The forms and sources of cytokinins in developing white lupine seeds and fruits

A comprehensive range of cytokinins (CK) was identified and quantified by g as chromatography-mass spectrometry in tissues of and in xylem and phloem s erving developing white lupine (Lupinus albus) fruits. Analyses were initia ted at anthesis and included stages of podset, embryogenesis, and seed fill ing up to physiological maturation 77 d post anthesis (DPA). In the first 1 0 DPA, fertilized ovaries destined to set pods accumulated CK. The proporti on of cis-CK:trans-CK isomers was initially 10:1 but declined to less than 1:1. In ovaries destined to abort, the ratio of cis-isomers to trans-isomer s remained high. During early podset, accumulation of CK (30-40 pmol ovary( -1)) was accounted for by xylem and phloem translocation, both containing m ore than 90% cis-isomers. During embryogenesis and early seed filling (40-4 6 DPA), translocation accounted for 1% to 1 1% of the increases of CK in en dosperm (20 nmol fruit(-1)) and seed coat (15 nmol fruit(-1)), indicating s ynthesis in situ. High CK concentrations in seeds (0.6 mu mol g(-1) fresh w eight) were transient, declining rapidly to less than 1% of maximum levels by physiological maturity. These data pose new questions about the localiza tion and timing of CK synthesis, the significance of translocation, and the role(s) of CK forms in reproductive development.