Peroxidase activity in leaves ofSyngonium podophyllum following transition fromin vitro toex vitro conditions

A low activity of peroxidase (POD, EC 1.11.1.7) was found in crude extracts fromin vitro plants ofSyngonium podophyllum cv. Butterfly sealed in the multiplication vessels. Removal of the lids from the vessels increased the POD activity. A greater increase in the POD activity was measured whenin vitro plants were transplanted into a weaning growth medium. The POD activity was further promoted by removal of the phenolic substances from the extracts by polyvinyl-polypyrrolidone (PVPP).     

Effects of temperature on phyllody expression and cytokinin content in floral organs of rose flowers

Formation of leaf-like organs known as phylloids in Rosahybrida cv. Motrea flowers was promoted by exposure of plants toelevated temperatures. At a day/night temperature regime of26°C/21°C respectively theproportion of malformed flowers exhibiting phyllody was four times higher thanthat in flowers of plants grown at21°C/15°C. The number ofpetals in phyllody-expressing flowers was higher than that in normal flowers.The total content of endogenous cytokinins in young flower buds of plantsexposed to the lower temperature was six times higher than that at the highertemperatures. The effects of the reduced temperature were pronounced on all thegroups of cytokinins examined. However, the proportion of the various cytokiningroups remained similar at both temperature regimes. In contrast to thecytokinins in the flower buds, the content of all cytokinin types in youngleaves increased following exposure to the higher temperature and was reducedbythe lower temperatures. After 11 weeks at the lower temperature, about18% of the flowers remained malformed, whereas at the higher temperatureabout 20% of the flowers still remained normal. All thephyllody-exhibiting flowers were formed on vigorously grown basal shootscharacteristic to Rosa hybrida plants, whereas the normalflowers at the elevated temperatures were formed on lateral shoots which weremost distal to the plant base. However, irrespective of the season, thepresenceof normal and malformed flowers was observed on plants kept growing at standardconditions of 30°C/17°C inthegreenhouse. This phenomenon led us to examine the cytokinins in floral organsofnormal and malformed cv. Motrea flowers grown in the greenhouse as well as inflowers of a complete rose mutant known as a 'Green Rose(Rosa chinensis viridiflora). The highest content ofcytokinins was found in the pistils and stamens of normal 'Motreaflowers. On the other hand, the content of cytokinins in leaf-like style-tubesin the malformed flowers as well as in partially malformed ovaries at the baseof phylloids was significantly lower. A low content of cytokinins was alsopresent in petals of both normal and phyllody-exhibiting flowers and the lowestcontent has been found in the phylloids of the 'Green Rose. Apossibility of mutant deviations in metabolism of cytokinins in rose plants isdiscussed.     

Effects of applied auxin,gibberellin and cytokinin on the activity of peroxidases in the peduncles of rose flowers

The activity of peroxidases in the proximal part of the flower peduncle of rose cv. Nubia was promoted by exogenous application of auxin but not by gibberellin or cytokinin. In cv. Mercedes the activity was promoted also by gibberellin and cytokinin. In the distal parts of the peduncles of both cultivars, peroxidase activity was not affected by any of the applied growth regulators. In young flowers of cv. Nubia the protein content of the penduncles was affected only by cytokinin, and in aged flowers only by auxin, while in Mercedes peduncles the content of protein was not affected by any of the applied growth regulators. The specific activity of peroxidases was promoted by auxin in peduncles of Nubia and by both auxin and cytokinin in peduncles of Mercedes flowers.     

Involvement of ethylene in the abscission of flowers and petals of Leptospermum scoparium

The growth of cotyledons and primary leaves of I-day-old Sinapis alba L. plants were studied under various light conditions and action spectra produced. For both responses blue and red light are most effective and a strong fluence rate dependency can be observed. The red light effect appears to be mediated through phytochrome, that of blue light being due to a separate blue light receptor, although this receptor requires the presence of far-red absorbing phytochrome (P_fr) in order to be effective.     

Growth of rose flower peduncles and effects of applied plant growth regulators

Removal of flower buds results in abscission of peduncles of the rose cv. Nubia and cessation of peduncle growth in cv. Mercedes. Peduncle growth was inhibited when pistils and stamens were removed, but was not affected by removal only of sepals and petals. Growth of the decapitated peduncles of Mercedes was partially restored by the application of auxin in lanolin paste on the base of the peduncle and was completely restored by the application of gibberellin, while the combined application of auxin and gibberellin was the most effective for growth restoration. Growth of non-decapitated Nubia peduncles was promoted by application of gibberellin or gibberellin and auxin but not auxin alone.Peduncle elongation of both cultivars was not affected by application of cytokinin and the effect of gibberellin was antagonized by combined application with cytokinin. The peduncles strength (resistance to bending) was affected more strongly by auxin than by gibberellin, and most strongly when auxin and gibberellin were combined. The effect of auxin on the strength of peduncles, but not of gibberellin, was antagonized by application of cytokinin. Excised, non-decapitated flowering stems of Nubia treated with gibberellin and auxin in situ, showed, recovery of the peduncles from wilting after exposure to heat conditions.     

Involvement of cytokinin,ABA and endogenous inhibitors in sprouting of basal buds in rose plants

Sprouting of basal buds in rose plants with a completely removed canopy was restrained by inhibitors in a water soluble fraction of an ethanolic extract from the bark tissue of the plant stump (the crown) extracted before the top removal. The inhibitory effect of this fraction disappeared if the bark was extracted one week after the removal of the plant canopy. A similar inhibition was obtained with extracts from stem segments. The organic fraction did not show any inhibitory activity. Both fractions, aqueous and organic, were inhitory in the lettuce hypocotyl elongation bioassay. High levels of ABA in the cis-configuration were found in extracts before the top removal. The amount of cis-ABA decreased in extracts made one week after top removal and a different peak of activity, probably corresponding to trans-ABA or phaseic acid was shown in the GLC-system used.A high content of cytokinins has been found in the bark tissue of the crown. There were qualitative differences in cytokinin activity between the tissue from plants after the removal of the canopy and from plants with main branches left intact. A balance between cytokinins and inhibitory complex was proposed to be involved in the regulation of basal buds outgrowth and plant regeneration.     

Effect of different night temperature regimes on the assimilation, transport and metabolism of carbon in rose plants

A decrease in CO₂ uptake, an increase in leaf starch and sucrose content and a decrease in the content of reducing sugars were found in rose ( Rosa hybrida cvs: Sonia and Golden Times) plants exposed to lower night temperature (12°C) in comparison with those grown at 18°C. These responses were not present when plants were grown under a night temperature regime of alternating temperature, 2 h at 18°C followed by 2 h at 12°C for 3 repetitive periods of a total of 12 h. The export of labelled carbon from the source leaves and translocation into the adjacent axillary buds were inhibited by lower night temperature, but not by the alternating temperature regime. The translocation of labelled carbon toward the basal plant parts was promoted by the lower temperature but not by alternating temperature. The partitioning of labelled carbon between the 2 uppermost lateral buds was also affected by the night temperature regime.     

Effects of temperature and gibberellin on the activity of endogenous cytokinin-like substances in leaves of Begonia x cheimantha

Changes in activity of endogenous cytokinin-like substances were examined in intact plants and excised leaves of Begonia x chemantha Everett cv. Prinsesse Astrid (Christimas Begonia) by means of the tobacco callus bioassay. Cytokinin activity in the leaves of intact plants was higher in plants grown at 18°C than in those grown at 21° or 24°C. In excised leaves, an increase in cytokinin activity was observed during the first 4 days following leaf detachment. However, after the seventh day cylokinin activity decreased again. This decrease was more profound in leaves exposed to 24°C than in those exposed to 18°C.
Treatment of detached leaves with gibberellic acid (2.8 m M ) caused an increase in measurable cytokinin activity. This increase was more profound in the zones of activity which correspond with zeatin glucosides on paper and Sephadex LH-20 chromatography. Additional zones of activity appeared after Sephadex chromatography. These were of a more slow moving nature with elution volumes corresponding to N^b-(Δ²-isopentenyl)adenine and its derivaties. Water-treated control leaves had higher activity in the regions corresponding to zeatin and zeatin riboside.     

Contribution of sepals and gibberellin treatments to growth and development of rose (Rosa hybrida) flowers

The fresh weight of sepals during the development of the rose flowerbuds from 4 mm to 22 mm in diameter increased fromabout 30 mg to ca. 350 mg. However, due to a morerapid gain in the total fresh weight of the flower, the sepal fresh weight as aproportion of the total weight of the buds decreased from about 55% to only 8%at the end of the measurement period. The net photosynthesis of sepals,measuredclose to the flower harvest, was approximately 60% of that in the youngest,uppermost leaves whereas no photosynthesis occured in the petals. Theconcentration of sucrose in petals of almost fully developed, desepalledflowerswas 15% lower in comparison with the control flowers with intact sepals. On theother hand, the concentration of sucrose in petals of control and desepalledflowers that were kept for 10 days in complete darkness was equal, reachingabout 50% of the concentration in petals of flowers grown in the light.Periodicmeasurements of reducing sugars in the petals did not show differences in theirconcentration between the control and desepalled flowers during the first 8daysafter sepal removal. After an additional four days the concentration ofreducingsugars in petals of the desepalled flowers was only 50% in comparison to thatinpetals of control flowers. Excising the sepals reduced fresh and dry weights,aswell as the length of buds and the peduncles, indicating that sepals may be asource of gibberellins during flower development. Treatment with50mg GA₃ in lanolin paste, completely restored thelength of the peduncles, but only partially restored the other measuredparameters of the flowers. Formation of 'star-shape' abnormality indesepalled flowers, which is a common phenomenon in rose flowers exposed toexternal ethylene was completelly prevented by applying GA₃ afterthesepals were excisied. This supported the previously suggested hypothesis aboutthe flinction of gibberellins in reducing the sensitivity of rose flower organsto ethylene.