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• Nutrient hot spots in the soil have a limited life span, but the costs and benefits for root foraging are still underexposed. We assessed short-term costs that may arise when a nutrient-rich patch induces root proliferation, but then rapidly disappears. • Rumex palustris plants were grown with a homogeneous or a heterogeneous nutrient application. After root proliferation in a nutrient-rich patch, nutrient supply was switched from homogeneous to heterogeneous, and vice versa, or the patch location was changed. • R. palustris proliferated its roots in the rich patch. After switching, the relative growth rates of the roots were adjusted to the novel pattern of nutrient availability. However, the changes in local root biomass lagged behind the rapid shift in nutrient supply, because the root mass realized in specific sectors could not be rapidly relocated. Despite this, R. palustris did not exhibit costs of switching in terms of biomass or nitrogen uptake. • Our data suggest that rapid shifts in uptake rate and redistribution of nitrogen within the plant may have lowered the costs of incorrect root placement. [ABSTRACT FROM AUTHOR]

The flooding tolerance of Carex species was studied in relation to their field distribution and their capacity to form root aerenchyma under controlled conditions. In an alpine meadow, six Carex species were selected which were distributed in a clear zonation correlating with water content of the soil. Carex sempervirens and C. ferruginea were only found on nonflooded soil, the latter species preferring moister conditions. Carex davalliana and C. nigra were both associated with water-saturated soil, whereas C. limosa and C. rostrata preferred partially submerged conditions. Carex davalliana and C. limosa were bound to flooded soils with a relatively high redox potential and horizontally flowing groundwater. Carex rostrata and C. nigra grew in stagnant soil-flooded conditions with low soil redox potentials. The amount of aerenchyma in the roots of all species increased when grown in oxygen-deficient stagnant agar. This increase in root porosity, combined with increased root diameter, presumably improved internal aeration of the roots. Although all species survived experimental soil flooding, partial submergence was lethal to C. sempervirens and, surprisingly, also to the wetland species C. davalliana. Carex ferruginea showed a reduced growth rate during partial submergence. The three other species, all wetland plants, reached highest biomass production under soil-flooded and partially submerged conditions, with slower growth on free-draining soil. It is concluded that aerenchyma is not constitutive in the Carex species under study, and is best developed in Carex species from wetlands. Species with less aerenchyma perform poorly when soil-flooded, but conditions of partial submergence could even affect species with a considerable amount of root aerenchyma. [ABSTRACT FROM AUTHOR]

ABSTRACTEthylene emission from wild-type Agrobacterium tumefaciens (C58)-induced stem tumours of Ricinus communis was continuously measured with two different methods, process gas chromatography and photo-acoustic spectrometry. Ethylene production was as high as 700 pmol g FW–1 h–1, namely 140 times greater than emitted by non-tumourized control stems. It was highest in 5-week-old tumours, independent of light, depressed by anoxia and, during water deficit it was stimulated by rewatering. A remarkable concomitant CO-production was discovered. Accumulation of 1-aminocyclopropane-1-carboxylic acid (ACC), the substrate of ACC-oxidase, preceded ethylene emission with a maximum 2 weeks after tumour induction. Simultaneously, the xylem in the tumour-adjacent host stem underwent drastic changes: it increased two to three times in thickness, vessel diameters decreased, the rays remained unlignified and became multiseriate. With increasing emission of ethylene aerenchyma developed in the non-transformed, tumour-surrounding tissue that formerly was stem cortex. Cotyledons reacted with epinastic symptoms indicating induction of senescence. The present results reveal an important role of ethylene, in addition to cytokinin and auxin, for the differentiation and physiology of A. tumefaciens-induced tumours. [ABSTRACT FROM AUTHOR]