INTRODUCTION
Salinity is the main environmental factor accountable for decreasing crop productivity in many areas of the world especially in arid and semi-arid regions (De Pascale and Barbieri, 1997). On the other hand, not only uncontrolled irrigation but also poor-quality water may cause salinity (Tanji, 1990; Maas and Grattan, 1999). It was estimated that about one-third of irrigated land has been affected by salinity (Shannon, 1984).
Salinity reduces growth and yield of the non-halophytes plants by decreasing the availability of water to the roots due to the osmotic effect of external salt and by toxic effects of excessive salt accumulation within the plant (Mass and Hoffman, 1977; Turan et al., 2007a).
NaCl toxicity, the predominant form of salt in most saline soils, enhances the Na and Cl contents and consequently affects the absorption of other mineral elements (Greenway and Munns, 1980). It is stated that high levels of Na inhibits Ca and K absorption, which results in a Na/K antagonism (Al-Karaki, 1997) and net photosynthesis is affected strongly by NaCl-saline conditions, which is related directly to the closure of stoma as well as to low intercellular CO2 levels.
Under salt stress, plants have evolved complex mechanisms allowing for adaptation to osmotic and ionic stress caused by high salinity. These mechanisms include osmotic adjustment by accumulation of compatible solutes such as proline and lowering the toxic concentration of ions in the cytoplasm by restriction of Na influx or its sequestration into the vacuole and/or its extrusion. However, the significance of proline accumulation in osmotic adjustment is still debated and varies according to the species (Lutts et al., 1996; Rodriguez et al., 1997; Turan et al., 2007a and b).
The lentil is an annual winter/summer grain legume, needing low to medium rainfall. Lentils (Lens culinaris) have been used as a staple food since the beginning of agriculture, in south west Asia. They are an important source of protein for people in the Mediterranean, Africa, the Middle East, Southern Asia and South America.
Currently the lentil ranks about fifth in the world production of pulses. Food and Agriculture Organisation statistics indicate that the lentil is grown on about 3.4 million hectares. Total world production was 2.7 million tonnes in 1993. India produces nearly one-third of the worlds annual production, largely for domestic consumption. Other major producers are Turkey, Canada, Bangladesh, Syria, Nepal, United States of America, Iran and New Zealand. Turkey is the largest exporter of lentils in the world and produces 0.3-0.5 million tonnes of split lentils per year (Anonymous, 2005).
Lentil grown in Turkey might be exposed to salt stress because of dry-growing and low rainfall areas. Therefore, objective of this research is to examine the influence of soil salinity on the growth and stomatal resistance, proline, total chlorophyll and some mineral element concentrations of lentil plants.
