Title

The Geometry of the Forisome-sieve Element-sieve Plate Complex in the Phloem of Vicia faba L. leaflets

Document Type

Article

Publication Date

2006

Publication Source

Journal of Experimental Botany

Volume

57

Issue

12

Inclusive pages

3091-3098

ISBN/ISSN

00220957

Peer Reviewed

yes

Abstract

Forisomes are contractile protein bodies that appear to control flux rates in the phloem of faboid legumes by reversibly plugging the sieve tubes. Plugging is triggered by Ca2+ which induces an anisotropic deformation of forisomes, consisting of a longitudinal contraction and a radial expansion. By conventional light microscopy and confocal laser-scanning microscopy, the three-dimensional geometry of the forisome–sieve element–sieve plate complex in intact sieve tubes of leaflets of Vicia faba L. was reconstructed. Forisomes were mostly located close to sieve plates, and occasionally were observed drifting unrestrainedly along the sieve element, suggesting that they might be utilized as internal markers of flow direction. The diameter of forisomes in the resting state correlated with the diameter of their sieve elements, supporting the idea that radial expansion of forisomes is the geometric basis of reversible sieve tube plugging. Comparison of the present results regarding forisome geometry in situ with previously published data on forisome reactivity in vitro makes it questionable, however, whether forisomes are capable of completely sealing sieve tubes in V. faba leaves.

Keywords

forisome sieve, crops

Disciplines

Medical Sciences

 
 

Link to Original Published Item

http://dx.doi.org/10.1093/jxb/erl072