Ion transport and distribution in three grape strains under salt stress

Abstract:【Objective】Soil salinization is an important environmental problem that restricts agriculturaldevelopment and crop growth.High saline and alkaline soils cover approximately 36 million hm2 of land inChina, and accounts for approximately 1/3 of the total saline-alkaline land in Asian.In China, saline andalkaline lands are chiefly distributed in the northern arid, semi-arid and semi-humid areas, and those inXinjiang account for about a third of the total cultivated land.Grape plants have strong salt tolerance com-pared with other fruit trees, but the salinity tolerance of Vitis labrusca is generally lower than that of V.vinifera.'Beta'is a widely used rootstock, but its salt tolerance is weak, and rootstock 1103P also can notsatisfy the needs of production either.So it is important to breed salt-resistant rootstocks with cold hardi-ness to solve the ecological problem in northwest grape-producing areas.In our previous study, the salttolerance of hybrids (V.amurensis 'Zuoshan'×SO4) with cold hardiness and phylloxera resistance wereevaluated, and rootstock 1103P was used as the control.The results showed A34, A35, A15 and A17 hadstrong salt tolerance;A38, A48 and B24 had medium salt resistance;and the salt resistance of 1103P and B26 were weak.In this study, ion transport and distribution of A17, A38 and 1103P under 100 mmol·L-1 NaCl treatment were studied.【Methods】One-year-old cuttings of A17, A38 and rootstock 1103P wereplanted in pots (diameter 17 cm, height 25 cm) containing mixture of soil, sand and peat (2∶1∶1) .Whenthe plants had 8-10 fully expanded leaves, some of the plants were irrigated with 1 000 mL 100 mmol·L-1 NaCl every 3 days at 5:00—6:00 pm, while the other plants irrigated with water as the control.The con-tents of ions in roots, stems and leaves of each strain were determined after 20 days of stress treatment.A17, A38 and rootstock 1103P in vitro were used to study the Na+net flow in root system.Plants were cul-tured in 30 mL MS liquid culture medium for 2 days, and then transferred to 30 mL MS liquid culture me-dium containing 100 mmol·L-1 NaCl.The control plants were transferred to 30 mL MS liquid culture medi-um without NaCl.Six individuals were used for each treatment.Na+net flow in root system was evaluatedusing NMT (non-invasive micro-test technique) after 24 h of NaCl treatment.The site examined was locat-ed at 600 μm from the root tip, where vigorous Na+fluxes were usually observed with 6 root tips from 6 in-dividuals for each treatment.Na+net flow in root system was traced for 10 min.Flux was calculated usingFick's law of diffusion:J=-D× (dc/dx) , where J represents the ion flux in the x direction, dc/dx the ion con-centration gradient and D the ion diffusion constant in a particular medium.The data acquisition, prelimi-nary processing, control of the three-dimensional electrode positioner and stepper motor-controlled finefocus of the microscope stage were performed with the Mage Flux software, which was part of the NMT sys-tem.The Na+fluxes were measured for 10-12 minutes.Na+fluxes were calculated using Mage Flux soft-ware.【Results】Under 100 mmol·L-1 NaCl treatment, the contents of Na+in the leaves and whole plant ofstrain A17 with strong salt-tolerance were the lowest and 4 and 2.24 times of the control, respectively.Na+efflux ability of A17 was high (1 513 pmol·cm-2·s-1) and Na+interception in root was 53.21%.Na+in or-gans above ground of A17 was low (3.63 times of control) .The contents of Na+in the leaves and wholeplant were the highest in 1103P, which were 14.65 and 2.86 times of the control, respectively.Na+effluxability of 1103P was low (863 pmol·cm-2·s-1) ;Na+interception in root of 1103P was 29.14%, and Na+in or-gans above ground was 5.42 times of control.The ratios of K+/Na+, Ca2+/Na+and Mg2+/Na+in leaves in salt-resistant strain were higher.The SK, Navalue of A17 increased after 100 mmol·L-1 NaCl treatment;SCa, NaandSMg, Naof A17 had no significant difference with control;SK, Na, SCa, Naand SMg, Naof 1103P and A38 decreased after salt treatment, indicating that the selective transportation of K+, Ca2+and Mg2+to organs above groundwas decreased in the two strains by NaCl treatment, while the selective transportation of K+, Ca2+and Mg2+to organs above ground of A17 was higher.【Conclusion】The results showed that the rootstocks with strongsalt tolerance absorbed less Na+, had stronger Na+efflux and Na+interception ability, which reduced theaccumulation of Na+in the leaves and maintained ion balance in plants.