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Salt-tolerance Mechanisms In The Marine Halophyte Eelgrass

Posted on:2003-04-23Degree:MasterType:Thesis
Country:ChinaCandidate:C J YeFull Text:PDF
GTID:2120360062995827Subject:Botany
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The paper is mainly concerned with three aspects in the salt-tolerance mechanisms of the marine halophyte eelgrass (Zostera marina L.) namely study on the plant's micro- and ultra-structure; study on osmotica and their subcellular localization in the marine halophyte and study on effects of adaptation to elevated salinity on enzymes' salt-tolerance in vitro and physiological changes of eelgrass.The micro- and ultra-structure of the plant showed that aerial cavity was a continuous structure, which made the plant less dependent on seawater for carbon dioxide and oxygen for photosynthesis and respiration respectively; the cell wall exposed to seawater in leaf epidermal cells was highly thickened but the other three sides are very thin, which may function as a barrier against toxic ions to enter the epidermal cells; chloroplasts were found mainly in epidermal cells, indicating that epidermal cells were main site where photosynthesis occurred; the plasma membrane of leaf epidermal cells had a transfer cell-like appearance at the part facing the mesophyll cells, namely with many protuberances as a result of invaginated plasma membrane, which led to a increased plasma membrane area, accelerating the transfer of photosynthates and Na+, Cl~ ions from epidermal cells into mesophyll cells; where the epidermal cells adjoin the mesophyll cells, many chloroplasts and mitochondria, both of which are ATP makers, could always be found in the mesophyll cells, indicating a active material transferring between the two types of cells at this site.Although the cell wall was also very thick in the root epidermal cells, the thickness was the same for each side of the cell wall and the cell wall ingrowth did not exist in root epidermal cells, which may be accounted by the lack of active transport of material from the root epidermal cells into the inner cells: root epidermal cells did not produce photosynthates and Na+ and Cl" ions can be compartmentalized into the central vacuoles in the epidermal cells (root epidermal cells are highly vaculate)so it is not necessary for the epidermal cells to sequester the toxic ions into inner cells like that occurred in the leaf epidermal cells. For the same reason the ATP maker mitochondria was not always found in the inner cells just next to the root epidermal cells where the two types of cells adjoin.The determination of the contents of various organic and inorganic osmotica in eelgrass and the calculation of their contributions to the osmotic adjustment indicated that Na+, K+ were the main inorganic osmotica and dissolved sugars and free amino acids were the main organic osmotica. And ion X-ray microanalysis indicated that vacuoles in the mesophyll cells were the main sites hi leaves to accumulate toxic ions. Also the study indicated that ion compartmentalization between different cells is very crucial for the plant to avoid the accumulation of toxic ions hi photosynthesis cells.Effects of adaptation to elevated salinities on eelgrass showed that under increased salinities (concentrated seawater), Na+, Cl", MDA and glucose contents and the osmotic potentials in the leaves increased with the salinity elevation in the medium (ASW), but K+, free amino acids (mainly proline) decreased. And MDH from the plant leaves under a salinity gradient showed its activities (A) as follows: A100%Asw>A150%ASw>A200%ASW. PEPC from the 100%ASW-and 200%ASW-treatedplants showed similar activities (insensitive to salinity) under salinity gradient in vitro, but that from the 150%ASW-treated plants was dependent on salinity. Results from X-ray microanalysis showed that under 150%ASW treatment the contents of Na+ and Cl- ions in the cytoplasma of leaf epidermal cells had been elevated to a new level mainly as a result of the saturation of vacuoles with Na+ and Cl" ions. But the Cl" content in the cytoplasma of leaf mesophyll cells, distinct from the case for Na+, did not change visibly, which may indicate that the plant was more selective for Cl" absorption than for Na+ absorption. Whether or not the plant was...
Keywords/Search Tags:Eelgrass, micro-and ultra-structure, ion compartmentalization, X-ray microanalysis, MDH, PEPC
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