SERK gene homolog expression, polyamines and amino acids associated with somatic embryogenic competence of Ocotea catharinensis Mez. (Lauraceae)

In the present work, we investigate the association of SERK gene homolog expression, polyamines (PAs) and amino acids related to putrescine synthesis ( arginine and ornithine) and polyamines degradation (gamma-aminobutiric acid) or S-adenosylmethionine synthesis ( methionine), with the embryogenic competence in cell aggregates of Ocotea catharinensis Mez. ( Lauraceae). Cell aggregates were cultivated during 7 days in woody plant medium ( WPM) supplemented with 20 g l(-1) sucrose, 22 g l(-1) sorbitol, 400 mg l(-1) glutamine and 2 g l(-1) phytagel, and in Murashige and Skoog medium (MS) supplemented 20 g l(-1) sucrose, 3 g l(-1) activated charcoal, 2 g l(-1)Phytagel with and without 40 mg l(-1) 2,4-dichlorophenoxyacetic acid (2,4-D). The cell aggregates cultivated in MS plus 2,4-D and in the WPM medium showed hybridization with a SERK gene homolog both in northern and in situ hybridization experiments. Cell aggregates cultivated in an MS basal medium, without 2,4-D, did not exhibit any hybridization signal to the SERK probe used, thus they were considered potentially non-embryogenic cells. In all three media only free polyamines were detected. The higher putrescine levels occurring in WPM callus were associated with a higher arginine and ornithine content, lower gamma-aminobutiric acid level, and SERK homolog expression. Putrescine was also the major polyamine in the MS medium. In the MS plus 2,4-D medium, the levels of putrescine, spermidine and spermine were similar. Spermine exhibited similar and the lowest levels in all media. Spermidine intermediary levels occurred in the WPM and MS media. In cell aggregates methionine level was lowest in the MS plus 2,4-D medium, but similar in the MS and WPM media.