae includes fusion and fission of chromosome arms (giving different numbers of acrocentric and metacentric chromosomes with a relatively conserved total number of arms) and evolution in both DNA sequence and copy number of the pericentromeric alpha-satellite I repetitive DNA sequence. Here, a probe representing the sheep alpha-satellite I sequence was isolated and hybridized to genomic DNA digests and metaphase chromosomes from various Bovidae species. The probe was highly homologous to the centromeric sequence in all species in the tribe Caprini, including sheep (Ovis aries), goat (Capra hircus) and the aoudad or Barbary sheep (Amnotragus lervia), but showed no detectable hybridization to the alpha-satellite I sequence present in the tribe Bovini and at most very weak to species in the tribes Hippotragini, Alcelaphini or Aepycerotini. The sex chromosomes of sheep, goat and aoudad did not contain detectable alpha-satellite I sequence; in sheep, one of the three metacentric autosomal chromosomes does not carry the sequence, while in aoudad, it is essentially absent in three large autosomal pairs as well as the large metacentric chromosome pair. The satellite probes can be used as robust chromosome and karyotype markers of evolution among tribes and increase the resolution of the evolutionary tree at the base of the Artiodactyla.     

AN INTERPRETATION OF THE HYDRODYNAMICS OF POLLEN

The pollen grains of angiosperms are usually desiccated to some extent at the time of dispersal. Rehydration is an essential prelude to germination, and this takes place by uptake of water from the stigma after capture, water entering from the cells of the stigma surface following a water potential gradient. The passage of water into the pollen grain is regulated by the cuticle of the stigma papilla in the vicinity of the contact face, and also by the apertural mechanisms of the pollen grain exine, which act by varying the degree of exposure of the underlying pectocellulosic intine according to the degree of hydration of the grain. The sequence of events during rehydration suggests that at first the vegetative cell of the male gametophyte is without a normal plasmalemma, so that the initial dilation of the grain is followed by an interval of exudation. Thereafter, with the re-establishment of the cell membranes, the vegetative cell behaves in the manner of a normal plant cell through the period of germination.     

Stigma form and surface in relation to self-incompatibility in the Onagraceae

The Onagraceae is unique among families of comparable size in the heterogeneity of stigma form and physiology. Studies of the receptive surfaces of stigmas from representatives of all genera of the family have shown that a range of types exists from papillate to non-papillate, and from "wet", bearing a free-running secretion, to "dry", lacking such a secretion, most genera falling in the former category. Self-incompatibility is wholly restricted to wet-stigma species, and direct and circumstantial evidence indicates that it is always likely to be of the gametophytic type, as in certain Oenothera species that have been the subjects of detailed genetical and physiological research. Whilst Oenothera and most other self-incompatible species in the family appear to reject incompatible pollen mainly in the stigma surface layers, the precise site is subject to both genetical and environmentally-determined variation. Intraspecific polymorphy in sex function is known in the genus Fuchsia , most species of which have wet stigmas. Female sterility in the functionally male flowers of certain species of this genus appears simply to be due to a failure to produce adequate stigma secretion. All species of the dry-stigma genera in the family are self-compatible, but not all are inbreeding because of the existence of other mechanisms enforcing outcrossing. The stigmas of some possess certain unique features, apparently related to water conservation. Possible evolutionary trends in the family and in the breeding and pollination systems are briefly discussed in the light of what is now known of pollen-stigma relationships.     

Some permeability properties of angiosperm pollen grains,pollen tubes and generative cells

Summary The permeability of pollen grains, pollen tubes and generative cells of Helleborus foetidus and Galanthus nivalis has been investigated using four probes spanning a wide range of molecular weights: 4,6-diamidino-2-phenyl indole (DAPI; mol.wt. 350). Evans blue (mol.wt. 960), FITC-dextran (average mol.wt. 19400) and FITC-albumin (average mol.wt. 67000). DAPI penetrated into the vegetative cells of desiccated and hydrated pollen, and also entered growing pollen tubes. In contrast, the generative cells of hydrated pollen and of pollen tubes were highly resistant to penetration, as they were when isolated in osmotically balancing medium. Evans blue failed to enter intact generative cells under any of the conditions tested. The dye ultimately entered the vegetative cells of some pollen grains, but these were non-germinable. Growing pollen tubes invariably resisted penetration. Neither of the high molecular weight conjugates entered germinable pollen grains or intact pollen tubes. The results suggest that it is highly unlikely that DNA fragments of high molecular weight can enter viable pollen, pollen tubes or generative cells under any normal conditions.     

Technical comment on Boersma et al. (2016) Temperature driven changes in the diet preference of omnivorous copepods: no more meat when it's hot? Ecology Letters, 19, 45–53

A recent study concluded that omnivorous plankton will shift from predatory to herbivorous feeding with climate warming, as consumers require increased carbon:phosphorous in their food. Although this is an appealing hypothesis, we suggest the conclusion is unfounded, based on the data presented, which seem in places questionable and poorly interpreted.     

Comparative analysis of the nucleosomal structure of rye,wheat and their relatives

Analysis of the structure of chromatin in cereal species using micrococcal nuclease (MNase) cleavage showed nucleosomal organization and a ladder with typical nucleosomal spacing of 175–185 bp. Probing with a set of DNA probes localized in the authentic telomeres, subtelomeric regions and bulk chromatin revealed that these chromosomal regions have nucleosomal organization but differ in size of nucleosomes and rate of cleavage between both species and regions. Chromatin from Secale and Dasypyrum cleaved more quickly than that from wheat and barley, perhaps because of their higher content of repetitive sequences with hairpin structures accessible to MNase cleavage. In all species, the telomeric chromatin showed more rapid cleavage kinetics and a shorter nucleosome length (160 bp spacing) than bulk chromatin. Rye telomeric repeat arrays were shortest, ranging from 8 kb to 50 kb while those of wheat ranged from 15 kb up to 175 kb. A gradient of sensitivity to MNase was detected along rye chromosomes. The rye-specific subtelomeric sequences pSc200 and pSc250 have nucleosomes of two lengths, those of the telomeric and of bulk nucleosomes, indicating that the telomeric structure may extended into the chromosomes. More proximal sequences common to rye and wheat, the short tandem-repeat pSc119.2 and rDNA sequence pTa71, showed longer nucleosomal sizes characteristic of bulk chromatin in both species. A strictly defined spacing arrangement (phasing) of nucleosomes was demonstrated along arrays of tandem repeats with different monomer lengths (118, 350 and 550 bp) by combining MNase and restriction enzyme digestion.