Culture of cotyledons of Douglas‐fir on a medium for the induction of adventitious shoots induces rapid changes in polypeptide profiles and mRNA populations

Cotyledons of 3‐ to 4‐week‐old seedlings of Douglas‐fir [Pseudotsuga menziesii (Mirb). Franco] were treated with shoot induction medium (SIM) containing 5 μM 6N‐benzylaminopurine (BAP) and 5 nM naphthaleneacetic acid (NAA). Fresh weight, dry weight and soluble protein levels were not altered within the first 48 h of SIM treatment. SIM‐treated cotyledons were labelled in vivo with ³⁵SO₄^2‐, and TCA‐insoluble proteins were analyzed electrophoretically by a 2‐dimensional system consisting of non‐equilibrium electrophoresis (NEPHGE) followed by sodium dode‐cylsulfate polyacrylamide gel electrophoresis (SDS‐PAGE). A basic polypeptide with a relative molecular weight of 14.5 kDa was detected 32 h after induction and after 48 h a number of polypeptides in the 14 to 35 kDa range were induced. Translation products of poly‐A⁺ RNA isolated from cotyledons treated with SIM for 4, 16, 32 and 48 h were analyzed by using 2‐dimensional NEPHGE‐SDS‐PAGE. Both qualitative and quantitative differences in the translation products were observed at all time points investigated. Expression of a specific RNA coding for a 30 kDa polypeptide was demonstrated as early as 4 h after culture on SIM. This RNA was also present at 16 h, but decreased with longer SIM treatments. Thus, culture of excised cotyledons on a medium inducing the formation of adventitious shoots results in rapid quantitative and qualitative changes in the polypeptide composition and translatable RNA population prior to morphological evidence of shoot induction. 1992 Physiologia Plantarum