Synthesis of characteristic proteins in nutrient-depleted cell suspension cultures of parsley

Cell suspension cultures of parsley (Petroselinum crispum) exhibited an altered pattern of protein synthesis after transfer from complete growth medium to water or medium containing no macronutrients. Similar changes occurred when cultures were grown in the original medium until the nutrients were depleted. The effect was reversible upon transfer to fresh medium and was not observed during regular subculturing of the cells. While total protein synthesis decreased sharply after nutrient depletion, the synthesis of a few characteristic proteins (starvation-related proteins, STPs) increased strongly. The protein labeled at highest rates with [(35)S]methionine in vivo (STP 62) had an apparent molecular weight of about 62000 and a pI of about 6.3. Although its increased rate of synthesis was therefore easily detected by labeling in vivo, translation of mRNA in vitro did not give comparable results. Thus, regulatory control may be exerted mainly at the level of translation. Synthesis of STP ceased rapidly when heat shock (37° C) was applied under conditions of nutrient depletion, whereas heat-shock proteins were strongly induced.