[Experiments in the analysis of the protonema development in mosses : V. The action of kinetin in caulonema regeneration].

1. On isolated caulonema branches of Funaria hygrometrica buds can be induced by kinetin in the same way as on intact protonemata. This is possible even in the case of isolated caulonema composed of only 5 cells. The buds are also formed at the same places as in intact protonemata. 2. The number of buds induced is dependent on the concentration of kinetin and the age at which the caulonemata were isolated. The largest increase occurs when the concentration of kinetin in the culture medium is between 0.1 and 0.5 mg/l. This concentration range is the same for protonemata 13 to 17 days old. More than 1 mg/l kinetin results in no further propagation of buds. The highest number of buds was formed on caulonemata of 19-day-old protonemata. 3. If the isolated caulonemata are at first laid out on agar free of kientin and only after 1 to 10 hrs transferred to kinetin medium, the number of buds decreases in an exponential curve. The half-life is 5 hrs. It is independnet of the age of caulonemata, i.e. of the number of buds formed immediately after the isolation. 4. Inhibition of DNA-synthesis by 5-FUDR has no influence on the regeneration process responsible for the decrease of bud formation or on the induction of buds by kinetin. During regeneration on medium containing FUDR, the number of buds decreases in the same way as in the control. Even when DNA-synthesis and cell division are suppressed for several days, the induction of buds can be demonstrated with Acridine Orange. 5. The experiments support the view that a reaction partner of kinetin is present in caulonema cells which during regeneration to the chloronema stage is either changed in one step so that it cannot react any longer with kinetin or is no longer present.