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†Background and Aims The duration of the plant life cycle is an important attribute that determines fitness and coexistence of weeds in arable fields. It depends on the timing of two key life-history traits: time from seed dispersal to germination and time from germination to flowering. These traits are components of the time to reproduction. Dormancy results in reduced and delayed germination, thus increasing time to reproduction. Genotypes in the arable seedbank predominantly have short time to flowering. Synergy between reduced seed dormancy and reduced flowering time would create stronger contrasts between genotypes, offering greater adaptation in-field. Therefore, we studied differences in seed dormancy between in-field flowering time genotypes of shepherd’s purse. †Methods Genotypes with early, intermediate or late flowering time were grown in a glasshouse to provide seed stock for germination tests. Secondary dormancy was assessed by comparing germination before and after darkincubation. Dormancy was characterized separately for seed myxospermy heteromorphs, observed in each genotype. Seed carbon and nitrogen content and seed mass were determined as indicators of seed filling and resource partitioning associated with dormancy. †Key Results Although no differences were observed in primary dormancy, secondary dormancy was weaker among the seeds of early-flowering genotypes. On average, myxospermous seeds showed stronger secondary dormancy than non-myxospermous seeds in all genotypes. Seed filling was similar between the genotypes, but nitrogen partitioning was higher in early-flowering genotypes and in non-myxospermous seeds. †Conclusions In shepherd’s purse, early flowering and reduced seed dormancy coincide and appear to be linked. The seed heteromorphism contributes to variation in dormancy. Three functional groups of seed dormancy were identified, varying in dormancy depth and nitrate response. One of these groups (FG-III) was distinct for earlyflowering genotypes. The weaker secondary dormancy of early-flowering genotypes confers a selective advantage in arable fields.

†Background and Aims Myxospermy is a term which describes the ability of a seed to produce mucilage upon hydration. The mucilage is mainly comprised of plant cell-wall polysaccharides which are deposited during development of those cells that comprise the seed coat (testa). Myxospermy is more prevalent among those plant species adapted to surviving on arid sandy soils, though its significance in determining the ecological fitness of plants is unclear. In this study, the first mathematical model of myxospermous seed mucilage expansion is presented based on seeds of the model plant species Capsella bursa-pastoris (shepherd’s purse). †Methods The structures underpinning the expansion process were described using light, electron and time-lapse confocal micrographs. The data and experimental observations were used to create a mathematical model of myxospermous seed mucilage expansion based on diffusion equations. †Key Results The mucilage expansion was rapid, taking 5 s, during which the cell mucilage volume increased 75-fold. At the level of the seed, this represented a 6-fold increase in seed volume and a 2.5-fold increase in seed surface area. These increases were shown to be a function of water uptake (16 g water g 21 mucilage dry weight), and relaxation of the polymers which comprised the mucilage. In addition, the osmotic pressure of the seed mucilage, estimated by assessing the mucilage expansion of seeds hydrated in solutions of varying osmotic pressure, was ‐0.54 MPa (equivalent to 0.11 M or 6. 6g L 21 NaCl). †Conclusions The results showed that the mucilage may be characterized as hydrogel and seed-mucilage expansion may be modelled using the diffusion equation described. The potential of myxospermous seeds to affect the ecological services provided by soil is discussed briefly.

An enzyme-linked immunosorbant assay (ELISA) method based on a monoclonal antibody (MAC236) is described in which relative amounts of an intercellular glycoprotein were quantified in extracts of whole legume nodules. This glycoprotein has recently been shown to be an important component of the cortical oxygen diffusion barrier. The ELISA method is demonstrated on three examples of soybean (Glycine max L. Merr.) nodule systems which have been the subject of previously published investigations: (a), cv. Clarke inoculated with Bradyrhizobium japonicum RCR3442, nodulated root systems of which were subject to 10, 21 or 40% oxygen continuously for 28 d; (b), cv. Bragg and its supernodulating mutant derivative (nts382) inoculated with Bradyrhizobium japonicum USDA110; (c), cv. Clarke inoculated with Bradyrhizobium japonicum RCR3442 or RCR3407. ELISA results are related to oxygen diffusion characteristics defined in previous publications and show that increases in the amount of glycoprotein present correlated with increases in supra-ambient (40%) levels of rhizosphere pO2, in minimum gas diffusion resistance and in speed of diffusion barrier response. Area data of component parts of nodule inner cortices suggest that diffusion resistance control under sub-ambient (10%) oxygen levels also involves cell expansion. The amount of MAC236 antigen in nodules is affected by both host plant genotype and rhizobial strain and the latter also appears to be involved in determining the morphological development of the nodule inner cortex.