effect of alkaline stress on some morphophysiologic characteristics of two varieties of safflower (carthamus tinctorius l.)

introduction safflower (carthamus tinctorius l.) is an important oilseed crop grown throughout the semiarid regions in many parts of the world. it has been cultivated for its oil and flowers and as a meal. alkaline stress is caused by alkaline salts such as na2co3 or nahco3 in the soil. alkaline stress, is widespread environmental constraint affecting crop productivity ,which can inhibit absorption of inorganic anions such as cl–, no3– and h2po4–, greatly affect the selective absorption of k+-na+, and break the ionic balance. however, under alkali stress, accumulation of compatible solutes, such as betaine, proline and soluble sugar into the vacuole are considered as the basic strategies for plant re-established cellular homeostasis. some reports have clearly demonstrated that alkaline salts (nahco3 and na2co3) are more destructive to plants than neutral salts (nacl and na2so4). moreover, the salt-alkali stress can directly damage plant growth, alter the availability of nutrients and disrupt the balance of ions and mineral nutrition. the objective of this study was to investigate the effects of alkaline stress on growth and some physiological characteristics of safflower. materials and methods this study was conducted in a greenhouse in vali-e-asr university of rafsanjan as factorial arrangement in completely randomized design with three replications. experimental factors included alkaline stress in 7 levels (0, 10, 20, 30 , 40, 50 and 60 mm) and two varieties of safflower (sofeh and 411). seeds were planted in pots filled with perlite and cocopite (1:1). the pots were irrigated with a nutrient solution with half strength hoagland's solution. after the fourth true leaves appeared, alkaline stress in the pot was created by adding nahco3, to half strength hoagland’s solution. control plants were only irrigated with half strength hoagland’s solution. plants were harvested after 40 days of seed sowing. after forty days, shoot and root height, shoot and root dry weight, fv/fm, pi, proline, total carbohydrate, malondialdehyde content, cha, chb, total chlorophyll, cartonoied content, potassium, sodium content and sodium to potassium rate were measured. results and discussion result showed that with increasing alkaline stress, decreased shoot and root height, shoot and root dry weight. a similar result had observed previously in sugar beet. researches have indicated that plants respond to elevated nahco3 concentrations in soil or in growing medium solution with decreased shoot and root growth. this could be due to either hco3− or na+. many of the data test showed high ph as a key factor in limiting plant growth and development under alkaline conditions. 411 variety showed superiority compared to sofeh cultivar in mentioned characteristics. also, fv/fm and pi decreased under alkaline stress condition, whereas proline, total carbohydrate and malondialdehyde content increased. also, the increases in proline and total carbohydrate content were reported in wheat under alkaline stress condition. baghre and roosta (2012) reported that fv/fm values and pi reduced under alkalinity stress. in the present experiment, alkaline stress decreased cha, chb and total chlorophyll whereas it increased cartonoied content. yang et al., (2009a) concluded that in alkalinity stress, the contents of chl and car in the barley plants decreased sharply with increased stress in comparison to salinity stress. they also stated that high ph might decrease contents of photosynthetic pigments. potassium content decreased under alkaline stress condition whereas sodium and sodium to potassium rate increased. also, zhang and chun-sheng (2009) reported that with increasing alkaline stress, potassium content decreased in lathyrus quinquenervius whereas, sodium content and sodium to potassium rate increase. in wheat stems, a decrease in potassium content and potassium to sodium rate and an increase in sodium content were also observed. a high-ph environment surrounding the roots can cause metal ions and phosphorus to precipitate, with loss of normal physiological functions of roots and destruction of root cell structure. conclusions result showed that alkaline stress decreased shoot and root height, shoot and root dry weight, whereas proline, total carbohydrate and malondialdehyde content increased. also, with increasing alkaline stress fv/fm, pi, cha, chb, total chlorophyll and potassium content decreased whereas cartonoied content, sodium and sodium to potassium rate increased. 411 variety showed superiority compared to sofeh cultivar in growth characteristics, cha, total chlorophyll. also, both cultivars showed same reaction under alkaline stress.