A number of studies have shown a transition from a primarily xylem to a primarily phloem flow of water as fleshy fruits develop, and the current hypothesis to explain this transition, particularly in grape (Vitis vinifera L.) berries, is that the vascular tissue (tracheids) become non-functional as a result of post-veraison berry growth. In most studies, pedicels have been dipped in a vial cont...

The current scenario of global warming has resulted in considerable uncertainty regarding the capacity of forest trees to adapt to increasing drought. Detailed ecophysiological knowledge would provide a basis to forecast expected species dynamics in response to climate change. Here, we compare the water balance (stomatal conductance, xylem water potential, needle osmotic adjustment) of Abies pi...

The vulnerability of plant water transport tissues to a loss of function by cavitation during water stress is a key indicator of the survival capabilities of plant species during drought. Quantifying this important metric has been greatly advanced by noninvasive techniques that allow embolisms to be viewed directly in the vascular system. Here, we present a new method for evaluating the spatial...

We are studying the process of movement of Xylella fastidiosa (Xf) cells between xylem vessels and through plants by analyzing the changing proportion of genetically distinct strains, initially introduced into the plants by distance and time from point of inoculation. We are also determining whether bottlenecks in movement of Xf cells in plants are more extreme in resistant plants than in susce...

Here, hypotheses about stem and root xylem structure and function were assessed by analyzing xylem in nine chaparral Rhamnaceae species. Traits characterizing xylem transport efficiency and safety, mechanical strength and storage were analyzed using linear regression, principal components analysis and phylogenetic independent contrasts (PICs). Stems showed a strong, positive correlation between...

Water is a key resource, and the plant water transport system sets limits on maximum growth and drought tolerance. When plants open their stomata to achieve a high stomatal conductance (gs) to capture CO2 for photosynthesis, water is lost by transpiration(1,2). Water evaporating from the airspaces is replaced from cell walls, in turn drawing water from the xylem of leaf veins, in turn drawing f...

Continuous transpiration and beta-guage measurements were made on cotton plants, the stomatal apertures of which had been induced to oscillate, thus allowing a water balance to be made, and leaf potential to be measured as functions of time.Analyses showed phase differences between the water entering and leaving the leaf. Also, from the phase relationship between the flow into the leaf and the ...

Main resistances of the plant water transport system are situated in leaves. In contrast to angiosperm leaves, knowledge of conifer needle hydraulics and of the partitioning of resistances within needles is poor. A new technique was developed which enabled flow-meter measurements through needles embedded in paraffin and thus quantification of the specific hydraulic conductivity (K(s)) of the ne...

The interesting species-specific relationship between maximum daily shrinkage (MDS) and stem water potential (stem) was investigated in order to understand the mechanisms involved. Vulnerability curves of Vitis, Citrus, Olea and Prunus were analysed and the air entry stem in the xylem (Pe) was calculated. The water relations parameters of the living tissue of the bark were also studied by bui...

In flooded soils, the rapid effects of decreasing oxygen availability on root metabolic activity are likely to generate many potential chemical signals that may impact on stomatal apertures. Detached leaf transpiration tests showed that filtered xylem sap, collected at realistic flow rates from plants flooded for 2 h and 4 h, contained one or more factors that reduced stomatal apertures. The cl...