Anton M. Kofranek

Ethylene evolution and sensitivity in cut orchid flowers

Abstract The effects of ethylene and the rate of ethylene production were studied in several orchid flowers. Orchid flowers showed a wide range of sensitivity to ethylene; Vanda ‘Miss Joaquim’ was most sensitive, Cattleya, Cymbidium and Paphiopedilum were less sensitive, while Dendrobium and Oncidium were not sensitive. Ethylene production in opened flowers was low, less than 1 nl/flower/h. In Cattleya , a peak in ethylene production was observed at the onset of senescence. Emasculated and/or pollinated flowers of Vanda, Cattleya and Paphiopedilum produced high levels of ethylene; Dendrobium did not react to these treatments in ethylene production. The anionic silver-thiosulfate complex (STS) was partially inhibitory to ethylene production in emasculated Cymbidium flowers, but appeared to stimulate the process in pollinated flowers. It was, however, effective in decreasing anthocyanin synthesis in both emasculated and pollinated Cymbidium flowers. In Cattleya , aminoxyacetic acid (AOA) and STS had no effect on longevity of cut flowers.

Role of the ovary in carnation senescence.

Abstract Ovary growth in carnation flowers was inhibited by pre-treatments with silver thiosulfate which retarded petal senescence. Although the start of ovary growth preceded visible wilting of untreated flowers, the ovary does not appear to control carnation senescence. Its removal did not alter the time of senescence, and isolated petals wilted at the same time as those on intact flowers. The ovary normally competes weakly for metabolites with the petals; growth of the ovary occurred only when the petals were removed or started to senesce, if the sink strength of the ovary was increased by injecting growth regulators or if sucrose was supplied exogenously. It seems unlikely that the growth of the ovary is dependent on reallocation of carbohydrate materials from the petals.

High night temperatures delay flowering, produce abnormal flowers and retard stem growth of cut-flower chrysanthemums

Abstract The responses of chrysanthemum ( Dendranthema grandiflora Tzvelev) cultivars ‘Polaris’ and ‘White Marble’ to night temperatures of 32°C depended on the duration of exposure and the time of transfer to the high night temperature. Transfer for 7 nights at the start of short-day treatment (SD) delayed the onset of flower bud initiation, while transfer for longer, delayed the completion of flower bud formation. When transfer was made for 42 nights from the start of SD, no florets were initiated at the extreme tip of the receptacle in either cultivar throughout the period of transfer. Transfers that delayed flower bud initiation also delayed anthesis, though the effect was generally less. The greatest delay in anthesis occurred when the high night temperature was given at the onset of floret initiation, i.e. between 14 and 21 SD. Transfer at this time also caused the production of more disc florets in ‘Polaris’ and the formation of bracts among the disc florets of ‘White Marble’. Transfer to high night temperature at any stage induced foliar chlorosis and retarded stem extension, though final stem length was not significantly shortened. Attention is drawn to the need to reduce night temperature under black-out covers in summer, especially between 14 and 21 SD, and to some methods of achieving this.

Reversal of ethylene inhibition of tulip stem elongation by silver thiosulphate

Abstract Cut flowering stems of Tulipa cultivars were treated with a range of silver thiosulphate (STS) solutions (0.01–2.0 mM) for different times (10 min–24 h). The extension of the stem and longevity of the perianth were then observed at 18°C with the stems in water. At the highest dose (2.0 mM STS), a metallic silver sheen appeared on the surface of the STS solution and leaves were damaged. At non-toxic levels there appeared to be no effect on perianth longevity. However, the STS treatment completely reversed the inhibition of stem elongation caused by treatment with ethephon (48 mg l −1 for 24 h) or with ethylene (C 2 H 4 , 1 v.p.m. for 41 h). The results suggest that in spite of the lack of effect of STS on corolla longevity, the STS is freely mobile in the vascular tissue and in trace amounts blocks the effects of C 2 H 4 . Silver nitrate was not as effective as STS. Measurements of STS uptake suggest that about 1 μmol of silver is sufficient to counter the inhibitory effects of ethylene on stem elongation.

Respiratory and carbohydrate changes during ethylene-mediated flower induction in Dutch iris

Abstract The promotion of flowering in small Dutch iris (Iris × hollandica Hoog., cv. ‘Ideal’) bulbs by treatment for 24 h with 10 μl l−1 ethylene was associated with enhanced respiration, which continued long after the end of ethylene treatment. Shorter ethylene treatments, which were partially effective in inducing flowering, resulted in lower and shorter bursts of respiration. Changes in the soluble carbohydrate contents of the ethylene-treated bulbs were not detected until following the cold treatment. The possible mechanisms by which ethylene stimulates flowering are discussed.