Seasonal variation of nitrogenous compounds in components of the kiwifruit vine

Free amino acids in 6-year-old kiwifruit vines [Actinidia deliciosa (A. Chev.) C. F. Liang et A. R. Ferguson] were measured over the course of 1 year using components obtained from whole-vine harvests. Tissues examined from the perennial structure consisted of the wood and cortex of structural roots, wood and bark of stem, leader and 1-year-old fruiting canes. Free acids in the annual growth (fine roots, flowers, fruit, leaves and non-fruiting shoots) were also measured. The range of amino acids extracted indicated that kiwifruit conforms to a conventional pattern of nitrogen metabolism. Acids present in greatest concentration depended on tissue type and sampling time. In perennial components and fine roots, arginine and glutamine were the predominant species, followed by gamma-aminobutyrate, aspartate, glutamate, alanine and valine. Generally, maximum concentrations of all free acids were measured in a 10-week period around budbreak. These same acids, plus asparagine, serine and threonine, were also prevalent in annual growth. In leaves, flowers and non-fruiting shoots, concentrations were greatest in the young tissue and declined with age. By contrast, concentrations of arginine, asparagine and glutamine in fruit peaked approximately 10 weeks after anthesis, subsequent to the cell division phase of growth. During the year, free arginine averaged 44, 48 and 58% of the total N in the fine roots, and the cortex and wood of structural roots, respectively (the quantity of total N and amino-N in other components of the structural framework was much less than that in root tissue). Arginine was the principal N-containing species measured in xylem sap vacuum-extracted from 1-year-old canes over winter. During the period of vegetative growth, however, glutamine and nitrate were the principal N-transport forms present. The study highlights the importance of the fine root system as the primary location of nitrogenous reserves in this plant and identifies arginine as the dominant N-storage form.