Protein synthesis is differentially required for germination in Poa pratensis and Trifolium repens in the absence or in the presence of cadmium

The objective of this study was to determine the importance of protein synthesis during germination of white clover (Trifolium repens) and Kentucky bluegrass (Poa pratensis) and to assess the impact of osmopriming on seed germination in the presence of cadmium. Cycloheximide (Cx, 20 and 100 mu M), a translation inhibitor, delayed germination and reduced final germination percentage in both species, although to a higher extent in P. pratensis than in T. repens. This suggests that in white clover, some proteins involved in reserve mobilisation and metabolic activation were already present in mature seeds. Actinomycin-D (Act-D; 20 and 100 mu M) and alpha-amanitin (alpha-Am 20 mu M), both inhibitors of transcription, did not reduce P. pratensis germination, demonstrating that for this species, transcription is not essential for radicle protrusion and that long-lived mRNA are used for initial protein synthesis. In contrast, incised white clover seeds showed delayed germination in presence of alpha-Am, suggesting that expression of some specific genes may help in the first germination steps. Osmopriming (PEG 8,000 60%) improved germination of seeds exposed to 100 mu M Cd but the positive effect of this pretreatment was suppressed (T. repens) or drastically mitigated (P. pratensis) when Act-D or Cx were added to the priming medium. Cadmium reduced alpha- and beta-amylase activities in germinating seeds but osmoprimed seeds exhibited higher activities than unprimed seeds. The presence of inhibitors in the priming medium reduced alpha- and beta-amylase activities. These results suggest that the two studied species differed significantly in the mechanisms occurring during early seed germination and that the beneficial effect of priming requires gene expression and protein synthesis.