The Forms and Sources of Cytokinins in Developing White Lupine Seeds and Fruits

Abstract

A comprehensive range of cytokinins (CK) was identified and quantified by gas chromatography-mass spectrometry in tissues of and in xylem and phloem serving developing white lupine (Lupinus albus) fruits. Analyses were initiated at anthesis and included stages of podset, embryogenesis, and seed filling up to physiological maturation 77 d post anthesis (DPA). In the first 10 DPA, fertilized ovaries destined to set pods accumulated CK. The proportion 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-isomers remained high. During early podset, accumulation of CK (30-40 pmol ovary Ϫ1 ) was accounted for by xylem and phloem translocation, both containing more than 90% cis-isomers. During embryogenesis and early seed filling (40-46 DPA), translocation accounted for 1% to 14% of the increases of CK in endosperm (20 nmol fruit Ϫ1 ) and seed coat (15 nmol fruit Ϫ1 ), indicating synthesis in situ. High CK concentrations in seeds (0.6 mol g Ϫ1 fresh weight) were transient, declining rapidly to less than 1% of maximum levels by physiological maturity. These data pose new questions about the localization and timing of CK synthesis, the significance of translocation, and the role(s) of CK forms in reproductive development.

Characterization of Cytokinin and Adenine Transport in Arabidopsis Cell Cultures

“…On the other hand, the translocation of cytokinins from roots to shoots via the xylem and their reflux occurring in the phloem support the hypothesis that they serve as long-distance signaling molecules (Weiler and Ziegler, 1981;Beveridge et al, 1997;Emery et al, 2000). Thus, multiple cellular importers and exporters are required to allow efficient mobilization and targeted translocation.…”

Translocation in Legumes: Assimilates, Nutrients, and Signaling Molecules1

“…Both xylem and phloem exudates contain CK but unambiguous information on the forms and their mobility is at best fragmentary. Despite a general belief that the prominent translocated forms are the nucleosides (Sakakibara, 2006), detailed analysis of exudates from white lupin indicates that the composition of CK forms in translocation channels, especially phloem, is far from constant (Emery et al, 2000). Significant shifts from cis-to transisomers in both xylem and phloem appear to be related to changes in reproductive development and during a period of 77 d, over which exudates were collected, 12 individual CK species were detected in varying amounts.…”

“…This approach has been extended in lupin to the carbon and nitrogen nutrition of individual organs (Layzell et al, 1981;Fig. 1), to translocation of inorganic nutrients (Jeschke et al, 1985), specific amino acids (Pate et al, 1981), plant growth regulators (Emery et al, 2000), and quinolizidine alkaloids (Lee et al, 2007). These models have been summarized (Pate et al, 1998) and provide a basis for experimental perturbation of carbon and nitrogen partitioning, identification of specific solute/assimilate exchanges between xylem and phloem, and for development of an integrated view of translocation in relation to plant growth (Fig.…”

Comparison of stimulatory effect of cytokinins adenine and urea derivatives on the level of some components in Wolffia arrhiza (L.) Wimm. (Lemnaceae)

“…Rhizobium sp. Cytokinins are synthesized mainly in root tissue, developing seeds, cambial tissue, shoot apex, and are easily distributed to a wide range of plant cells, moving trough vascular tissues (Letham 1994;Benková et al 1999;Emery et al 2000).…”