A Proposed Drought Response Equation Added to the Münch-Horwitz Theory of Phloem Transport.

Theoretical and experimental evidence for an effect of sieve tube turgor pressure on the mechanisms of phloem unloading near the root tips during moderate levels of drought stress is reviewed. An additional, simplified equation is proposed relating decreased turgor pressure to decreased rate kinetics of membrane bound transporters. The effect of such a mechanism would be to decrease phloem transport speed, but increase concentration and pressure, and thus prevent or delay negative pressure in the phloem.

Carbon partitioning patterns of mycorrhizal versus non-mycorrhizal plants: real-time dynamic measurements using CO.

Gas exchange and carbon allocation patterns were studied in two populations of Panicum coloratum, an Africa C-4 grass. The plants were grown in split-root pots, containing partially sterilized soil, with one side either inoculated (I) or not inoculated (NI) with a vesicular arbuscular (VA) mycorrhizal Fungus, Gigaspora margarita. Net carbon exchange rates (CER) and stomatal conductances were measured with conventional gas exchange apparatus, and carbon assimilation, translocation, and allocation were measured using photosynthetically-fixed CO .

Cell wall elasticity: I. A critique of the bulk elastic modulus approach and an analysis using polymer elastic principles.

The traditional bulk elastic modulus approach to plant cell pressure-volume relations is inconsistent with its definition. The relationship between the bulk modulus and Young's modulus that forms the basis of their usual application to cell pressure-volume properties is demonstrated to be physically meaningless. The bulk modulus describes stress/strain relations of solid, homogeneous bodies undergoing small deformations, whereas the plant cell is best described as a thin-shelled, fluid-filled structure with a polymer base.

Low night temperature effect on photosynthate translocation of two C grasses.

Translocation of assimilates in plants of Echinochloa crus-galli, from Quebec and Mississippi, and of Eleusine indica from Mississippi was monitored, before and after night chilling, using radioactive tracing with the short-life isotope C. Plants were grown at 28°/22°C (day/night temperatures) under either 350 or 675 μl·l CO. Low night temperature reduced translocation mainly by increasing the turn-over times of the export pool.

Carbon import among vegetative tillers within two bunchgrasses: assessment with carbon-11 labelling.

Carbon allocation among bunchgrass tillers was examined with carbon-11 (CO) steady state labelling. Labelled carbon was continuously transported from parent tillers to anatomically attached daughter tillers at a time when morphological characteristics indicated that tiller maturation had occurred. Steady state levels of import into monitored daughter tillers increased within 30 min of either defoliation or shading.