Journal article
SEORious business: structural proteins in sieve tubes and their involvement in sieve element occlusion
Journal of experimental botany, Vol.65(7), pp.1879-1893
04/2014
Handle:
https://hdl.handle.net/2376/102073
PMID: 24591057
Abstract
Summary
Sieve element occlusion (SEO) and SEO-related (SEOR) genes encode structural phloem proteins. This review discusses controversial views of SEOR function in plant physiology and plant insect interactions.
The phloem provides a network of sieve tubes for long-distance translocation of photosynthates. For over a century, structural proteins in sieve tubes have presented a conundrum since they presumably increase the hydraulic resistance of the tubes while no potential function other than sieve tube or wound sealing in the case of injury has been suggested. Here we summarize and critically evaluate current speculations regarding the roles of these proteins. Our understanding suffers from the suggestive power of images; what looks like a sieve tube plug on micrographs may not actually impede translocation very much. Recent reports of an involvement of SEOR (sieve element occlusion-related) proteins, a class of P-proteins, in the sealing of injured sieve tubes are inconclusive; various lines of evidence suggest that, in neither intact nor injured plants, are SEORs determinative of translocation stoppage. Similarly, the popular notion that P-proteins serve in the defence against phloem sap-feeding insects is unsupported by empirical facts; it is conceivable that in functional sieve tubes, aphids actually could benefit from inducing a plug. The idea that rising cytosolic Ca2+ generally triggers sieve tube blockage by P-proteins appears widely accepted, despite lacking experimental support. Even in forisomes, P-protein assemblages restricted to one single plant family and the only Ca2+-responsive P-proteins known, the available evidence does not unequivocally suggest that plug formation is the cause rather than a consequence of translocation stoppage. We conclude that the physiological roles of structural P-proteins remain elusive, and that in vivo studies of their dynamics in continuous sieve tube networks combined with flow velocity measurements will be required to (hopefully) resolve this scientific roadblock.
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Details
- Title
- SEORious business: structural proteins in sieve tubes and their involvement in sieve element occlusion
- Creators
- Michael Knoblauch - School of Biological Sciences, Washington State UniversityDaniel R Froelich - School of Biological Sciences, Washington State UniversityWilliam F Pickard - Department of Electrical and Systems Engineering, Washington UniversityWinfried S Peters - School of Biological Sciences, Washington State University
- Publication Details
- Journal of experimental botany, Vol.65(7), pp.1879-1893
- Academic Unit
- Biological Sciences, School of
- Publisher
- Oxford University Press; UK
- Identifiers
- 99900546682501842
- Language
- English
- Resource Type
- Journal article