Effects of Ventilation and Sucrose Concentrations on the Growth and Plantlet Anatomy of Micropropagated Persian Walnut Plants

Plantlets grown in conventional tissue culture systems usually encounter physiological and anatomical abnormalities including inability to photosynthesize, low chlorophyll content, open stomata, lack of a cuticle layer in the leaf, abnormal xylem parenchyma etc. Photoautotrophic and photomixotrophic systems could diminish these problems. The purpose of this study was to increase the chlorophyll content and photosynthetic ability of shoots grown in vitro and to improve the adaptation of walnut plantlets. Walnut apical leaf buds were cultured in vessels containing DKW medium supplemented with 0, 15, 30 and 45 g L-1of sucrose. The vessels were closed with a clear polypropylene lid with two syringe filters on the lid (V1) or with a 50 mm microporous polypropylene membrane (V2). Natural ventilation had a significant effect on most of the growth indices. Furthermore, different levels of sucrose had significant effects on growth characteristics. Natural ventilation increased chlorophyll content significantly. By using ventilated vessels containing 15 g L-1 sucrose, the total chlorophyll was significantly increased. Stomata under non-ventilated conditions were spherical with wide openings, whereas those in ventilated vessels were elliptical with narrow openings. As a result, ventilated vessels with 15 g L-1of sucrose produced healthy plantlets.