There are several issues complicating somatic embryogenesis in conifers, for instance the low initiation frequency, the weak maturation capacity, and the loss of an embryogenic potential after a prolonged cultivation. The aim of our study was to clarify molecular details of the this process in the tree Pinus nigra Arn. We performed comparative proteomic analysis based on the two-dimensional gel electrophoresis in 2 genotypes coded 362 and 366 of: 1) proliferating embryogenic tissues (E) initiated from immature zygotic embryos, 2) non-embryogenic calli (NEC) started from cotyledons of somatic seedlings, 3) embryogenic tissues that lost the maturation capacity (E-L). Pine tissues showed distinct morphologic features: a) E362 and E366 were characterized by the presence of early bipolar structures capable of maturation and plantlet regeneration; b) NEC362 and NEC366 were composed of round shaped cells without any organisation; c) for E-L362 and E-L366 the long-term culture of initially embryogenic tissues resulted in the disorganisation of early bipolar structures. We found 24 differentially accumulated protein spots common for both genotypes after comparison of E versus NEC.