Mind the bubbles: achieving stable measurements of maximum hydraulic conductivity through woody plant samples

The maximum specific hydraulic conductivity (kmax) of a plant sample is a measure of the ability of a plants’ vascular system to transport water and dissolved nutrients under optimum conditions. Precise measurements of kmax are needed in comparative studies of hydraulic conductivity, as well as for measuring the formation and repair of xylem embolisms. Unstable measurements of kmax are a common problem when measuring woody plant samples and it is commonly observed that kmax declines from initially high values, especially when positive water pressure is used to flush out embolisms. This study was designed to test five hypotheses that could potentially explain declines in kmax under positive pressure: (i) non-steady-state flow; (ii) swelling of pectin hydrogels in inter-vessel pit membranes; (iii) nucleation and coalescence of bubbles at constrictions in the xylem; (iv) physiological wounding responses; and (v) passive wounding responses, such as clogging of the xylem by debris. Prehydrated woody stems from Laurus nobilis (Lauraceae) and Encelia farinosa (Asteraceae) collected from plants grown in the Fullerton Arboretum in Southern California, were used to test these hypotheses using a xylem embolism meter (XYL'EM). Treatments included simultaneous measurements of stem inflow and outflow, enzyme inhibitors, stem-debarking, low water temperatures, different water degassing techniques, and varied concentrations of calcium, potassium, magnesium, and copper salts in aqueous measurement solutions. Stable measurements of kmax were observed at concentrations of calcium, potassium, and magnesium salts high enough to suppress bubble coalescence, as well as with deionized water that was degassed using a membrane contactor under strong vacuum. Bubble formation and coalescence under positive pressure in the xylem therefore appear to be the main cause for declining kmax values. Our findings suggest that degassing of water is essential for achieving stable and precise measurements of kmax through woody plant samples. For complete rehydration of woody samples, incubation in water under vacuum for 24 h is suggested as a reliable technique that avoids bubble problems associated with flushing under high positive pressure

Wound-induced and bacteria-induced xylem blockage in roses, Astilbe and Viburnum

We previously concluded that the xylem blockage that prevents water uptake into several cut flowers is mainly due to the presence of bacteria, whilst in chrysanthemum and Bouvardia we observed a xylem occlusion that was mainly due to a wound-reaction of the plant. We have further tested which of these two mechanisms was dominant in Astilbe,Viburnum and rose flowers. Astilbe x arendsii (cvs. Erica and Glut) flowers were stored dry in plastic bags (24 h at 5 degreesC, 100% RH) and placed in water at 20 degreesC without recutting the steins. The dry storage treatment considerably hastened a wounding-induced xylem occlusion in the stems. A 5 h pulse treatment with inhibitors of peroxidase (hydroquinone) and catechol oxidase (tropolone and 2,3-dihydroxynaphtalene), prior to dry storage, considerably delayed the xylem blockage. The 24 h dry storage treatment had no effect in rose (Rosa x hybrida cv. Red One), and Viburnum opulus (cv. Roseum). These flowers were therefore directly placed in water, with and without enzyme inhibitors. Except hydroquinone, all tested enzyme inhibitors reduced bacterial growth in the vase water. The latter chemicals could therefore not be used to distinguish between a plant-induced and a bacterial occlusion of the xylem. Hydroquinone had no effect on the time to wilting in roses, nor in Viburnum. It considerably delayed wilting in Astilbe flowers that were directly placed in water after harvest. It is concluded that the blockage in Astilbe is mainly due to the plant-induced xylem occlusion. The xylem occlusion in the tested rose and Viburnum cultivar was apparently not due to this mechanism. (C) 2004 Elsevier B.V. All rights reserved

Dispositif de recherche du plan médio-labyrinthique adapté au nouveau vestibulographe

Fenart R., Blain A., Deblock R., Loubaud J.P. Dispositif de recherche du plan médio-labyrinthique adapté au nouveau vestibulographe. In: Bulletins et Mémoires de la Société d'anthropologie de Paris, XIII° Série. Tome 4 fascicule 1, 1977. pp. 19-21

Effects of three different nano-silver formulations on cut Acacia holosericea vase life

The relative efficacies of three chemically different nano-silver (NS) formulations were evaluated for their potential to extend the vase life of short-lived cut Acacia holosericea foliage. The novel proprietary formulations were neutral NS, acidic NS and ionic NS. They were characterised in terms of particle size, pH value, colour and odour. The NS treatments were applied as vase (lower concentrations) or pulse (higher concentrations) solutions. Among the treatments compared, neutral NS as a 4 mg L-1 vase solution or as a 40 mg L-1 24 h pulse treatment and acidic NS as a 0.5 mg L-1 vase solution or as a 5 mg L-1 24 h pulse treatment significantly (

Cu2+ inhibition of gel secretion in the xylem and its potential implications for water uptake of cut Acacia holosericea stems

Maintaining a high rate of water uptake is crucial for maximum longevity of cut stems. Physiological gel/tylosis formation decreases water transport efficiency in the xylem. The primary mechanism of action for post-harvest Cu2+ treatments in improving cut flower and foliage longevity has been elusive. The effect of Cu2+ on wound-induced xylem vessel occlusion was investigated for Acacia holosericea A. Cunn. ex G. Don. Experiments were conducted using a Cu2+ pulse (5 h, 2.2 mM) and a Cu2+ vase solution (0.5 mM) vs a deionized water (DIW) control. Development of xylem blockage in the stem-end region 10 mm proximal to the wounded stem surface was examined over 21 days by light and transmission electron microscopy. Xylem vessels of stems stood into DIW were occluded with gels secreted into vessel lumens via pits from surrounding axial parenchyma cells. Gel secretion was initiated within 1-2 days post-wounding and gels were detected in the xylem from day 3. In contrast, Cu2+ treatments disrupted the surrounding parenchyma cells, thereby inhibiting gel secretion and maintaining the vessel lumens devoid of occlusions. The Cu2+ treatments significantly improved water uptake by the cut stems as compared to the control. © 2013 Scandinavian Plant Physiology Society