title: Slower phloem transport in gymnosperm trees can be attributed to higher sieve element resistance.
abstract: In trees, carbohydrates produced in photosynthesizing leaves are transported to roots and other sink organs over distances of up to 100 m inside a specialized transport tissue, the phloem. Angiosperm and gymnosperm trees have a fundamentally different phloem anatomy with respect to cell size, shape and connectivity. Whether these differences have an effect on the physiology of carbohydrate transport, however, is not clear. A meta-analysis of the experimental data on phloem transport speed in trees yielded average speeds of 56 cm h(-1) for angiosperm trees and 22 cm h(-1) for gymnosperm trees. Similar values resulted from theoretical modeling using a simple transport resistance model. Analysis of the model parameters clearly identified sieve element (SE) anatomy as the main factor for the significantly slower carbohydrate transport speed inside the phloem in gymnosperm compared with angiosperm trees. In order to investigate the influence of SE anatomy on the hydraulic resistance, anatomical data on SEs and sieve pores were collected by transmission electron microscopy analysis and from the literature for 18 tree species. Calculations showed that the hydraulic resistance is significantly higher in the gymnosperm than in angiosperm trees. The higher resistance is only partially offset by the considerably longer SEs of gymnosperms.
authors: Department of Plant and Environmental Sciences, University of Copenhagen, 1871 Frederiksberg, Denmark joli@plen.ku.dk.
authors: Johannes
authors: J
authors: Liesche
authors: Forschungszentrum Jülich, IBG-2: Plant Sciences, 52428 Jülich, Germany.
authors: Carel
authors: C
authors: Windt
authors: Department of Physics, Technical University of Denmark, 2800 Kgs Lyngby, Denmark.
authors: Tomas
authors: T
authors: Bohr
authors: Department of Plant and Environmental Sciences, University of Copenhagen, 1871 Frederiksberg, Denmark.
authors: Alexander
authors: A
authors: Schulz
authors: Department of Physics, Technical University of Denmark, 2800 Kgs Lyngby, Denmark.
authors: Kaare H
authors: KH
authors: Jensen
mesh_terms: D001692:Biological Transport; D050260:Carbohydrate Metabolism; D032462:Cycadopsida / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D052585:Phloem; D010788:Photosynthesis; D059828:Plant Cells / Q000502:physiology*; D014197:Trees / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D014867:Water / Q000502:physiology*
chemical_list: D014867:Water
keywords: 14CO2 labeling; carbon allocation; isotope labeling; resistance model; sieve area; sieve plate; sieve pores; theoretical modeling; transmission electron microscopy