Stem End Blockage in Cut Grevillea 'Crimson Yul-lo' Inflorescences

Grevillea Crimson Yul-lo inflorescences have cut flower potential, but their vase life is short. End of vase life is characterised by early wilting. The possibility of physiologically mediated stem end blockage was investigated. Hydraulic conductance of 2 cm long stem end segments declined rapidly and remained lower throughout vase life than that of 2 cm long stem segments from immediately above. Re-cutting daily to remove basal 2 cm stem ends increased solution uptake, delayed declines in inflorescence water potential and water content, and improved inflorescence vase life. S-Carvone is a potential inhibitor of wound related suberin formation, via inhibition of phenylalanine ammonia-lyase, and vase solution treatments with S-carvone (0.318 and 0.636 mM) delayed the decline in hydraulic conductance of basal 2 cm long stem end segments and decreases in vase solution uptake and relative fresh weight of cut stems, and extended vase life. Treatments with the catechol oxidase inhibitor 4-hexylresorcinol (2.5-10 mM) also delayed stem end blockage. These findings suggest that stem end blockage in cut G. Crimson Yul-lo stems is physiologically mediated

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

Wounding-induced xylem occlusion in stems of cut chrysanthemum flowers : roles of peroxidase

A wounding-induced xylem occlusion, resulting in severe leaf wilting, occurs in stems of cut chrysanthemum flowers (Dendranthema grandiflora), cv. Vyking. The blockage develops after about 1 h in flowers held in air at 20 °C. It is initially located in the lowermost 2 cm of the stem and upon prolonged exposure to air it is also found above 2 cm. We tested the possible role of peroxidase (EC 1.11.1.7) and phenoloxidases in the blockage. Some peroxidase inhibitors (copper ions and 3-amino-1,2,4-triazole) delayed the occlusion, and treatment with compounds that inhibit peroxidase but stimulate phenoloxidase (catechol, hydroquinone, p-phenylene diamine) had the same effect. Some inhibitors of phenoloxidase (p-nitrophenol, p-chlorophenol, p-nitrocatechol, and sodium metabisulfite) also delayed the occlusion. Phenoloxidase activity in plants comprises catechol oxidase (EC 1.10.3.1) and laccase (EC 1.10.3.2). The blockage was considerably delayed by catechol oxidase inhibitors (tropolone and 4-hexylresorcinol), even more so than with general phenoloxidase inhibitors. The results indicate that the occlusion is mainly due to a physiological (oxidative) process, requiring both peroxidase and catechol oxidase activit

Xylem occlusion in Bouvardia flowers : evidence for a role of peroxidase and catechol oxidase

During vase life, Bouvardia flowers show rapid leaf wilting, especially if they are stored dry prior to placement in water. Wilting is due to a blockage in the basal stem end. We investigated the possible role of peroxidase and catechol oxidase in the blockage in cv. van Zijverden flowers, which were placed, for 5 h at 20 °C, in an aqueous solution containing enzyme inhibitors. Flowers were then stored dry in plastic bags (24 h at 5 °C, 100% RH) and placed in water at 20 °C without recutting the stems. Inhibitors of both peroxidase (hydroquinone, p-phenylene diamine, copper ions) and catechol oxidase (tropolone, 2,3-dihydroxynaphtalene) considerably delayed the time to leaf wilting. It is concluded that the blockage is apparently due to a wounding reaction and that it involves both peroxidase and catechol oxidase activit

Low hydrocarbon mixtures ignition delay times investigation behind reflected shock waves

International audienc

Adhesion of aluminium alloys : morphology, surface chemistry and adhesive bond durability

International audienc

Controlling surface properties for bonding application of structural composites and metals used in aeronautic

International audienc

Controlling adhesion of composites and aluminium alloys for aeronautic applications

International audienc

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