The essential mineral nutrient potassium (K + ) is the most important inorganic cation for plants and is recognized as a limiting factor for crop yield and quality. Nonetheless, it is only partially understood how K + contributes to plant productivity. K + is used as a major active solute to maintain turgor and to drive irreversible and reversible changes in cell volume. K + also plays an important role in numerous metabolic processes, for example, by serving as an essential cofactor of enzymes. Here, we provide evidence for an additional, previously unrecognized role of K + in plant growth. By combining diverse experimental approaches with computational cell simulation, we show that K + circulating in the phloem serves as a decentralized energy storage that can be used to overcome local energy limitations. Posttranslational modification of the phloem-expressed Arabidopsis K + channel AKT2 taps this "potassium battery," which then efficiently assists the plasma membrane H + -ATPase in energizing the transmembrane phloem (re) loading processes.channel gating | energy limiting condition | phloem reloading | posttranslational regulation | potassium channel

Background and AimsOxygen can fall to low concentrations within plant tissues, either because of environmental factors that decrease the external oxygen concentration or because the movement of oxygen through the plant tissues cannot keep pace with the rate of oxygen consumption. Recent studies document that plants can decrease their oxygen consumption in response to relatively small changes in oxygen concentrations to avoid internal anoxia. The molecular mechanisms underlying this response have not been identified yet. The aim of this study was to use transcript and metabolite profiling to investigate the genomic response of arabidopsis roots to a mild decrease in oxygen concentrations.MethodsArabidopsis seedlings were grown on vertical agar plates at 21, 8, 4 and 1 % (v/v) external oxygen for 0·5, 2 and 48 h. Roots were analysed for changes in transcript levels using Affymetrix whole genome DNA microarrays, and for changes in metabolite levels using routine GC-MS based metabolite profiling. Root extension rates were monitored in parallel to investigate adaptive changes in growth.Key ResultsThe results show that root growth was inhibited and transcript and metabolite profiles were significantly altered in response to a moderate decrease in oxygen concentrations. Low oxygen leads to a preferential up-regulation of genes that might be important to trigger adaptive responses in the plant. A small but highly specific set of genes is induced very early in response to a moderate decrease in oxygen concentrations. Genes that were down-regulated mainly encoded proteins involved in energy-consuming processes. In line with this, root extension growth was significantly decreased which will ultimately save ATP and decrease oxygen consumption. This was accompanied by a differential regulation of metabolite levels at short- and long-term incubation at low oxygen.ConclusionsThe results show that there are adaptive changes in root extension involving large-scale reprogramming of gene expression and metabolism when oxygen concentration is decreased in a very narrow range.

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Background: Respiratory supercomplexes are known to exist, but their function remains to be revealed.Results: Plant supercomplexes are affected by hypoxia and a concomitant drop in pH.Conclusion: Respiratory supercomplexes are dynamic structures that are affected by the intracellular environment.Significance: Supercomplexes could have a regulatory function in guiding electrons through alternative respiratory pathways.

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