The role of abscisic acid in controlling leaf water loss, survival and growth of micropropagated Tagetes erecta plants when transferred directly to the field

Plants of Tagetes erecta L. (marigold) cultivated in vitro in ventilated containers exhibited greater control of leaf water loss and increased survival in the field than plants cultivated in sealed containers. Increased field survival of plants cultivated in ventilated containers was attributed to higher levels of endogenous abscisic acid (ABA). Therefore, ABA was supplied exogenously to plants in sealed or ventilated containers by adding ABA (10(-6), 10(-5), 10(-4) M) to the in vitro culture media in order to evaluate control of leaf water loss, growth and field survival. The addition of 10(-4) M ABA to the culture media in sealed containers produced plants that had similar control of leaf water loss and were morphologically similar to plants cultivated in ventilated containers without the addition of ABA. Field survival of 10(-4) M ABA plants (75%) was increased compared to plants cultivated in sealed containers without ABA (31%), with survival being closer to that of plants cultivated in ventilated containers (90-100%). Plants cultivated with 10(-4) M ABA (sealed and ventilated) also exhibited increased plant vigour and leaf area in the field compared to plants cultivated without ABA. The results suggest that the limited field survival and growth of plants cultured in vitro are related to the limited ABA concentrations they accumulate while in vitro. Consequently, conditions that increase the endogenous ABA concentrations of in vitro plants (like ventilation or ABA addition to the medium) would improve the control of leaf water loss, field survival and plant vigour.     

Research on arbuscular mycorrhizae in Mexico: an historical synthesis and future prospects

This review analyzes the historical development and advances of the research on arbuscular mycorrhizal fungi (AMF) in Mexico, as well as the prospects for future research. AMF-research has been focused on studying both diversity and functionality in several ecosystems of Mexico, but mainly in the tropical dry and rainy ecosystems, and the agricultural systems. In Mexico, 95 species of AMF have been recorded, representing 41% of the known species worldwide. The functional effects of AMF colonization have been examined in approximately 10% of the known host plants, but greenhouse studies continue to dominate over those conducted under field conditions. Even though research to date has been at the organismic level, further effort is needed due to the high plant diversity in Mexico. Studies on AMF biomass under field conditions and more taxonomic determination are required based on morphological features, biochemical determinations (fatty acids) and molecular tools. In addition, ecophysiological and ecological in situ studies would help in understanding the relationships among AMF, soil fauna, nutrients, and host plants. The contribution of AMF to ecosystemic processes is a priority line of research that requires an integrated approach (inter- and multidisciplinary) in order to define the role of AM symbioses for biogeochemical models. The creation of a Mexican mycorrhizal research network has and will help to identify the main challenges. Generating similar research protocols, and sharing databases and experience will assist mycorrhizologists working under the diverse financial and ecological contexts that is to be found in Mexico and Latin America.     

Chlorella sorokiniana UTEX 2805, a heat and intense, sunlight-tolerant microalga with potential for removing ammonium from wastewater

In the summer of 2003, a microalga strain was isolated from a massive green microalgae bloom in wastewater stabilization ponds at the treatment facility of La Paz, B.C.S., Mexico. Prevailing environmental conditions were air temperatures over 40 degrees C, water temperature of 37 degrees C, and insolation of up to 2400 micromol m2 s(-1) at midday for several hours at the water surface for four months. The microalga was identified as Chlorella sorokiniana Shih. et Krauss, based on sequencing its entire 18S rRNA gene. In a controlled photo-bioreactor, this strain can grow to high population densities in synthetic wastewater at temperatures of 40-42 degrees C and light intensity of 2500 micromol m2 s(-1) for 5h daily and efficiently remove ammonium from the wastewater under these conditions better than under normal lower temperature (28 degrees C) and lower light intensity (60 micromol m2 s(-1)). When co-immobilized with the bacterium Azospirillum brasilense that promotes growth of microalgae, the population of microalga grew faster and removed even more ammonium. Under exposure to extreme growth conditions, the quantity of four photosynthetic pigments increased in the co-immobilized cultures. This strain of microalga has potential as a wastewater treatment agent under extreme conditions of temperature and light intensity.     

The role of asymmetric interactions on the effect of habitat destruction in mutualistic networks

Plant-pollinator mutualistic networks are asymmetric in their interactions: specialist plants are pollinated by generalist animals, while generalist plants are pollinated by a broad range involving specialists and generalists. It has been suggested that this asymmetric--or disassortative--assemblage could play an important role in determining the observed equal susceptibility of specialist and generalist plants under habitat destruction. At the core of the analysis of the phenomenon lies the observation that specialist plants, otherwise candidates to extinction, could cope with the disruption thanks to their interaction with a few generalist pollinators. We present a theoretical framework that supports this thesis. We analyze a dynamical model of a system of mutualistic plants and pollinators, subject to the destruction of their habitat. We analyze and compare two families of interaction topologies, ranging from highly assortative to highly disassortative ones, as well as real pollination networks. We found that several features observed in natural systems are predicted by the mathematical model. First, there is a tendency to increase the asymmetry of the network as a result of the extinctions. Second, an entropy measure of the differential susceptibility to extinction of specialist and generalist species show that they tend to balance when the network is disassortative. Finally, the disappearance of links in the network, as a result of extinctions, shows that specialist plants preserve more connections than the corresponding plants in an assortative system, enabling them to resist the disruption.     

Ubiquitin plays an atypical role in GPCR-induced p38 MAP kinase activation on endosomes

Protease-activated receptor 1 (PAR1) is a G protein–coupled receptor (GPCR) for thrombin and promotes inflammatory responses through multiple pathways including p38 mitogen-activated protein kinase signaling. The mechanisms that govern PAR1-induced p38 activation remain unclear. Here, we define an atypical ubiquitin-dependent pathway for p38 activation used by PAR1 that regulates endothelial barrier permeability. Activated PAR1 K63-linked ubiquitination is mediated by the NEDD4-2 E3 ubiquitin ligase and initiated recruitment of transforming growth factor-β–activated protein kinase-1 binding protein-2 (TAB2). The ubiquitin-binding domain of TAB2 was essential for recruitment to PAR1-containing endosomes. TAB2 associated with TAB1, which induced p38 activation independent of MKK3 and MKK6. The P2Y₁ purinergic GPCR also stimulated p38 activation via NEDD4-2–mediated ubiquitination and TAB1–TAB2. TAB1–TAB2-dependent p38 activation was critical for PAR1-promoted endothelial barrier permeability in vitro, and p38 signaling was required for PAR1-induced vascular leakage in vivo. These studies define an atypical ubiquitin-mediated signaling pathway used by a subset of GPCRs that regulates endosomal p38 signaling and endothelial barrier disruption.     

Contribution of engineered electrostatic interactions to the stability of cytosolic malate dehydrogenase.

Protein engineering is a promising tool to obtain stable proteins. Comparison between homologous thermophilic and mesophilic enzymes from a given structural family can reveal structural features responsible for the enhanced stability of thermophilic proteins. Structures from pig heart cytosolic and Thermus flavus malate dehydrogenases (cMDH, Tf MDH), two proteins showing a 55% sequence homology, were compared with the aim of increasing cMDH stability using features from the Thermus flavus enzyme. Three potential salt bridges from Tf MDH were selected on the basis of their location in the protein (surface R176-D200, inter-subunit E57-K168 and intrasubunit R149-E275) and implemented on cMDH using site-directed mutagenesis. Mutants containing E275 were not produced in any detectable amount, which shows that the energy penalty of introducing a charge imbalance in a region that was not exposed to solvent was too unfavourable to allow proper folding of the protein. The salt bridge R149-E275, if formed, would not enhance stability enough to overcome this effect. The remaining mutants were expressed and active and no differences from wild-type other than stability were found. Of the mutants assayed, Q57E/L168K led to a stability increase of 0.4 kcal/mol, as determined by either guanidinium chloride denaturalization or thermal inactivation experiments. This results in a 15 degrees C shift in the optimal temperature, thus confirming that the inter-subunit salt bridge initially present in the T.flavus enzyme was formed in the cMDH structure and that the extra energy obtained is transformed into an increase in protein stability. These results indicate that the use of structural features of thermophilic enzymes, revealed by a detailed comparison of three-dimensional structures, is a valid strategy to improve the stability of mesophilic malate dehydrogenases.