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°.
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.
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.
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.
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.
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.
Microscopic examination of longitudinal tangential sections of stems of rose (Rosa hybrida L. cv. Red American Beauty) revealed vascular occlusions due to microbial growth and gum deposition. Microbial occlusions reacted positively with the protein stain mercuric bromphenol blue and were restricted to the basal 2.5 cm of the stem. Gum deposition was identified by a positive reaction with periodic acid-Schiff's reagent and gas liquid chromatographic analysis of monomer content of acid-hydrolyzed occluding material. Location of gum deposition was dependent on the depth of the holding solution on the stem, always occurring above the solution level. Quantitative and qualitative comparison of sugar and uronide monomer content between areas of no gum deposition and areas of high gum deposition showed no differences, suggesting that gum formation was due to redeposition rather than net synthesis of gum constituents.
Stems and leaves of Pyracantha coccinea Roem. ‘Lalandii’ Dipp. acclimated to —26°, and mature roots to —17°, when previously exposed to 4° for 5 weeks. Young roots, however were killed at —5° even after exposure to 4° for 16 weeks. Differential thermal analysis was used to determine whether the initial freezing processes were altered following exposure to 4°. A higher percentage of tissue water was frozen during the initial period of ice formation in young roots grown at 18° than those grown at 4°. No difference in the percentage of tissue water frozen in mature roots grown at either 18° or 4° was evident. The rate of ice formation in both young and mature roots was highest in tissues grown at 18°. Thus, after exposure to 4°, the physical stresses in root tissue due to ice formation were decreased in both young and mature tissue. While growing the tissue at 4° alters the physical stresses imposed by ice formation, young roots do not survive below —5° whereas mature root roots do. Therefore, it is suggested that differences in survival of mature and young roots of pyracantha are not solely due to a mitigation of the physical stresses imposed by ice formation.
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.