Drought is one of the major abiotic stresses affecting crop quality and yield, especially in the condition of actual climate changes. Although, due to its long and deep roots, sunflower is considered to be a drought-tolerant crop, severe water deficit causes the reduction or delay of seed germination, compromises seedlings establishment and their particularities. To characterize how sunflower seedlings respond to drought stress the physiological responses and drought-induced gene expression (DHNs) were analysed in a model system consisting of a drought-tolerant (1718R) and a drought-sensitive (413S) sunflower hybrids subjected to progressive hydric stress. Polyethylene glycol 6000 (PEG-6000) solution of 10% and 20% (osmotic potential −0.55 and −1.60 MPa, respectively) was used to induce stress. Germination rate (GR), promptness index (PI), germination stress tolerance index (GSTI), plant height stress index (PHSI), root length stress index (RLSI) and dry matter stress index (DMSI) were investigated to determine the physiological response to water stress. Total RNA was extracted from cotyledon and roots of 10-day old sunflower seedlings. Three genes (Rab18-like, Xero1 and COR47-like) related to drought stress response were analyzed by quantitative Real-time PCR. A significant reduction of all analyzed physiological indices, except root length of 1718R hybrid, was observed with the increase of PEG concentration in both sunflower genotypes. In the case of hybrid 413S the most affected traits were root length, followed by plant height. In contrast, the effect of hydric stress on root elongation in drought tolerant hybrid 1718R was insignificant and greater values were observed in PEG treated samples as compared to control. The drought tolerant hybrid showed higher values of PI and GSTI for both levels of applied osmotic potential compared to sensible hybrid. All analyzed dehydrins changed their transcript content due to PEG treatment, both in the cotyledons and in the roots. However, there is a higher response reaction in the roots compared to cotyledons, especially in sensitive genotype. Also, it is obvious the trend of upregulation in dehydrin expression of Rab18-like in case of tolerant genotype and of Xero1 in case of the sensitive one. A more contrasting response due to the induced stress is highlighted for expression of dehydrin COR47-like depending on all experimental factors (genotype, PEG concentration, tissues). Analysis of the relative gene expression ratio of control plants 1718R versus 413S revealed a higher concentration of Rab18-like (1.51-fold) and COR47-like transcripts in roots and of Xero1 in cotyledons and roots. Quantitative variations of DHN transcripts (mostly upregulated than downregulated), in normal conditions and in hydric stress conditions, in a tissue-specific manner and depending on severity of stress were revealed.