Smellmelon is an invasive weed in the Golestan and Mazandran provinces of Iran. In a series of experiments, germination of freshly harvested seeds, cardinal temperatures, plant burial depth, and distribution and chemical control of smellmelon were evaluated to assist us in developing a management program to help growers manage this weed more effectively. The optimal seed germination temperature was estimated at 32.7 C by a two-piece segmented model. Mature fresh seeds of smellmelon exhibited no dormancy, whereas mucilage of the seed negatively affected germination. The greatest seed sowing depth from which seedlings emerged was 5 cm. Geographical distribution of smellmelon occurred up to an elevation of 350 m above sea level, whereas the density of smellmelon decreased at elevations higher than 151 m. Imazethapyr reduced plant growth and the reproductive capacity of smellmelon. Germination of seed from smellmelon plants treated with imazethapyr was significantly reduced compared with seed treated with bentazon or bentazon plus acifluorfen. A combination of tillage of deeper than 5 cm, early planting time, and the use of imazethapyr can reduce smellmelon competition in various field crops.

The myxocarpic diaspores of Artemisia taxa are characterized by the presence of mucilage cells in the achene coat, which differ between taxa and subgenera in shape and arrangement, and the ability to form a mucilage envelope after hydration. A detailed analysis of 38 taxa revealed three main achene behaviours related to achene coat structure and the modes of water retention after hydration. The most common achene coat possessed mucilage cells which formed a mucilage envelope after hydration; normally developed mucilage cells were able to produce mucilage after wetting. In taxa where the mucilage cells were not present in the achene coat, water was gathered under a loosely adhered achene coat or in the spaces between the covering trichomes. Myxocarpic diaspores were mostly observed in taxa occurring in dry habitats, whereas taxa devoid of the ability to produce mucilage grew predominately in mesotropic habitats. The ability to form a mucilage envelope was also related to the ploidy level. The shape and arrangement of the mucilage cells in the achene coat may differ between taxa and subgenera. In Tridentatae, the mucilage cells were dispersed in groups, forming a characteristic pattern. The role of myxocarpy in the dispersal and distribution of the Artemisia taxa is discussed.

A group of flowering plant species is known to germinate in less than 24 h from imbibition, but this phenomenon is often overlooked in the current literature. Here, I review this topic by searching the literature published since 1967 and listing the 28 most detailed cases found. Of these, 20 are species of Amaranthaceae (all formerly treated as Chenopodiaceae); 15 of these are from the subfamily Salsoloideae, which is characterized by the possession of spiral embryos. The non-chenopods listed are small numbers of species from the families Acanthaceae, Cruciferae, Gramineae (one species) and Salicaceae (Populus and Salix). Seeds of the Salsoloideae contain fully differentiated embryos. On imbibition, the embryo cells elongate and the spiral embryo uncoils and ruptures the thin seed coat. This can occur in as little as 10 min. Nearly all of the families showing very fast germination have small to very small seeds and little or no endosperm. Most species have soft, thin seed coats that imbibe water readily. All are from high-stress habitats, either arid or saline or from active floodplains, where they can rapidly exploit temporarily favourable conditions for germination. They exhibit one of two contrasting germination behaviours, either having seeds which all germinate within a very short time of wetting or having seed persistence whereby small amounts of rain cause germination of small fractions of seed from a long-living soil seed bank. Serious confusion in the literature in the use of the term ‘opportunistic’ is pointed out and clarified.

The production of hydrophilic mucilages by the seed coat or pericarp, which are released upon seed hydration, is a commonly found adaptation in angiosperms, known as myxodiaspory. These are composed primarily of pectins and hemicelluloses that undergo substantive swelling upon hydration. Synthesized in the Golgi apparatus and secreted to an apoplastic space via secretory vesicles, mucilages can also contain cellulose microfibrils or cellulosic fibres that are synthesized at the plasma membrane in association with microtubules. Investigation of mucilage production in, and differentiation of, the mucilage secretory cells of the genetic model plant Arabidopsis thaliana has identified a number of regulatory genes and enzymes involved in pectin synthesis and secretion, in muro pectin modification and secondary cell wall synthesis. Studies of the role of mucilages in both a number of species and in Arabidopsis mutants affected in its production suggest that they have multiple ecological roles. These include facilitation of seed hydration, mediation of germination under waterlogged conditions, prevention of seed dispersal or predation by adherence to soil, and promotion of seed dispersal by attachment to animals. The precise role of mucilages appears to be dependent on species and their environmental context.

This study was implemented to determine the environmental factors and causative organisms of the recent mucilage formation in the Marmara Sea. Samples were taken during the study from 7 different depths (0.5–30 m) of one sampling point of the Büyükada Island shore between January and June 2008. As a result, 62 phytoplankton species belonging to 5 different groups were identified. Dinoflagellates were dominant in terms of species number, and diatoms in terms of cell number. In January and February, mucilage formation was very dense, where 5 phytoplankton species (Clindrotheca closterium, Pseudo-nitzschia sp., Skeletonema costatum, Thalassiosira rotula (Bacillariophyceae) and Gonyaulax fragilis (Dinophyceae)) were reported as dominant organisms. Among them, Gonyaulax fragilis has never been reported in the Marmara Sea previously, thus that organism appeared firstly with the formation of dense mucilage and then when the mucilage decayed in May and June 2008, G. fragilis disappeared. Autofluorescent single-celled organisms were classified in three groups depending on their cell sizes (>20 μm, >2 μm, >0.2 μm) by membrane filtration and total count of bacteria were determined by epifluorescence microscope after dying with DAPI. The highest total bacteria was recorded in April at 25 m depth (6655 ± 44.4 cells ml−1) while the lowest count was in June at 0.5 m depth (1077 ± 26.1 cells ml−1). The seawater temperature ranged between 7.0 and 21.5°C, salinity between 20.9 and 37.4 ppt and dissolved oxygen amount between 2.75 and 12.75 mg l−1. The chlorophyll-a amount ranged between 0.10 and 6.35 μg l−1, the higher values were recorded in January at 15 m depth (6.35 μg l−1) and in April at 10 m depth (4.89 μg l−1). Among the nutrients, the amounts of nitrite + nitrate-N varied between 0.02 and 7.67 μg-at N l−1, phosphate-P between 0.11 and 0.96 μg-at P l−1 and silicate-Si between 0.37 and 8.93 μg-at Si l−1. The highest values were determined at a deeper layer where nutrients are accumulated. On the other hand, the N:P ratio interval was found as 0.1–11.3, Si:P ratio as 2.92–52.33 and N:Si ratio as 0.01–1.10 during the sampling period. Nitrogen was the limiting nutrient and the silica amount was enough to enable the development of diatoms.

Introduction. Mature green vanilla pods accumulate 4-O-(3-methoxy-benzaldehyde)-β-D-glucoside (glucovanillin), which, upon hydrolysis by an endogenous β-glucosidase, liberates vanillin, the major aroma component of vanilla. Sites of storage of glucovanillin in the pod have been controversially reported for decades; we aim, using precise and widely accepted technical terminology, to clarify this controversy by providing an anatomical, histochemical and biochemical evidence-based picture of glucovanillin accumulation sites. The pod also synthesizes an oleoresin and a mucilage of unknown constitutions; we report here their localization and structures. Materials and methods. The pod anatomy was examined by light and epifluorescence microscopy. A protocol was established allowing fine hand-dissection of diverse anatomical parts of the pod (mesocarp, placentae, trichomes, intralocular interstitial cell-free region and seeds). Glucovanillin and γ-pyranones were extracted and analyzed by HPLC, while the structures of the mucilaginous polysaccharides were determined after permethylation. Results and discussion. Glucovanillin is essentially stored in the placentae (92%) and marginally in trichomes (7%); traces were measured in the mesocarp and intralocular interstitial cell-free medium. Trichomes store massive amounts of a fluorescing oleoresin (44%) rich in alkenylmethyldihydro-γ-pyranones and synthesize a mucilage made of a glucomannan and a pectic polysaccharide carrying monomeric arabinose and galactose side-chains. Conclusion. To date, the physiological roles of glucovanillin, long-chain pyranones, and mucilage remain unknown.

Different classes of fibres differ in their potential to lower lipid levels. In order to examine how chemically diverse fibres differ in their hypolipidaemic activity, mucilages of varying chemical composition isolated from three different sources were administered to experimental animals and the metabolism of lipids and lipoproteins was studied. The mucilages used were a galactomannan isolated from fenugreek (Trigonella foenum-graecum) seeds, a glucomannan from Dioscorea esculenta tubers and an arabinogalactan from Colocasia esculenta tubers. Rats were fed these mucilages at a dose of 4 mg/100 g body weight per d for 8 weeks and the changes in the levels of total cholesterol and triacylglycerols in serum, liver and aorta were analysed. All these mucilages decreased lipid levels both in serum and tissues. Among these mucilages, glucomannan showed the most hypolipidaemic effect followed by galactomannan and arabinogalactan. Further, hepatocytes were isolated from the livers of mucilage-fed rats and the synthesis and secretion of lipoproteins were studied using metabolic labelling. There was a decrease in the synthesis and secretion of apoB-containing lipoproteins, mainly VLDL, by hepatocytes isolated from mucilage-fed rats when compared to control (P < 0·05). This was further confirmed by pulse chase analysis. Among the different mucilages, mannose-rich glucomannan showed the most effect followed by galactomannan, and mannose-free arabinogalactan showed minimal effect. Comparison of relative viscosity and water-holding capacity showed that mannan-rich mucilages like galactomannan and glucomannan, which showed greater hypolipidaemic effect, had greater relative viscosity and water-holding capacity. The present results suggested that the hypolipidaemic effect of dietary fibre involves a decrease in hepatic production of VLDL and further that it varies with the nature of the fibre.

Marine snow is a ubiquitous feature of the ocean and an important agent in the transport of energy and nutrients through marine ecosystems. Diatom aggregates, which form during blooms and, to a lesser extent, by the resuspension of benthic biofilms, are a primary source of marine snow. Genera commonly found in diatom aggregates are: Nitzschia, Chaetoceros, Rhizosolenia, Leptocylindricus, Skeletonema and Thalassionema. Most fieldwork has been restricted to a limited number of locations in the Northern Hemisphere. To quantify the global impact of diatom aggregation there is a need to conduct fieldwork in a wider range of areas, particularly in the Southern Hemisphere. Aggregates form when particles collide and stick together. Collisions in the water column are affected by turbulence, differential settlement and animal feeding, whereas diatom stickiness is affected by extracellular polymeric substances (EPS). Laboratory experiments have demonstrated that diatoms produce more EPS under nutrient limitation, although little is known about how limitation by different nutrients affects the quantity and composition of EPS and subsequent stickiness. EPS form three pools in the environment: cell coatings, soluble EPS and transparent exopolymeric particles (TEP). There is a need to investigate the dynamics of conversion between the pools of EPS by both abiotic and biological processes and how these conversions affect aggregate concentration and structure. Processes governing disaggregation have been largely overlooked, although they are as important as aggregation in determining the dynamics of aggregate concentrations in the water column. The biogeochemical significance of diatom aggregates as a means of transporting carbon and other nutrients from the euphotic zone to the seabed is well established. However, the internal biogeochemistry of aggregates is not well understood. Aggregates contain anaerobic microsites and further work is required to establish whether aggregates are significant sinks for nitrogen in the water column through anaerobic denitrification. Several hypotheses have been proposed to explain diatom aggregation in the field, but many of these are flawed because the mechanisms and adaptive explanations proposed require natural selection to operate at the level of populations rather than genes or individuals.

Sloughing of root cap cells and exudation of mucilage plays an important role in the penetration of compacted soils by roots. For the first time we have quantified the rate of sloughing of root cap cells in an abrasive growth medium that was compacted to create mechanical impedance to root growth. The number of maize (Zea mays) root cap cells sloughed into sand increased as a result of compaction, from 1930 to 3220 d−1 per primary root. This represented a 12-fold increase in the number of cells sloughed per mm root extension (from 60 to >700). We estimated that the whole of the cap surface area was covered with detached cells in compacted sand, compared with c. 7% of the surface area in loose sand. This lubricating layer of sloughed cells and mucilage probably decreases frictional resistance to soil penetration. The total carbon deposited by the root was estimated at c. 110 μg g−1 sand d−1. Sloughed cells accounted for <10% of the total carbon, the vast majority of carbon being contained in mucilage exudates.

Frictional resistance to a penetrating body can account for more than 80% of the total resistance to penetration of soil. We measured the frictional resistance between growing root caps of maize and pea and ground and smooth glass surfaces, which was linearly correlated to load, allowing calculation of the coefficient of kinetic friction and adhesion. Coefficients of kinetic friction between the root caps and the ground and smooth glass surfaces were approximately 0.04 and 0.02, respectively, the first measurements of the frictional properties of root tips at rates approaching those of root elongation, and an order of magnitude smaller than those previously reported. Results suggest that roots are well designed for penetrating soil, and encounter only small frictional resistance on the root cap. These data provide important parameters for modelling soil stresses and deformation around growing root tips.