The alternative oxidase of the inner mitochondrial membrane catalyses cyanide-insensitive respiration in plants and fungi. The molecular biology and regulation of this oxidase have been intensively studied over the past 10 years. Genes have been isolated, expression has been investigated and novel mechanisms for the regulation of activity have been discovered. This paper reviews these recent advances, focusing on the regulation of gene expression and activation by protein modification and organic acids, and possible roles of the alternative oxidase are discussed.

When slices of barley endosperm are incubated with gibberellic acid in aseptic conditions the activities of salt‐soluble endo‐β‐glucanase and endopentosanase are greatly augmented and enzymes and soluble products of cell‐wall degradation (hexosan and pentosan) are secreted into the surrounding medium. This cytolytic action, together with the enhanced amylolytic activity which can be detected in isolated endosperms subjected to gibberellic acid, is sufficient to cause complete solubilization of the starchy endosperm in 3 days at 25° C. Gibberellic acid acts through the respiring aleurone layer; it has no effect on aleurone‐free endosperm or on endosperm slices in which the aleurone has lost the power of reducing tetrazolium salts. Gibberellic acid‐induced sugar secretion from endosperm slices is maximal at 30° C. and completely inhibited at 37° C. and secretion both of sugars and of endo‐β‐glucanase is unaffected in conditions which inhibit proteolysis. Excised barley embryos show no response to added gibberellic acid. It is suggested that, when barley germinates without additions of gibberellic acid, endogenous gibberellin present in the embryo is translocated to the aleurone where it induces secretion of hydrolytic enzymes from subcellular particles, so causing modification to proceed inwards from the aleurone; if this is so, then added gibberellic acid merely enhances the effects of the endogenous component.

The cytosolic 80S ribosome is composed of protein and RNA molecules and its function in protein synthesis is modulated through interaction with other cytosolic components. Defining the role of each of the proteins associated with ribosomes in plants is a major challenge which is hampered by difficulties in attribution of different proteins to roles in ribosome biogenesis, the mature cytosolic ribosome (r-proteins) or to the broader translatome associated with functioning ribosomes. Here we refined the core r-protein composition in plants by determining the abundance of proteins in low, partially and highly purified ribosomal samples from Arabidopsis thaliana cell cultures. To characterise this list of proteins further we determined their degradation (KD) and synthesis (KS) rate by progressive labelling with 15 N combined with peptide mass spectrometry analysis. The turnover rates of 55 r-proteins, including 26 r-proteins from the 40S subunit and 29 r-proteins from the 60S subunit could be determined. Overall, ribosome proteins showed very similar KD and KS rates suggesting that half of the ribosome population is replaced every 3-4 days. Three proteins showed significantly shorter half-lives; ribosomal protein P0D (RPP0D) with a half-life of 0.5 days and RACK1b and c with half-lives of 1-1.4 days. The ribosomal RPP0D protein is a homolog of the human Mrt4 protein, a trans-acting factor in the assembly of the pre-60S particle, while RACK1 has known regulatory roles in cell function beyond its role as a 40S subunit. Our experiments also identified 58 proteins that are not from r-protein families but co-purify with ribosomes and co-express with rproteins in Arabidopsis. Of this set, 26 were enriched more than 10-fold during ribosome purification. A number have known roles in translation or ribosome-association while others are newly proposed ribosome-associated factors in plants. This analysis provides a more robust understanding of Arabidopsis ribosome content, shows that most r-proteins turnover in unison in vivo, identifies a novel set of potential plant translatome components, and reveals how protein turnover can identify r-proteins involved in ribosome biogenesis or regulation in plants. Data are available via ProteomeXchange with identifier PXD012839.

ePlant was introduced in 2017 for exploring large Arabidopsis thaliana data sets from the kilometre to nanometre scales. In the past four years we have used the ePlant framework to develop ePlants for 15 agronomically-important species: maize, poplar, tomato, Camelina sativa, soybean, potato, barley, Medicago truncatula, eucalyptus, rice, willow, sunflower, Cannabis sativa, wheat and sugarcane. We also updated the interface to improve performance and accessibility, and added two new views to the Arabidopsis ePlant - the Navigator and Pathways viewers. The former shows phylogenetic relationships between homologs in other species and their expression pattern similarities, with links to view data for those genes in the respective ePlants. The latter shows Plant Reactome metabolic reactions. We also describe new Arabidopsis data sets including single cell RNA-seq data from roots, and how to embed ePlant eFP expression pictographs into any web page.