Assessment of Cytotoxic Ions Sequestration as salt tolerant indicators in Tomato ( Solanum lycopersicum L . ) Ja ’ afar

This study determines the genetic diversity of 20landraces and released cultivars of tomato collected from Market places and research institutes in Nigeria. Ion homeostasis and cytotoxic sequestration significantly (P>0.05) affected by concentration of salt in a concentration dependent manner. Accumulation of Na+, Cl-, K+ and Ca2+ ions increased in salt treated groups (30 and 60 mg/L of NaCl) as compared to controls. Potassium ion uptake was salt concentration dependent in all cultivars; the magnitude of Na+/K+ levels is lower in released cultivars than in landraces cultivars. It can be concluded from these findings that Na+ was compartmentalized both in tomato by membrane transporters and that low level was a good indicator of salt tolerant in tomato genotype studied.


Introduction
Tomato (Solanum lycopersicum L.) originated from South America, is nowadays one of the most economically important and widely grown plants in Solanaceae family.Soil salinity is one of the major factors of soil degradation and is recorded 19.5% of the irrigated land and 2.1% of the dry land agriculture existing on the globe (Jamil and Rha, 2006).Salinity is conspicuous in arid and semi-arid areas where 25% of the irrigated land is affected by salt (Lira et al., 2014).Salinity inhibition of plant growth is the result of osmotic and ionic effect, and different plant species have developed different mechanisms to cope with those effects (Munns, 2002).Excess amount of salt in the soil adversely affects plant growth and development (Zhu, 2001).Several factors may contribute to reduction in growth exhibited by plant under salinity stress.Processes such as seed germination, seedling growth and vigour, vegetative growth, flowering and fruit set are adversely affected by high salt concentration ultimately causing diminishing economic yield and also quality of production (Sairam and Tygyi, 2004).Salinity also affects the diffusion both at stomata and the mesophyll (Dudly, 1992).
Morphology, anatomy, ultra-structure and metabolism of plant species are also deeply affected by salt (Prat, and Fathi-Ettai, 2013).Salinity impairs seed germination reduce nodules formation, retard plant development and reduce crop yield.These concentrations fluctuate because of change in water sources, drainage, evapotranspiration and solute availability (Shininger, 1997).Salinity affects plant through hyper osmotic effect, ion disequilibrium and oxidative stress.The homeostasis of intra cellular For determination of sodium, potassium, calcium and chloride in leaf tissue, 1g of the plant leaves were prepared by grinding with distilled water (about 10 mL) at 25 0 C for 10 min.The homogenate was centrifuged at 3000×g for 15 min, and the supernatant filtered through qualitative filter paper.An aliquot of filtrate was used for Na + ,Ca 2+ and K + determination using flame photometry and Cl − by precipitation titration with silver nitrate by Mohr's method .

Elemental Analysis
Tab. 3 summarized the accumulation of ions (both cytotoxic and non cytotoxic) by different cultivars of tomato.The sodium ion (Na + ) of the 20 cultivars increased with the increasing concentration of NaCl.Controls recorded the least level of Na + and the highest levels were recorded in plants treated with 60 mg/L of NaCl.However, Dan Gainakawa and Dan dubukamiya recorded the highest level of Na + with 3200.0 respectively.The least level of Na + on plant treated with 60 mg/L of NaCl was recorded in Tropemech tomato and UC82B with 1323.67 and 1500.00Na + respectively (Table 2).The result differ significantly (P<0.05).UC82B and UTC recorded the highest levels of K + with 8,700.00followed by Roma with 8814.67.The least K + levels were recorded at plant treated with the highest concentration of NaCl (Table 2).Mean comparisons in some cultivars shows that differ (P<0.05) from the treated plant while in some did not differ significantly (P> 0.05).
Calcium (Ca 2+ ) and chlorine (Cl -) content differs significantly (P< 0.05).The lowest content of Ca 2+ was recorded in UC 82B with 0.56 at control.Highest value of 1.56 was observed at plants treated with 60 mg/L of NaCl (Table 2).The least chlorine content was observed at control and the levels increases with increase in the concentration of salt (Table 3).

Discussion
The amount of inorganic ions such as Na + , K + , Ca 2+ and Cl -increased with increasing salt concentrations except in K + increased at one time and decreased at higher salt concentration in order to sustain the osmotic potential and maintain water influx in the plant.High level of Na + , Cl -, and Ca 2+ was recorded in all the plant treated with 60mg/L of NaCl and the low level of these ions was significantly (P<0.05)recorded in the controls of the entire plants respectively.In contrast, the highest concentration of K + content in all the plants was recorded at control followed by plants treated with 30mg/L of NaCl and the lowest is recoded in those treated with 60mg/L of NaCl.However, in some of the cultivars the lowest content of K + was recorded at plants treated with 30mg/L of NaCl.Under salt stress, Na + competes with K + for uptake in roots through common transport system effectively, since the Na + in saline environments is usually is usually considerably greater than K + (Rains, 1989;Maathius et al., 1992).These findings can be attributed to the competitive interactions between K + and Na + and the inhibition of K + uptake by high concentration of Na + as reported by Berntein, (1995).The maintenance of cytosolic of Na + concentration and Na + /K + homeostasis is an important aspect of salinity tolerance and that salt tolerant lines shows lower Na + /K + ratio levels (Chattopadhyay et al., 2002).Based on the Na + /K + ratio observed in this study, the tomato cultivars studied could be classified as salt tolerant line.
Tab. 2 Effects of different salt concentration on ionic content (mgKg -1 ) of 20 cultivars of tomato.

Conclusion
In conclusion, Na + was sequestered plant tissue by active antiporters to minimize cytosolic toxicity and that the ratio of Na + to K + is a good indication of salt tolerant property due to competitive interactions of these ions.

Acknowledgements
Gratitude to Dr. A.M. Gummi and those that contributed directly or indirectly to the successful completion of this research work.
Values represent means of elemental analysis.Mean in a column with the same superscript are not significantly different at (P<0.05).