Introduction Plant peroxidases (PO) are known to catalyze the oxidation of a wide variety of substrates using H2O2 or other peroxides. Due to their capacity to be expressed as numerous multiple isoforms, PO are considered to mediate a diverse plant metabolic activities, including synthesis of the plants cells walls, growth, morpho- and organogenetic processes, as well as responses to abiotic and biotic stresses (1). There are numerous reports about the PO activity in relation to the state of endogenous plant hormones. Particular interest represents results of exogenously application of plant growth regulators (PGR), separated from higher plants, including algae. Studies on plant responses to PGR application are important, because the appropriate treatments are essential for the improvement of the parameters of plant growth and resistance to abiotic and biotic stress factors. The aim of this study was the investigation of the effects of spraying of Cucumis sativus L. seeds with solution of Reglalg, PGR extracted from algae, on seedlings growth and PO activity in different compartments of roots cells. Material and methods The seeds of Cucumis sativus L., cultivar Concurrent, were immersed during 24 hours and 4oC in solutions of different modifi cations of Reglalg, extracted from algae Spirogyra in different periods of their life cycle. Three modifi cations or Reglalg were used, marked as Reg. 1, Reg. 2 and Reg. 3. Subsequently, seeds were germinated in the darkness, at 25ºC. The infl uence of Reglalg on parameters of seedling growth, soluble and bound PO isoenzyme patterns and activity were evaluated. Results and discussions It was established that utilised in three dilutions (1/100, 1/200, 1/400), Reg. 1, Reg. 2 and Reg. 3 exerted a benefi cial effecs on seedlings growth and biomass accumulation. In this regard the most effective was Reg. 2 diluted with water in ratios 1/200. Seeds treatments with solutions of Reg. 1, Reg. 2 and Reg. 3 in dilution 1 /200 did not infl uenced the activity of roots soluble PO and as well their isoforms patterns. At the same time, the changes in activity of PO, embedded in the cell walls and linked to the biochemical residues by hydrophobic, ionic and cationic bonds were marked. The level of the activity of ionic and cationic PO, bounded on roots cells walls, was marked after seeds treatments with all three modifi cations of Reglalg. In the roots of treated with Reglalg samples the activity of PO linked by hydrophobic bonds to cells walls was comparable with that in roots of control plants. Apparent differences were observed in isoenzymes patterns of cells walls bound PO in dependence of membrane fractions and modifi cation of Reglalg. Conclusions 1. Treatments of cucumber seeds with different modifi cations of PGR Reglalg induce the benefi cial effects on seedling growth and development. 2. The activity of ionic and cationic cells walls bound PO is inversely related to Reglalg-mediated biomass accumulation of cucumber seedlings.