Physiological effects of short-term salinity changes on Ruppia maritima

Changes in Ruppia maritima L. leaf-tissue osmolality, compatible solute synthesis in leaf tissues, and maximum effective quantum yield in response to short-term changes in salinity were investigated. Plants cultured at 20parts per thousand S were exposed to 0parts per thousand S, 10parts per thousand S (half-ambient), 20parts per thousand S (ambient), and 40parts per thousand S (twice-ambient) salinities. Total and non-vacuolar leaf osmolality for cultured plants significantly decreased (total: from 1464 +/- 266 to 712 +/- 210 mmol kg(-1); non-vacuolar: from 880 +/- 108 to 257 +/- 80 mmol kg(-1)) or increased (total: from 1464 to 2532 +/- 673 mmol kg(-1), non-vacuolar from 880 to 1168 15 mmol kg(-1)), within 1 min of exposure to 0 and 40parts per thousand S, respectively. After the initial rapid change in leaf osmolality, values were relatively constant for the first 180 min of exposure. Osmolality then changed again over the period from 1 to 2 days post-treatment with values again increasing (40parts per thousand S: total = 3152 +/- 335 mmol kg(-1), non-vacuolar 1967 +/- 103 mmol kg(-1)) or decreasing (0parts per thousand S: total = 357 +/- 46 mmol kg(-1), non-vacuolar = 74 +/- 32 mmol kg(-1)) with salinity. Soluble and total carbohydrates in leaf tissues responded differently to changing salinity. Total carbohydrates decreased by 65%, while soluble levels increased by 34%, in high salinity. Total and soluble proline levels increased (63 and 18%, respectively), and decreased (-36 and -20% for 10parts per thousand S; -72 and -32% for 0parts per thousand S, respectively), with salinity. These results suggest that both proline and soluble carbohydrates act as compatible solutes. Maximum quantum yields (F-v/F-m) were measured over a 48 h period in response to changes in medium salinity and inorganic carbon (ambient and similar to2.0 mM bicarbonate-equilibrium treatments). F-v/F-m exhibited significant variation in response to salinity, bicarbonate-level and time as main effects, with significant interactions. Quantum yields were lowest in the 0 and 40parts per thousand S treatments; the 10 and 20parts per thousand S treatments had significantly higher quantum yields. These short-term responses indicated that both increases and reductions of external ion concentrations are initially stressful for R. maritima, but that it can physiologically adjust after several days. (C) 2003 Elsevier Science B.V. All rights reserved.