Spectrophotometric characterization of phytochromes in dimorphic cocklebur seeds in relation to capacity for germination

Katsushi Manabe, Miki Nakazawa, Yuuichi Sato, Yohji Esashi

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)


Phytochrome was measured spectrophotometrically in different tissues of the upper (positively photoblastic) and lower (negatively photoblastic) seeds of the cocklebur (Xanthium pennsylvanicum Wallr.). Axial parts of the seeds, in particular parts of the radicle, contained high levels of phytochrome, while cotyledonary parts contained only low levels. These results were consistent with the distribution of the light‐sensitive areas of the seeds that were associated with germination. Phytochrome levels in both types of dimorphic seeds increased gradually with increasing duration of dark imbibition for 4–8 h, then the rates of increase in levels of phytochrome accelerated. In both types of seed, some phytochrome was measurable even before imbibition. In the lower seeds, up to 20% of the phytochrome was occasionally observed as Pfr in samples imbibed in darkness for a short time (up to 12 h). A slight blue shift of the peak of PT in the difference spectrum of phytochrome was observed in the case of lower seeds imbibed for 0–2 h. These results suggest that, to some extent, the lower axes contain dehydrated Pfr or intermediate(s) in the photoconversion of phytochrome. The dark reactions of Pfr were also examined in excised axes of both types of dimorphic seed after they had been pre‐imbibed for 16 h in darkness. Dark destruction of Pfr was observed in both types of seed. In addition, net increases in levels of Pr were observed in the dark controls and in the samples irradiated with red light after the level of Pfr diminished. No ‘inverse’ dark reversion from Pr to Pfr was detected. Thus, after 16 h of imbibition, there were no differences in terms of properties of phytochrome between the two types of seed, and the different responses to light of upper and lower seeds might depend mainly on a difference in the physiological state of the two types of seed rather than the properties of phytochrome.

Original languageEnglish
Pages (from-to)163-168
Number of pages6
JournalPhysiologia Plantarum
Issue number2
Publication statusPublished - Feb 1991
Externally publishedYes


  • Cocklebur
  • dimorphic seeds
  • germination
  • phytochrome
  • spectrophotometry
  • Xanthium pennsylvanicum

Field of Science*

  • 1.6 Biological sciences
  • 1.4 Chemical sciences

Publication Type*

  • 1.1. Scientific article indexed in Web of Science and/or Scopus database


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