The experiment was carried out under greenhouse conditions. Three sunflower genotypes were tested: Oro 9 (a variety population) and two hybrids (Isostar and Flamme).

N and K deficiency affected significantly shoots and roots morphological parameters for all examined sunflower cultivars. Shoots appeared to be more sensitive than roots. Reduction were more pronounced for dry weight under N deficiency than under K deficiency.

Root volume play an essential role in water and mineral absorption. Under normal supply of N and K root volume vas highly correlated, to shoot dry weight (r=0.89), to root dry weight (r=0.84) and to total dry weight (r=0.86). Under No and Ko, reduction of root volume and root dry weight reflected growth inhibition caused by N and K deficiency. Root volume, under No and Ko, was highly correlated, to root dry weight (r=0.99 and r=0.97 respectively for No and Ko), to shoot dry weight (r=0.89 and r=0.96 respectively for No and Ko) and total biomass (r =- 0.93 and r=0.99 respectively for No and Ko).

Total soluble sugars accumulation under No and Ko was observed at two pairs of leaves for all genotypes. The accumulation was highly and negatively correlated to root biomass (r =- 0.98) under No. However. a weak and negative correlation (r =- 0.16) between these two parameters was found for Ko. Total soluble sugars were also strongly and negatively correlated, to root volume for No (r =- 0.98) and Ko (r =- 0.99). Cultivars with high root total soluble sugars content seems to be more sensitive to N and K deficiency like Isostar.

Response of cultivars to N and K deficiency resulted in an accumulation of amino acids.

Genotype Isostar, whose morphological characters (except leaf area) were severely affected, was the most sensitive. On the contrary Flamme was the least sensitive because of its capability to maintain an adequate growth rate causing a small reduction of morphological parameters. Oro9 had an intermediate behaviour.