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The Biochemistry and Physiology of Wound Plug Formation in the Marine Chlorophyte Dasycladus vermicularis

Abstract

Upon injury, selected coenocytic algae are capable of forming temporary wound plugs to prevent detrimental cytoplasmic loss. Wound plugs of Dasycladus vermicularis ([Scropoli] Krasser) were harvested 5 min post injury and dried. The plug material contained 94% water and can be considered a hydrogel. The gel plug extended several millimeters from the cut end and filled the space inside the cell wall, which resulted from cytoplasmic retraction. Total organic carbon included 55% sugars, 5-15% protein and 0.18 % lipids. The major sugars were glucose, galactose, mannose and galacturonic acid. FITC-lectins specific for these sugars were localized around the plug matrix. Sulfur content calculated as sulfate corresponded to 17% of the carbohydrate by weight, and sulfated material was detected in plugs by Alcian Blue staining. Formation of the initial plug occurred within one minute of injury and was not significantly perturbed by the addition of ionic, antioxidant, or chelating agents to the seawater medium. However, addition of exogenous D (+) galactose and D (+) glucose prevented formation of the nascent gel plug. Wound plugs that were allowed to form from 10 min up until 24 h post-injury were isolated and incubated with selected biochemical probes in order to identify the biochemical processes involved in plug formation.

The kinetics and composition of the second phase of the wound repair process of Dasycladus vermicularis was investigated using fluorescent probes, chromatography, UV spectroscopy and histochemistry. New evidence supports the hypothesis that the second phase of the wound repair (initiated at 35-45 min post injury) is based on the activation of an oxidative burst that produces micromolar H202 levels. Based on the chemical reactivity of 3,6,7-trihydroxycoumarin, it is suggested that the addition of cellular nucleophiles may serve as the basis for oxidative crosslinking as part of a wound response in injured Dasycladus vermicularis. Finally new evidence supports the hypothesis that an oxidative burst (initiated at 35-45 minutes post injury) is regulated by a series of signal transduction events.

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