Journal of Plant Nutrition Growth, sodium, and ...

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Journal of Plant Nutrition

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Growth, sodium, and potassium uptake and translocation in salt stressed tomato Ghazi N. Al-Karakia a Department of Plant Production, Jordan University of Science and Technology, Irbid, Jordan

To cite this Article Al-Karaki, Ghazi N.(2000) 'Growth, sodium, and potassium uptake and translocation in salt stressed

tomato', Journal of Plant Nutrition, 23: 3, 369 — 379 To link to this Article: DOI: 10.1080/01904160009382023 URL: http://dx.doi.org/10.1080/01904160009382023

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JOURNAL OF PLANT NUTRITION, 23(3), 369-379 (2000)

Growth, Sodium, and Potassium Uptake and Translocation in Salt Stressed Tomato Ghazi N. Al-Karaki Department of Plant Production, Jordan University of Science and Technology, P.O. Box 3030, Irbid, Jordan

ABSTRACT Salinity tolerance in some plant species has been related to characteristics of potassium (K) and sodium (Na) uptake and transport. Tomato (Lycopersicon esculentum Mill., cv. Rossel) plants were grown in nutrient solution to determine effects of two K levels [0.2 (low) and 2 mmol (high)] combined with 0, 100, and 200 mmol NaCl on growth, and on Na and K uptake and translocation. Net uptake rates of Na and K were determined by disappearance in the growth medium and by plant accumulation. At the low level of K in solution, salinity decreased shoot and root dry weight and leaf area. Addition of 2 mmol K ameliorated of the added NaCl effects and improved growth parameters. Salinity reduced net K uptake rates and to a lesser extent K translocation from root to shoot, which resulted in higher K shoot concentration and a lower K root concentration. The inhibitory effect of salinity on K translocation was greater with low K level in nutrient solution. Net uptake of K was dependent on K level in the growth medium. Addition of K resulted in decreases of shoot Na uptake. The translocation of Na from roots to shoots was reduced by K level in nutrient solution. These results indicate that K supply and K accumulation and regulation in plant tissue contribute to salt tolerance and growth enhancement.

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INTRODUCTION

High salt levels in soil and water can limit agricultural production in arid and semiarid regions. In general, salinity inhibits plant growth and productivity. Excess Na and chlorine (Cl), the predominant ions in saline soils, create high ionic imbalances that may impair selectivity of root membranes (Bohra and Dorffling, 1993). Potassium is an important nutrient in many physiological processes such as photosynthesis and maintenance of turgidity in plant cells (Carroll et al., 1994; Peoples and Koch, 1979). Maintenance of high cytoplasmic levels of K is essential for plant survival in saline habitats (Chow et al., 1990). Benlloch et al. (1994) suggested that the characteristics of K and Na transport are associated with NaCl tolerance in plants. Salinity conditions can reduce K uptake by plants (Botella et al., 1997; Chow et al., 1990; Romero et al., 1994). Sodium is the major cation in saline water and soil even though Na is not considered essential for tomato growth (Brownell and Crossland, 1972). High levels of Nacan displace calcium (Ca) from root membranes to change their integrity and affect membrane selectivity for K uptake (Cramer et al., 1987). In addition, high concentrations ofNa can interfere with K uptake (Lazof and Cheeseman, 1988). Uptake at low external K levels is highly specific for K, while at higher K concentrations (>0.5 mmol), Na can competitively inhibit K influx (Epstein et al., 1963). Excess Na in root media may result in high Na/K ratios in dry plant tissues, which may lead to metabolic disorders such as reductions in protein synthesis and enzymatic activities (Runge, 1983; Brady et al., 1984). Regulation of K translocation in intact plants is not well understood. Salinity tolerance in some plant species has been related to higher K and to lower Na uptake (Hajibagheri et al., 1989), to greater capacity to exclude Na from the leaves and to maintain higher K/Na ratios in plant tissues (Al-Karaki, 1996; Cerda et al., 1995; Satti et al., 1994). Enhanced K nutrition may ameliorate saline conditions (Botella et al., 1997; Hagin et al., 1990; Shaviv and Hagin, 1993 ; Song and Fujiyama, 1996). The objective of this study was to investigate effects of NaCl and K levels on growth, and on Na and K uptake and translocation in tomato. MATERIALS AND METHODS

Seeds of tomato (cv. Rössel) were germinated in sand. Four 14-d-old uniform size seedlings were transplanted to 2-L containers containing full-strength nutrient solution (Clark, 1982) modified to contain K (as KNO3) at 0.2 or 2.0 mmol. The seedling stems were wrapped with sponge rubber, and placed firmly through plastic lids, with roots suspended in nutrient solution. Seedlings were grown in solution 7 d after which NaCl treatments were initiated. The NaCl added was 0 (control), 100 and 200 mmol NaCl [equivalent to 0.07,4.4, and 7.6 dS m'1, respectively] added in 25 mmol increments every other day until the


GROWTH, Na, AND K IN SALT STRESSED TOMATO

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desired NaCl levels had been reached (8 d for the 200 mmol treatment). Initially solution pH was 6.2 and nutrient solutions were changed every 7 d. Distilled water was added periodically throughout the 21 d growth period in which plants were in the NaCl treatment solutions. Plants were grown in a growth chamber at 14/10 h and 24/18±2°C (light/dark) conditions, using cool-white florescent lamps providing 220 umol m 2 s 1 photosynthetic photon flux density at plant height. Two plants were harvested 15 d after plants had been in NaCl treatment solutions (first harvest) and the remainder harvested 6 d later (second harvest). Plants were separated into shoots and roots. Leaf area of plants (second harvest) was determined using LI-3000 area meter (Li-Cor Inc., Lincoln, NE). Shoots and roots were oven-dried (70°C for 48 h), weighed, and prepared for mineral analysis. Dried shoot and root material was ground to pass a 0.5 mm screen in a cyclone laboratory mill, weighed into crucibles, ashed overnight (550°C) in a muffle furnace, and the ash suspended in 2 MHC1 for determination of mineral elements. Potassium and Na from solutions and from plant material were determined by flame photometer (ATS 200 MK1, GMBH, UK). Net uptake rates (NUR) of K and Na in whole plants were calculated according to Hunt (1982) as: NUR=[(M2-M,)/(t2-t1)]x[lnRw2-lnRwl)/(Rw2-Rwl)]

[1]

1

where M, and M2 are the whole plant content (mg plant ) of K or Na at harvests 1 and 2, respectively, t2-t, is the time between harvests, and Rwl and Rw2 are the root dry weights at harvests 1 and 2, respectively. For calculation of net Na and K translocation rates (NTR) from roots to shoots, K and Na contents in whole plants (M, and M2 in Equation 1) were replaced by shoot contents. The K and Na transported to shoots (ITS) as percentage of total absorbed was calculated as described by Botella et al. (1997). Data were statistically analyzed using analyses of variance in the MSTATC PROGRAM (Michigan State Univ., East Lansing, MI). Probabilities of significance were used to indicate significance among treatments and interactions and LSD values (PO.05) were used to compare means. RESULTS Nearly all salt and K treatment effects were significant for growth and mineral uptake traits, but fewer salt x K interactions were significant (Table 1). Plants grown with NaCl had differentially lower shoot and root dry matter (DM), with the greatest reduction noted at the 200 mmol NaCl level (Figure 1). Consequently, the shoot/root DM ratio decreased by increasing NaCl level in solution (Figure 2). Shoots were more detrimentally affected than roots. Leaf area was significantly lower from the control by increasing NaCl level in solution (Figure 2).

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TABLE 1. Probabilities of significance for different traits of tomato grown in nutrient solution with varied NaCl and K levels.


Trait

Salt level

Shoot DM Root DM

A*

Shoot/root r a t i o Leaf area Shoot Na concentration Shoot K concentration Root Na concentration Root K concentration Shoot K/Na r a t i o Root K/Na r a t i o K NOR t

**

K NTR t K TTS t Na NUR f Na NTR t Na TTS t

**

** ** ** ** ** ** ** ** **

NS ** ** NS

K level * * * ** ** ** ** ** ** ** ** ** * NS NS NS

Salt x K NS NS NS ** * ** * NS ** ** ** ** NS NS NS NS

*=P < 0.05, **=P