The modulation of leaf metabolism plays a role in salt tolerance of Cymodocea nodosa exposed to hypersaline stress in mesocosms

摘要

Applying proteomics, we tested the physiological responses of the euryhaline seagrassCymodocea nodosa to deliberate manipulation of salinity in a mesocosm system.Plants were subjected to a chronic hypersaline condition (43 psu) to compare proteinexpression and plant photochemistry responses after 15 and 30 days of exposurewith those of plants cultured under normal/ambient saline conditions (37 psu). Resultsshowed a general decline in the expression level of leaf proteins in hypersaline stressedplants, with more intense reductions after long-lasting exposure. Specifically, thecarbon-fixing enzyme RuBisCo displayed a lower accumulation level in stressed plantsrelative to controls. In contrast, the key enzymes involved in the regulation of glycolysis,cytosolic glyceraldehyde-3-phosphate dehydrogenase, enolase 2 and triose-phosphateisomerase, showed significantly higher accumulation levels. These responses suggesteda shift in carbon metabolism in stressed plants. Hypersaline stress also induced asignificant alteration of the photosynthetic physiology of C. nodosa by means of a downregulationin structural proteins and enzymes of both PSII and PSI. However we foundan over-expression of the cytochrome b559 alpha subunit of the PSII initial complex,which is a receptor for the PSII core proteins involved in biogenesis or repair processesand therefore potentially involved in the absence of effects at the photochemical levelof stressed plants. As expected hypersalinity also affects vacuolar metabolism byincreasing the leaf cell turgor pressure and enhancing the up-take of Na+ by overaccumulatingthe tonoplast specific intrinsic protein pyrophosphate-energized inorganicpyrophosphatase (H(+)-PPase) coupled to the Na+/H+-antiporter. The modulation ofcarbon metabolism and the enhancement of vacuole capacity in Na+ sequestration andosmolarity changes are discussed in relation to salt tolerance of C. nodosa.