Indoleacetic acid oxidase activity of apoperoxidase.

The conventional activity of electrophoretically purified horseradish peroxidase toward guaiacol, pyrogallol, 2,6-dimethoxyphenol, and benzidine is abolished by removal of the heme prosthetic group with a mixture of cold acetone and hydrogen chloride. The apoenzyme, though devoid of peroxidase activity, retains its activity as an indoleacetic acid oxidase when it is supplied with 10(-5) mole of manganous ion and 2,4-dachlorophenol per liter. This oxidase activity is cyanide-sensitive; azide also inhibits under specific conditions of both pH and cofactor concentration. Partial restoration of the peroxidase activity by recombination of apoprotein with heme produces no effect on the oxidase activity, except that cofactors are no longer absolutely required. Therefore, it appears that the activity of peroxidase as an indoleacetic acid oxidase need not directly involve the heme prosthetic group, or that manganous ions and dichlorophenol can substitute for the heme group in the reaction between indoleacetic acid and oxidase.

Polyamines and plant stress: activation of putrescine biosynthesis by osmotic shock.

The putrescine content of oat leaf cells and protoplasts increases up to 60-fold within 6 hours of exposure to osmotic stress (0.4 to 0.6 molar sorbitol). Barley, corn, wheat, and wild oat leaves show a similar response. Increased arginine decarboxylase activity parallels the rise in putrescine, whereas ornithine decarboxylase remains unchanged. DL-alpha-Difluoromethylarginine, a specific irreversible inhibitor of arginine decarboxylase, prevents the stress-induced rise in increase in arginine decarboxylase activity and putrescine synthesis, indicating the preferential activation of this pathway.

Potassium flux: a common feature of albizzia leaflet movement controlled by phytochrome or endogenous rhythm.

Leaflets close when potassium moves into dorsal and out of ventral pulvinule motor cells and open when the flux direction is reversed. This is true whether leaflet movement is controlled by an endogenous rhythm or by phytochrome.

Hormone-induced repression of a peroxidase isozyme in plant tissue.

Young stem sections of dwarf peas (Progress No. 9) grown in light contain at least seven peroxidase isozymes separable by electrophoresis on starch gel. An eighth isozyme appears as the tissue elongates and ages, on or off the plant. The appearance of this isozyme in excised sections is repressed by application of the plant growth hormone, indole-3-acetic acid.

Osmotically induced changes in electrical properties of plant protoplast membranes.

The internal electrical potential of protoplasts from six different plant species was positive. Plasmolyzed cells of leaves had positive voltages of similar magnitude. Both Elodea leaf cells and tobacco protoplasts with regenerated cell walls became more electronegative during deplasmolysis. These findings suggest that cell turgor affects membrane components that determine cellular potential.

Protein synthesis during endogenous rhythmic leaflet movement in Albizzia.

A rhythm was found in protein synthesis accompanying rhythmic leaflet opening and closing in the dark in the plant Albizzia. More protein was synthesized during the opening of the leaflets than during the closing. Furthermore, an inhibitor of protein synthesis, cycloheximide, prevented rhythmic opening of leaflets but had no effect on rhythmic closing. It is suggested that protein synthesis is involved in the movement across membranes of K(+) ions that cause turgor changes and leaflet movement.

Potassium flux and leaf movement in Samanea saman. I. Rhythmic movement.

Samanea leaflets usually open in white light and fold together when darkened, but also open and dose with a circadian rhythm during prolonged darkness. Leaflet movement results from differential changes in the turgor and shape of motor cells on opposite sides of the pulvinus; extensor cells expand during opening and shrink during closure, while flexor cells shrink during opening and expand during closure but change shape more than size. Potassium in both open and closed pulvini is about 0.4 N. Flame photometric and electron microprobe analyses reveal that rhythmic and light-regulated postassium flux is the basis for pulvinar turgor movements. Rhythmic potassium flux during darkness in motor cells in the extensor region involves alternating predominance of inwardly directed ion pumps and leakage outward through diffusion channels, each lasting ca 12 h. White light affects the system by activating outwardly directed K(+) pumps in motor cells in the flexor region.

Potassium flux and leaf movement in Samanea saman. II. Phytochrome controlled movement.

Phytochrome, a membrane-localized biliprotein whose conformation is shifted reversibly by brief red or far-red light treatments, interacts with the rhythmic oscillator to regulate leaflet movement and potassium flux in pulvinal motor cells of Samanea. Darkened pinnae exposed briefly to red light (high P(fr) level) have less potassium in motor cells in the extensor region, more potassium in motor cells in the flexor region, and smaller angles than those exposed to far-red light (low P(fr) level). Increase in temperature from 24 degrees to 37 degrees increases the differential effect of the light treatments during opening (the energetic phase) but not during closure, implying that phytochrome controls an energetic process. It seems likely that phytochrome interacts with rhythmically controlled potassium pumps in flexor and extensor cells. During nyctinastic closure of white-illuminated pinnae, exposure to far-red light before darkening results in larger angles than does exposure to red. As in rhythmic opening, the angles of all pinnae and the differential effect of the light treatments increases with increasing temperature.