The role playing by the “soft” (κT < 1 GeV/c) region in the small-x behaviour ofg1(x,Q2) and the non-singlet structure functionf1, NS(x, Q2) has been studied with the help of the effective QCD Lagrangian which takes into account the lightest degrees of freedom — the constituent quarks and the π-mesons (Goldstone bosons). It has been shown that the quark-quark interaction due to the pion exchange has a negative couplingg for the isovector component (I = 1 in thet-channel) off1(x,Q2) and isosinglet component ofg1(x, Q2). Here the pion induced interaction changes mainly the normalization of the quark distribution (it decreasesf1,NSI = 1 (x,Q2) two times atx < 3·10−3) and changes slightly the effective exponents λ (ℕ1,NS,g1 ∼x−λ atx → 0). On the other hand due to a positive value of couplingg the value of λ increases by 15% for the isovector part ofg1 (x,Q2) and up to λ ≈ 0.5 (instead of λ ≈ 0.2 without the pion contribution) for the isoscalar non-singlet structure functionf1,NSI = 0 (x,Q2).