JXB Advance Access originally published online on July 28, 2003
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Journal of Experimental Botany, Vol. 54, No. 390, pp. 2133-2139,
September 1, 2003
© 2003 Oxford University Press
Vessel contents of leaves after excision: a test of the Scholander assumption
Received 15 January 2003; Accepted 10 June 2003
1 USDA Forest Service, Northeast Experiment Station, 705 Spear St., PO Box 968, Burlington, Vermont 05402, USA
2 Unité Mixte de Recherche Physiologie Intègrée de l’Arbre Frutier et Forestier, Institute National de la Recherche Agronomique, Université Blaise Pascal, Site de Crouelle, 234 avenue du Brezet, 63039 Clermont-Ferrand cedex 2, France
* To whom correspondence should be addressed. Fax : +1 802 951 6368. E-mail: mtyree{at}fs.fed.us
When petioles of transpiring leaves are cut in the air, according to the ‘Scholander assumption’, the vessels cut open should fill with air as the water is drained away by tissue rehydration and/or continued transpiration. The distribution of air-filled vessels versus distance from the cut surface should match the distribution of lengths of ‘open vessels’, i.e. vessels cut open when the leaf is excised. A paint perfusion method was used to estimate the length distribution of open vessels and this was compared with the observed distribution of embolisms by the cryo-SEM method. In the cryo-SEM method, petioles are frozen in liquid nitrogen soon after the petiole is cut. The petioles are then cut at different distances from the original cut surface while frozen and examined in a cryo-SEM facility, where it is easy to distinguish vessels filled with air from those filled with ice. The Scholander assumption was also confirmed by a hydraulic method, which avoided possible freezing artefacts. In petioles of sunflower (Helianthus annuus L.) the distribution of embolized vessels agrees with expectations. This is in contrast to a previous study on sunflower where cryo-SEM results did not agree with expectations. The reasons for this disagreement are suggested, but further study is required for a full elucidation.
Key words: Embolism, Helianthus annuus, open-vessel length, Scholander assumption.
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