Ameliorative Effect of Chelating Agents on Photosynthetic Attributes of Cd Stressed Sunflower

Excessive input of heavy metals in water reservoir and cultivated land primarily affects the growth and yield of crops. The aim of this work was to study the mechanism of Cd toxicity and damage to photosynthetic pigments and their efficiency and the potential of natural (OA) and synthetic chelators (EDTA) in assisting the phytoextractor sunflower plant. The pot experiment was laid out in a complete randomized way for Cd, chelators and hybrids at seedling, vegetative and reproductive stages with three replications. Cd affects the gas exchange parameters directly or indirectly by affecting the light and dark reactions, while indirect effect includes inhibition of chlorophyll and carotenoids biosynthesis and degradation and alteration in Chl a/b ratio. Among two chelators, natural chelator OA found to be very supportive in ameliorating the Cd tocixity by phytoextractor in assistance to sunflower hybrid Hysun-33.

Morpho-Anatomical Changes in Roots of Chickpea （Cicer arietinum L.） under Drought Stress Condition

Chickpea （Cicer arietinum L.） is a crop cultivated in semi-arid and rainfed areas of Pakistan and it experiences terminal drought stress. In this paper, the morpho-anatomical study regarding roots of chickpea was carried out to investigate the drought adaptation strategies. Twelve cultivars of chickpea were grown in pots under drought stress of 70% and 35% field capacity in addition to control （100%）. Root segments of mature chickpea plants were sectioned in 2 cm from root-shoot junction and used for making transverse sections. The development of sleeve and stele tissues and their proportion were markedly influenced by moisture availability to the root system. Roots length, flesh and dry weight, and number of secondary roots were decreased under field capacity of 70% and 35% as compared to control in 12 cultivars of chickpea. Root epidermis and cortex of CH47/04 consisted of cells with thickened walls and with 2-3 cell layers of sclerenchymatous cells below the epidermis. Increased number of medullary rays and high vascular region was observed in cultivars CH120/04, CH47/04, CH587/05 and CH87/02. Anatomical studies showed that CH47/04 was highly tolerant among 12 cultivars of chickpea, while CH587/05 and CH87/02 behaved moderately under both levels of drought stress （70% and 35% field capacity）.

Influence of Foliar Applied Nitrogen on Reproductive Growth of Sunflower (<i>Helianthus annuus</i>L.) under Water Stress

Nitrogen is a major nutrient involved in plant growth and yield. Plants cannot get the nutrients from the soil medium under water stress condition to testify foliar application in stress condition to fulfil plant need for better performance. In this regard, a field study was conducted to evaluate the effect of foliar-applied nitrogen (0, water and 1% urea) on sunflower (cv. Hysun-33) under normal and water stress at reproductive stage. Two soil applied nitrogen levels control (0 kg·ha-1) and recommended dose (115 kg·ha-1). Supplemental foliar application of nitrogen in the form of urea significantly increased the growth, yield and yield components of sunflower under water stress. The increase in yield with 1% urea spray was recorded up to 1.37 t·ha-1 in comparison to water spray (1.07 t·ha-1) and no spray (1.00 t·ha-1). While maximum values of all factors were obtained where 1% urea spray with soil applied nitrogen was used in both stresses as well as in non-stress condition. Therefore, reasonable yield can be achieved by applying foliar application of urea (1%) as a supplemental source to soil applied nitrogen under water stress.

Allelochemicals as Growth Stimulators for Drought Stressed Maize

Sorgaab, an aqueous extract of sorghum leaves was applied to probe the modulation in growth and physiological attributes of maize under drought in lab and greenhouse studies. Sorgaab soaked seeds (10 dilutions) were germinated to assess drought tolerance at germination and seedling growth stages. More concentrated Sorgaab solutions (2 mL&middot;L-1) were damaging, while lower concentration in the range of 0.75 to 1.5 mL&middot;L-1 improved the root and shoot growth of maize under drought. Applied drought stress decreased chlorophyll b greater than chlorophyll a that improved the chl a/b ratio. Application of Sorgaab also improved the internal CO2 assimilation, which increased the net photosynthesis and A/E ratio of drought affected plants. Soluble phenolics and anthocyanins were also more increased in plant receiving Sorgaab under drought than control. Although greater concentrations of phenolic acids inhibit the uptake of ions, but its lower concentrations stimulate the uptake of K+, Ca2+, NO3, PO4. In conclusion, although high concentrations of Sorgaab reduced the growth of plants, it might alleviate the adverse effects of drought, if applied at the low concentration. Dilute concentrations of Sorgaab can be utilized as a natural source for improving drought resistance in maize both at germination and later growth stages.

Vulnerability of Sunflower Germination and Metal Translocation under Heavy Metals Contamination

The germination and metal translocation ability of two sunflower seedlings were compared to identify the cultivar differences towards metal contamination at juvenile stage. The heavy metal treatments include: 0, 50, 100, 150 and 200 mM Ni, Cd and Pb applied in sand filled pots to Hysun-33 and FH-533 sunflower. The highest germination percentage (79%) and vigor index were recorded for Hysun-33 with no heavy metal treatment. Pb and Cd treatments reduced the growth attributes of 20 days old seedlings of both the cultivars. The Ni translocation effectively enhanced the shoot and root biomass of Hysun-33. The high concentration of 150 and 200 mM Cd and Pb drastically reduced Mn and K contents, vigor, length and biomass of two sunflower cultivars. Among three of the heavy metals, Cd was found more toxic than Pb and Ni. Roots of 20 days old seedlings of Hysun-33 were able to hold more Cd metal and stop its translocation to epigenous parts. Although 150 and 200 mM Ni effects the germination and vigor of sunflower cultivars more than 50 and 100 mM Ni, it is found less toxic in comparison to Cd and Pb. The Cd accumulation in roots suggests that it is physiologically most active sink for Cd metal while epigenous parts of sunflower cultivars are sink for Pb and Ni metal as shoot of sunflower cultivars accumulates high contents of Pb and Ni.

Exogenous Application of Thiourea Ameliorates Salt Stress Effects by Alleviation of Oxidative Damage in Hybrid Maize

Salinity is the most damaging factor towards crop production. The aim of this study was to investigate the possible role of thiourea in salinity tolerance. These experiments were carried out on two maize hybrids （DK6789 and 33M15） using the optimized thiourea level （400 μM） in autumn and spring seasons, and the growth and physiological attributes were observed. Salt stress caused a substantial suppression of growth, and damaging effects were observed, as reduction in shoot and root length, their fresh and dry weights, decreased root number and shoot/root ratio, increased accumulation of H202, malondialdehyde （MDA） in root and shoot tissues, and enhancement in activities of some key antioxidant enzymes （catalase, peroxidase and superoxide dismutase） with altered ascorbate peroxidase level in leaves of both maize hybrids. Medium supplemented thiourea was found to be very effective in improving growth may be due to decreased H202, MDA and further enhanced the activities of antioxidants with higher accumulation of ascorbate peroxidase under control and saline conditions. Salinity tolerance induced by thiourea was superior in the spring than in autumn grown maize. From the changes in the growth and physiological attributes of maize, it can be concluded that thiourea application has a great potential to alleviate the deteriorating effects of salt stress on maize and is recommended for improving growth in marginally to moderately saline soils.