Journal of Experimental Botany, Vol. 54, No. 385, pp. 1213-1219,
April 1, 2003
© 2003 Oxford University Press
Effects of the experimental blockage of the major veins on hydraulics and gas exchange of Prunus laurocerasus L. leaves
Received 27 September 2002; Accepted 10 January 2003
Dipartimento di Biologia, Università di Trieste, Via L. Giorgieri 10, 34127 Trieste, Italia
1 To whom correspondence should be addressed. Fax: +39 40 568855. E-mail: nardini{at}univ.trieste.it
The impact of leaf vein blockage on leaf hydraulic conductance (KL), gas exchange (gL) and water potential (
L) was studied in Prunus laurocerasus L., a broad-leaved evergreen. For this purpose, leaves were measured for the three variables above, either with an intact leaf blade (controls) or with the midrib cut a third of the way up (cut a), or with the midrib cut at three different points and the first-order veins cut through near their insertion to the midrib (cut b), or with the midrib cut at 2 mm from the leaf base (cut c). All the cut surfaces were sealed with cyanoacrylate. A serial decrease of KL was recorded from cut a to cut c with respect to that measured for the controls, i.e. a KL loss of about 37% (cut a), 57% (cut b) and 87% (cut c). A positive linear relationship appeared to exist between gL and KL with a high correlation coefficient (r2=0.99) and a high statistical significance (P <0.01). Even under a severe drop in KL (as that induced by cut c), leaf water potential remained approximately constant and not statistically different from L measured for the controls. In fact, L ranged between –0.83 and –0.98 MPa, i.e. within the cavitation threshold of leaves in terms of the critical L inducing a significant production of ultrasound acoustic emissions which was –0.94±0.09 MPa. The conclusion was that stomata were very sensitive to changes in KL and that stomatal closure led to the homeostatic maintenance of L and cavitation avoidance.
Key words: Cavitation, gas exchange, hydraulic conductance, leaves, major veins, Prunus laurocerasus L., stomatal response, water potential.
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