Tobacco (Nicotiana tabacum L, cv. Samsun) plantlets were cultured in vitro
on Murashige-Skoog medium photoautotrophically (without sucrose) or photomi
xotrophically (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 a
fter 35 d of culture. Stomatal density was higher in upper leaves and on ab
axial leaf side. Higher irradiance enhanced stomatal density in photoautotr
ophic 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 sto
matal elongation in photoautotrophic plantlets was similar in all leaves.