Ultrastructural study of the relationship between generative and vegetative cells inMagnolia ×soulangeana Soul.-Bod. pollen grains

Summary InMagnolia ×soulangeana pollen grains the generative cell (GC) does not become totally free within the vegetative cell (VC), at least until the pollen tube emergence. Due to a deviation in its detachment process from the sporoderm, the opposing ends of the VC plasmalemma do not fuse themselves when the GC moves away from the intine. Consequently, the interplasmalemmic space surrounding the GC does not become isolated but rather maintains continuity with the sporoderm through a complex formation that we have called plasmalemmic cord. The real existence of this formation was confirmed through serial sectioning showing the plasmalemmic cord to consist of the VC plasmalemma. In its initial portion it is occupied by a reasonably accentuated wall ingrowth of the inner layer of the intine (intine 3). In the remainder portion, neither of the cytochemical tests used in this work have revealed the presence of a significant amount of wall material. However, ultrathin sections of samples processed either chemically or by cryofixation showed the existence of an intricate system of tubules and vesicles, some of which are evaginations of the VC plasmalemma. The hypothesis that the plasmalemmic cord may have a role in the complex interactions between the two pollen cells is discussed.     

In vitro organogenesis and somatic embryogenesis from punctured leaf of Populus nigra × P. maximowiczii

Various explant sources of Populus nigra × P. maximowiczii were used to examine the effects of growth hormones on morphogenesis in vitro. Initial experiments indicated that punctured leaves were superior to non-punctured ones for both callus growth and formation of shoots and roots on MS medium containing various types and concentrations of growth hormones. After 6 weeks in culture, an average of 178 shoots, 129 roots and 3.1 g fresh weight of callus were directly produced from the abaxial side of each punctured leaf. The best combinations of growth hormones for shoot, root and callus proliferation were 0.88 M BA plus 0.05 M 2,4-D, 0.44 M BA plus 2.69 M NAA and 0.44 M BA plus 2.26 M 2,4-D, respectively. Embryoids were also formed on callus derived from punctured leaves. The number of embryoids varied from 0 to 30 per punctured leaf. Adventitious shoots also developed simultaneously with the embryos. Embryoids were removed with a scalpel at the early developmental stages and placed on MS medium lacking growth regulators. Regenerated plantlets were transferred to pots containing vermiculite for normal growth in the greenhouse.     

Temporal effect of 2,4-D on induction of embryogenic nuclellar cultures and somatic embryo development of ‘Carabao’ mango

Summary Embryogenic nucellar cultures were established on B5 major salts, MS minor salts and organics, 400 mg/l⁻¹ glutamine, 60 g/l⁻¹ sucrose, 2 g/l⁻¹ gellan gum, and 4.5 μM 2,4-dichlorophenoxyacetic acid (2,4-D). There was no clear relationship between developmental age of the nucellar explants and induction of embryogenic cultures. The temporal requirements for culture initiation and for induction of embryogenic competence from nucellar explants were determined by pulsing the cultures for 0, 7, 14, 21, 28, 35, 42, 49, 56, and 63 d. Culture initiation required a minimum 7–14 d pulse with 2,4-D, and was maximum after a 56-d pulse; however, embryogenic competence was optimum after a minimum of 28 d exposure to 2,4-D. Somatic embryogenesis occurred directly from the nucellar explants at low frequencies. Somatic embryo maturation only occurred following plating of suspensions onto semisolid medium, and was stimulated by 2.4–4.8 μM kinetin and 4.4 μM 6-benzyladenine.     

Microscale’s relationship between Young’s modulus and tissue density. Prediction of displacements

The study presents an experimental verification of Wagner et al.’s relationship in microscale and proposes a modification of this relationship. For this purpose, 11 cubic specimens were microcomputed tomography scanned and mechanically tested with the displacement full-field measurements using a digital image correlation system. Then, numerical simulations of the compression tests were performed using a finite elements method. The Young’s modulus distributions assigned to the finite elements models were calculated using both of Wagner et al.’s relationships: original and modified. Comparison of the experimental and numerical results indicated the accuracy of numerical solutions for both relationships.     

Is the relationship between fertility of parents and children really weak?

The relationship between fertility of parents and children has been designated as "weak" by most investigators. This paper reviews the evidence over the past century and argues that, even allowing for problems with available data sources, the relationship was probably close to zero for pre-transitional populations. However, over time, the relationship has tended to become more substantial and is now of a similar order of magnitude in developed countries as other widely used explanatory variables. Possible mechanisms for the observed relationship are discussed, especially the roles of socialization and inherited factors. The types of data used are compared to the scientific questions posed, and the limitations of the common comparison of married-mother/married-daughter pairs are considered. Finally, some evidence from recent large-scale surveys in Britain and the United States is presented to show changes over recent periods and the relative effects of sibship size of fathers and mothers.     

Somatic embryogenesis and shoot regeneration from excised adventitious roots of the rootstock Rosa hybrida L. ‘Moneyway’

Plants were regenerated from excised adventitious roots of the rose rootstock Moneyway via a three step procedure: callus induction, induction of somatic embryos and shoot development. Callus was induced on excised roots after incubation for 4 weeks in the dark on SH-medium (Schenk and Hildebrandt) containing 50 M 2,4-dichlorophenoxyacetic acid. For embryo induction, calluses were transferred to hormone-free SH-medium and incubated for 8 weeks. The use of Gelrite instead of agar during callus induction stimulated somatic embryogenesis (up to 16% of the explants formed organized structures), whereas the presence of 6-benzylaminopurine in this phase inhibited subsequent regeneration. Yellow solid calluses with embryo-like cotyledons or primordia and friable calluses with embryos were selected, and upon incubation in the light shoots developed. Shoot development was faster and more frequent on solid callus than on friable callus (64% and 21% of the calluses finally formed one or more shoots, respectively). Eleven out of thirteen regenerants developed similarly to control shoots. Finally this regeneration method is compared with other systems for somatic embryogenesis and opportunities for the production of transgenic rose rootstocks and rose cultivare are discussed.Abbreviations BAP 6-benzylaminopurine - BM basal medium - BM+ enriched basal medium - 2,4-D 2,4-dichlorophenoxyacetic acid - DAPI-4,6 diamidino-2-phenylindole - FeEDDHA ferric ethylenediamine di(ohydroxyphenylacetate) - FeEDTA ferric ethylenediamine tetraacetate - IBA indole-3-butyric acid     

What is the relationship between the global structures of apo and holo proteins?

It is well known that ligand binding and release may induce a wide range of structural changes in a receptor protein, varying from small movements of loops or side chains in the binding pocket to large‐scale domain hinge‐bending and shear motions or even partial unfolding that facilitates the capture and release of a ligand. An interesting question is what in general are the conformational changes triggered by ligand binding? The aim of this work is analyze the magnitude of structural changes in a protein resulting from ligand binding to assess if the state of ligand binding needs to be included in template‐based protein structure prediction algorithms. To address this issue, a nonredundant dataset of 521 paired protein structures in the ligand‐free and ligand‐bound form was created and used to estimate the degree of both local and global structure similarity between the apo and holo forms. In most cases, the proteins undergo relatively small conformational rearrangements of their tertiary structure upon ligand binding/release (most root‐mean‐square‐deviations from native, RMSD, are <1 Å). However, a clear difference was observed between single‐ and multiple‐domain proteins. For the latter, RMSD changes greater than 1 Å and sometimes larger were found for almost 1/3 of the cases; these are mainly associated with large‐scale hinge‐bending movements of entire domains. The changes in the mutual orientation of individual domains in multiple‐domain proteins upon ligand binding were investigated using a mechanistic model based on mass‐weighted principal axes as well as interface buried surface calculations. Some preferences toward the anticipated mechanism of protein domain movements are predictable based on the examination of just the ligand‐free structural form. These results have applications to protein structure prediction, particularly in the context of protein domain assembly, if additional information concerning ligand binding is exploited. Proteins 2008. © 2007 Wiley‐Liss, Inc.     

A global relationship between the heterotrophic and autotrophic components of soil respiration?

Soil surface CO₂ flux (R_S) is overwhelmingly the product of respiration by roots (autotrophic respiration, R_A) and soil organisms (heterotrophic respiration, R_H). Many studies have attempted to partition R_S into these two components, with highly variable results. This study analyzes published data encompassing 54 forest sites and shows that R_A and R_H are each strongly (R²>0.8) correlated to annual R_S across a wide range of forest ecosystems. Monte Carlo simulation showed that these correlations were significantly stronger than any correlation introduced as an artefact of measurement method. Biome type, measurement method, mean annual temperature, soil drainage, and leaf habit were not significant. For sites with available data, there was a significant (R²=0.56) correlation between total detritus input and R_H, while R_A was unrelated to net primary production. We discuss why R_A and R_H might be related to each other on large scales, as both ultimately depend on forest carbon balance and photosynthate supply. Limited data suggest that these or similar relationships have broad applicability in other ecosystem types. Site‐specific measurements are always more desirable than the application of inferred broad relationships, but belowground measurements are difficult and expensive, while measuring R_S is straightforward and commonly done. Thus the relationships presented here provide a useful method that can help constrain estimates of terrestrial carbon budgets.     

Plantlet regeneration from mature zygotic embryos and embryonic explants of masson pine （Pinus massoniana Lamb.）

Excised zygotic embryos,cotyledons and hypocotyls of juvenile seedlings of masson pine were grown on DCR medium supplemented with several concentrations of various plant phytohormones.BA(1.0mg/L) in combination with NAA(0.05mg/L) in DCR medium was found to increase the formation of adventitious buds from mature zygotic embryos,but most of them were formed at the tips of embryonic cotyledons.Adventitious buds were obtained from cotyledons and hypocotyls from juvenile seedlings when they were cultured on DCR medium containing BA 3-5 mg/L and NAA 0.1-0.2 mg/L.Elongation of buds were observed on hormone-free DCR medium with or without activated charcoal(0.5%).Root initiation was achieved with full or half strength DCR medium supplemented with IBA 1.0 mg/L and NAA 0.25-0.5 mg/L.Approximately 11-20 axillary buds formed on each explant when juvenile seedling explants were treated(3-20h) with BA 50-100 mg/L,followed by transfer to hormone-free DCR medium.The maximum number of shoots obtained per explant within six months was 33.     

Does there exist an intrinsic relationship between the flexibility and self-assembly of pepfactants?

Short peptide surfactants (pepfactants) bearing the amphiphilic molecular architecture of hydrophobic and hydrophilic moieties are attractive for a wide range of biological and medical applications. Understanding of structural basis and molecular mechanism underlying the self-assembling behaviour of pepfactants is fundamentally important for rationally designing surfactant-like peptides to function as diverse biomaterials. To date, however, the relationship between the physicochemical properties and self-assembly of pepfactants still remains largely unexplored. In this study, we attempt to elucidate the role of structural flexibility and dynamics in peptide self-assembly. Two fast and reliable quantitative structure–property relationship predictors are carefully developed with the sophisticated genetic algorithm/partial least squares method; the predictors are then applied to estimate molecular flexibility and self-assembling ability for 10,000 randomly generated surfactant-like peptides. As a result, a significant negative correlation between the flexibility and self-assembly is observed, which can be fitted fairly well using an exponential curve. Furthermore, atomistic molecular dynamics simulations also reveal a noticeable difference of flexibility profile between strong and weak self-assembling peptides. All these come together to suggest that the self-assembling behaviour of pepfactants is highly dependent on their structural flexibility.     

Is there a relationship between the supramolecular organization of the mitochondrial ATP synthase and the formation of cristae?

Blue native polyacrylamide gel electrophoresis (BN-PAGE) analyses of detergent mitochondrial extracts have provided evidence that the yeast ATP synthase could form dimers. Cross-linking experiments performed on a modified version of the i-subunit of this enzyme indicate the existence of such ATP synthase dimers in the yeast inner mitochondrial membrane. We also show that the first transmembrane segment of the eukaryotic b-subunit (bTM1), like the two supernumerary subunits e and g, is required for dimerization/oligomerization of ATP synthases. Unlike mitochondria of wild-type cells that display a well-developed cristae network, mitochondria of yeast cells devoid of subunits e, g, or bTM1 present morphological alterations with an abnormal proliferation of the inner mitochondrial membrane. From these observations, we postulate that an anomalous organization of the inner mitochondrial membrane occurs due to the absence of ATP synthase dimers/oligomers. We provide a model in which the mitochondrial ATP synthase is a key element in cristae morphogenesis.     

Parental epigenetic control of embryogenesis: a balance between inheritance and reprogramming?

At fertilization, fusion of two differentiated gametes forms the zygote that is capable of forming all of the varied cell lineages of an organism. It is widely thought that the acquisition of totipotency involves extensive epigenetic reprogramming of the germline state into an embryonic state. However, recent data argue that this reprogramming is incomplete and that substantial epigenetic information passes from one generation to the next. In this review we summarize the changes in chromatin states that take place during mammalian gametogenesis and examine the evidence that early mammalian embryogenesis may be affected by inheritance of epigenetic information from the parental generation.     

What determines the relationship between plant diversity and habitat productivity?

The relationship between biodiversity and habitat productivity has been a fundamental topic in ecology. Although the relationship between these parameters may exhibit different shapes, the unimodal shape has been frequently encountered. The decrease in diversity at high productivity has usually been attributed to competitive exclusion. We suggest that evolutionary history and dispersal limitation may be even more important in shaping the diversity–productivity relationship. On a global scale, unimodal diversity–productivity relationships dominate in temperate regions, whereas positive relationships are more common in the tropics. This difference can be accounted for by contrasting evolutionary history. Temperate regions have smaller species pools for productive habitats since these habitats have been scarce historically for speciation, while the opposite is true for the tropics. In addition, dispersal within a region may limit diversity either due to the lack of dispersal syndromes at low productivity or the low number of diaspores at high productivity. Thereafter, biotic interactions (competition and facilitation) can shape the relationship. All these processes can act independently or concurrently. We recommend that the common approach to examining empirical diversity–environmental relationships should start with the role of large‐scale processes such as evolutionary history and dispersal limitation, followed by influences associated with ecological interactions.     

In vitro studies on the relationship between polyunsaturated fatty acids and cancer: tumour or tissue specific effects?

In vitro cell culture experiments have lead to the consensus in the literature that certain PUFAs have a selective cytotoxic or anti-proliferative effect on tumour cells and a minimal, or no effect on normal cells. Re-examination of key publications showed that when normal cells were used for comparison, they were generally not from the same cell, tissue, or species type as the tumour cells. Recently, investigations have included more appropriate normal control cells, and though tumour specific cytotoxic/anti-proliferative PUFA effects are found in some cell types, in others the normal cells are more sensitive. Cell type differences were found in the relative ability of individual PUFAs to act. However, within a cell type differences in susceptibility were influenced by grade and stage of tumour, immortalisation and tumourigenic status, cell culture media and cell plating density. Together these results suggest that the consensus is not valid, and that susceptibility to PUFA is cell type specific, and alters during neoplastic progression. Furthermore, the cytotoxic/anti-proliferative effect induced by both n-3 and n-6 PUFAs on a wide variety of cell types, associated with an increase in lipid peroxidation in vitro, cannot account for the in vivo data on the relationship between dietary fat and certain cancers. However, the effects of PUFAs and their metabolites on cell signalling pathways may explain the in vivo data.     

How does the meristem of sunflower capitulum cope with tissue expansion and floret initiation? A quantitative analysis

The coordination between floret initiation and tissue expansion has been studied and quantified in the apical meristem of sunflower (Helianthus annuus) plants grown under different light availability. A method was developed to quantify tissue expansion in the meristem during floret initiation from measurements of meristem area, number of florets and primordium size. Initially, floret initiation and tissue expansion occurred simultaneously at the meristem surface. The duration of this phase remained unchanged across environments, whereas the rate of tissue expansion varied greatly. Floret initiation rate depended on meristem initial size and tissue-expansion rate. Thereafter, floret initiation continued without tissue expansion in the meristem, resulting in a rapid decrease of meristem area. A set of equations was proposed to predict floret initiation rate and floret number as a function of the rates of tissue expansion in the meristem before and during floret initiation. This formalism demonstrated the role of tissue expansion in determining the final number of florets, and provided a framework to analyse the response of floret initiation to genotype and environment.     

Is the existence of a mutualistic relationship between Lobesia botrana and Botrytis cinerea well-founded?

Some studies have highlighted benefits for Lobesia botrana by adding Botrytis cinerea mycelium to an artificial larval diet and have suggested a mutualistic relationship between the two organisms on grapevine, hypothesizing that fungal sterols were the nutritional factor involved. Because the nutritional quality of an artificial diet should be similar to grapes to allow extrapolation of the results to the field conditions, in the current study L. botrana larval performance was compared when larvae were fed on grapes (berries) or two artificial diets either with or without enrichment with B. cinerea. Based on sterol analysis, the two artificial diets had high cholesterol content, but relative to berries showed comparable and low phytosterol contents, respectively (high- and low-phytosterol, HPh, and LPh). While larval fitness on the HPh diet was similar to berries, the LPh diet led to higher mortality and worse larval performance. The addition of the fungus compensated for the shortage in the LPh diet but did not improve the HPh diet. Supplementing the LPh diet with linoleic acid, which is supplied also from B. cinerea, partially improved larval performance. In a field experiment, females did not show any egg-laying preferences towards naturally botrytized bunches. The positive effect of B. cinerea on the moth's next generation that is reported in the literature could be a consequence of fungus developed inside berry tunnels bored by larvae. Therefore, based on our data and previous reports the existence of a mutualistic relationship between L. botrana and B. cinerea is not well-founded.