Translocation of copper and other micronutrients in tomato plants (Lycopersicon esculentum Mill.): nicotianamine-stimulated copper transport in the xylem

The influence of the endogenous micronutrient chelator, nicotianamine(NA), and of Cu nutrition on the distribution of Cu, Fe, Mn,Zn, and NA was investigated in eight different shoot organs,roots, and in xylem exudates of the NA-containing tomato wildtype Lycopersicon esculentum Mill. cv. Bonner Beste and itsNA-less mutant chloronerva. Contrary to the other heavy metals, copper transport in thexylem was inefficient in the mutant and was enhanced by an applicationof NA to the roots or leaves in proportion to the applied NAconcentration. Also, with NA application, the Cu concentrationin mutant roots decreased significantly, and increased in theshoot. Fe and Mn transport in the xylem was greater in the mutantthan in the wild type, and was decreased in the mutant by theapplication of NA to the leaves. Zn transport in the xylem wasthe same in both genotypes and was unaffected by NA application.After application of NA to leaves and roots of the mutant itwas possible to detect NA in the xylem exudate (up to 2nmolNA(g^–1 root FWh^–1). High Cu supply (3 µM) resulted in higher Cu and Mn concentrationsin all organs of the wild type as compared to mutant organs,but Fe concentrations were not influenced. Under high Cu supply(3µM) the NA concentrations of roots and the three youngestleaves of the wild type were higher than under normal Cu supply(0.3 µM). The highest concentrations were found in theshoot apex under both Cu conditions (up to 361 nmol NAg^–1FW). It is concluded from our experiments and from the high stabilityconstant of the NA-Cu-complex (log K= 18.6) that NA is involvedin Cu translocation whereas for the translocation of Fe, Mn,and Zn, NA is not essential. Key words: Copper transport, micronutrients, mobilization, nicotianamine, xylem     

First immunohistochemical localization of the endogenous Fe2+-chelator nicotianamine

Antibodies produced against nicotianamine-keyhole limpet haemocyanin(NA-KLH) conjugate selectively labelled cells of the stele intomato root tips (Lycopersicon esculentum Mill. cv. Bonner Beste),where labelling was mostly confined to vacuoles. In competitionELISA this antibody preparation shows no cross-reactivitieswith precursors for nicotianamine (NA), L-methionine, s-adenosyl-L-methionine,and azetidine-2-carboxylic acid. The antibodies against NA recognizefree and metal-bound NA. The usefulness of fixation of NA byglutaraldehyde as a bifunctional reagent is checked by dot blotexperiments. The fixation and embedding procedure gave excellentultrastructural preservation of the cells. The combination ofthe embedding procedure with the specificity of the used antiserum,the absence of labelling of the NA-free mutant chloronerva,and this lack in immunocytochemical controls, give evidencethat it is possible to monitor the NA distribution in situ.Based on this first report on the cellular localization of NA,a low molecular weight iron chelator in plants, the possibleroles of NA in mineral metabolism are discussed. Key words: Immunocytochemical localization, Lycopersicon esculentum, micronutrient, nicotianamine, vacuoles     

Changes in the Structure of Chromatin in Pea Shoots upon a Shift in Growth Temperature from 2C to 25C

Low temperature-resistant pea seedlings (Pisum sativum cv. Alaska),which had been kept at 2C in darkness, during which time growthhad been almost totally suppressed, were either transferredto 25C (warmed sample) or kept at 2C (chilled sample) for1 day. Rapid growth occurred at 25C. The number of nuclei inthe shoot tips of the warmed sample was twice that in the chilledsample. Nuclei prepared from the warmed and chilled samples were digestedby micrococcal nuclease at the same rate and appeared to havenucleosomal repeats of similar length, namely, approximately150 base pairs, and they generated similar patterns in termsof ladders of multimers of the basic fragment. However, significant differences in terms of chromatin structurewere observed when the chromatins isolated from the warmed andchilled samples were compared. The digestibility by DNase IIwas apparently greater in the case of chromatin prepared fromthe warmed sample. The analysis of the melting curves of thechromatins revealed three phases. The T_m of each phase was higherin the case of chromatin prepared from the chilled sample. Furthermore,an analysis by sucrose density gradient centrifugation revealedthat the chromatin prepared from the chilled sample migratedto a region of slightly higher density in the gradient thanthe chromatin from the warmed sample. Taken together, theseresults suggest that the structure of the chromatin preparedfrom the chilled sample may be more compact than that of thechromatin prepared from the warmed sample. (Received December 10, 1992; Accepted June 23, 1993)