Insertion profiles in stomatal density and sizes in Nicotiana tabacum L. plantlets

Tobacco (Nicotiana tabacum L, cv. Samsun) plantlets were cultured in vitro on Murashige-Skoog medium photoautotrophically (without sucrose) or photomixotrophically (with 3 % sucrose) under two irradiances [70 or 230 mu mol m(-2) s(-1)]. Significant differences in stomatal density and sizes in leaves of different insertion levels (3(rd), 5(th) and 7(th) leaves from bottom) in photomixotrophic plantlets but not in photoautotrophic ones were found after 35 d of culture. Stomatal density was higher in upper leaves and on abaxial leaf side. Higher irradiance enhanced stomatal density in photoautotrophic plantlets. Stomatal sizes decreased with leaf insertion level but no significant differences between leaf sides were found. Abaxial stomata were more circular than the adaxial ones. In photomixotrophic plantlets stomata tended to be more elongated in the 3(rd) and the 5(th) leaves, whereas stomatal elongation in photoautotrophic plantlets was similar in all leaves.