The occurrence of an endogenous circadian rhythm in a plant tissue culture.

Abstract

Leaves of the succulent plants Bryophyllumn, fedtschenkoi and B. daigremnontianutni, show an endogenous circadian rhythm in their rate of CO., metabolism (9, 10, 11, 12). The extent to which the occurrence of the rhythm depends upon the organization of the leaf has been investigated with callus cultures of Bryophyllumi. leaf tissue. There has been but one previous report of a persistent rhythm in a plant tissue culture. Enderle (3) observed rhythmic fluctuations in growth and turgidity of cultures of Daucus carota and found the rhythmicity to persist in prolonged darkness. Investigation of the rhythm necessarily involved microscopic examination of the cultures and this was done with red light at intervals of approximately 4 hours. Since red light is particularly active in affecting plant rhythms (4, 5, 7, 11), and some organisms (e.g. Euglena) are known to have the capacity for frequency demultiplication (1, 2), the diurnal periodicity in growth and turgidity might have arisen from the periodic stimulation with red light. Enderle (3) does not appear to have established whether or not the phase of the rhythm can be set at different times of day. Unequivocal evidence of the occurrence of endogenous rhythms in plant tissue cultures is therefore lacking. The endogenous nature of rhythmicity in animal tissue cultures (6, 8) has also yet to be firmly established.