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Vessel contents of leaves after excision: a test of the Scholander assumption
Journal of Experimental Botany, (2003)
Аннотация
When petioles of transpiring leaves are cut in the air, according to the `Scholander assumption', the vessels cut open should ll with air as the water is drained away by tissue rehydration and/or continued transpiration. The distribution of air-lled 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 lled with air from those lled with ice. The Scholander assumption was also conrmed by a hydraulic method, which avoided possible freezing artefacts. In petioles of sunower (Helianthus annuus L.) the distribution of embolized vessels agrees with expectations. This is in contrast to a previous study on sunower 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.
