Plant Systematics and Evolution

, Volume 126, Issue 2, pp 221–237

Molecular and cytological characteristics of nuclear DNA and chromatin for angiosperm systematics: Basic data forHelianthus annuus (Asteraceae)

  • W. Nagl
  • I. Capesius
Article

DOI: 10.1007/BF00981672

Cite this article as:
Nagl, W. & Capesius, I. Pl Syst Evol (1976) 126: 221. doi:10.1007/BF00981672

Abstract

As a contribution for the study of systematic and evolutionary relationships it is suggested to analyze nuclear DNA and chromatin by means of CsCl ultracentrifugation, thermal denaturation and renaturation, scanning densitometry, and (ultra)structural analyses. Relevant data have been obtained forHelianthus annuus as a first example.

The 2C DNA content of four cultivars ofHelianthus annuus L. was calibrated by comparative measurement withAllium cepa nuclei using a scanning densitometer in on-line operation with a computer. Significant infraspecific variation could be detected: cvar. “Amerikanische Riesen” displayed 6.1 pg, cvar. “Gefüllte Vielblütige” 9.9 pg, cvar. “Russian Mammoth” 8.9 pg, and a Heidelberg strain 8.7 pg.

The buoyant density in neutral CsCl was determined for cvar. “Amerikanische Riesen” to be 1.695 g · cm−3; this corresponds to an average GC content of 35.1%. Thermal denaturation revealed a melting temperature of 86.4°C. Derivative thermal denaturation profiles led to the detection of several distinct DNA fractions.

The species-specific nuclear structure is of the chromonematic type, but in differentiated cells the chromatin fibers may be more decondensed so that a chromomere-interchromomere structure appears. The heterochromatin constitutes an average of 4.5% of the total genome. Chromatin ultrastructure is characterized by a diffuse distribution of chromatin threads and patches. Nucleosomes of 110 Å diameter can be recognized.

The data are discussed (a) in relation to findings on DNA variation in other plants, (b) in relation to the systematic usefulness and further characterization of nuclear DNA and chromatin, and (c) in relation to tissue-specific and functional variation of the species-specific chromatin structure.

Key words

Asteraceae Helianthus DNA content infraspecific DNA variation DNA thermal denaturation profile buoyant density base composition chromatin structure heterochromatin content chromatin ultrastructure 

Copyright information

© Springer-Verlag 1976

Authors and Affiliations

  • W. Nagl
    • 1
  • I. Capesius
    • 2
  1. 1.Dept. of BiologyThe UniversityKaiserslauternGermany
  2. 2.Institute of BotanyThe UniversityHeidelbergGermany

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