Tropic responses of potato single-node explant cultures
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A special in-vitro protocol was elaborated enabling the production of potato single-node explant plantlets that can be used as objects for tropic studies. In light-grown plantlets, achievement of a full (90°) phototropic (PT) curvature required 75 to 120 min of continuous unilateral blue light irradiation or 120-135 min of gravitropic stimulation (GT). Time-lapse photography revealed that the curves describing PT and GT bending have a sigmoid shape. Continuous BL irradiation was necessary for the induction of continuous PT bending. If the BL was turned off after 30-50 min of PT stimulation, the bending gradually decreased and stopped in darkness after 25.0 ± 2.0 min. Within this period, curvature increased by 15.5 ± 1.5°. When the BL was turned off upon completion of PT bending (when the plantlets reached an angle of 90°), the plantlets entered the phase of fast straightening. The 90° PT curvature was significantly exaggerated in darkness by turning the jars from a vertical to horizontal position providing 120.74 ± 2.5° as the final curvature angle after two more hours in darkness.