Stomatal characteristics and leaf anatomy of potato plantlets cultured in vitro under photoautotrophic and photomixotrophic conditions

Potato plantlets (Solanum tuberosum L. cv. Benimaru) were cultured under photoautotrophic (without any sucrose in the nutrient medium and with enriched CO₂ and high photosynthetic photon flux) and photomixotrophic conditions (20 g l^-1 sucrose in the medium). Leaf anatomy and stomatal characteristics of the leaves were studied in relation to stomatal size and density. Leaf diffusive resistance, transpiration rate, and wax content of the leaves were also investigated. In the photoautotrophic treatment, stomata behaved normally by closing in the dark and opening in the light. The stomatal density increased twofold compared to that of the photomixotrophic treatment. Relatively thick leaves and an organized palisade layer were observed and the epicuticular wax content was remarkably higher in this treatment, i.e., seven times greater than that of photomixotrophic treatment. In general, higher diffusive resistance of the leaves was observed than under photomixotrophic conditions; also the resistance increased in darkness and decreased in the light. All these characteristics led the plantlets to have a normal and controlled transpiration rate, which was exceptionally high in the photomixotrophic treatment throughout the light and the dark period.