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JXB Advance Access originally published online on June 4, 2004
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Journal of Experimental Botany, Vol. 55, No. 402, pp. 1549-1556, July 2004
Journal of Experimental Botany, Vol. 55, No. 402, © Society for Experimental Biology 2004; all rights reserved

RESEARCH PAPER

Hydraulic architecture of plants of Helianthus annuus L. cv. Margot: evidence for plant segmentation in herbs

M. A. Lo Gullo1, L. Castro Noval2, S. Salleo3,* and A. Nardini3

1Dipartimento di Scienze Botaniche, Università di Messina, Salita Sperone 31, 98166 Messina S. Agata, Italia
2UD Anatomia y Fisiologia Vegetal, ETS Ingenieros de Montes (UPM), Ciudad Universitaria s/n, 28040 Madrid, España
3Dipartimento di Biologia, Università di Trieste, Via L. Giorgieri 10, 34127 Trieste, Italia

* To whom correspondence should be addressed. Fax: +39 040 568855. E-mail: salleo{at}univ.trieste.it

The hydraulic architecture of sunflower (Helianthus annuus L. cv. Margot) was studied in terms of the partitioning of the hydraulic conductance (Kleaf) of leaves inserted at progressively more apical nodes both in growing plants (GP) and in plants at full anthesis (mature plants, MP). Leaf conductance to water vapour (gL), leaf water potential ({Psi}L), leaf water potential at zero turgor ({Psi}tlp), and leaf osmotic potential at full turgor ({pi}0) were also measured. Sunflower plants showed gL and Kleaf values significantly increasing in the acropetal direction, while {Psi}L of basal leaves was significantly more negative than that of distal leaves; {Psi}tlp markedly decreased in the acropetal direction in MP so that leaves of MP retained increasingly more turgor the more apical they were. This hydraulic pattern, already present in very young plants (GP), strongly favours apical leaves. These data suggest that the progressive leaf dieback starting from the stem base, as observed when the inflorescence of sunflower reached maturity, might be due to time-dependent loss of hydraulic conductance. In fact, Kleaf loss was correlated with {Psi}L drop and stomatal closure. Leaf dehydration was aggravated by solute exportation from the basal towards the apical leaves, as revealed by the acropetal decrease of {pi}0. Kleaf was shown to be linearly and positively related to the prevailing ambient irradiance during plant growth, thus suggesting that leaf hydraulics is very sensitive to environmental conditions. It was concluded that the pronounced apical dominance of some sunflower cultivars is determined, among other factors, by plant hydraulic architecture.

Key words: Apical dominance, Helianthus annuus L., hydraulic architecture, leaf hydraulics, senescence, sunflower


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