ONTOGENIC EFFECTS ON THE STOMATAL APPARATUS OF 4 BELGIAN SUGAR-BEET (BETA-VULGARIS SUBSP VULGARIS L) CULTIVARS

Characteristic features of stomatal apparatus, i.e. stomatal density, area of the stomatal porus, relative stomatal area and diffusion resis tance (r(s)) were examined in young (10 d) and old (30 d) leaves of fo ur sugar beet cultivars (Allyx, Arigomono, Monohil and Primahill). Sin ce the plant age was also considered to be an important ontogenetic fa ctor, all measurements were repeated at plant ages of 40, 47, 57 and 6 5 d. Genotypical differences among the cultivars studied could be expl ained in terms of the level of polidy, i.e. an increasing number of ch romosome sets was accompanied by an increase of stomatal size and a de crease of stomatal density. The other stomatal characteristics did not significantly differ among the cultivars. The increase in plant age r esulted in a higher stomatal density and a gradually decreasing stomat al size. These phenomena generally induced a plant ontogeny controlled increase of the relative stomatal area of all leaf series. Young leav es showed higher stomatal densities, but the stomata were smaller and pore area was reduced by 40 to 60%, compared to the old leaves. The yo ung leaves also exhibited a smaller r(s).