草莓愈伤组织超低温贮藏及植株再生研究

本文介绍了草莓愈伤组织的诱导,超低温贮藏及不同解融方法对其细胞存活率和芽分化的影响。     

Cold requirement for maximal activity of the bacterial ice nucleation protein INAZ in transgenic plants

The bacterial ice nucleation gene inaZ confers production of ice nuclei when transferred into transgenic plants. Conditioning of the transformed plant tissue at temperatures near 0°C greatly increased the ice nucleation activity in plants, and maximum ice nucleation activity was achieved only after low-temperature conditioning for about 48 h. Although the transgenic plants contain similar amounts of inaZ mRNA at both normal and low temperatures, low temperatures are required for accumulation of INAZ protein. We propose that the stability of the INAZ protein and thus ice nucleation activity in the transgenic plants is enhanced by low-temperature conditioning.     

The freezing characteristics of cauliflower curd

Cultivar differences in frost resistance and the heritable nature of resistance were demonstrated using seedling cauliflower plants. Such cultivar differences were not however expressed in the curd. Selection for frost resistance in cauliflower should therefore use whole plant screening techniques. Curd material when frozen as isolated florets, supercooled over the range – 1°C to – 12°C and the mean freezing point of all curds tested was -6°C to -7.25°C (overall mean -6.44°C). Curd florets which supercooled but did not freeze were completely undamaged, whereas freezing always led to cell damage and death observed as water-soaking of the floret surface and measured using an electrical conductivity method. The large range of freezing points measured suggests a range of active ice nucleators either on or within the florets. When curds were frozen intact the ability of florets to supercool was severely restricted which was attributed to the seeding of freezing by the internal growth of ice crystals. A crop protection strategy needs to identify and control or modify warm temperature nucleators in cauliflower curd.     

Calcification in aquatic plants

Abstract. The CaCO₃ deposits of aquatic plants may be intra-, inter- and extracellular. Calcification is mainly the result of photosynthetic CO₂ or HCO⁻₃ assimilation. This raises the local pH and CO²⁻₃ concentration resulting from shifts in the dissolved inorganic carbon equilibrium, due to either net CO₂ depletion as in Halimeda or localized OH⁻ efflux (or H⁺ influx) as in Chara. The plant cell wall may be important in CaCO₃ nucleation by acting as an epitaxial substratum or template, or by creating a microenvironment enriched in Ca²⁺ compared to Mg²⁺. Hypotheses on the reason for the lack of calcification in many aquatic plants are presented.     

CARBONIC ANHYDRASE AND CARBON FIXATION IN COCCOLITHOPHORIDS1

Rates of carbon fixation in coccolithophorids in culture, unlike many other algae, are carbon limited at ambient levels of dissolved inorganic carbon (DIC). Apparently, plants often rely on activity of carbonic anhydrase (CA) to raise the level of CO₂ in cells and achieve carbon saturation. However, CA activities in the coccolithophorids, Coccolithus (= Emiliania) huxleyi Lohmann and Hymenomonas (=Cricosphaera) carterae Braarud, were either not detectable or very low compared to activities in other systems, including other algae, higher plants, and representative animals. Furthermore, additions of CA to medium with 2 mM DIC at pH 8.1 resulted in nearly 30% enhancement of photosynthesis, but not coccolith formation. Although carbon fixation in coccolithophorids can be suppressed by the CA inhibitor acetazolamide, studies of CaCO₃ nucleation revealed a non-specific effect of the inhibitor. Using a 30 min assay based on pH decreases accompanying loss of dissolved. CO₃^2-, inhibition of crystal formation in the absence of CA at 1 mM acetazolamide was demonstrated for decalcified crab carapace, a tissue with which normal CaCo₃ deposition in vitro has been shown. The results suggest only a minor role for CA in coccolithophorids.     

Biosynthesis of Cephalosporins

Abstract

Certain aerobic, Gram-negative bacteria, including the epiphytic plant pathogen, Pseudomonas syringae, possess a membrane protein that enables them to nucleate crystallization in supercooled water. Currently, these ice-nucleating (IN) bacteria are being used in snow making and have potential applications in the production and texturing of frozen foods, and as a replacement of silver iodide in cloud seeding. A negative aspect of these IN bacteria is frost damage to plant surfaces. Thus, of the various types of biological ice nucleators, bacteria have been the subject of most research and also appear relevant to the anticipated practical uses. The intent of this review is to explain the identification and ecology of the ice-nucleating bacteria, as well as to discuss aspects of molecular biology related to ice nucleation and consider existing and potential applications of this unique phenomenon.     

Species‐specific influences of shrubs on the non‐dormant soil seed bank of native and exotic plant species in central‐northern Monte Desert

Deserts shrubs are well known to facilitate vegetation aggregation, mostly through seed trapping, and stress amelioration during and after plant establishment. Because vegetation aggregation effects are a by‐product of shrub presence, beneficiary species may not only be native, but also exotic. However, despite the high risk that exotic invasive species pose to ecosystem services, little is known of the role of desert shrubs on plant invasions. We assessed the influence of two shrub species on the non‐dormant soil seed bank (i.e. the number of seeds that readily germinate with sufficient water availability) of an invasive annual grass (Schismus barbatus) and of coexisting native species in a central‐northern Monte Desert (Argentina). Soil samples were collected beneath the canopies of two dominant shrub species (Bulnesia retama and Larrea divaricata) and in open spaces (i.e. intercanopies) in May 2001. Overall, the density of germinated seedlings of Schismus and that of the native species were negatively associated across microsite types. Schismus density was similar to that of all native species pooled together (mostly annuals), and was highest in Larrea samples (with no significant differences between Bulnesia and intercanopies). On the contrary, the density of all native species pooled together was highest in Bulnesia samples. Our results suggest that shrubs may contribute to plant invasions in our study system but, most importantly, they further illustrate that this influence can be species specific. Further research is needed to assess the relative importance of in situ seed production (and survival) and seed redistribution on soil seed bank spatial patterns.     

An Investigation of Freezing of Supercooled Water on Anti-Freeze Protein Modified Surfaces

This work investigates how functionalization of aluminium surfaces with natural type III Anti-Freeze Protein (AFP) affects the mechanism of heterogeneous ice nucleation. First the bulk ice nucleation properties of distilled water and aqueous solution of AFP were evaluated by differential scanning calorimetry. Then the modified surface was characterized by Secondary Ions Mass Spectroscopy (SIMS), Fourier Transform InfraRed (FTIR) spectroscopy and contact angle measurement. Freezing experiments were then conducted in which water droplets underwent a slow controlled cooling. This study shows that compared to uncoated aluminium, the anti-freeze proteins functionalized surfaces exhibit a higher and narrower range of freezing temperature. It was found that these proteins that keep living organisms from freezing in cold environment act in the opposite way once immobilized on surfaces by promoting ice nucleation. Some suggestions regarding the mechanism of action of the observed phenomena were proposed based on the Classical Nucleation Theory (CNT).     

Microtubule nucleation and organization in dendrites

Dendrite branching is an essential process for building complex nervous systems. It determines the number, distribution and integration of inputs into a neuron, and is regulated to create the diverse dendrite arbor branching patterns characteristic of different neuron types. The microtubule cytoskeleton is critical to provide structure and exert force during dendrite branching. It also supports the functional requirements of dendrites, reflected by differential microtubule architectural organization between neuron types, illustrated here for sensory neurons. Both anterograde and retrograde microtubule polymerization occur within growing dendrites, and recent studies indicate that branching is enhanced by anterograde microtubule polymerization events in nascent branches. The polarities of microtubule polymerization events are regulated by the position and orientation of microtubule nucleation events in the dendrite arbor. Golgi outposts are a primary microtubule nucleation center in dendrites and share common nucleation machinery with the centrosome. In addition, pre-existing dendrite microtubules may act as nucleation sites. We discuss how balancing the activities of distinct nucleation machineries within the growing dendrite can alter microtubule polymerization polarity and dendrite branching, and how regulating this balance can generate neuron type-specific morphologies.