Harsh hakea (Hakea prostrata R.Br.) is a member of the Proteaceae family, which is highly represented on the extremely nutrientimpoverished soils in southwest Australia. When phosphorus is limiting, harsh hakea develops proteoid or cluster roots that release carboxylates that mobilize sparingly soluble phosphate in the rhizosphere. To investigate the physiology underlying the synthesis and exudation of carboxylates from cluster roots in Proteaceae, we measured O 2 consumption, CO 2 release, internal carboxylate concentrations and carboxylate exudation, and the abundance of the enzymes phosphoenolpyruvate carboxylase and alternative oxidase (AOX) over a 3-week time course of cluster-root development. Peak rates of citrate and malate exudation were observed from 12-to 13-d-old cluster roots, preceded by a reduction in cluster-root total protein levels and a reduced rate of O 2 consumption. In harsh hakea, phosphoenolpyruvate carboxylase expression was relatively constant in cluster roots, regardless of developmental stage. During cluster-root maturation, however, the expression of AOX protein increased prior to the time when citrate and malate exudation peaked. This increase in AOX protein levels is presumably needed to allow a greater flow of electrons through the mitochondrial electron transport chain in the absence of rapid ATP turnover. Citrate and isocitrate synthesis and accumulation contributed in a major way to the subsequent burst of citrate and malate exudation. Phosphorus accumulated by harsh hakea cluster roots was remobilized during senescence as part of their efficient P cycling strategy for growth on nutrient impoverished soils.In some plant species, a shortage of phosphorus induces the development of dense clusters of determinate branch roots (rootlets) that arise, en masse, from a localized region of the parent root axis. These short-lived structures have been termed proteoid roots because they were first described for Proteaceae (Purnell, 1960) but have since been found in a wide range of other species and families and are now often referred to as cluster roots . Most of our advances in cluster-root biology have been derived from studies of the crop species Lupinus albus (Fabaceae family) (Gardner et al

Polyploidy affects photosynthesis by causing changes in morphology, anatomy and biochemistry. However, in newly developed polyploids, the genome may be unstable. In this study, diploid (2×) and synthetic autotetraploids in initial (4×-C0) and 11th generations (4×-C11) of Phlox drummondii Hook were used to study the effects of chromosome doubling and genome stabilisation on leaf photosynthesis and anatomical properties. The light-saturated photosynthetic rate on a leaf area basis at 360 µmol CO2 mol–1 air (A360) was highest in 4×-C11 leaves, intermediate in 4×-C0 leaves, and lowest in 2× leaves. Rubisco amounts, CO2-saturated photosynthetic rate at 1200 µmol CO2 mol–1 air at PPFD of 1000 µmol m–2 s–1 (A1200, representing the capacity for RuBP regeneration), cumulative surface areas of chloroplasts facing intercellular spaces (Sc), all expressed on a leaf area basis, were all higher in 4× leaves than in 2× leaves, and stomatal conductance (gs) at 360 µmol CO2 mol–1 air was only higher in the 4×-C11 leaves. A360 for the 4×-C11 leaves was greater than that in the 4×-C0 leaves despite having similar amounts of Rubisco. This was presumably associated with a greater RuBP regeneration capacity, as well as an increase in Sc and gs, which would increase the CO2 concentration of Rubisco. These results indicate that the higher rate of photosynthesis in 4×-C11 leaves was not an immediate outcome of chromosome doubling; rather, it was due to adjustment and adaptation during the process of genome stabilisation.

Nitrogen fixation in nodules that contain symbiotic rhizobial bacteria enables legumes to thrive in nitrogen-poor soils. However, this symbiosis is energy consuming. Therefore, legumes strictly control nodulation at both local and systemic levels. Mutants deficient in such controls exhibit a range of phenotypes from non-nodulation to hypernodulation. Here, we isolated a novel hypernodulation mutant from the M(2) progeny derived from Lotus japonicus MG-20 seeds mutagenized by irradiation with a carbon ion beam. We named the mutant 'plenty' because it formed more nodules than the wild-type MG-20. The nodulation zone in the plenty mutant was wider than that in the wild type, but not as enhanced as those in other previously reported hypernodulation mutants such as har1, klv or tml of L. japonicus. Unlike these hypernodulation mutants, the plenty mutant developed nodules of the same size as MG-20. Overall, the plenty mutant exhibited a unique phenotype of moderate hypernodulation. However, a biomass assay indicated that this unique pattern of hypernodulation was a hindrance to host plant growth. The plenty mutant displayed some tolerance to external nitrates and a normal triple response to ethylene. Grafting experiments demonstrated that the root of plenty was responsible for its hypernodulation phenotype. Genetic mapping indicated that the PLENTY gene was located on chromosome 2.

Genes of CLE (CLAVATA3/ESR-related) family encode peptide ligands that regulate plant development in response to external stimuli such as rhizobial infection and the nitrate application as well as various internal stimuli. To investigate whether LjCLE gene(s) may involve in plant response to inorganic phosphate (Pi), we analyzed Pi responses of 39 LjCLE genes in hydroponically grown Lotus japonicus plants (ecotype Miyakojima 'MG-20'). Two LjCLE genes, LjCLE19 and 20, were up-regulated specifically and greatly in roots of L. japonicus by Pi addition to the hydroponic solution. When the external Pi level increased, expressions of LjCLE19 and 20 increased before the increase in the Pi content in plants. On the other hand, when the external Pi level decreased, the Pi content in plants decreased first, then expression levels of LjCLE19 and 20 decreased. Based on our results, we discuss the relationship between LjCLE19 and 20 and the tissue Pi levels in plants. This is the first report showing induction of specific CLE genes by phosphate.