Studies on growth and flowering in axenic cultures of insectivorous plants: III. Effects of photoperiod, ethrel, morphactin and a few other growth substances and metabolic inhibitors on Utricularia inflexa

Abstract

Summary Shoot tips cultured in White’s basal medium containing 20 g/l sucrose and 10 mg/l Fe-EDTA perceived the flowering stimulus when exposed to 7 short days followed by transference to non-inductive conditions. However, flower buds failed to develop unless the shoot tips were allowed to grow for 4 weeks under short-day conditions. For cultures raised for 4 weeks in long-days the minimum number of inductive photocycles required to support normal flower, fruit and seed development was found to be 7. Induction of flowering but not flower development occurred even on exposure to 2 short days provided the plants had grown for 6 weeks in long days. A new type of growth termed “Bushy”, which appears to be a spontaneous bud mutation was isolated in cultures raised on the basal medium. It is characterised by thread-like, profusely branched stolons, with shorter, sparingly dissected leaves, and fewer, pinkish bladders. This clone produces the same type of growth in subculture and does not flower under any photoperiodic conditions. Of the various growth substances tried on the Utricularia plants, MEFA showed a strong herbicidal effect and killed the plants. AMO-1618 and coumarin inhibited apical as well as lateral bud growth. The above three compounds and ABA, kinetin, BA and zeatin were unable to promote flowering under non-inductive conditions. BA stimulated growth in both long and short days. Even in the latter conditions AMO-1618 and coumarin totally inhibited flowering, whereas ABA, kinetin and BA permitted 80–100 per cent of the cultures to flower. Zeatin lowered the percentage of flowering cultures. The commercial sample of ethrel (10 −7 M) stimulated the production of a larger number of inflorescences and flowers as compared to controls in short days. In one experiment, all the 6 plants treated with ethrel at 10 −8 M flowered in long days. However, when this experiment was repeated with a pure crystalline sample of ethrel, only float primordia developed and the flower buds failed to differentiate. Under partially induced conditions, ethrel showed a quantitative stimulation of flowering. Ethylene gas and methionine, failed to cause flowering under non-inductive conditions whereas propionic acid stimulated the formation of only float primordia. A morphactin, chlorflurenol (1T-3456), caused malformation of leaves and bladders. Under inductive conditions it increased the number of inflorescences but affected flower development. The flower buds remained undeveloped or produced fleshy petals and sepals, and sometimes no sex organs. In some cases the inflorescence became transformed into a vegetative structure. Surprisingly in 40 % of the cultures, treated with chlorflurenol, inflorescences bearing green, fleshy and abnormal flowers developed under non-inductive conditions. Of the several inhibitors of nucleic acid synthesis tested under inductive conditions, 5FDU at 10-4 and 10-5 M suppressed both growth and flowering, 5FU, 2TU and 8AG specifically inhibited flowering but modified vegetative growth whereas 6AU proved toxic at 10-4 M but failed to inhibit flowering at 10-5 M. Simultaneous application of uracil was ineffective in overcoming the effects of these inhibitors. 5BU and Actinomycin D neither affected flowering nor vegetative growth.