Evidence of Root Zone Hypoxia inBrassica rapaL. Grown in Microgravity

Autor:	Anxiu Kuang, S. C. Stout, M. E. Musgrave, L. G. Briarty, D. M. Porterfield
Rok vydání:	2001
Předmět:	Brassica Plant Science Root system Glucosephosphate Dehydrogenase Spaceflight Plant Roots law.invention Cell Wall law Brassica rapa Botany Ecology Evolution Behavior and Systematics biology Weightlessness Protoplasts Alcohol Dehydrogenase food and beverages Space Flight Protoplast biology.organism_classification Cell Hypoxia Plant Leaves Protoplasm Shoot Carbohydrate Metabolism Extracellular Space Cotyledon Pyruvate Decarboxylase Plant Shoots
Zdroj:	International Journal of Plant Sciences. 162:249-255
ISSN:	1537-5315 1058-5893
DOI:	10.1086/319585
Popis:	A series of experiments was conducted aboard the U.S. space shuttle and the Mir space station to evaluate microgravity-induced root zone hypoxia in rapid-cycling Brassica (Brassica rapa L.), using both root and foliar indicators of low-oxygen stress to the root zone. Root systems from two groups of plants 15 and 30 d after planting, grown in a phenolic foam nutrient delivery system on the shuttle (STS-87), were harvested and fixed for microscopy or frozen for enzyme assays immediately postflight or following a ground-based control. Activities of fermentative enzymes were measured as indicators of root zone hypoxia and metabolism. Following 16 d of microgravity, ADH (alcohol dehydrogenase) activity was increased in the spaceflight roots 47% and 475% in the 15-d-old and 30-d-old plants, respectively, relative to the ground control. Cytochemical localization showed ADH activity in only the root tips of the space-grown plants. Shoots from plants that were grown from seed in flight in a particulate medium on the Mir station were harvested at 13 d after planting and quick-frozen and stored in flight in a gaseous nitrogen freezer or chemically fixed in flight for subsequent microscopy. When compared to material from a high-fidelity ground control, concentrations of shoot sucrose and total soluble carbohydrate were significantly greater in the spaceflight treatment according to enzymatic carbohydrate analysis. Stereological analysis of micrographs of sections from leaf and cotyledon tissue fixed in flight and compared with ground controls indicated no changes in the volume of protoplast, cell wall, and intercellular space in parenchyma cells. Within the protoplasm, the volume occupied by starch was threefold higher in the spaceflight than in the ground control, with a concomitant decrease in vacuolar volume in the spaceflight treatment. Both induction of fermentative enzyme activity in roots and accumulation of carbohydrates in foliage have been repeatedly shown to occur in response to root zone oxygen deprivation. These results indicate that root zone hypoxia is a persistent challenge in spaceflight plant growth experiments and may be caused by microgravity-induced changes in fluid and gas distribution.
Databáze:	OpenAIRE
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