Evidence for a sodium efflux mechanism in the leaf cells of the seagrass Zostera marina L.

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• 作者：Lourdes Rubio^a ; ^{Lrubio@uma.es"" rel=""nofollow} ; André ; s Belver^b ; Kees Venema^b ; Mar&#xed ; a Jesú ; s Garc&#xed ; a-Sá ; nchez^a ; José ; Antonio Ferná ; ndez^a
• 关键词：Cytosolic sodium concentration ; Microelectrodes ; Plasma membrane vesicles ; Salinity tolerance ; Sodium– ; proton antiport ; Zostera marina
• 刊名：Journal of Experimental Marine Biology and Ecology
• 出版年：2011
• 出版时间：15 June 2011
• 年：2011
• 卷：402
• 期：1-2
• 页码：56-64
• 全文大小：488 K

文摘

The efficient exclusion of excess Na⁺ from the cytoplasm is of vital importance in cells from the seagrass Zostera marina L., a vascular plant that lives in seawater and exhibits Na⁺-dependent high affinity nitrate and phosphate uptake systems. Intracellular measurements with Na⁺-selective microelectrodes show a low cytosolic Na⁺ concentration in leaf cells (13.2 ± 2.8 mM Na⁺) of this species. This value, similar to the concentrations detected in terrestrial glycophyte plants, increases about 10 mM in the presence of respiration inhibitors. A rise in sodium concentration is also detected when external pH is increased, whereas a decrease is recorded at lower external pH levels. These results suggest that H⁺-dependent systems are involved in the maintenance of a low cytosolic Na⁺ concentration in Z. marina cells. To investigate this further, plasma membrane vesicles were isolated from leaves and cation/H⁺ antiport activities were analyzed using a fluorescent probe. Na⁺/H⁺ exchange activity was detected and showed saturation around 35 mM Na⁺. This activity was highly selective for Na⁺ as no exchange activity was detected with Rb⁺ or TMA⁺, whereas Li⁺ showed only 25 % of the Na⁺ activity. Furthermore, K⁺ did not affect Na⁺/H⁺ exchange activity, which showed similar K_m values in the presence of 5 mM K⁺ (4.1 ± 2.1 mM Na⁺) or 50 mM K⁺ (3.9 ± 2.6 mM Na⁺). These K_m values are lower than the mean sodium concentration measured in the cytoplasm of Z. marina cells, indicating that the presence of Na⁺/H⁺ exchangers in the plasma membrane, whose activity has been detected for the first time in a seagrass, can be a very effective Na⁺ efflux mechanism in this plant. This activity can be crucial both for salinity tolerance and for the energetization of nutrient uptake in this species.