[Compartmentation of free alanine and its consequences for the quantitative consideration of protein synthesis: Experiments with fern gametophytes [Dryopteris filix-mas (L.) SCHOTT] in blue and red light].

In fern gametophytes (= sporelings) there is a strong correlation between the degree of blue light mediated photomorphogenesis and the protein content of the organism (cf. MOHR, 1963). In a previous paper (PAYER et al., 1969) we have shown that blue light specifically increases the rate of protein synthesis in the fern sporelings over the rate which is maintained under red light. - In the present paper blue light mediated protein synthesis has been dealt with further using one representative amino acid, alanine, which was labelled with (14)C from (14)CO2 under steady state conditions of photosynthetic (14)C incorporation under blue or red light.Synthesis of free alanine is proportional to the rate of photosynthesis (Table 1). For a number of reasons we conclude that alanine is derived directly from primary photosynthetic products. Since the pool size of the thoroughly (14)C-labelled pool of free alanine is much less than the actual, pool size of this amino acid, (Table 1), and since the specific activity of the isolated (14)C-alanine is much below the value we can expect on the basis of the specific activity of the (14)CO2 applied we conclude that there are separate pools of free alanine; "active" (with respect to protein synthesis) and "inactive" pools which do not mingle. Taking into account this possibility of compartmentation of pools of free amino acids we have calculated in the case of (14)C-alanine the rate of protein synthesis for two extreme instances (Table 2). A comparison of the theoretical values with the actual data indicates that indeed protein synthesis is fed from "active" pools of amino acids while the "inactive" pools are possibly located in the vacuoles. The total pool of alanine is much larger in red grown than in blue grown sporelings while the active pools seem to have the same size under both conditions. The cells of the red grown sporelings have much larger vacuoles than the cells of the blue grown sporelings.The rate of protein synthesis is under our conditions 1.8 times higher in blue light than in red light. The rate of turnover of the total protein is 0.29% per hour in the blue and 0.23% in the red light. The absolute turnover of protein is 1.5 times higher in blue light than in red light. It is concluded that the blue light mediated increase of protein synthesis is very real. Blue light must act specifically at the level of polypeptide synthesis.