Morphological, physiological, anatomical and histochemical responses of micropropagated plants of Trichosanthes kirilowii to hydroponic and soil conditions during acclimatization

Acclimatization of tissue cultured plants to greenhouse or field conditions is the final and most crucial step of micropropagation. Hydroponic system has the potential to harden in vitro plants in an efficient and convenient way. Herein, in vitro regenerated plants of Trichosanthes kirilowii were cultured in 1/4, 1/2 and full strength Hoagland nutrient solution under a simple hydroponic system during acclimatization, respectively, and soil culture was prepared as a control. Morphological, physiological, anatomical and histochemical alterations of the plants treated by different concentrations of nutrient solution and soil conditions were analyzed after 30 days of growth. Results showed that all the three concentrations of nutrient solution significantly improved the survival rate, plant growth, pigment content, photosynthesis capacity, and stomatal density compared with those grown in soil, and there were no significant differences of the plant morphological parameters and the stomatal characteristics among the three hydroponic treatments. The plants grown in the 1/4 Hoagland solution yielded the highest net photosynthesis rate, transpiration rate and stomatal conductance, as might be attributed to their highest photosynthetic pigment content among the treatments. Anatomical and histochemical studies revealed that enlarged air spaces, multiple lignified Φ thickenings, and heavier suberin and lignin were formed in the cortex of the adventitious roots grown in 1/4 Hoagland nutrient solution as compared with those cultured in soil conditions, indicating that T. kirilowii had enough phenotypic plasticity in the root structure to grow in hydroponic conditions by formation of larger aerenchyma spaces and apoplastic barriers. This study clearly demonstrates that hydroponics is an alternative for the tissue cultured plants of T. kirilowii to adapt to great environmental changes during acclimatization.