Populus euphratica Displays Apoplastic Sodium Accumulation, Osmotic Adjustment by Decreases in Calcium and Soluble Carbohydrates, and Develops Leaf Succulence under Salt Stress

Abstract

Populus euphratica Olivier is known to exist in saline and arid environments. In this study we investigated the physiological mechanisms enabling this species to cope with stress caused by salinity. Acclimation to increasing Na 1 concentrations required adjustments of the osmotic pressure of leaves, which were achieved by accumulation of Na 1 and compensatory decreases in calcium and soluble carbohydrates. The counterbalance of Na 1 /Ca 21 was also observed in mature leaves from field-grown P. euphratica trees exposed to an environmental gradient of increasing salinity. X-ray microanalysis showed that a primary strategy to protect the cytosol against sodium toxicity was apoplastic but not vacuolar salt accumulation. The ability to cope with salinity also included maintenance of cytosolic potassium concentrations and development of leaf succulence due to an increase in cell number and cell volume leading to sodium dilution. Decreases in apoplastic and vacuolar Ca 21 combined with suppression of calcineurin B-like protein transcripts suggest that Na 1 adaptation required suppression of calcium-related signaling pathways. Significant increases in galactinol synthase and alternative oxidase after salt shock and salt adaptation point to shifts in carbohydrate metabolism and suppression of reactive oxygen species in mitochondria under salt stress.

Genomic insights into salt adaptation in a desert poplar

“…However, our current understanding of these aspects of salt tolerance remains limited, especially for woody plants 22,27 . Populus euphratica is an excellent candidate for the analysis of salt tolerance 22 , as it displays apoplastic sodium accumulation and develops leaf succulence after prolonged salt exposure 8 . Consequently, in the last decade it has become a model for elucidating both physiological and molecular mechanisms of salt tolerance in tree species [5][6][7][8][9][10][11] .…”

“…Populus euphratica is an excellent candidate for the analysis of salt tolerance 22 , as it displays apoplastic sodium accumulation and develops leaf succulence after prolonged salt exposure 8 . Consequently, in the last decade it has become a model for elucidating both physiological and molecular mechanisms of salt tolerance in tree species [5][6][7][8][9][10][11] . Using a newly developed fosmid-pooling strategy 14 , we sequenced and assembled the complex genome of P. euphratica with high heterozygosity and compared it with the closely related salt-sensitive model plant, P. trichocarpa.…”

“…More than 30 wild Populus species occur across diverse habitats over a wide geographical range, thereby providing an excellent system for unravelling the genetic bases of adaptive divergence 4 . Populus euphratica Oliv., which is native to desert regions ranging from western China to North Africa, is characterized by extraordinary adaptation to salt stress [5][6][7][8] . Notably, at high salinity it maintains higher growth and photosynthetic rates than other poplar species 9,10 and can survive concentrations of NaCl in nutrient solution up to 450 mM 11 .…”

Salt-induced respiration in Bruguiera cylindrica — role in salt transport and protection against oxidative damage

“…Engagement of the AOX pathway has been reported under increasing salinity in wheat (Kong et al, 2004), but not in halophytes. In Poplus plants subjected to salt shock, AOX activity was much higher than that observed when the plants were subjected to a gradual increase in salt concentration (Ottow et al, 2005). This may explain the lack of AOX engagement in SW plants subjected to 4M NaCl treatment, where the salt shock was milder than that experienced by the FW plants.…”

“…B. cylindrica is a facultative mangrove and can grow in soils irrigated with fresh water. Further, respiration rates were also studied when the leaves of these two types of plants were immersed in 4M NaCl to try and uncover the possible salt adaptive strategies, which may not be prominent when plants are exposed to gradual increases in salt concentration (see Ottow et al, 2005). collected from the seacoast (Mumbai) were called seawater (SW) plants.…”