Salinity is a build-up of soluble salts (Levy and Syvertsen, 2004). This build-up causes adverse morphological, physiological, and biochemical effects in different organs of citrus plants through an increased concentration of sodium and chloride (Camara-Zapata et al., 2004; Rachmilevitch et al., 2004; Raveh and Levy, 2005; Romero-Aranda et al., 1998; Zekri, 2004). Excess amounts of these salts enhance the osmotic potential (ψS) of the soil matrix, restricting the plant's water intake (Garcia-Sanchez et al., 2002a, 2002b). Plants have developed many adaptive strategies in response to abiotic stresses such as salinity that ultimately influence plant growth and yield (McCue and Hanson, 1990).
Sodium and chloride are major ions and can cause various disorders in citrus plants (Romero-Aranda et al., 1998). Sodium chloride is reported to be a major source of ions in salt solutions compared with Na2SO4 because NaCl liberates ≈60% more ions than Na2SO4 does (Rachmilevitch et al., 2004). Beyond the osmotic effects of salt in the root zone, salt stress causes oxidative stress in plant cells through the generation of reactive oxygen species (ROS), including hydroxyl and superoxide radicals, through various metabolic processes such as photorespiration (Noreen and Ashraf, 2009). Salinity reduces stomatal function and favors the denaturation of chlorophyll (Hernandez et al., 1999), which ultimately leads to a reduction in gS, photosynthetic activity, and the generation of free oxygen radicals, thus inducing oxidative stress. ROS can cause toxic reactions such as lipid peroxidation, protein degradation, and DNA mutation (McCord, 2000). In response, a plant may synthesize more antioxidant enzymes (Sairam et al., 2005), including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) (Noreen and Ashraf, 2009).
The growth and productivity of citrus plants are inhibited by saline as a result of the ion toxicity of Na+ and Cl– as well as the ion antagonisms that occur with Na+ and Cl– that limit nutrient availability (Munns and James, 2003). In citrus production, rootstocks are used to control a plant's size and form and play a key role in establishing excellent fruit quality and yield. Rootstocks also may impart a tolerance to various biotic and abiotic factors, thus contributing to higher production (Waqar et al., 2007). In citrus plants, excess salts in the root zone may negatively affect plant morphological features, mineral nutrition, and various physiobiochemical mechanisms; i.e., photosynthesis, gS and transpiration (Garcia-Sanchez and Syvertsen, 2006; Garcia-Sanchez et al., 2006). Citrus rootstocks may play an important role with regard to the emerging threat of soil salinity. Therefore, the present study was conducted to assess the effect of salt stress on the various physiological and biochemical aspects of salt-tolerant and salt-sensitive citrus rootstocks. The findings of this investigation also clearly demonstrate the differences that occur with respect to various morphological, biochemical, enzymatic, and ionic attributes of salt-tolerant and salt-sensitive citrus rootstocks. The results may indicate the degree to which rootstocks enhance citrus performance under saline conditions and lead to early screening methods to detect tolerant rootstocks.
Almansa, S.M., Hernandez, J.A., Jimenez, A., Botella, M.A. & Sevilla, F. 2002 Effect of salt stress on superoxide dismutase activity in leaves of Citrus limonium in different rootstock–scion combinations Biol. Plant. 45 545 549
Arbona, V., Macro, A.J., Iglessias, D.J., Lopez-Clements, M.F., Talon, M. & Gomez-Cadnas, A. 2006 Carbohydrate depletion in roots and leaves of salt-affected potted Citrus clementina L Plant Growth Regulat. 46 153 160
Ashraf, M. & Ahmad, S. 2000 Influence of sodium chloride on ion accumulation, yield components and fibre characteristics in salt-tolerant and salt-sensitive lines of cotton (Gossypium hirsutum L.) Field Crops Res. 66 115 127
Garcia-Sanchez, F. & Syvertsen, J.P. 2006 Salinity tolerance of Cleopatra mandarin and Carrizo citrange citrus rootstock seedling is affected by CO2 enrichment during growth J. Amer. Soc. Hort. Sci. 131 24 31
Garcia-Sanchez, F., Syvertsen, J.P., Martinez, V. & Melgar, J.C. 2006 Salinity tolerance of ‘Valencia’ orange trees on rootstocks with contrasting salt tolerance is not improved by moderate shade J. Expt. Bot. 57 3697 3706
Garcia-Sanchez, M.R., Bernet, P., Puchades, J., Gomez, E.A. & Asins, M.J. 2002a Evaluation of salt tolerance of five citrus rootstocks using screening technique Aust. J. Agr. Res. 53 653 662
Garcia-Sanchez, F., Jifon, J., Carvajal, M. & Syvertsen, J.P. 2002b Gas exchange, chlorophyll and nutrient contents in relation to Na+ and Cl– accumulation in ‘Sunburst’ mandarin grafted on different rootstocks Plant Sci. 162 705 712
Gorai, M., Ennajeh, M., Khemira, H. & Neffati, M. 2010 Combined effect of NaCl-salinity and hypoxia on growth, photosynthesis, water relations and solute accumulation in Phragmites australis plants Flora 205 462 470
Grewal, H.S. 2010 Water uptake, water use efficiency, plant growth and ionic balance of wheat, barley, canola and chickpea plants on a sodic vertosol with variable subsoil NaCl salinity Agr. Water Mgt. 97 148 156
Hayat, S., Hasan, S.A., Yusuf, M., Hayat, Q. & Ahmad, A. 2010 Effect of 28- homobrassinolide on photosynthesis, fluorescence and antioxidant system in the presence or absence of salinity and temperature in Vigna radiata Environ. Exp. Bot. 69 105 112
Heidari, M. 2010 Nucleic acid metabolism, proline concentration and antioxidants enzyme activity in canola (Brassica napus L.) under salinity stress Agr. Sci. China 9 504 511
Hernandez, J.A., Campillo, A., Jimenez, A., Alarcon, J.J. & Sevilla, F. 1999 Response of antioxidant systems and leaf water relations to NaCl stress in pea plants New Phytol. 141 241 251
Hessini, K., Martinez, J.B., Gandour, M., Albouchi, A., Soltani, A. & Abdelly, C. 2009 Effect of water stress on growth, osmotic adjustment, cell wall elasticity and water-use efficiency in Spartina alterniflora Environ. Exp. Bot. 67 312 319
Hoagland, D.R. & Arnon, D.J. 1950 The water culture method for growing plants without soil. California Agr. Expt. Sta. Circ. 347.
Hu, Y. & Schmidhalter, V. 2005 Drought and salinity: A comparison of their effects on mineral nutrition of plants J. Plant Nutr. Soil Sci. 168 541 549
Hwang, Y.H. & Chen, S.C. 1995 Anatomical responses in Kandelia candel (L.) druce seedlings growing in the presence of different concentrations of NaCl Bot. Bull. Acad. Sin. 36 181 188
Ltaief, B., Sifi, B., Zaman-Allah, M., Drevon, J. & Lachaal, M. 2007 Effect of salinity on root–nodule conductance to the oxygen diffusion in the Cicer arietinum–Mesorhizobium ciceri symbiosis J. Plant Physiol. 164 1028 1036
Martins, M.B.G. & Castro, P.R.C. 1999 Growth regulators and tomato leaf anatomy (Lycopersicon esculentum Mill.) cv. Angela Gigante Scientia Agricola 56 693 703
Moya, J.L., Gomez-Cadenas, A., Primo-Millo, E. & Talon, M. 2003 Chloride absorption in salt-sensitive Carrizo citrange and salt tolerant Cleopatra mandarin citrus rootstocks is linked to water use J. Expt. Bot. 54 825 833
Neto, A.A.D. & Tabosa, J.N. 2000 Salt stress in maize seedlings: II. Distribution of cationic macronutrients and its relation with sodium Revista Brasileira de Engenharia Agrícola e Ambiental 4 165 171
Noreen, Z. & Ashraf, M. 2009 Assessment of variation in antioxidative defense system in salt treated pea (Pisum sativum) cultivars and its putative use as salinity tolerance markers J. Plant Physiol. 166 1764 1774
Rachmilevitch, S., Cousins, A.B. & Bloom, A.J. 2004 Nitrate assimilation in plants shoots depends on photorespiration Proc. Natl. Acad. Sci. USA 101 11506 11510
Ramarao, C.S., Patil, V.H., Dhak, B.D. & Kadrekar, S.B. 1983 A simple in vivo method for the determination of nitrite reductase activity in rice roots Zentrum Pflanzen Physiological 109 81 85
Romero-Aranda, R., Moya, J.L., Tadeo, F.R., Legaz, F. & Primo-Millo, E. 1998 Physiological and anatomical disturbances induced by chloride salts in sensitive and tolerant citrus: Beneficial and detrimental effects of cations Plant Cell Environ. 21 1243 1253
Sairam, R.K., Srivastava, G.C., Agarwal, S. & Meena, R.C. 2005 Differences in antioxidant activity in response to salinity stress in tolerant and susceptible wheat genotypes Biol. Plant. 49 85 91
Sym, G.J. 1984 Optimization of the in vivo assay conditions for nitrate reductase in barley (Hordeum vulgare L. cv. irgri) J. Food Sci. Agr. 35 725 730
Waqar, A., Nawaz, M.A., Iqbal, M.A. & Khan, M.M. 2007 Effect of different rootstocks on plant nutrient status and yield in Kinnow mandarin (Citrus reticulata Blanco) Pak. J. Bot. 39 1779 1786