Abies cephalonica embryogenic cell masses (ECMs) were grown on proliferation media in the presence and absence of 100 g/plate humic acids (HA) or fulvic acids (FA). Proliferation rate, proportion of consecutive developmental stages of proembryogenic masses (PEMs) and some biochemical parameters, such as cellular levels of ATP and glucose-6-phosphate (Glu-6-P), were detected. FA increased significantly the proliferation rate, affected the proportion of PEMs and were able to invert the negative effects of the anti-auxin p-chlorophenoxyisobutyric acid (PCIB). It was also shown that the proton pumping ATPase and PPase activities were decreased in microsomes obtained from PCIB-treated ECMs, while increasing when ECMs were grown in the presence of FA. The effects of humic substances were also evaluated on the maturation phase, where both HA and FA, if present in the pre-treatment media during the proliferation phase, induced a delay in somatic embryo formation. These results suggest that humic substances could improve the proliferation of PEMs, thus affecting the subsequent maturation process of A. cephalonica.
