Introduction: Circumnutation is a revolving movement of elongating cylindrical plant organs such as stems, hypocotyls, tendrils and roots. It is the consequence of helical growth and reversible volume variations occurring in the cells of the moving part of the organ (the bending zone below the apex). The bending is caused by the difference in the water content and cell volume between the convex and concave sides of the bending zone, associated with turgor and ion concentration differences between opposite sides of the stem. It is proposed that turgor changes are generated by endogenous, spontaneous oscillations. As a consequence oscillatory growth and movement are generated. We aimed to compare the rhythmicity of circumnutation in sunflower with regard to the trajectory length, period, shape and surface area of individual nutations in different photoperiod conditions.
Material and Methods: Measurements lasting about 7 weeks were executing using a picture analysis system. Variable photoperiods – a 24h photoperiod (LD 16:8 followed by LL), a 30h photoperiod (LD 20:10 followed by LL and again by LD 20:10) and a 16h photoperiod (LD 8:8 followed by LL) were applied. In order to determine whether a periodicity of circumnutation parameters existed or not, the data were processed by the Fourier spectral analysis and the wavelet analysis.
Results and conclusions: We found that all parameters revealed a beautiful daily modulation in each LD condition applied. After LD-LL transition, the parameters were gradually loosing their modulation. In the transient phase (about 7 days after LD-LL transition) the rhythms of the circumnutation parameters turned out to be close to 24h in the 24h photoperiod as well as in the 30h and 16h photoperiod. These findings suggest the possibility for circumnutation of being circadian regulated. After the LL-LD transition the rhythms regained their daily modulation after one night. These findings strongly support the view that circumnutation in sunflower, widely known as an ultradian rhythm, also possesses daily modulations of its intensity and it can tune in a wide range to the frequency of environment.

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