S. Salleo

Hydraulic architecture of Vitis vinifera L. and Populus deltoides Bartr. 1-year-old twigs: I-Hydraulic conductivity (LSC) and water potential gradients

Abstract The Leaf Specific Conductivity (LSC) of nodal and internodal segments of 1-year-old twigs of Vitis vinifera L. and Populus deltoides Bartr. was measured. It turned out to be greater in the internodes than in the nodes in both species, the differences being much bigger in Vitis than in Populus. The nodes can be considered as « hydraulic constriction zones » of the stem. Their resistance to flow increases acropetally in both species, causing a characteristic hyperbolic behaviour of the water potential gradients along the twigs in Vitis, while in Populus it is not so marked. Some hypotheses are advanced about the possible functional significance of the nodes.

Hydraulic architecture of Vitis vinifera L. and Populus deltoides Bartr. 1-year-old twigs: II-The nodal regions as « constriction zones » of the xylem system

Abstract The present study tries to clarify the anatomical basis of the hydraulic properties of the internodes and nodes of one-year-old twigs of Vitis vinifera L. and Populus deltoides Bartr‥ In particular, the higher resistance to flow as exhibited by the nodal regions of both species, appears to be due to a lower number of large-diameter vessels in the nodes as compared with that in the internodes. In Populus, beside this aspect, the nodal constriction is also due to a larger number of narrow-diameter vessels.

Viscosity and density of lysozyme in water

Abstract The viscosity and density of solutions of lysozyme in water have been measured in the range of concentration from 0.2% to 26% by weight. It is found that a critical concentration exists, namely 17% by weight, which separates two distinct kinds of behaviour. The results agree with those previously obtained by other authors using Raman spectroscopy, and are also compared with results obtained from some electrolytic solutions.

Root hydraulic conductance of six forest trees: possible adaptive significance of seasonal changes

ABSTRACT Root hydraulic conductance (KR was measured in terms of the ratio of volume flow through roots (F) and to the pressure (P) driving the flow in six forest trees growing in habitats characterized by different water availabilities Le. Acer campestre L., Castanea sativa Miller, Fraxinus ornus L., Fraxinus oxycarpa Bieb., Ceratonia siliqua L. and Olea oleaster Hoffmg. et Link. Measurements were made in May, August and November 1996. KR as normalized for unit leaf surface area (KRL), was higher in species growing in humid environments (A. campestre and C. sativa) than in others (C. siliqua and O. oleaster) typical of aria zones. A. campestre and C. sativa showed declining KRL values from spring to autumn while the latter had highest KRL values in summer. This is in agreement with the typical drought avoidance strategy of C. siliqua which is based on large water losses balanced by equal water uptake from the soil. Plots of F and of A (leaf surface area) to KRL as well as annual percent changes in F, AL ...

Diffusion Coefficient of Lysozyme in Water

The diffusion coefficient in aqueous solution of lysozyme has been measured by means of the optical beating spectroscopy, at different concentrations and scattering angles. It has been found that the decay of the fluctuation of the concentration cannot be represented by a single exponential law. There is a long tail associated with some slow decaying quantity. In addition, both the short- and the long-time behaviour turns out to be angle and concentration dependent, indicating the existence of some sort of structure. The commonly accepted literature value for the diffusion coefficient is recovered only in the limit of large scattering vectors. The above-mentioned results are also discussed in the frame of other experimental results obtained for the same system.

Wood anatomy of some trees with diffuse- and ring-porous wood : some functional and ecological interpretations

Abstract The xylem conduit dimensions (i.e. their width and length) have been measured in 1-year-old internodes, nodes and node-to-petiole (N-P) junctions of three species with diffuse-porous wood, namely Ceratonia siliqua L., Laurus nobilis L. and Olea europaea L. as well as of three species with ring-porous wood, namely Quercus ilex L., Q. suber L. and Q. pubescens Willd‥ The xylem conduit diameter and length distributions have been related to the drought resistance strategies adopted by the six species. C. siliqua and Q. ilex (drought avoiding water spenders) showed the widest xylem conduits (each species within its characteristic pattern of wood anatomy). This is consistent with their high demand of efficient water transport to leaves. L. nobilis (drought avoiding water saver) showed relatively narrow xylem conduits, efficient enough, however, to assure water supply to leaves at the reduced transpiration rate exhibited by the species. O. europaea, Q. suber and Q. pubescens (drought tolerants) showed t...

Water transport pathways in nodes and internodes of 1-year-old twigs of Olea europaea L

Abstract Measurements of Leaf Specific Conductivity (LSC) of the vertical water potential gradients and of vessels diameters in 1-year-old twigs of young olive trees have been made. LSC prooves to vary along the twigs differently from other species we have already studied in that it is significantly lower in the proximal twigs segment. Consequently, the water potential gradients are in this region higher so indicating that a higher resistance to flow exists. The frequency distribution of the vessels diameters shows that changes in the xylem hydraulic conductivity are mainly due to analogous changes in the relative number of large-diameter vessels. Also the nodes appear to behave as constriction zones of the xylem system. The functional significance of such constrictions in terms of a safety system against cavitation is discussed.

Functional aspects of water conduction pathways in vascular plants

Abstract The study of the hydraulic architecture of plants suffers, at present, of a lack of proper methodological approaches. This means that xylem hydraulic conductivity is measured without enough taking into account the non-ideality of the xylem system. Measurements of hydraulic parameters in wood show that a relation exists between the efficiency of water conduction (through large and long xylem conduits) and its safety (which implies narrow and short conduits). In particular, in diffuse-porous trees, « safety zones » of the xylem system appear to be localized in the nodes. In ring-porous trees, on the contrary, narrow and short vessels are formed in the latewood all along the stem.

Generazione di potenziali elettrici durante scorrimento di fluidi nello xilema. (Nota preliminare)

Abstract Generation of electric potentials during flow of fluids in the xylem vessels (Preliminary Report).—The streaming potential generated by the flow of fluids in the xylem vessels has been studied on segments of stem of Cucurbita sechium edule recently excised. The streaming potentials encountered in such experiments exhibit a much longer time constant than those observable in glass capillaries. The streaming potential so generated induces a superimposed rapid electric activity consisting of spikes. Finally, a peculiar relationship between the streaming potential and applied Δp has been encountered. Some tentative explanations of such results are suggested.