Differences in transcription products and in translation and enzymatic activities during the early stages of imbibition of Phacelia tanacetifolia seeds with germination inhibited by light

Abstract

To elucidate the inhibitory effect of light on the germination of the negatively photo‐blastic seeds of Phacelia tanacetifolia Benth. (cv. Bleu Clair). we have compared the changes that occur during the first 24 h of imbibition in the dark and in the light. Here, we give data on transcription products, translation activity, activities of some enzymes involved in the metabolic reactivation of seeds (glucose‐6‐phosphate dehydrogenase, pyruvate kinase, glucokinase and malate dehydrogenase), and the capability to absorb L‐[U‐14C]‐leucine. During the first stages of imbibition, the changes in the protein pattern and in the mRNA populations that occurred were not related to the light/dark regimes. Differences due to the light treatment did not appear until after 24 h. when new microsomal proteins appeared in the dark and some mRNA populations encoding low molecular mass polypeptides were increased in the light. The translation activity, measured as L‐[U‐14C]‐leucine incorporated into proteins and as the ratio polysomes/monosomes, increased with time in both darkness and light, but to a much higher extent in the dark. The activities of the four enzymes tested were higher in the light than in the dark before 16 h, then decreased in the light and increased sharply in the dark. Together with the behaviour of the increase in the ratio polysomes/monosomes in the dark, this suggests an increased rate of protein degradation in the dark during the period 0–16 h. The absorption of L‐[U‐14C]‐leucine was severely inhibited by light during the whole period studied, as expected since light inhibits the reactivation of the transport mechanisms at the plasma membrane. In seeds imbibed in the dark and then transferred to light, the inhibition by light of absorption and of incorporation into proteins of L‐[U‐14C]‐leucine, as well as the inhibition of the increase in the ratio poly‐somes/monosornes, was effective before the 22nd h; after which time the control exerted by light disappeared.