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The cohesion theory debate continues

2001; Elsevier BV; Volume: 6; Issue: 10 Linguagem: Inglês

10.1016/s1360-1385(01)02048-9

1878-4372

Martin J. Canny, Cheng Huang, M. E. McCully,

Photosynthetic Processes and Mechanisms

Gas embolisms can be seen in the xylem vessels of transpiring plants with the aid of a cryo-scanning electron microscope (CSEM) 1 Canny M.J. Vessel contents of leaves after excision: a test of Scholander's assumption. Am. J. Bot. 1997; 84: 1217-1222 Crossref PubMed Scopus (46) Google Scholar , 2 McCully M.E. et al. Daily embolism and refilling of xylem vessels in the roots of field-grown maize. New Phytol. 1998; 138: 327-342 Crossref Scopus (127) Google Scholar , 3 Tyree M.T. et al. Refilling of embolized vessels in young stems of laurel: do we need a new paradigm?. Plant Physiol. 1999; 120: 11-21 Crossref PubMed Scopus (282) Google Scholar . Embolisms are near zero at night, increase rapidly after sunrise, and decline during the afternoon to near zero around sunset. These observations, particularly the refilling during transpiration, contradict the cohesion–tension theory of water transport, which requires a continuous water phase under considerable tension from leaves to soil. However, these observations confirm the presence of gas embolisms in vessels observed using other techniques 4 Strasburger E. Über den Bau und die Verrichtungen der Leitungsbahnen in den Pflanzen. Gustav Fischer, Jena, Germany1891 Google Scholar , 5 Haines F.M. Observations on the occurrence of air in conducting tracts. Ann. Bot. 1935; 49: 367-379 Google Scholar , 6 Holbrook N.M. et al. In vivo observation of cavitation and embolism repair using magnetic resonance imaging. Plant Physiol. 2001; 126: 27-31 Crossref PubMed Scopus (209) Google Scholar , 7 Canny M.J. et al. Cryo-scanning electron microscopy observations of vessel content during transpiration in walnut petioles. Facts or artifacts?. Plant Physiol. Biochem. 2001; 39: 555-563 Crossref Scopus (20) Google Scholar .