Abstract
Potato is an important cultivated crop species and since it is moderately salt sensitive there is a need to develop more salt tolerant cultivars. A high activity of Na+ transport across the tonoplast in exchange for H+ is essential to reduce Na+ toxicity. The proton motive force (PMF) generated by the V-H+-ATPase and the V-H+-PPase energizes the Na+(K+)/H+ antiport. We compared the activity, gene expression, and protein levels of the vacuolar proton pumps and the Na+/H+ antiporters in two potato cultivars (Solanum tuberosum) contrasting in their salt tolerance (cv. Desiree; tolerant and Mozart; sensitive) grown at 0 and 60 mM NaCl. Tonoplast-enriched vesicles were used to study the pump activity and protein levels of the V-H+-ATPase and the V-H+-PPase and the activity of the Na+/H+ antiporter. Although salt stress reduced the V-H+-ATPase and the V-H+-PPase activity in both cultivars, the decline in H+ pump activity was more severe in the salt-sensitive cultivar Mozart. After salt treatment, protein amounts of the vacuolar H+ pumps decreased in Mozart but remained unchanged in the cultivar Desiree. Decreased protein amounts of the V-H+-PPase found in Mozart may explain the reduced V-H+-PPase activity found for Mozart after salt stress. Under non-stress conditions, protein amounts of V-H+-PPase were equal in both cultivars while the V-H+-PPase activity was already twice as high and remained higher after salt treatment in the cultivar Desiree as compared to Mozart. This cultivar-dependent V-H+-PPase activity may explain the higher salt tolerance of Desiree. Moreover, combined with reduced vacuolar H+ pump activity, Mozart showed a lower Na+/H+ exchange activity and the Km for Na+ is at least twofold lower in tonoplast vesicles from Desiree, what suggests that NHXs from Desiree have a higher affinity for Na+ as compared to Mozart. From these results, we conclude that the higher capacity in combination with the higher affinity for Na+ uptake can be an important factor to explain the differences in salt tolerance of these two potato cultivars.
Highlights
Salinity is a serious threat to agricultural production of many crops
We found a strong premature senescence response in the leaves of the potato cultivar Mozart combined with relatively high Na+ leaf accumulation, while the potato cultivar Desiree accumulated less Na+ in leaves and did not show a senescence response after 7 days of salt treatment and we concluded that Desiree was salt tolerant and that Mozart was salt sensitive (Jaarsma et al, 2013)
Leaves collected from salt-treated plants of Mozart showed a significantly lower fresh weight (FW)/DW ratio as compared to Annotation/Gene accession
Summary
Salinity is a serious threat to agricultural production of many crops. Potato is an important staple food in the human diet in many countries worldwide and the trend of potato production is toward more hectares in warmer and dryer climates (Levy and Veilleux, 2007). Tonoplast Transport Activity in Potato on specific criteria, potato was found to be moderately sensitive to salinity and considering the importance of potato as a staple food, relatively few studies address the physiological, biochemical, and molecular responses that take place during salt stress in potato (Hmida-Sayari et al, 2005; Aghaei et al, 2009; Legay et al, 2009; Batelli et al, 2012; Jaarsma et al, 2013). If Na+ travels into cells of leaves, efficient removal by compartmentalizing Na+ in vacuoles prevents detrimental effects on cellular processes (Munns and Tester, 2008) such as premature senescence, already occurring over several days to weeks after salt stress (Roy et al, 2014). We hypothesized that the vacuolar sequestration capacity of Na+ in leaves of Mozart was lower than that of the more salt tolerant potato cultivar
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