Linking salinity stress tolerance with tissue-specific Na(+) sequestration in wheat roots.
Salinity stress tolerance is a physiologically complex trait that is conferred by the large array of interacting mechanisms. Among these, vacuolar Na(+) sequestration has always been considered as one of the key components differentiating between sensitive and tolerant species and genotypes. However, vacuolar Na(+) sequestration has been rarely considered in the context of the tissue-specific expression and regulation of appropriate transporters contributing to Na(+) removal from the cytosol. In this work, six bread wheat varieties contrasting in their salinity tolerance (three tolerant and three sensitive) were used to understand the essentiality of vacuolar Na(+) sequestration between functionally different root tissues, and link it with the overall salinity stress tolerance in this species. Roots of 4-day old wheat seedlings were treated with 100 mM NaCl for 3 days, and then Na(+) distribution between cytosol and vacuole was quantified by CoroNa Green fluorescent dye imaging. Our major observations were as follows: (1) salinity stress tolerance correlated positively with vacuolar Na(+) sequestration ability in the mature root zone but not in the root apex; (2) contrary to expectations, cytosolic Na(+) levels in root meristem were significantly higher in salt tolerant than sensitive group, while vacuolar Na(+) levels showed an opposite trend. These results are interpreted as meristem cells playing a role of the "salt sensor;" (3) no significant difference in the vacuolar Na(+) sequestration ability was found between sensitive and tolerant groups in either transition or elongation zones; (4) the overall Na(+) accumulation was highest in the elongation zone, suggesting its role in osmotic adjustment and turgor maintenance required to drive root expansion growth. Overall, the reported results suggest high tissue-specificity of Na(+) uptake, signaling, and sequestration in wheat roots. The implications of these findings for plant breeding for salinity stress tolerance are discussed.
Faculty of Science, Engineering and Technology, School of Land and Food, University of Tasmania Hobart, TAS, Australia.
Honghong
H
Wu
Faculty of Science, Engineering and Technology, School of Land and Food, University of Tasmania Hobart, TAS, Australia.
Lana
L
Shabala
School of Science and Health, University of Western Sydney Sydney, NSW, Australia ; School of Chemical Engineering and Technology, Tianjin University Tianjin, China.
Xiaohui
X
Liu
Department of Agrifood Production and Environmental Sciences, University of Florence Florence, Italy.
Elisa
E
Azzarello
Faculty of Science, Engineering and Technology, School of Land and Food, University of Tasmania Hobart, TAS, Australia.
Meixue
M
Zhou
Department of Agrifood Production and Environmental Sciences, University of Florence Florence, Italy.
Camilla
C
Pandolfi
School of Science and Health, University of Western Sydney Sydney, NSW, Australia.
Zhong-Hua
ZH
Chen
Faculty of Science, Engineering and Technology, School of Land and Food, University of Tasmania Hobart, TAS, Australia.
Jayakumar
J
Bose
Department of Agrifood Production and Environmental Sciences, University of Florence Florence, Italy.
Stefano
S
Mancuso
Faculty of Science, Engineering and Technology, School of Land and Food, University of Tasmania Hobart, TAS, Australia.
Sergey
S
Shabala
Na+ distribution; bread wheat; cytosolic Na+; root zones; salinity stress tolerance; vacuolar Na+ sequestration