Mechanism of endocarp-imposed constraints of germination of Lannea microcarpa seeds

Lannea microcarpa, a multipurpose tree species from the dry African savanna, sheds seeds that often display inhibition of germination. The underlying mechanism was investigated using seeds processed from fully matured fruits collected from natural stands in Burkina Faso. Germination of fresh seeds was variable (16¿28%), while they did not germinate after drying and rehydration. Mechanical scarification of the endocarp at the proximal end of the seeds increased germination to 83¿94%. Scarification on the distal end led to delayed radicle emergence through the produced hole in c. 40% of the seeds. The endocarp was permeable to water and respiratory gases. Increased water content in scarified seeds was associated with radicle extension during germination. Intact and scarified non-germinated seeds displayed a moderate rate of respiration with respiratory quotient (RQ) values of c. 1. Respiration increased and RQ decreased to c. 0.7 with radicle emergence. Ethylene evolution peaked in both intact and scarified seeds at the beginning of incubation and then decreased to low values. Inhibition of ethylene production by 1¿5 mM 2-amino-ethoxyvinylglycine (AVG) caused only a partial decrease of germination of the scarified seeds. Intact non-germinated seeds gradually lost viability during incubation at 30°C, but could be rescued by delayed scarification before day 15 of incubation. It is concluded that radicle emergence in dry L. microcarpa seeds is inhibited only mechanically. The mechanical properties of the endocarp are attributed to irreversible structural changes of the lignin¿hemicellulose complex, which occur during drying

Glass-formingproperty of hydroxyectoine is the cause of its superior function as a desiccation protectant

We were able to demonstrate that hydroxyectoine, in contrast to ectoine, is a good glass-forming compound. Fourier transform infrared and spin label electron spin resonance studies of dry ectoine and hydroxyectoine have shown that the superior glass-forming properties of hydroxyectoine result from stronger intermolecular H-bonds with the OH group of hydroxyectoine. Spin probe experiments have also shown that better molecular immobilization in dry hydroxyectoine provides better redox stability of the molecules embedded in this dry matrix. With a glass transition temperature of 87°C (vs. 47°C for ectoine) hydroxyectoine displays remarkable desiccation protection properties, on a par with sucrose and trehalose. This explains its accumulation in response to increased salinity and elevated temperature by halophiles such as Halomonas elongata and its successful application in “anhydrobiotic engineering” of both enzymes and whole cells

Ageing increases the sensitivity of neem (Azadirachta indica) seeds to imbibitional stress

Imbibitional stress was imposed on neem (Azadirachta indica) seeds by letting them soak for 1 h in water at unfavourable, low temperatures before further incubation at 30degreesC. Sensitivity to low imbibition temperatures increased with a decrease in seed moisture content (MC). To investigate a possible involvement of seed age in the extent of imbibitional damage, initially high-quality seed lots that differed in storage history (10 weeks versus 10 months) were examined at 4 and 7% (fresh weight basis). After 10 months of storage, the 7% MC seeds had become sensitive to imbibitional stress. Further drying (1 week) to 4% MC affected aged seeds more than non-aged seeds. Barrier properties of cellular membranes in axes excised after 1 d of rehydration were estimated using a spin-probe technique. The proportion of cells with intact membranes increased with increasing imbibition temperature. For each temperature tested, there were more cells with leaky membranes after 10 months than after 10 weeks of dry storage. Localization of embryo cells displaying loss of turgor and abnormal cellular structure was accomplished using cryo-planing, followed by cryo-scanning electron microscopy. Inspection of the cryo-planed surfaces confirmed that imbibitional damage was temperature dependent, occurring at the periphery. Ageing increased the number of imbibitionally damaged, peripheral cell layers. Germination was estimated to fail when less than 70% of axis cells were alive. We conclude that ageing increases the sensitivity to imbibitional stress. Both the fast ageing and the sensitivity to imbibitional stress might explain the apparent controversies about neem seed desiccation tolerance and storage behaviour

Покрытия на основе двумерно упорядоченного линейно-цепочечного углерода для защиты титановых имплантатов от микробной колонизации

Purpose of the study – to evaluate the antibacterial activity and biological compatibility of alloy coatings based on two-dimensionally ordered linear chain carbon (TDOLCC).Materials and Methods. Coatings based on TDOLCC were synthesized using alloying additions like nitrogen (TDOLCC+N) and silver (TDOLCC+Ag) on the surfaces of titanium plates and polystyrene plates by the ion-stimulated carbon condensation in a vacuum. The authors examined the superficial bactericidal activity of the coatings and its resistance to mechanical effects. Coated plates were evaluated in respect of rate of microbial biofilms formation by clinical isolates with multiple and extreme antibiotic resistance. Specimens were colored with crystal violet solution to visualize the biofilms. Cytotoxic effect of coatings was evaluated in respect of primary culture of fibroblasts and keratinocyte cell line HaCaT.Results. The authors observed pronounced superficial bactericidal effect of TDOLCC+Ag coating in respect of microorganisms of several taxonomic groups independently of their resistance to antibacterial drugs. TDOLCC+Ag coating proved capable to completely prevent microbial biofilm formation by antibiotic resistant clinical isolates of S. aureus and P. aeruginosa. Silvercontaining coating demonstrated mechanical resistance and preservation of close to baseline level of superficial bactericidal activity even after lengthy abrasion treatment. TDOLCC based coatings did not cause any cytotoxic effects. Structure of monolayers formed in cavities coated by TDOLCC+N and TDOLCC+Ag was indistinguishable from the monolayers in cavities of control plates.Цель исследования — оценить антибактериальную активность и биологическую совместимость легированных покрытий металлоконструкций для остеосинтеза на основе двумерно упорядоченного линейно-цепочечного углерода (ДУ ЛЦУ).Материал и методы. Методом ионно-стимулированной конденсации углерода в вакууме на поверхностях титановых пластин и полистироловых планшетов синтезированы покрытия на основе ДУ ЛЦУ с легирующими добавками: азотом (ДУ ЛЦУ+N) и серебром (ДУ ЛЦУ+Ag). Изучена поверхностная бактерицидная активность покрытий и ее устойчивость к механическим воздействиям. На пластинах с покрытиями оценена интенсивность формирования микробных биопленок клиническими изолятами микроорганизмов со множественной и экстремальной антибиотикорезистентностью, для визуализации сформированных биопленок выполнено окрашивание образцов раствором кристаллического фиолетового. Оценка цитотоксичности покрытий выполнена в отношении первичной культуры фибробластов и клеточной линии кератиноцитов HaCaT.Результаты. Выявлен выраженный поверхностный бактерицидный эффект покрытий ДУ ЛЦУ+Ag в отношении микроорганизмов нескольких таксономических групп, не зависящий от их устойчивости к антибактериальным препаратам. Для покрытия ДУ ЛЦУ+Ag установлена способность полного предотвращения формирования микробных биопленок антибиотико-резистентными клиническими изолятами S. aureus и P. aeruginosa. Показана механическая устойчивость серебросодержащего покрытия с сохранением уровня поверхностной бактерицидной активности, близкого к исходному, даже после продолжительной абразивной обработки. Покрытия на основе ДУ ЛЦУ не вызывали цитотоксических эффектов. Структура монослоя, сформированного в лунках с покрытиями ДУ ЛЦУ+N и ДУ ЛЦУ+Ag, была неотличима от лунок контрольных планшетов

Impact of amphiphile partitioning on desiccation tolerance

Sugars are reputed to protect membranes in dehydrated desiccation-tolerant organisms, such as seeds and pollens. They interact with the polar headgroups of the membrane phospholipids and control the gel-to-liquid crystalline transition temperature (Tm). Because the amount of sugar may be insufficient for full interaction in some organisms, another mechanism of membrane protection was sought. A mechanism is proposed that is based on the partitioning of amphiphilic compounds into membranes depending on the water available. This mechanism was tested (principally in experiments with Typha latifolia pollen) with an amphiphilic nitroxide spin probe, using EPR spectroscopy. It was found that, apart from the spin probe, endogenous amphiphiles may also partition into membranes during dehydration. The amphiphiles reduce the dehydration-induced increase of Tm and cause fluidization. The advantages and disadvantages of such a mechanism are discussed. The proposed mechanism is extremely effective at automatically inserting amphiphilic antioxidants into membranes with dehydration, which could promote desiccation tolerance and extend storage longevity

Acquisition of desiccation tolerance in developing wheat embryos correlates with appearance of a fluid phase in membranes

Membrane behaviour in developing wheat (Triticum aestivum cv Priokskaya) embryos was studied in relation to the acquisition of desiccation tolerance, using spin probe techniques. Fresh embryos were able to develop into seedlings at day 15 after anthesis, but it took 18 d before fast-dried, isolated embryos could germinate. On the basis of membrane integrity measurements it was estimated that between 14 and 18 d after anthesis the proportion of embryonic cells surviving fast drying increased and the critical moisture content, to which embryonic cells could be dehydrated, decreased. Apparently, embryonic cells do not acquire the same level of desiccation tolerance simultaneously. Only when all cells had become desiccation tolerant was germination of air-dried embryos possible. Using 5-doxylstearic acid as the probe molecule, an approximately similar lipid-water interface ordering of membranes was observed in all hydrated embryos, irrespective of age. Dehydration had a dual effect on the lipid interface: further ordering of the major part of the interface and the appearance of additional, disturbed regions. The proportion of these regions correlated with the proportion of desiccation-tolerant cells. We propose that the membrane surface disturbance be caused by endogenous amphiphiles that partition from the cytoplasm into membranes during drying. The absence of such disturbed regions in dried, desiccation-sensitive embryos might reflect a lack of sufficient amphiphiles. The relevance of membrane surface disturbance for desiccation tolerance is discussed

Membrane behavior as influenced by partitioning of amphiphiles during drying : a comparative study in anhydrobiotic plant systems

During cellular desiccation, reduction in volume can in principle cause amphiphilic compounds to partition from the cytoplasm into membranes, with structural perturbance as the result. Here, we studied the effect of partitioning of endogenous amphiphiles on membrane surface dynamics in desiccation-tolerant and -intolerant, higher and lower plant systems, using electron paramagnetic resonance (EPR) spin probe techniques. Labeling cells with the amphiphilic spin probe perdeuterated TEMPONE (PDT) enabled partitioning into the various phases to be followed. During drying, PDT molecules preferentially partitioned from the aqueous cytoplasm into the membrane surface and, at advanced stages of water loss, also into oil bodies. There was no specific partition behavior that could be correlated with lower/higher plants or with desiccation-tolerance. In vivo labeling with 5-doxylstearate (5-DS) enabled membrane surface fluidity to be characterized. In hydrated plants, the 5-DS spectra contained an immobile and a fluid component. The characteristics of the immobile component could not be specifically correlated with either lower or higher plants, or with desiccation tolerance. The relative contribution of the fluid component to the 5-DS spectra was higher in lower plants than in higher plants, but considerably decreased with drying in all desiccation-tolerant organisms. In contrast, the proportion of the fluid component in desiccation-sensitive wheat seedling root was higher than that in desiccation-tolerant wheat axis and considerably increased at the onset of water loss. We suggest that partitioning of amphipaths fluidize the membrane surface, but that in desiccation-tolerant systems the membranes are protected from excessive fluidization