Mitochondrial folates and methionyl-tRNA transformylase activity during germination and early growth of seeds

Abstract

Mitochondria were isolated from the cotyledons of pea ( Pisum sativum cv Homesteader) and peanut ( Arachis hypogaea cv Early Spanish) seeds over a 7-day growth period. The rate of mitochondrial oxygen uptake increased 3-4-fold during the first 4 days of growth and parallel changes were observed in the respiratory control and ADP/O ratios. In both species, the total cotyledonary pool of folate derivatives increased 3-4-fold during this period of germination whereas that associated with isolated mitochondria increased 5-10-fold. Until day 3 of growth, the mitochondrial folates were principally polyglutamates of 10-formyltetrahydrofolate but between day 4 and day 7 increasing levels of 5-methyltetrahydrofolate polyglutamates were detected. Pea and peanut mitochondria contained methionyl-tRNA transformylase (EC 2.1.2.9) activity that displayed an absolute requirement for 10-formyl-tetrahydrofolate. The specific activity of this enzyme rose during germination, reaching maximal levels between days 3 and 4. Isolated pea mitochondria had the ability to incorporate [ 3H]leucine and [ 35S]methionine into protein in a reaction that required ADP and malate but was strongly inhibited by chloramphenicol. Organelles isolated after 4 days of germination incorporated leucine at rates ca 5-fold greater than shown by mitochondria of 16-hour-old seedlings. The inter-relationships between respiratory activity, mitochondrial formyltetrahydrofolates and methionyl-tRNA transformylase activity suggest a role for organelle protein synthesis during germination of these legume species.