Studies on the Initial Biochemical Reactions in the Germination of Pollen Grains

Abstract

Tritiated water (3HHO) has been used as the medium for the germination of pollen grains of Pinus radiata D.Don (a gymnosperm), Ulex europaeus L., Salix caprea L. (dicotyledonous angiosperms), and Phormium tenax Forst. (a monocotyledonous angiosperm). 3H-labelled compounds formed during the initial germination (egersis) period have been separated and identified to give information on the metabolism taking place. Since the earliest labelled compounds were y-aminobutyric acid, alanine, aspartic acid, and glutamic acid, it is concluded that these amino acids play an important part in the biochemical reactions during the early stages of germination. Citric acid, malic acid, and glutamine do not become labelled until later while carbohydrates, phosphate esters, and lipids do not appear to incorporate tritium within the first hour of germination. The gross labelling pattern and the nature of the individually labelled meta bolites, their intensity and sequence of labelling are similar for all the species investigated except gorse, which showed a decrease in the intensity and the number of labelled metabolites with time. P. radiata pollen stored for 3 years under vacuum or carbon dioxide has a labelling pattern similar to freshly collected P. radiata pollen, except for a con siderable increase in the amount of an unknown metabolite (Compound X).