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Identification of chloroplast coupling factor particles, by the freeze-etching and negative-staining techniques, was made utilizing chloroplast thylakoids isolated from spinach leaves. Complete removal of particles, comparable in diameter to purified coupling factor particles, from the outer surface of freeze-etched thylakoids was achieved by treatment with 0.8% silicotungstate. Reappearance of particles, comparable in diameter to purified coupling factor particles, on the outer surface of freeze-etched thylakoids was demonstrated by combining silicotungstate-treated thylakoids with purified chloroplast coupling factor. Negative-staining results were in agreement with the freeze-etch data. The results demonstrate that the chloroplast coupling factor particles are exposed on the outer surface.

When placed in either the modified Cornell Solution (2% sucrose + 200 mg/1 8-hydroxyquinoline sulphate) or distilled water, levels of l4C-labelled compounds in Rosa hybrida “Red American Beauty” flowers increased linearly. Girdling the stems decreased accumulation of 14C in the petal tissue by only 25%. Fructose and glucose were the predominant sugars in petal tissues with only minor amounts of sucrose. Addition of sucrose to the preservative solution increased the levels of glucose and fructose but had little affect on the sucrose content. The data indicate that inferences of sugar accumulation in petals cannot be made from data on xylem conductivity.

A gravity system was developed for measuring xylem conductivity in excised stem sections from ‘Red American Beauty’ roses. The system was reliable for measurement of the potential xylem conductivity which closely corresponded to actual water uptake in cut roses. Distilled water, sucrose, 8-hydroxy quinoline sulfate (8-HQS), and a modified Cornell solution (2% sucrose + 200 mg/liter 8-HQS) were tested for their effects on xylem conductivity and vascular blockage in excised stem sections. The modified Cornell solution showed the most favorable effects on conductivity, vase life, and appearance. The browning of stem tissue with 8-HQS was associated with a depressed rate of metabolism as measured by a modified triphenyl tetrazolium chloride test. Good xylem conductivity and a low incidence of vascular blockage was associated with the 8-HQS-depressed metabolic rate indicating an active process, attributed to a wound response triggered by excision of the cut flower, in the stem is responsible for vascular blockage. However, microscopic observations of fresh, frozen, and permanent tissue sections of rose xylem showed no evidence of lignin, tannins, or tyloses which are reputed to accompany wound response in plants.

Phosfon retardation of growth was studied in 2 cultivars of Chrysanthemum morifolium Ramat., ‘Jet Fire’ and ‘Maple Leaves’. Retarded growth of ‘Jet Fire’ was the result of fewer and shorter internodes, whereas in ‘Maple Leaves’ the number of internodes remained the same but their length was less compared to the controls. In both cultivars, the shorter internodes were the result of a reduction in cell division and hence cell number. The length of cells in the pith of fully developed internodes remained the same. Application of gibberellin overcame the growth retarding effect of phosfon while indoleacetic acid was ineffective. Combined applications of gibberellin and indoleacetic acid had the same effect on growth of phosfon-treated plants as gibberellin alone. The gibberellin content of the shoot apex was much less in phosfon-treated plants, but there was a larger reduction in the gibberellin content in ‘Jet Fire’ than in ‘Maple Leaves’. Protein, RNA and DNA contents of the leaves and apices were determined colorimetri-cally and there were no measurable differences as a result of phosfon treatment.

By using microautoradiography to study the incorporation of thymidine-3H, uridine-3H and lysine-3H in the shoot apex of Chrysanthemum morifolium Ramat. cv. ‘Jet Fire’, phosfon was shown to inhibit both DNA and RNA synthesis in the apical and subapical meristems. The resultant decrease in cell division in both the apical and sub-apical meristem accounts for the reduction of both the number and length of internodes. Gibberellic acid, which reverses growth inhibition by phosfon, increased incorporation of thymidine-14C and uridine-14C into DNA and RNA respectively.

The light-enhanced production and accumulation of sugars is only one step in the process of cold acclimation in Hedera helix L. var. Thorndale (English ivy). Applications of 2,4-dinitrophenol to plants with different portions exposed to light and dark indicated that the mere presence or accumulation of the light-generated promoters did not invoke an increase in hardiness. Kinetics of cold acclimation during alternating periods of light and dark also indicate that the light stimulation of cold acclimation is only a partial component of the total process. Incubation on 50 mm solutions of sucrose can replace the light requirement. A second phase which can proceed in the dark is thought to result in the production of proteins which, due to an altered composition or configuration, have a greater capacity to bind sugars. This is evidenced by the fact that protein from cold acclimated tissue exhibited a higher sugar-binding capacity than protein from nonacclimated tissue. Furthermore, the two phases can proceed independently of each other, but only upon complementation of the products of the two phases is an increase in cold hardiness manifested.

The role of light in cold acclimation of Hedera helix L. var. Thorndale appears to differ from that reported for winter annuals. Although light greatly enhances the degree of hardiness attained, cold acclimation is not obligatorily linked to a light requirement. Photoperiods, varying from 8 to 24 hours, received during the cold acclimation period were equally effective in promoting maximum hardiness. Relatively low light intensities and short photoperiods stimulated maximum hardiness, and proportional increases in hardiness in response to increased photoperiods were demonstrated only in stems of prestarved plants. Exclusion of CO(2) and high concentrations of photosynthetic inhibitors decreased hardiness, but in no instance was hardiness reduced to the level of the dark control. The data are only compatible with a photosynthetic role of light if it is assumed that only a small portion of the total photosynthates are required to elicit maximum hardiness. Alternatively, the light stimulation which was elicited by low light intensities, short photoperiods, in the absence of CO(2), and in the presence of photosynthetic inhibitors, may be a light signal similar to a phytochrome response.

Temperature exposures which normally decrease growth of Pisum sativum seedlings by 50 % were found to be lethal in plants whose cotyledons were removed. Utilization of the two major reserves, starch and protein, decreased at high temperatures. However, the two enzymes responsible for their hydrolysis were thermostable. It appears that the influence of high temperatures on seedling growth is not due to direct effects of temperature on cotyledon metabolism, but rather indirectly through the axis.

Comparisons of activities of various dehydrogenases isolated from frozen and unfrozen tissues of Hedera helix indicate that freezing does not result in denaturation of the various dehydrogenases examined. Preincubation in 2, 4-dinitrophenol mimiced the effects of freezing on reduction of TTC. Additions of various substrates and cofactors to previously frozen tissues increased the amount of TTC reduction. It is suggested that the high correlation between the amount of freezing injury in plant tissue and the ability to reduce TTC is due to physically and metabolically imposed substrate limitations rather than denaturation of specific dehydrogenases.

The light stimulation of cold acclimation of Hedera helix L. var. Thorndale has been shown to result in the production of translocatable promoters of hardiness. Movement of the promoters from an illuminated donor portion to a darkened receptor portion was demonstrated. The majority of transport was acropetal through the phloem and to a much lesser degree basipetal through the xylem. In the early stages of hardening, transport was strictly acropetal. It is suggested that acropetal transport is under the influence of a mobilizing center located in the apex of the plant. Mobilization of the promoters of hardiness was induced by applications of (6)N-benzyladenine. Attempts to characterize the light-generated promoters through fixation of (14)CO(2) and subsequent translocation of (14)C-labeled compounds from the illuminated donor to the darkened receptor indicated that the translocatable promoting material was either some component of the Dowex 1 fraction or sucrose. Furthermore, the hardiness of leaves was significantly increased by sucrose solutions but not by equi-molar solutions of glucose, galactose or mannitol.

The method of evaluating cold injury in woody plants by the use of triphenyl tetrazolium chloride has been refined to eliminate bias associated with visual differentiation between varying degrees of tetrazolium reduction and to predict tissue survival at a later date. An advantage of the method described here is that a small amount of tissue (50-100 mg) is required; this, therefore, allows for hardiness determinations at precise locations on the plant. The high correlation between cold injury and triphenyl tetrazolium chloride reduction may be due to cofactor and substrate limitations rather than inactivation of dehydrogenases.

CHUA1 has recently reported that 8-quinolinol sulphate, a compound with known antifungal and antibacterial properties, also has cytokinin-like activity. This conclusion was based on the fact that 8-quinolinol sulphate retarded the senescence of excised oat leaves. Two facts tend to diminish the validity of this conclusion: the bioassay is not specific for cytokinins—compounds other than cytokinins defer loss of chlorophyll and protein—and bacterial contamination hastens the senescence process. Thus in non-sterile conditions (which seem to be the conditions of Chua's1 experiment), a substance which merely inhibits micro-organism growth could indirectly retard senescence but still not in fact have cytokinin-like activity.

Cold hardiness of Hedera helix L. var. Thorndale was ultimately unaffected by photoperiod. Anthocyanin accumulation was a photoperiodic-high light intensity response. There was no correlation between anthocyanin content and cold hardiness in plants exposed to different photoperiods and light intensities.

A modified Murashige and Skoog medium (5) containing 10% sucrose maintained viable tissue cultures of chrysanthemum at −3.5°C for 28 days. The high concn of sucrose resulted in supercooling of the tissue to −5.5° whereas in tissue maintained on 3% sucrose supercooling occurred at −3.3°.