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Four cultivars of kurume azalea (Rhododendron sp.), ‘Hersey Red’, ‘Snow’, ‘Coral Bells’ and ‘Hino Crimson’ reported to have different susceptibilities to winter injury in the nursery were compared for their sensitivities to direct freezing injury (both to roots and leaves) and desiccation injury under controlled conditions. Sensitivity to root freezing injury was inversely correlated with winter injury. A positive association between leaf hardiness to freezing injury and resistance to winter injury was found only in ‘Hino Crimson’. Susceptibility to winter injury was most closely associated with desiccation, as indicated by the minimum water potentials under conditions of frozen soil and high evaporative demand.

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.

The possibility that low cellular concentration of sucrose was limiting the expression of hardiness in young roots of Pyracantha coccinea Roem. ‘Lalandii’ Dipp. was investigated. While the sucrose content of young roots increased four-fold following exposure to 4°C, the highest concentration was not higher than that found in non-acclimated mature roots. Attempts to increase hardiness by incubating young roots on sucrose solutions were unsuccessful. However, intracellular sucrose concentrations were not significantly increased by this treatment. Cytochrome oxidase incorporated into a membrane fraction containing plasmalemma vesicles isolated from Pyracantha young roots or from tissue capable of acclimation (Hedera helix L. ‘Thorndale’ callus cultures) was used as a probe for architectural alterations of this membrane following exposure to 4° and 5°. The apparent first order rate constant of the cytochrome oxidase reaction was used to indicate membrane fluidity. Above the Arrhenius discontinuity, membrane fluidity in both species was greatest when plants were grown at 4° or 5°. However, below the Arrhenius discontinuity fluidity remained greater in ivy callus grown at 5°, but not in Pyracantha young roots exposed to 4°. Altered properties of the membrane surface, inferred from the second order rate constant, were observed only in plasmalemma of young roots. Several possibilities to account for the lack of young root hardiness are presented.

Equal average container temperatures during prolonged periods of low outside air temperatures were achieved by unheated structures covered with either a double-layer of clear polyethylene or a double-layer with the inner layer translucent and the exterior clear polyethylene. Single-layer structures were less effective, with clear polyethylene affording more protection than translucent. Excessively high mid-day temperatures in both the single- and double-layer clear houses increased the probability of desiccation injury and affected the quality of the nursery stock. Fluctuations of air temperatures below 0°C were most rapid in the clear houses, and appear to depend greatly on the relative humidity, which affects the thermal conductivity of the air. Container temperature fluctuations were similar whether the container soil water was frozen or unfrozen. The best covering tested thus far appears to be a double-layer with the interior translucent and the exterior clear polyethylene. This covering moderates low container temperatures, high mid-day temperatures, desiccation problems, rapid temperature fluctuations and concomitant management problems.

Callus cultures of various cultivars of Chrysanthemum morifolium Ramat. have been shown to undergo cold acclimation. Unacclimated callus was able to survive freezing down to only −6.6°C, whereas callus acclimated for 6 weeks at 4.5° exhibited complete survival down to −16.1°. Callus age was an important factor in determining the ability to undergo cold acclimation. Callus, 28 days old or older (from subculturing), was severely limited in acclimation capacity. This time coincided with depletion of substrates in the medium and increased formation of vascular tissue. Regrowth measurements were of limited value in measuring freezing survival due to the variability in growth rates of individual calluses. However, the refined triphenyl tetrazolium test was satisfactory for quantitatively measuring callus survival immediately following freezing, but was unsuitable for predicting the amount of callus regrowth four weeks after freezing.

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.

Vase-life of roses (Rosa hybrida L. cv. Forever Yours) placed in the modified Cornell Solution (2% sucrose + 200 mg 8-hydroxyquinoline sulfate/liter) was increased over distilled water by nearly a week. Petal sugars decreased only slightly in roses maintained in distilled water but a rapid decline of respiratory control (RC) of mitochondria occurred after 3 days and was finally lost as vase-life ended. However, petal sugars nearly doubled in flowers in the preservative and the decline in RC of mitochondria occurred at a gradual rate and was never lost. The data indicate that the end of vase-life and the decline in respiration during rose flower senescence is not due to substrate limitations, but to the inability of the mitochondria to utilize the substrate. Exogenous sugars seem to be maintaining mitochondrial structure and function rather than providing substrates.