Drought tolerance of two black poplar (Populus nigra L.) clones: contribution of carbohydrates and oxidative stress defence

Drought is expected to become an increasingly important factor limiting tree growth caused by climate change. Two divergent clones of Populus nigra (58-861 and Poli) originating from contrasting environments were subjected to water limitation (WL) to elucidate whether they differ in tolerance to drought, which mechanisms to avoid stress they exhibit and whether drought has an impact on the interactions between roots and shoots. Limiting water availability caused photosynthetic rate and total non-structural carbohydrate (TNC) levels to decrease in 58-861. However, starch-degrading enzyme activity and gene expression were induced in roots, and soluble sugar levels were higher than in well-watered (WW) plants. These data suggest that assimilation and partitioning of carbon to the roots are decreased, resulting in mobilization of stored starch. In contrast, the photosynthetic rate of Poli was reduced only late in the treatment, and carbohydrate levels in WL plants were higher than in WW plants. Superoxide dismutase (SOD) activity and gene expression were higher in Poli than in 58-861, even in WW plants, leading to a higher capacity to defend against oxidative stress.     

Competence of roots for race-specific resistance and the induction of acquired resistance against Magnaporthe oryzae

Generally, Magnaporthe oryzae , the causal agent of rice blast disease, is considered to be a typical leaf-infecting plant pathogenic fungus. However, it was recently reported that M. oryzae shares many characteristics in common with root-infecting pathogens and indeed was able to infect roots. Here, we report on studies testing for the capacity of roots of rice and barley to resist infections with M. oryzae . We established that roots of rice plants were colonized by M. oryzae in a manner which is different from the gene-for-gene specificity seen in leaves for the same genotypes. Furthermore, treatment of rice seedlings with benzo-(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH), a chemical that protects leaves effectively against blast by conditioning acquired resistance, was not able to prevent colonization of roots by M. oryzae although a reduction in disease levels was observed. Moreover, BTH was not able to protect barley roots against infection with M. oryzae . Taken together, our results suggest that although roots show intrinsic variation in their ability to resist colonization by M. oryzae , neither gene-for-gene incompatibility nor aquired resistance are as effective at blocking the pathogen as they are in leaves.     

Soil microbial responses to increased concentrations of atmospheric CO2

Terrestrial ecosystems respond to an increased concentration of atmospheric CO₂. While elevated atmospheric CO₂ has been shown to alter plant growth and productivity, it also affects ecosystem structure and function by changing below-ground processes. Knowledge of how soil microbiota respond to elevated atmospheric CO₂ is of paramount importance for understanding global carbon and nutrient cycling and for predicting changes at the ecosystem-level. An increase in the atmospheric CO₂ concentration not only alters the weight, length, and architecture of plant roots, but also affects the biotic and abiotic environment of the root system. Since the concentration of CO₂ in soil is already 10–50 times higher than that in the atmosphere, it is unlikely that increasing atmospheric CO₂ will directly influence the rhizosphere. Rather, it is more likely that elevated atmospheric CO₂ will affect the microbe–soil–plant root system indirectly by increasing root growth and rhizodeposition rates, and decreasing soil water deficit. Consequently, the increased amounts and altered composition of rhizosphere-released materials will have the potential to alter both population and community structure, and activity of soil- and rhizosphere-associated microorganisms. This occurrence could in turn affect plant health and productivity and plant community structure. This review covers current knowledge about the response of soil microbes to elevated concentrations of atmospheric CO₂.     

O2-Polarographic Studies on Soluble and Mitochondrial Enzymes of Crithidia fasciculata; Glycerophosphate Enzymes*

SYNOPSIS. Mitochondrial and supernatant fractions were isolated from Crithidia fasciculata by grinding with neutral alumina and differential centrifugation. Supernatant fractions contained at least 2 NAD-linked enzymes: an α-glycerophosphate dehydrogenase and a malate dehydrogenase. The properties of these enzymes were investigated polarographically with phenazine ethosulfate acting as electron acceptor. Agaricic acid, cinnamic acid and p-NO₂-cinnamic acid were specific inhibitors of the α-glycerophosphate dehydrogenase. Succinate, malate, DL-α-glycerophosphate and NADH stimulated respiration of mitochondrial preparations; O₂ uptake was greatest with succinate. KCN and antimycin A inhibited succinate respiration more than α-glycerophosphate respiration. Amytal did not affect succinate, α-glycerophosphate or NADH oxidation. The trypanocide suramin inhibited mitochondrial respiration at least 77% with each substrate. The relevance of these results to other members of the Trypanosomatidae is discussed.     

Pressure Effects on Catalysis and Control of Catalysis by Liver Fructose Diphosphatase from an Off-Shore Benthic Fish

SYNOPSIS: At low temperature (2°C), in the absence of FDPand Mg²⁺, the enzyme fructose disphosphatase (FDPase), extractedfrom the liver of an off-shore benthic Coryphaenoides species,is inactivated by exposures to relatively low pressures. Thesubstrate, FDP, and the cofactor, Mg²⁺, protect against thisinactivation, so that catalysis per se is not retarded by pressure.In contrast, at alkaline pH, pressure dramatically acceleratesthe catalytic rate when FDP and Mg²⁺ are saturating. The volumechange of activation, V*, for Coryphaenoides FDPase under theseconditions is about –40 cm³/mole. At low concentrationsof FDP and saturating concentrations of cofactor, the reactionrate at alkaline pH is pressure-independent. Similarly, at lowconcentrations of Mg²⁺ but saturating concentration of FDP,the reaction rate is pressure-independent. The K_m for FDP doesnot change measureably with pressure, while the K_a for Mg²⁺increases slightly with pressure. Under conditions of low (probablephysiological) FDP and Mg²⁺ concentrations, it is evident thatthe reaction rate is determined by the kinetic characteristicsof the enzyme and not by its energy-volume relationships, asituation which would appear to be of functional and selectivesignificance to an organism living under constantly high hydrostaticpressure. AMP is a potent specific inhibitor of CoryphaenoidesFDPase. The K₄ for AMP is essentially pressure-independent bothat neutral and alkaline pH, suggesting that efficiency of AMPcontrol of this enzyme is comparable at all pressures likelyto be encountered in nature.     

On the Nature of the Neurotrophic Phenomenon in Urodele Limb Regeneration

The nervous control of regeneration of body parts in the urodeleamphibian and other animals has been one of the best model systemsfor the study of the neurotrophic phenomenon. In the past mostof these studies were experimental morphological, but recentlythe salient problems on the nature of the cellular responseto the neurotrophic agent and the nature of the nervous agentitself are also analyzed molecularly. The ensemble of studiesreviewed in the present work, which also show that the agentof the nerve is a peptide and defines aspects of its effecton molecular synthesis in regenerate cells, leads me to advancethe following theories. I propose that the neurotrophic agentaffects only the rate of ongoing events in the cell and notthe quality and kind of the events; that the events are alreadyindigenous to the responding cells; that alteration in therateof events, for example increasing the rate of molecular syntheses,yields an increased cell population which by its size and increasedcellular interactions has formative and differentiated capabilitieswhich do not exist in a smaller cell population; and finallythat the neurotrophic factor (NTF) is one of many "conversational"peptides including nervegrowth factor (NGF) and epidermal growthfactor (EGF) which function to alter the absolute rate of ongoingcellular events.