sour cherry, 6 to 8 weeks was optimum for promoting shoot growth, but longer than 8 weeks was detrimental ( Borkowska, 1986 ). Cytokinin in the media is necessary for proliferation, but can inhibit shoot elongation at concentrations that promote rapid
Broccoli (Brassica oleracea L. var. italica `Citation') florets were treated postharvest with either benzyladenine or trans-zeatin at either 10 or 50 ppm before packaging in perforated polyethylene bags and storage at 16C. The most pronounced effects were observed with benzyladenine at 50 ppm. Compared to controls, respiration rate was reduced 50% and ethylene production increased 40% throughout the first 4 days of storage. Total chlorophyll content had dropped 60% in controls, but was unchanged in cytokinin-treated florets, which had a 90% longer shelf life than controls. These effects depended on the amount of cytokinin applied and were of greater magnitude with benzyladenine than with zeatin.
Abstract
One-year-old apple trees (Malus domestica Borkh. cv. EMLA 106) were subjected to all combinations of 10° and 20°C root and shoot temperatures after their chilling requirement had been satisfied at 5°. Extracted xylem sap was tested for trans-zeatin riboside-like cytokinin activity using an immunoassay. Cytokinin activity in the xylem sap increased during the first 6 days of treatment regardless of temperature, but decreased only as budbreak occurred. This decline was in proportion to the amount of budbreak, which primarily was dependent on shoot temperature.
Abstract
Cytokinin activity from purified xylem sap of ‘McIntosh’ apple trees on Malling Merton 106 (MM 106) rootstocks and from ethanol extracts of MM 106 rootstocks was determined using the soybean callus bioassay. Activity declined in the xylem sap by the third day after removal of the top of the tree. Over 2/3 of the cytokinin activity in young MM 106 rootstocks was found in the young leaves and actively growing stems. Shoots and leaves may be an important source and/or sink for cytokinins in apple trees.
We examined two aspects of treating plants with a cytokinin-containing seaweed extract (SWE). In the first series of experiments, we tested the hypothesis that immature lima bean (Phaseolus lunatus L.) and tomato (Lycopersicon esculentum Mill.) plants provided with exogenous cytokinins could recover from defoliation by a generalist insect herbivore, Spodoptera exigua (Hübner), more rapidly than plants without cytokinin supplements. However, the SWE inhibited growth of lima beans at all levels of herbivore damage. The SWE neither inhibited nor stimulated growth of tomatoes following defoliation. Because SWE effects largely were neutral for tomato growth, we conducted a second series of experiments to test the hypothesis that SWE treatments alter the attractiveness of tomato foliage to S. exigua larvae. In these experiments, we determined consumption of, and preference for, SWE-treated tomato foliage by S. exigua larvae. Repeated root applications of SWE led to increased consumption and preference by S. exigua. Repeated foliar applications did not alter consumption or preference compared with controls. Spodoptera exigua larvae gained significantly more mass when feeding on SWE-treated foliage compared with controls. While these data indicate that plant responses to exogenous cytokinin-containing materials depend on taxa and application method, the practical uses of SWE appear limited given the negative effects on plant growth and increased attractiveness of treated foliage to herbivores.
Abstract
A gas chromatograph equipped with a nitrogen-phosphorus detector was used for quantitation of cytokinins. The described system, utilizing permethylated derivatives, will detect as little as 0.1 pg adenine, isopentenyl adenine, benzylamino purine, and kinetin, and 10 pg zeatin. As with all highly sensitive instrumentation, scrupulous procedures for sample preparation are essential.
The effects of different cytokinin-like compounds on invertase activities at different tuberization stages of potato (Solanum tuberosum L. `Atlantic') were examined. Single nodal segments were cultured on MS medium plus 6% sucrose and supplemented with either 2 mg kinetin/L, 0.1 mg thidiazuron (TDZ)/L, 1.0 mg AC 243,654/L, 0.1 mg AC 239,604/L, or no cytokinin. Tissue samples for determining invertase activity were taken at three stages of tuberization: stage 1, the “hook stage”; stage 2, the “swelling stage”; and stage 3, “tuber initials.” Invertase activity was significantly affected by the interaction between cytokinin-like compounds and tuberization between cytokinin-like compounds and tuberization stages. The highest invertase activities in the stolons at stage 1 were found in kinetin and TDZ treatments. Invertase activity in the stolons on the control medium significantly increased from stage 1 to 2 and decreased at stage 3. Invertase might play a role in either stolon elongation or carbohydrate utilization by increasing the pool of reducing sugars.
Abstract
Cytokinins delay the onset of senescence in cut carnation flowers (Dianthus caryophyllus) by affecting the biosynthesis and action of ethylene in the tissue. The onset of senescence is marked by an increase in ethylene sensitivity and production by the tissue. A characteristic rise in 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor of ethylene, accompanies the initial stages, but the greatest increases in ACC are associated with the decline in ethylene production during the later stages of senescence. Cytokinins delay the onset of senescence and reduce ethylene sensitivity and production. Benzyladenine (BA), a cytokinin, prevents the rise in endogenous ACC levels and reduces the capacity of the tissue to convert ACC to ethylene. The effects of other anti-senescence agents, aminoethoxy vinylglycine (AVG), silver ions and cobalt ions, are compared with those of BA on ethylene sensitivity and production. The mechanism of action of BA in the delay in flower senescence is discussed.
Abstract
Cytokinin and auxin levels were examined in the roots of peach cultivars, resistant (‘Nemaguard’ and ‘Okinawa’) and susceptible (‘Baladi’ and ‘L 198-12’) to the root knot nematode Meloidogyne javanica. This approach was taken in the light of our earlier finding that this nematode developed and completed its life cycle in seedlings of a resistant cultivar when they were wick-fed with kinetin and 1-naphthylacetic acid (NAA). The cytokinin activity in roots of resistant rootstocks was significantly lower when compared with susceptible rootstocks. Wick-feeding with kinetin and NAA increased cytokinin-like activity in the roots of a resistant rootstock. Significant differences were found in the activity of several basic-ether soluble auxin-like growth promoters.
Abstract
The dynamics of indoleacetic acid (IAA), cis-trans abscisic acid (c,t-ABA), and gibberellin (GA)- and cytokinin-like compounds were measured in pecan [Carya illinoensis (Wang) K. Koch; cv. Desirable] buds following their release from imposed dormancy. Both bound and free ABA levels in apical and basal primary buds and in secondary buds declined 27 days prior to budbreak until the time of budbreak, with the exception of a steady rise in free ABA in secondary buds. During this period IAA initially dropped sharply, remained low, and finally increased again at budbreak. Cytokinin-like substances peaked after the drop in IAA but prior to the peak in gibberellin-like substances which occurred during bud swelling. The findings raise the possibility of a key regulatory role for IAA, possibly through its influence on regulation of bud cytokinin and gibberellin levels via their metabolism in roots. Growth regulator dynamics during pecan budbreak are discussed in relation to the hormonal theory versus tissue sensitivity to growth regulators.