Promotion of Vegetative Growth in Force-ventilated Protea cynaroides L. Explants Cultured in Modified Temporary Immersion Culture Vessels

Abstract

Temporary immersion culture vessels were modified to culture Protea cynaroides L. microshoots on semisolid growth medium. The effects of different ventilation treatments and sucrose concentrations on the vegetative growth and physiological characteristics of P. cynaroides L. microshoots were investigated. Three ventilation treatments were used: microshoots were either ventilated naturally or forced ventilated for 2 minutes/2 hours or 2 minutes/4 hours. In addition, two sucrose concentrations were used in the growth medium: 30 and 10 g·L−1. Significant interaction effects were found between ventilation and sucrose in the number of shoots formed. When cultured on growth medium with 10 g·L−1 sucrose, microshoots force-ventilated for 2 minutes/2 hours produced significantly higher number of shoots than those naturally ventilated or force-ventilated for 2 minutes/4 hours. In the 30 g·L−1 sucrose treatment, no significant differences in shoot numbers were observed among all ventilation treatments. The highest leaf areas were found in microshoots cultured in the 2 minutes/4 hours forced ventilation treatment, which were significantly higher than microshoots in the other ventilation treatments, irrespective of the sucrose concentration. Chlorophyll content was significantly higher in leaves of microshoots that were cultured in 30 g·L−1 sucrose compared with those grown in 10 g·L−1 sucrose in all ventilation treatments. Analysis of chlorophyll fluorescence of the leaves revealed that the Fv/Fm value of microshoots grown on 30 g·L−1 sucrose and force-ventilated for 2 minutes/4 hours was significantly higher than those naturally ventilated in the same sucrose treatment. Overall, the use of 30 g·L−1 sucrose in combination with 2 minutes/4 hours ventilation provided the best conditions for culturing P. cynaroides microshoots. This study demonstrated that these modified temporary immersion culture vessels can be used as a forced ventilation system to culture P. cynaroides microshoots and promote vegetative growth as well as improve their photosynthetic characteristics. The system described here introduces a simple and novel method of converting commercially available temporary immersion systems into force ventilation systems.