Plasmolysis, Plasmodesmata, and the Electrical Coupling of Oat Coleoptile Cells

Ultrastructural studies on oat coleoptile parenchyma cells (Avenasativa L. cv. Victory) reveal that severe plasmolysis eitherbreaks plasmodesmatal connections or leaves the protoplastsstill connected via strands of cytoplasm (Hechtian strands).Plasmolysis also induces the formation of callose around theplasmodesmata. The callose remains for several hours after recoveryof the cells to full turgor. Immediately following recovery of turgor, intercellular electricalcoupling cannot be detected. However, during the next 6 h, somedegree of coupling is restored. These results indicate that,while plasmolysis does not necessarily break all plasmodesmatalconnections, the treatment probably does disrupt them sufficientlyto interfere, at least temporarily, with symplastic transport.     

Observations on the Exchange of Salt Between the Xylem and Neighbouring Cells in Zea mays Primary Roots

Comparison of two preparations of Zea mays primary roots hasshown that the salt concentration in the xylem fluid is alteredas it passes through a region of the root where no absorptionof salts or water from the external bathing medium can occur.Salts are secreted to the xylem by such a region, presumablyfrom the vacuoles of the cortical cells. It has also been demonstratedthat longitudinal water movement through the root cortex isnegligibly small during root-pressure exudation.     

Characterization of Exudation from Excised Roots of Onion, Allium cepa: I. WATER FLUX

Measurements of the rates of fluid exudation from excised rootsof onion, and determinations of the osmolalities of the exudatefluids are found to be adequately related by the simplest modelin which the rate of fluid exudation is proportional to theosmotic pressure difference between the exudate fluid and thebathing solution. The mean hydraulic conductivity of roots producedby unsprouted onion bulbs is 0.44 x 10^–6 cm s^–1atm^–1 and of roots from sprouted bulbs is 0.91 x 10^–6cm s^–1 atm^–l.     

A Fine Structure Study of Physarum polycephalum During Transformation from Sclerotium to Plasmodium: A Six-Stage Description

ABSTRACT. Physarum polycephalum is classified presently as a sarcodinid in the class Eumycetozoea. It produces a sclerotial dormant stage consisting of a crustose deposit containing nucleated spherules of cytoplasm enclosed within a honey-comb-like matrix of organic walls. When rehydrated, the sclerotium reverts to a plasmodium: 1) the spherules become increasingly vacuolated, 2) electron-dense granules become dispersed within expanding vacuoles, and 3) pseudopodial extensions develop from the periphery of the spherule cytoplasm, penetrating the fragmenting walls, and making interconnections with surrounding spherules, eventually leading to a fully reticulated plasmodium. Six stages are identified during reversion from sclerotium to plasmodium in laboratory cultures, and their successive appearance was mapped over time. The six stages are: 1) sclerotial stage with crenulated nuclei, 2) cytoplasmic activation with smooth nuclear envelopes, 3) initiation of pseudopodial protrusions, 4) pseudopodial penetration into or across walls, 5) cytoplasmic interconnections among spherules with wall disintegration, and 6) fully formed cytoplasmic network as plasmodium. Cytochrome c oxidase activity, expressed per unit protein content of the homogenate, remains fairly constant throughout the developmental sequence, whereas acid phosphatase activity, expressed per unit protein concentration, is somewhat lower in the sclerotium than in subsequent stages of development after hydration.     

Studies on the mid-gut of the desert locust, Schistocerca gregaria.

ABSTRACT. The gross morphology of the mid-gut musculature of the desert locust, Schistocerca gregaria is described. Some of the electrophysiological characteristics of the external longitudinal muscle fibres were examined. The membrane potentials have mean values of -24.7mV (SE ± 7.3). Spontaneous post-synaptic potentials were recorded, and the responses of the muscle fibres to electrical stimulation of their nerve supply studied.