Red Beet Storage Tissue Research Articles

Determination of the membrane potential of vacuoles isolated from red-beet storage tissue

The membrane potential of isolated vacuoles of red beet (Beta vulgaris L.) was estimated using several methods. The quenching of the fluorescence of the cyanine dyes 3,3'-diethylthiodicarbocyanine iodide (DiS-C2-(5)) and 3,3'-dipropylthiodicarbocyanine iodide (DiS-C3-(5)) in vacuoles indicated a transmembrane potential difference, negative inside at low external potassium concentrations. The Δψ was found to be-55 mV with two other methods, the distribution of (204)T1(+) in the presence of valinomycin and the distribution of the lipophilic cation triphenylmethylphosphonium. Uncouplers reduced this value to-35 mV. High external potassium concentrations, comparable to cytosolic values, abolished the membrane potential almost completely. The addition of 1 mM Tris-Mg(2+)-ATP markedly hyperpolarized the membrane to-75 mV. This effect was prevented by inhibitors of the ATPase activity located in isolated vacuole membranes.

Isolation of Protoplasts and Vacuoles from Storage Tissue of Red Beet

A fast and efficient method is described for the isolation of protoplasts and vacuoles from storage tissue of Beta vulgaris L. The viability of the isolated protoplasts is indicated by the development within a few hours of plasma strands with active cyclosis as well as by transport activity.The effect of aging of the tissue on the yield and on the properties of the protoplasts is examined. Adding 1 millimolar dithiothreitol to the water during the aging of the tissue prevents a change of the cell wall structure which otherwise reduces the protoplast yield within 2 days to zero. When protoplasts are isolated from tissue after different times of aging, they show an increase in transport activity which parallels that in the intact tissue.

Effect of Anoxia on ATP Levels and Ion Transport Rates in Red Beet

The ATP content of disks of storage tissue of red beet is reduced under N(2) atmosphere to between 10 and 25% of its value in air. Plasmalemma fluxes of K(+) and Cl(-) are inhibited within 1 minute or less following removal of O(2), and the extent of this inhibition is entirely attributable to the depletion of ATP. The ATP content remains approximately constant or decreases slightly for up to 1 hour under N(2). On return to air, the ATP content recovers, reaching 75% of the aerobic level within 45 second.

Development and Characteristics of Sodium-selective Transport in Red Beet

Slices of storage tissue of red beet (Beta vulgaris L.) washed for only 1 day in distilled water readily absorb K(+) but lack a mechanism for rapid Na(+) uptake. A Na(+) transport mechanism develops if the tissue is washed for several days, and the tissue then excludes K(+) during Na(+) uptake.Both the high affinity and low affinity absorption mechanisms show a development of Na(+) transport with washing, and, in contrast to barley roots, cation selectivity in beet is not affected by the presence of calcium ions.K(+) and Na(+) do not appear to compete for binding sites at the surface of the cells, but, as in barley roots, the cations compete in some way for electrically balancing transported ions. Nevertheless, the development of Na(+) transport and the interaction of Na(+) with K(+) occur in the same way whether cation transport is balanced by Cl(-) uptake or by H(+) or HCO(3) (-) transport.

Specificity of Cycloheximide in Higher Plant Systems

Although cycloheximide is extremely inhibitory to protein synthesis in vivo in higher plants, the reported insensitivity of some plant ribosomes suggests that it may not invariably act at the ribosomal level. This suggestion is reinforced by results obtained with red beet storage tissue disks, the respiration of which is stimulated by cycloheximide at 1 microgram per milliliter. Inorganic ion uptake by these disks is inhibited by cycloheximide at 1 microgram per milliliter while the uptake of organic compounds, by comparison, is unaffected. Ion uptake by all nongreen tissues tested is inhibited by cycloheximide, but leaf tissue is unaffected, indicating that the ion absorption mechanism in the leaf may differ fundamentally from that in the root. It is concluded that cycloheximide can affect cellular metabolism other than by inhibiting protein synthesis and that the inhibition of ion uptake may be due to disruption of the energy supply.