Manipulation of the culture environment on in vitro air movement and its impact on plantlets photosynthesis

Two-dimensional air current speeds in the culture vessel were measured using a tracer-based visualization technique and the effect of the air movement in the culture vessel on the photosynthesis of in vitro potato plantlets was assessed under a photoautotrophic culture condition. The air current speeds inside the vessel were varied by controlling free convection induced by spatial variations of temperatures in the culture vessel. For all conditions examined, upward air currents were observed around the plantlets in the central part of the culture vessel and downward air currents were observed near inside walls in the culture vessel. The upward and downward air currents were restricted by the presence of the plantlet. The upward air current speeds were affected by plantlet size inside the vessel and it was 24, 8 and 4 mm s^-1 in culture vessels with no plantlets, a 10-mm-tall plantlet and a 60-mm-tall plantlet cultured inside the vessel, respectively. The upward air current speed was increased by 2 times by increasing wind velocity above the culture vessel from 0.1 to 1.0 m s^-1. Placing the black plate on the medium also increased the air current speeds by 1.5 times. The net photosynthetic rates of the plantlets increased from 2.0 to 2.5 μmol m^-2 s^-1 as the upward air current speed in the culture vessel increased from 2.4 to 8.0 mm s^-1. The air current speeds in the culture vessel were significantly slow. Enhancement of the air movement in the culture vessel is important to promote photosynthesis of the in vitro plantlets.