Anatomical and physiological characteristics of the petiole of Abutilon theophrasti in relation to circadian leaf movements

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Abstract
Leaf movements in Abutilon theophrasti Medic, were monitored manually and by a continuous electronic recording device. Plants entrained to a daily regime of a 15 h light span followed by 9 h of darkness showed rhythmic movements that persisted under conditions of continuous illumination and constant temperature with a circadian period. The rhythmic change in orientation of the leaf from a near horizontal (day) to a near vertical (night) position was attributed to movement of the blade and not the petiole. The end of the petiole next to the blade functions as a joint or pulvinus. Anatomical confirmation of the existence of a pulvinus in the Abutilon leaf was provided by light microscopy. Vascular tissue in this region forms a solid cylinder with no pith, and the cortex is parenchymatous. In the main part of the petiole, the vascular tissue is arranged in four to six bundles, a pith is present, and the cortex contains a sub‐epidermal ring of collenchyma. Both the functional and anatomical evidence indicate the presence of a pulvinus that functions in circadian leaf movements of Abutilon.