THE EFFECT OF CYTOKININS ON GROWTH and PIGMENT ACCUMULATION OF RADISH SEEDLINGS (RAPHANUS SATIVUS L.) GROWN IN THE DARK and AT DIFFERENT LIGHT QUANTA FLUENCE RATES*

Abstract

Abstract— The dependency of cytokinin effects upon irradiance was studied with radish seedlings (Raphanus sativus L. cv. Saxa Treib). Kinetin (6‐furfurylamino‐purine) or BAP (6‐benzylamino‐purine) were applied via the roots of plants growing either in continuous darkness or under high (90 Wm‐2) or low intensity white light (10Wm‐2). Apart from the different development of plants at low and high fluence rates, the following cytokinin effects were found: (1) Both cytokinins acted in a similar manner on growth characteristics and pigment accumulation at high and low light conditions, BAP being in many cases more effective than kinetin. (2) When compared with the control, the cytokinins suppressed hypocotyl and root lengthening in the dark and light‐grown plants. In darkness they led to increased cotyledon areas, whereas in the light the leaf expansion was suppressed. (3) In the etiolated and low light grown plants, the anthocyanin content of the hypocotyls was enhanced due to the action of cytokinins, whereas under high light the anthocyanin accumulation was decreased. (4) In the cotyledons of etiolated plants, more phototransformable protochlorophyll(ide) and more carotenoids were formed when cytokinins were present. In green leaves the carotenoid content was diminished due to the action of cytokinins, particularly in plants grown in strong light. The chlorophyll a/b ratio was increased in the cytokinin‐treated plants in most cases. The results suggest a light dependency of the cytokinin effects. It is believed that the response of a plant towards exogenously applied cytokinins is similar to that with high intensity light.

Cellular response of light/dark-grown green alga Chlorella vulgaris Beijerinck (Chlorophyceae) to exogenous adenine- and phenylurea-type cytokinins

“…Therefore, the increase in NADH-GDH activity correlates well with higher photosynthetic pigments accumulation in Chlorella vulgaris cells under the influence of cytokinins. This corresponds well to earlier papers demonstrated that cytokinin treatment abolishes the lag phase in chlorophyll synthesis and accelerates its rate (Buschmann and Lichtenthaller 1982). Phenylurea-and adenine-type cytokinins have also been reported to have the inhibitory effect on chlorophyll breakdown by chlorophyllase, Mg-dechelatase and peroxidase-linked chlorophyll bleaching in higher plants (Genkov et al 1997;Costa et al 2005).…”

Euglena gracilis(Euglenophyceae) produces abscisic acid and cytokinins and responds to their exogenous application singly and in combination with other growth regulators

“…Production of chlorophyll a and b is increased in response to adenine-type CKs in Chlorella vulgaris, a green unicellular alga (Piotrowska & Czerpak, 2009); this concurs with earlier papers stating that CK treatment abolishes the lag phase in chlorophyll synthesis and accelerates its production rate (Buschmann & Lichtenthaler, 1982). It is thought that CKs probably reduce chlorophyll destruction and/or increase chlorophyll synthesis (Piotrowska & Czerpak, 2009).…”

Role of Cytokinins in Senescence, Antioxidant Defence and Photosynthesis

“…Similarly, kin has repeatedly been reported as very active in senescence deceleration (e.g., [155,156,157]), however it showed an ambiguous effect on Anthurium [82]. It should be noted that the CK effect also depends on the age of cells and leaves [158] and light conditions [123,158,159].…”