Physiological effects of short-term salinity changes on Ruppia maritima

Abstract

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 20‰ S were exposed to 0‰ S, 10‰ S (half-ambient), 20‰ S (ambient), and 40‰ 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 40‰ 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 (40‰ S: total = 3152 ± 335 mmol kg-1, non-vacuolar = 1967 ± 103 mmol kg-1) or decreasing (0‰ 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 10‰ S; -72 and -32% for 0‰ S, respectively), with salinity. These results suggest that both proline and soluble carbohydrates act as compatible solutes. Maximum quantum yields (Fv/Fm) were measured over a 48 h period in response to changes in medium salinity and inorganic carbon (ambient and ∼2.0 mM bicarbonate-equilibrium treatments). Fv/Fm 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 40‰ S treatments; the 10 and 20‰ 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. © 2003 Elsevier Science B.V. All rights reserved.