Publication Date:
2013-01-22
Description:
Using 3-month-old seedlings of Bruguiera gymnorrhiza (L.) Savigny and Kandelia candel (L.) Druce, we compared species differences in ionic homeostasis control between the two non-secretor mangrove species. A high salinity (400 mM NaCl, 4 weeks) resulted in a decline of the K + /Na + ratio in root and leaf tissues, and the reduction was more pronounced in K. candel (41–66%) as compared with B. gymnorrhiza (5–36%). Salt-altered flux profiles of Na + , K + , H + and Ca 2+ in roots and effects of exogenous hydrogen peroxide (H 2 O 2 ), nitric oxide (NO) and Ca 2+ on root ion fluxes were examined in seedlings that were hydroponically treated short term with 100 mM NaCl (ST, 24 h) and long term with 200 mM NaCl (LT, 7 days). Short term and LT salinity resulted in Na + efflux and a correspondingly increased H + influx in roots of both species, although a more pronounced effect was observed in B. gymnorrhiza . The salt-enhanced exchange of Na + with H + was obviously inhibited by amiloride (a Na + /H + antiporter inhibitor) or sodium orthovanadate (a plasma membrane H + -ATPase inhibitor), indicating that the Na + efflux resulted from active Na + exclusion across the plasma membrane. Short term and LT salinity accelerated K + efflux in the two species, but K. candel exhibited a higher flux rate. The salt-induced K + efflux was markedly restricted by the K + channel blocker, tetraethylammonium chloride, indicating that the K + efflux is mediated by depolarization-activated channels, e.g., KORCs (outward rectifying K + channels) and NSCCs (non-selective cation channels). Exogenous H 2 O 2 application (10 mM) markedly increased the apparent Na + efflux and limited K + efflux in ST-treated roots, although H 2 O 2 caused a higher Na + efflux in B. gymnorrhiza roots. CaCl 2 (10 mM) reduced the efflux of K + in salinized roots of the two mangroves, but its enhancement of Na + efflux was found only in B. gymnorrhiza . Under ST treatment, sodium nitroprusside (SNP) (100 M, an NO donor) increased Na + efflux at the root apex of the two species; however, its inhibition of K + loss was seen only in K. candel . Of note, NaCl caused an obvious influx of Ca 2+ in B. gymnorrhiza roots, which was enhanced by H 2 O 2 (10 mM). Therefore, the salt-induced Ca 2+ benefits B. gymnorrhiza in maintaining K + /Na + homeostasis under high external salinity.
Print ISSN:
0829-318X
Electronic ISSN:
1758-4469
Topics:
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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