Anoxia-enhanced expression of genes isolated by suppression subtractive hybridization from pondweed (Potamogeton distinctus A. Benn.) turions

The ability to regulate voltage-gated K+-permeable channels in the mature root epidermis is essential for waterlogging tolerance in barley

Oxygen depletion under waterlogged conditions results in a compromised operation of H+-ATPase, with strong implications for membrane potential maintenance, cytosolic pH homeostasis, and transport of all nutrients across membranes. The above effects, however, are highly tissue specific and time dependent, and the causal link between hypoxia-induced changes to the cell's ionome and plant adaptive responses to hypoxia is not well established. This work aimed to fill this gap and investigate the effects of oxygen deprivation on K+ signalling and homeostasis in plants, and potential roles of GORK (depolarization-activated outward-rectifying potassium) channels in adaptation to oxygen-deprived conditions in barley. A significant K+ loss was observed in roots exposed to hypoxic conditions; this loss correlated with the cell's viability. Stress-induced K+ loss was stronger in the root apex immediately after stress onset, but became more pronounced in the root base as the stress progressed. The amount of K+ in shoots of plants grown in waterlogged soil correlated strongly with K+ flux under hypoxia measured in laboratory experiments. Hypoxia induced membrane depolarization; the severity of this depolarization was less pronounced in the tolerant group of cultivars. The expression of GORK was down-regulated by 1.5-fold in mature root but it was up-regulated by 10-fold in the apex after 48 h hypoxia stress. Taken together, our results suggest that the GORK channel plays a central role in K+ retention and signalling under hypoxia stress, and measuring hypoxia-induced K+ fluxes from the mature root zone may be used as a physiological marker to select waterlogging-tolerant varieties in breeding programmes.

Efficient use of energy in anoxia-tolerant plants with focus on germinating rice seedlings

Anoxia tolerance in plants is distinguished by direction of the sparse supply of energy to processes crucial to cell maintenance and sometimes to growth, as in rice seedlings. In anoxic rice coleoptiles energy is used to synthesise proteins, take up K(+) , synthesise cell walls and lipids, and in cell maintenance. Maintenance of electrochemical H(+) gradients across the tonoplast and plasma membrane is crucial for solute compartmentation and thus survival. These gradients sustain some H(+) -solute cotransport and regulate cytoplasmic pH. Pyrophosphate (PPi ), the alternative energy donor to ATP, allows direction of energy to the vacuolar H(+) -PPi ase, sustaining H(+) gradients across the tonoplast. When energy production is critically low, operation of a biochemical pHstat allows H(+) -solute cotransport across plasma membranes to continue for at least for 18 h. In active (e.g. growing) cells, PPi produced during substantial polymer synthesis allows conversion of PPi to ATP by PPi -phosphofructokinase (PFK). In quiescent cells with little polymer synthesis and associated PPi formation, the PPi required by the vacuolar H(+) -PPi ase and UDPG pyrophosphorylase involved in sucrose mobilisation via sucrose synthase might be produced by conversion of ATP to PPi through reversible glycolytic enzymes, presumably pyruvate orthophosphate dikinase. These hypotheses need testing with species characterised by contrasting anoxia tolerance.

Quantitative proteomics reveals the temperature-dependent proteins encoded by a series of cluster genes in thermoanaerobacter tengcongensis

Comprehensive and quantitative information of the thermophile proteome is an important source for understanding of the survival mechanism under high growth temperature. Thermoanaerobacter tengcongensis (T. tengcongensis), a typical anaerobic thermophilic eubacterium, was selected to quantitatively evaluate its protein abundance changes in response to four different temperatures. With optimized procedures of isobaric tags for relative and absolute quantitation quantitative proteomics (iTRAQ), such as peptide fractionation with high-pH reverse phase (RP) high performance liquid chromatography (HPLC), tandem MS acquisition mode in LTQ Orbitrap Velos MS, and evaluation of the quantification algorithms, high quality of the quantitative information of the peptides identified were acquired. In total, 1589 unique proteins were identified and defined 251 as the temperature-dependent proteins. Analysis of genomic locations toward the correspondent genes of these temperature-dependent proteins revealed that more than 30% were contiguous units with relevant biological functions, which are likely to form the operon structures in T. tengcongensis. The RNA sequencing (RNA-seq) data further demonstrated that these cluster genes were cotranscribed, and their mRNA abundance changes responding to temperature exhibited the similar trends as the proteomic results, suggesting that the temperature-dependent proteins are highly associated with the correspondent transcription status. Hence, the operon regulation is likely an energy-efficient mode for T. tengcongensis survival. In addition, evaluation to the functions of differential proteomes indicated that the abundance of the proteins participating in sulfur-respiration on the plasma membrane was decreased as the temperature increased, whereas the glycolysis-related protein abundance was increased. The energy supply in T. tengcongensis at high temperature is, therefore, speculated not mainly through the respiration chain reactions.

Transcriptional responses to flooding stress in roots including hypocotyl of soybean seedlings

To understand the transcriptional responses to flooding stress in roots including hypocotyl of soybean seedlings, genome-wide changes in gene expression were analyzed using a soybean microarray chip containing 42,034 60-mer oligonucleotide probes. More than 6,000 of flooding-responsive genes in the roots including hypocotyl of soybean seedlings were identified. The transcriptional analysis showed that genes related to photosynthesis, glycolysis, Ser-Gly-Cys group amino acid synthesis, regulation of transcription, ubiquitin-mediated protein degradation and cell death were significantly up-regulated by flooding. Meanwhile, genes related to cell wall synthesis, secondary metabolism, metabolite transport, cell organization, chromatin structure synthesis, and degradation of aspartate family amino acid were significantly down-regulated. Comparison of the responses with other plants showed that genes encoding pyrophosphate dependent phosphofructokinase were down-regulated in flooded soybean seedlings, however, those in tolerant plants were up-regulated. Additionally, genes related to RNA processing and initiation of protein synthesis were not up-regulated in soybean, however, those in tolerant plants were up-regulated. Furthermore, we found that flooding-specific up-regulation of genes encoding small proteins which might have roles in acclimation to flooding. These results suggest that functional disorder of acclimative responses to flooding through transcriptional and post-transcriptional regulations is involved in occurring flooding injury to soybean seedlings.

The floristic heterogeneity of the Pantanal and the occurrence of species with different adaptive strategies to water stress

The Pantanal is characterised by a diversity of environments with areas ranging from periodic or permanent heavy flooding to areas with low flood levels, and even environments that never flood. Plant species which inhabit the floodplain are distributed in specific niches, with influence of various phytogeographic domains, including the Seasonal Semi-deciduous Forest, Amazon Rainforest, Cerrado and Chaco, as well rocky remnants, with a wide ecological span in their components. In intensely flooded areas, aquatic macrophytes are widely distributed, with their dynamics closely linked to time, depth and extent of flooding. Although the term "Pantanal" suggests a huge swamp-type wetland, water level variation during a seasonal cycle does not directly reach the root system of many plants. The landscape diversity of the Pantanal wetland is molded by the flood pulse, which interferes with the dynamics of plant communities. Therefore, the retraction and expansion of populations or communities is reflected in important ecological characteristics, considering the variety of morphological, anatomical and ecophysiological features of the species, whose phenotype is the result of a particular genotype. The present study discusses peculiar issues in the adaptation of species distributed in the Pantanal biome and underscores the importance of multidisciplinary approaches to obtain conclusive data on adaptive studies.

Involvement of plasma membrane H+-ATPase in anoxic elongation of stems in pondweed (Potamogeton distinctus) turions

• Pondweed (Potamogeton distinctus) turions can elongate in the absence of O(2). Alcoholic fermentation serves to produce energy for anoxic elongation via the breakdown of starch stored in cells. However, the mechanism of cell growth during anoxic elongation is not fully understood. • Changes in pH, H(+) equivalent and lactate content of the incubation medium were measured during anoxic elongation. The effects of fusicoccin (FC), indole-3-acetic acid (IAA), vanadate, erythrosine B and K(+) channel blockers on anoxic elongation were examined. Cytoplasmic pH and vacuolar pH were measured by (31)P nuclear magnetic resonance (NMR) spectroscopy. • Acidification of the incubation medium occurred during anoxic elongation. The contribution of CO(2) and lactic acid was not sufficient to explain the acidification. FC and IAA enhanced the elongation of stem segments. Vanadate and erythrosine B inhibited anoxic elongation. Acid growth of notched segments was observed. The activity of plasma membrane H(+)-ATPase extracted from pondweed turions was increased slightly in anoxic conditions, but that from pea epicotyls sensitive to anoxic conditions was decreased by incubation in anoxic conditions. Both the cytoplasmic pH and vacuolar pH of pondweed turion cells chased by (32)P NMR spectroscopy were stabilized during a short period < 3 h after anoxic conditions. • We propose that the enhancement of H(+) extrusion by anoxic conditions induces acidification in the apoplast and may contribute to the stabilization of pH in the cytoplasm.