Metabolism of tritiated water during imbibition and germination of jack pine seeds

Abstract

Tritiated water was used to study the metabolic fate of water in seeds of jack pine (Pinusbanksiana Lamb.) during imbibition and under the influence of a reversible phytochrome reaction. Since levels of tritium greater than 15 mCi•mL water−1•g seeds−1 inhibited germination in more than 50% of the seeds, all studies were performed well below this level. During imbibition over 80% of the total covalently bound radioactivity derived from tritiated water resided in glucose and fructose. Enzymes involved in gluconeogenesis viz. fructose 1,6-bisphosphatase and glycolysis viz. phosphoglucose isomerase, in these fat-storing seeds were postulated contributing to the recovery of covalent tritium from glucose especially in red light. Brief exposures of seeds to red and far-red light during imbibition affected mainly the level and distribution of radioactivity in sugars and to a lesser extent the major components of the free amino acid pool, viz. alanine, glutamic acid, and amides. Under cool white light, the highest specific activities were seen with aspartate and γ-aminobutyrate. In germinating seedlings, the recovery of tritium, almost entirely from the deoxyribose moiety of newly synthesized DNA, pointed to the importance of (i) light-mediated ribonucleotide reductases for DNA synthesis, (ii) enzymes of the pentose phosphate shunt during imbibition, and (iii) structural integrity of developing subcellular organelles in embryonic cells during imbibition.