Cluster root formation in white lupin (Lupinus albus L.) is induced mainly by phosphorus (P) starvation, and seems to be regulated by the endogenous P status of the plant. Increased formation of cluster roots, when indole acetic acid is supplied to the growth medium of P sucient plants, and inhibitory eects of kinetin application suggest the involvement of endogenous phytohormones (auxins and cytokinins), which may act in an antagonistic manner in the P-starvation response. Phosphorus de®ciency-induced adaptations of white lupin, involved in P acquisition and mobilization of sparingly available P sources, are predominantly con®ned to the cluster roots, and moreover to distinct stages during their development. Increased accumulation and exudation of citrate and a concomitant release of protons were found to be mainly restricted to mature root clusters after prolonged culture (3±4 weeks) under P-de®cient conditions. Inhibition of citrate exudation by exogenous application of anion channel antagonists such as ethacrynic-and anthracene-9-carboxylic acids may indicate involvement of an anion channel. Phosphorus de®ciencyinduced accumulation and subsequent exudation of citric acid seems to be a consequence of both enhanced biosynthesis and reduced turnover of citric acid in the cluster root tissue, indicated by enhanced expression of sucrose synthase, fructokinase, phosphoglucomutase, phosphoenol-pyruvate carboxylase, but reduced activity of aconitase and slower root respiration. The release of acid phosphatase and of phenolic compounds (iso¯avonoids) as well as the induction of a putative high-anity P uptake system was more highly expressed in juvenile, mature and even senescent cluster regions than in apical zones of non-proteoid roots. An AFLP-cDNA library for cluster root-speci®c gene expression was constructed to assist in the identi®cation of further genes involved in cluster root development.

After-ripening is the mechanism by which dormant seeds become nondormant during their dry storage after harvest. The absence of free water in mature seeds does not allow detectable metabolism; thus, the processes associated with dormancy release under these conditions are largely unknown. We show here that sunflower (Helianthus annuus) seed alleviation of dormancy during after-ripening is associated with mRNA oxidation and that this oxidation is prevented when seeds are maintained dormant. In vitro approaches demonstrate that mRNA oxidation results in artifacts in cDNA-amplified fragment length polymorphim analysis and alters protein translation. The oxidation of transcripts is not random but selective, and, using microarrays, we identified 24 stored mRNAs that became highly oxidized during after-ripening. Oxidized transcripts mainly correspond to genes involved in responses to stress and in cell signaling. Among them, protein phosphatase 2C PPH1, mitogen-activated protein kinase phosphatase 1, and phenyl ammonia lyase 1 were identified. We propose that targeted mRNA oxidation during dry after-ripening of dormant seeds could be a process that governs cell signaling toward germination in the early steps of seed imbibition.

Understanding evolutionary change requires phenotypic differences between organisms to be placed in a genetic context. However, there are few cases where it has been possible to define an appropriate genotypic space for a range of species. Here we address this problem by defining a genetically controlled space that captures variation in shape and size between closely related species of Antirrhinum. The axes of the space are based on an allometric model of leaves from an F 2 of an interspecific cross between Antirrhinum majus and Antirrhinum charidemi. Three principal components were found to capture most of the genetic variation in shape and size, allowing a three-dimensional allometric space to be defined. The contribution of individual genetic loci was determined from QTL analysis, allowing each locus to be represented as a vector in the allometric space. Leaf shapes and sizes of 18 different Antirrhinum taxa, encompassing a broad range of leaf morphologies, could be accurately represented as clouds within the space. Most taxa overlapped with, or were near to, at least one other species in the space, so that together they defined a largely interconnected domain of viable forms. It is likely that the pattern of evolution within this domain reflects a combination of directional selection and evolutionary tradeoffs within a high dimensional space.leaf ͉ morphometry ͉ QTL analysis ͉ shape variation ͉ species