A pot experiment was conducted to investigate the role of potassium (K) in extenuating the injurious effect of salt stress on maize hybrids differing in salt tolerance at different growth stages. One salt-sensitive viz. 8441 and one salt-tolerant viz. 26,204 maize hybrids were sown in pots having 12 kg soil. The recommended dose of nitrogen and phosphorus @ 200 and 150 kg ha -1 with different rate of potassium (75, 150 and 300 kg ha -1 ) and salinity level (10 dS m -1 ) was developed in soil before filling the pots. Salinity stress reduced plant growth by affecting plant morphological characteristics, reducing relative water contents and membrane stability index, decreasing photosynthetic activities, altering K ? /Na ? ratios and antioxidant activities of both maize hybrids at all three growth stages. However, results also depicts that maximum relative water contents, membrane stability index, gas exchange attributes, photosynthetic pigments, antioxidant enzymes activities and proline contents was observed at reproductive growth stage as compared to vegetative and grain development growth stages in both hybrids. The inhibitory effect of salt stress was more pronounced on maize hybrid 8441 than 26,204. But, addition of potassium significantly alleviates harmful effect of salinity by improving the plant growth, gas exchange parameters, enhancing K ? /Na ? ratios and antioxidant activities of both maize hybrids. Potassium application (300 kg K ha -1 ) was found more effective in alleviating perilous effect of salinity as compared to other two levels. Salt tolerant maize hybrid (26,204) produced more biomass, less shoot Na ? concentration, high K ? concentration, exhibited more chlorophyll contents, gas exchange parameters and antioxidant enzymes activities under salt stress condition at all growth stages as compared to salt sensitive maize hybrids (8441). These results suggested that potassium application counteracted the unfavorable effects of salinity on growth of maize by civilizing photosynthetic capacity of maize plants against salinity-induced oxidative stress and maintaining ion homeostasis, however, these alleviating effects were cultivar specific.

The role of silicon (Si) in alleviating biotic and abiotic stresses in crops is well evidenced by empirical studies; however, the mechanisms by which it works are still poorly known. The aim of this study is to determine whether or not phytolith composition and distribution in wheat are affected by drought and, if so, why. Durum wheat was grown using hydroponics in the presence of polyethylene glycol (PEG)-6000 to perform a water-stress simulation. We developed an original method for in situ analysis of phytoliths in leaves via X-ray imaging. PEG was efficient in inhibiting water uptake by roots and creating stress, and prevented a small fraction of Si from being accumulated in the shoots. The application of Si with PEG maintained shoot and root fresh weights (FW) and relative water content at higher values than for plants without Si, especially at PEG 12%. Our data show that, under water stress in the presence of Si, accumulation of phytoliths over the veins provides better support to the leaf, thus allowing for a better development of the whole plant than in the absence of Si. The development of silicified trichomes in durum wheat depends primarily on the availability of Si in soil and is not an adaptation to water stress.

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IntroductionCrop production in fields is restricted by a number of abiotic stress factors like drought, salinity, light intensity, and temperature. Soil salinization is among the most severe abiotic threats to agriculture. According to a study on global land use patterns, 7% of the earth's total land area (1000 × 10 6 ha) has become saline (Tester and Davenport, 2003).Soil salinity not only affects plant growth but also developmental processes like seed germination, seedling vigor, flowering, and seed setting, primarily because of hyperosmotic stress and ionic imbalance (Sairam and Tyagi, 2004;Demiral et al., 2005). The increased osmotic pressure in the root environment decreases the availability of water to plants and its movement to reproductive organs such as fruits, and, as a result, fruit size is decreased, as seen in tomato and other crops (Li and Stanghellini, 2001;Mavrogianopoulos et al., 2002).Tomato (Solanum lycopersicum L., previously named Lycopersicon esculentum Mill.) is an important crop in several parts of the world, including the regions suffering from drought and soil salinity, such as the Mediterranean region, where these aspects have been studied (Savic et al., 2009;Jensen et al., 2010). Tomato is not regarded as tolerant to abiotic stress factors, but these stresses, such as salinity, may enhance fruit quality by increasing sugar concentration and dry matter content (Yurtseven et al., 2005).Potassium is one of the important macronutrients required for the growth, development, yield, and quality of plants, and it also plays a key role in the survival of plants under abiotic stress conditions, as stress negatively affects the physiological processes of plants such as root and shoot elongation, enzyme activity, water and assimilate transport, synthesis of protein, photosynthetic transport,

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1Producing vigorous seedlings and transplanting them at the appropriate age are the most important factors for obtaining high yield in rice (Oryza sativa L.) paddy production. The impact of seeding densities, N, and seedling age was evaluated in this experiment after transplanting 10, 20, 30 and 40-d old seedlings raised by using different seeding rates (high and low) and N conditions (with and without) in the 2008 and 2009 rice growing seasons. The study revealed that 10-d-old nursery seedlings, irrespective of seeding densities and fertilizer application, showed higher yields and yield attributes (productive tillers, plant height, 1000-grain weight, and straw yield), while at later stages significant interaction was observed with nursery management. Transplanting of 20-d older fertile seedlings grown with low seeding density at nursery-bed, resulted in a higher number of productive tillers m -2 (233.3, 227.3), straw yield (11.1, 10.7 t ha -1 ), and final yield (3.6, 3.4 t ha -1 ) in both years, 2008 and 2009, respectively. Yield and yield attributes were significantly reduced by transplanting older seedlings grown at high seeding density and without N application at nursery-bed. Minimum productive tillers (165.7, 133), straw yield (8.7, 8.1 t ha -1 ) and paddy yield (2.0, 1.8 t ha -1) were recorded with transplanting 40-d older seedlings grown at high seeding density and without N application. These findings support the use of young seedling in a system of rice intensification and illustrate that by making a minor additional investment to raise healthy and vigorous seedlings in nursery seed-bed, farmers can improve yields.

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