Hormonal extracts of cherry tomato fruits (Lycopersicon esculentum Mill.) cv. Small Fry at different stages of fruit development and maturation were bioassayed for their auxin, gibberellin, cytokinin and growth inhibitor activities. In general, the levels of endogenous growth promoters were much higher in the young developing fruits than in the more mature fruits. Free cytokinin levels were highest in the first two weeks of development then declined rapidly. However, cytokinin activity in the ribotide fraction, after treatment with alkaline phosphatase, decreased during thefirst three weeks of development then increased rapidly over the following four weeks. Auxin levels increased during early development to reach a maximum in three‐week‐old fruits after anthesis. Gibberellin levels during the first two weeks of development were much lower than those of auxins and cytokinins, but then increased to reach a peak in the fourth week after anthesis. A growth inhibiting substance with Rf similar to that of abscisic acid was found in the acidic fraction of the fruit extracts. This inhibitor increased gradually during fruit growth and development and reached a peak at the age of five weeks which coincides with the green mature stage.

No abstract

Chromatography of partially purified extracts of Danish cabbage (Brassica oleracea var. capitata L.) heads on polyvinylpyrrolidone columns using a weak phosphate buffer indicated a cytokinin complex containing nine components active in the modified Amaranthus betacyanin bioassay. Similar elution patterns were obtained with extracts of four different cabbage varieties but varietal differences occurred in the biological activity from each component peak. Paper and thin‐layer chromatography indicated the presence of both zeatin and zeatin riboside in the extracts but the other cytokinin‐active components were not identified. Separation of sweet‐corn extracts by this technique indicated that most of the cytokinin activity occurred in the elution volume where zeatin and zeatin riboside would normally occur.

Cabbage (Brassica oleracea L. capitata), freshly harvested and market-trimmed in Florida, was stored for 5 wk at 1 C ± 0.5 C in air containing 0.04, 1, 10 and 100 ppm ethylene. At the highest two ethylene concentrations, market quality was reduced due to loss of external green color and extensive leaf abscission. Similar external changes were seen in cabbage reported to have been stored with apples. Hormonal changes associated with these high ethylene concentrations were disappearance of an abscisic acid-type inhibitor and accumulation of auxins at the apical region.

Separation of a mixture of the main cytokinins occurring naturally in plant tissues was achieved by high pressure liquid chromatography using insoluble polyvinylpyrrolidone as the solid support. The separation of each cytokinin was first assessed over a range of salt and 1-butanol concentrations and pH using a mixture of borate buffer and 1-butanol as the mobile phase to determine the conditions necessary for optimum resolution. A discrete separation of zeatin, N-6-(A-2-isopentenyl)adenine, their related ribonucleosides, and kinetin was achieved using a simple isocratic elution with 0.025 M borate buffer at pH 6.8 and 4% (v/v) (6, 9,12,17,19).Until recently, GLC has been considered the most reliable technique for separating and analyzing the identification of growth regulators in plant extracts, providing the hormone activity of the extracts is high, such as in immature seeds (10). However, this technique suffers from the disadvantage that volatile derivatives of the hormones must first be prepared and very often the analysis is destructive. This is particularly so with cytokinins where high column temperatures are required and flame ionization detectors are used for the analysis (12,19).The recent use of HPLC (3, 4,13,19) has introduced yet another possible major tool for cytokinin analysis. However C18 on Porasil (Waters Associates Ltd.) for reverse phase chromatography of cytokinins, but again a gradient elution system was necessary to achieve good separation. In our laboratory, we wished to develop a simple, inexpensive HPLC system for separating cytokinins, which would operate under isocratic conditions. It had been shown previously that PVP, a weak hydrogen-bonding material, could be used on a normal column scale to give reasonable separation of some cytokinins using phosphate buffer as the eluting solvent (1, 5, 18). However, a more satisfactory separation of cytokinins can be achieved on PVP TLC plates with borate buffer, since the cytokinin ribonucleosides form quick moving complexes with the borate ions, thus moving away from the free bases (17). On the other hand, since the free bases tend to be more soluble in 1-butanol than their related ribonucleosides, a combination of borate buffer and 1-butanol might be expected to provide the optimum separation conditions in the shortest possible time on LC columns.In this paper, we describe the results of our investigations with borate buffer/1-butanol mixtures on PVP HPLC columns for separating pure cytokinin standards and endogenous cytokinins in extracts of cabbage heads. MATERIALS AND METHODSChromatographic Materials and Procedure. A 2-meter long chromatography column was prepared from 2 mm i.d. precision bore 316 stainless steel tubing obtained from Varian Aerograph Ltd. The column was fed with solvent from a 0 to 750 p.s.i. constant pressure pump and the eluate monitored with a Model 02-001426-00 UV-detector, both purchased from Varian Aerograph Ltd. The pump was pressurized with N2 and all the solvents were degassed before use.In preliminary ...