Metabolism of L[U-C-14]-arginine and L[U-C-14]-ornithine in maturing and vernalised embryos and megagametophytes of Picea abies

The metabolism of the polyamine precursors arginine and ornithine was studi ed in maturing and vernalised seeds of Picea abies (L.) Karst, (Norway spru ce) in feeding experiments. Incorporation of radioactivity from these C-14- labelled amino acids into liberated CO2, amino acids, polyamines, proteins and cell wall fractions, as well as polyamine levels were determined in emb ryos and megagametophytes. Ornithine and especially arginine decarboxylatio n was more active in the embryo than in the megagametophytic cells, and ver nalisation increased arginine metabolism more than it increased ornithine m etabolism. Both precursors were metabolised to each other, to other amino a cids, and to polyamines. The only polyamine in which radioactivity incorpor ated was free putrescine, showing either a slow synthesis or a high degrada tion rate of spermidine and spermine in maturing spruce seeds. The putresci ne level was approximately 10 times higher in the embryo than in the megaga metophytic tissues, whereas spermidine and spermine levels were almost the same in both tissues. The label from arginine and ornithine was also incorp orated into proteins as amino acids and post-translationally as polyamines. Higher radioactivity was seen in the small less than or equal to 14-kDa po lypeptides. Protein hydrolysates of the embryo and the megagametophytic tis sues contained spermidine and spermine and their degradation product 1,3-di aminopropane (DAP), suggesting that polyamines may play a role in the accum ulation of seed storage protein and in the maturation of spruce seeds.