BLACK SPRUCE SOMATIC EMBRYO GERMINATION AND DESICCATION TOLERANCE .2. EFFECT OF AN ABSCISIC-ACID TREATMENT ON PROTEIN-SYNTHESIS

In this paper, the biochemical changes associated with a 20 mu M abscisic acid (ABA) and desiccation treatment on mature black spruce somatic embryos (SEs) were examined. It was previously shown that this ABA treatment of black spruce SEs resulted in an earlier, more uniform germination (i.e., root and shoot growth synchrony) and increased SE tolerance to slow and fast desiccation. In this paper, mature SEs (control SEs) were either placed on maturation media containing 20 mu M ABA for 7 days (ABA-treated SEs) or placed on maturation media for 7 days without ABA (control-ABA SEs). Only the ABA treatment resulted in an increased SE protein content, dry mass, and SE ABA content compared with the control SEs. The ABA treatment was the only treatment that maintained a high percent germination following slow desiccation. Seven proteins with molecular mass of 42-, 33-, 32-, 28-, 27-, 21-, and 20-kDa were identified as storage proteins. An examination of in vivo protein synthesis showed that storage protein synthesis occurred in control SEs, ABA-treated SEs, and control-ABA SEs. There were minor changes, such as a cessation or decline in storage protein synthesis, in the ABA-treated and control-ABA SEs. Protein isolated from the treated and control SEs was probed with an antibody raised to the maize dehydrin. This antibody reacted strongly to a 23-kDa protein and reacted slightly to three other proteins in mature zygotic and somatic embryos and in all treated SEs. The ABA-treated SEs appeared to have a slightly elevated quantity of the 23-kDa dehydrin-like protein (based on intensity of the band in the Western blot). Desiccation of these SEs resulted in a decline in this protein to a level similar to that found in the controls. The ABA treatment induced the synthesis of two low molecular mass proteins (12- and 8-kDa) and their synthesis continued after these somatic embryos were desiccated. The synthesis of the 8-kDa protein was induced when control SEs were desiccated. These results suggest that the ABA treatment extended the maturation stage of development of the black spruce SEs and resulted in an increase in a dehydrin-like protein.