Influence of ventilation and sucrose on growth and leaf anatomy of micropropagated potato plantlets

Potato single nodes were cultured in vessels containing MS medium supplemented with 10, 20 and 30g/l of sucrose. Vessels were closed with a clear polypropylene lid with or without 10mm microporous polypropylene membrane. Sucrose concentration significantly increased plantlet height, shoot fresh weight and chlorophyll a content. Plantlets grown in ventilated vessels were significantly shorter, had lower shoot fresh weight and higher shoot dry weight than those in non-ventilated vessels. The highest leaf chlorophyll a content (21.83mg/g fresh weight) was found in plantlets grown in ventilated vessels using MS medium with 20g/l of sucrose, whereas those grown on medium with 10g/l of sucrose had the highest chlorophyll b content (24.00mg/g fresh weight). Total chlorophyll content was significantly higher when plantlets were grown in ventilated vessels containing medium with 10 or 30g/l sucrose than in non-ventilated vessels. There was no significant difference in total chlorophyll content among plantlets grown in ventilated vessels with different concentrations of sucrose. Stomatal density was significantly lower when plants were grown under ventilated conditions. Leaf replica examination showed that stomata under non-ventilated condition were spherical with wide openings whereas, those in ventilated vessels were elliptical with narrow openings. Plantlets grown in non-ventilated vessels had thinner leaves and failed to build up a distinct defined upper epidermis, palisade parenchyma layer and spongy cells. On the other hand, leaves under ventilated conditions showed comparatively well organized layers with small intercellular space. The vascular system of leaves under the ventilated conditions demonstrated very well developed xylem unlike leaves under non-ventilated conditions. Thus, ventilated vessels with the 20g/l of sucrose under ambient CO₂ in the growth room could successfully promote photomixotrophic culture and produce healthy plantlets.