Growth Response Of Sunflower Biology Essay

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Reclamation of salt affected soils is one of the ways to cope with salinity problem but it involves high input cost and is beyond the economic means of farmers in Pakistan. Ever increasing demand of food, fodder and fuel wood is pushing agriculture to marginal land, thus increasing the need of finding ways to utilize these lands. An alternate approach is to develop and select salt tolerant genotypes of crop species. Keeping above facts in view the present studies have been planned with the objectives to investigate salinity tolerance potential, quantity of oil and changes in chemical composition of different sunflower genotypes under different levels of salinity stress and boron. The parameters regarding agronomic yield and economic yield (oil contents) will be recorded. The chemical composition of leaf sap (Na, K, Cl and B) will also be calculated. Relative growth rate (RGR), relative water contents (RWC), membrane stability index (MSI), chlorophyll contents, proline in leaves and leaf water relation will be measured. Data regarding 1000 achene's weight, number of achene's per head, head diameter and oil contents will also be determined and analyzed statistically using standard procedures.


Salinity is soil condition characterized by a high concentration of soluble salts. Soil is classified as saline when ECe is 4 dS/m or more (USDA-ARS, 2008). More than 800 m ha of land through out the world are salt affected (FAO, 2008). Most of this salt affected land has arisen from natural causes from the accumulation of salts over long periods of time in arid and semi arid zones (Rengasamy, 2002).The detrimental effects of high salinity on plants can be observed at the whole plant level as the death of plants and/or decreases in productivity (Parida and Das, 2005). Adverse effects of salinity on crop growth stem from two characteristics (1) the increased osmotic potential of soil solution with salinity makes the water in the soil less available for plants and (2) specific effects of some elements (Na, Cl, B etc) present in excess concentrations (Yamaguchi and Blumwald, 2005; Munns, 2005).

Boron is often found in high concentration in association with saline soil and removed more slowly during leaching; therefore, it may still be present at excessive concentration in some reclaimed soils (Nable et al, 1997). Boron is essential for cell wall structure and plays an important role in membrane processes and metabolic pathways ( Blevins and lukaszewski, 1998; Lauchli, 2002. and Brown et al, 2002). High boron like salinity, is an important abiotic stress that adversely affects crops in many arid and semi arid climates. There are many agricultural areas around the world where both high salinity and high boron occur together, affecting the plants (Tanji, 1990). Salinity and boron toxicity affect membrane and photosynthesis by increasing stomatal resistance and disturbing biosynthesis of photosynthetic pigments (Karabal et al, 2003, Sairam et al, 2005).

Despite the common occurrence of high boron and high salinity in many parts of the world, very little research has been done to study the interaction of the two (Gratten and Grieve, 1999, Bengal and Shami, 2002).

Sunflower (Helianthus annuus L.) is an important source of vegetable oil i.e., unsaturated semidrying type like corn (Zea mays L.), sesame (Sesamum indicum L.), and cotton seed (Gossypium ssp.) used for cooking and food preparation worldwide. This crop is also grown as a food source for direct consumption (i.e., seeds in snacks, candies, and birdfeed) (Xianan and Wm. Vance Baird, 2003).In Pakistan during year 2006-2007 local production of edible oil is estimated at 0.855 m tons. During this period, 2.201 m tons edible oil was imported and 0.349 m tons edible was recovered from imported oil seeds (Anonymous 2006-07).

Francois, 1996, found sunflower to be a species moderately tolerant to salt stress being unaffected by soil salinity up to 4.8 dS m−1. Also (Katerji et al., 2000) classified sunflower as a salt tolerant crop on the basis of the estimation of the crop water stress index. Further more, as it requires less number of irrigations it can be grown successfully with saline sodic water with little harmful effects on soil physical and chemical properties.

Increasing salinity thus enhance the boron sorption, might be due to salt induced increase in dissociation of H3BO3. According to (Holloway and Alstton, 1992), high boron decreased dry matter production, grain yield, root length, increase concentration of boron and decreased the concentration of Na in the plants when grown under saline condition. However literature is limited regarding response boron under salt-affected soils. The aim of present study is to investigate the role of boron under saline environment and salt affected soils on growth, ionic and yield of sunflower genotypes of differential salt tolerance.

Keeping in view these considerations, the present studies will be planned with following objectives.

To evaluate the performance of different sunflower genotypes under salt stress.

To evaluate the aggravating effect of boron in salt stressed sunflower and its yield.

To describe the effect of boron on ion contents, chlorophyll contents and other biochemical changes in sunflower genotypes under salt stress.


Salinization of soils limits plant growth by inducing numerous physiological and biochemical changes in cells. Studies indicate that higher levels of salinity in the irrigation water cause more inhibition to shoot than to root growth. The decrease in roots and shoots weight might be due to nutrient deficiency mediated by roots (Khan et al., 1994). The effects of 10% and 20% seawater were studied in nutrient solutions in 30 day-old plants of sunflower. It was found that 20% seawater treatment reduced shoot and root growth of sunflower significantly, while plants treated with 10% seawater did not show significant differences in comparison with the control (Baccio et al., 2004).

As for as changes in plant growth is concerned, relative growth is an ideal index for evaluating seedling growth rather than absolute growth. Under low salinity and alkalinity stress growth of sunflower seedlings is not inhibited rather it is stimulated. It was also concluded that relative growth rate of a treatment with 50 mM NaCl was 83% relative to the control, but the relative growth rate of treatment with salinity level equal to 250 mM was reduced to -8.03% (Shi and Sheng, 2005). The permeability of the plasma membrane is an evident index that reflects the degree of stress-induced injury to plants (Surjus and Durand, 1996). Generally, plasma membranes are injured more seriously with intensifying stress, leading to an increase in the electrolyte leakage rate. Using mixed salt alkali stress (Shi and Sheng, 2005) showed that increasing salinity in sunflower seedling caused more serious injury on membranes and furthermore, given the same salinity values, the injury is more serious with increasing alkalinity.

Growth of green plants is dependent on photosynthesis. Since it is a primary process in plant productivity, increasing its efficiency has long been a goal of plant research. However, the rate of photosynthesis varies with the change in environmental factors, thereby affecting plant growth (Taiz and Zeiger, 2002). For instance, suppression of the photosynthetic capacity of different plant species by salinity stress has been reported in a number of studies (Makela et al., 1999). Reduction in photosynthesis by increased salinity could be due to lower stomatal conductance, depression in specific metabolic processes in carbon uptake, inhibition in photochemical capacity, or a combination of these (Dubey, 1997).

Salt stress increases the accumulation of NaCl in chloroplasts of higher plants, affecting growth rate, and is often associated with decrease in photosynthetic electron transport activities (Kirst, 1989). In higher plants, salt stress inhibits PSII activity (Parida et al., 2003). However sunflower seems to possess the ability of maintaining high physiological activities when subjected to mild salt stress. In addition to salt exclusion capacity of sunflower, the compartmentation of ions in its large vacuole (Greenway and Munns, 1980) can explain the scarce salinity effect on the biochemistry of photosynthesis. Ionic imbalance occurs in the cells due to excessive accumulation of Na+ and Cl- and reduces uptake of other mineral nutrients, such as K+, Ca2+, and Mn2+ ( Hasegawa et al., 2000). The accumulation of toxic amounts of salts in the leaf apoplasm leads to dehydration and turgor loss, and death of leaf cells and tissues (Marschner, 1995). Both the dehydration of cells and high sodium to potassium ratio due to accumulation of high amounts of sodium ions inactivate enzymes and affect metabolic processes in plants (Booth and Beardall, 1991). Osmotic stress is linked to salt stress: salt stress involves an excess of sodium ions whereas osmotic stress is primarily due to a deficit of water without a direct role of sodium ions (Munns, 2002). It now appears that the transport of Na+ across the tonoplast and its accumulation in the vacuole is an important mechanism of plant tolerance to salinity (Niu et al., 1995).

The evidence that sunflower roots appear to possess an inefficient mechanism of Na+ efflux to the root medium suggests the occurrence of a Na+ exclusion mechanism to the shoot based on an efficient Na+ accumulation in vacuole. Plant cells typically maintain a low Na+/K+ ratio in the cytosol, and there is evidence that Na+ is actively transported out of the cytosol at both plasma membrane and tonoplast (Niu et al., 1995). While salt sensitive species depend mainly upon exclusion of Na+ at the plasma membrane, salt tolerant species may accumulate large amount sequestered into the vacuole, serving as osmoticum (Jeschke, 1984).

Moreover, salt stress affects plant physiology at both whole plant and cellular levels through osmotic and ionic stress (Murphy et al., 2003). Osmotic stress is primarily due to a deficit of water without a direct role of sodium ions (Munns, 2002).

One of the main mechanisms that plants use to adapt to osmotic stress is the osmotic adjustment or osmoregulation, a mechanism by which cells accumulate ions in the vacuole and synthesize compatible solutes such as sugars and amino acids in the cytoplasm (Munns, 2002; Bartels and Sunkar, 2005). In general accumulation of organic and inorganic solutes in the cell is one of main physiological response of plant to salt stress. Proline accumulation under salt or drought stress is usually considered as an organic compatible osmolyte and a protecting agent or the activity of intracellular molecules (Tang, 1989). Studies indicate that proline has protecting role in plant growth and productivity by reducing the production of free radicals and/or scavenging the free radicals (Jain et al., 2001). (Shi and Sheng, 2005) clearly showed that proline contents in sunflower leaves increased with rising salinity stress; the degree of increase also tended to be higher with upsurges in salinity.


Experiment No. 1: Response of different Sunflower genotypes at different levels of salinity stress (Hydroponics study)

This study will be carried out at Saline Agriculture Research Centre, University of Agriculture, Faisalabad. The healthy seeds of 10 Sunflower genotypes will be sown in trays having 2 inch layer of gravels. At two leaf stage, the seedlings will be wrapped with foam at root shoot junction, will be transplanted in thermo pole sheets with holes in them floating on 200 L capacity iron tub, lined with polythene sheet containing ½ strength Hoagland's solution. Aeration will be given by bubbling air through the nutrient solution 8 hours a day. The solution will be changed every week. The design of the experiment will be CRD with three replicates. After one week of transplanting, salinity of 60, 120 and 180 mM NaCl will be developed step wise with NaCl, whereas, in control no salt will be added. The pH will be maintained 6.5± 0.5 throughout the experiment. Plants will be harvested after 40 days of imposition of salinity and data about shoot fresh weight, Shoot dry weight and root dry weight will be recorded. The fully expanded third leaf will be sampled and used for the determination of Na+, k+ and Cl- in the leaf sap. Leaf Na+ and K+ will be determined using the flame photometer and Cl- using Chloride analyzer. The data will be analyzed through suitable statistical package.



Growth conditions:

Healthy seeds of selected genotypes (Two tolerant, two sensitive) will be sown in ½ strength Hoagland's nutrients solution as described in experiment-1.After three days of transplanting required salinity levels (Control and 140 mM NaCl) will be developed with NaCl salt in three increments whereas no salt will be added in control; with supply of B-nutrition as H3BO3 i.e. Adequate level, 2.5mM and 5.0 mM.


At harvest, fresh and dry weight of roots and shoots will be measured. Plants from each genotype of same treatment will be harvested at 15 and 30 days after sowing and separated into leaves and stems after observing fresh shoot and root weight. RGR will be calculated .Leaf area will be measured by using a leaf area meter. Na+, K+, Cl- and B contents will be determined with flame photometer, chloride analyzer and spectrophotometer respectively.

Statistical analysis:

Statistical analysis will be also done by using some reliable statistical package



Growth conditions:

Growth conditions and treatments will be same as described in experiment-2.


At harvest, fresh and dry weight of roots and shoots will be measured. Leaf water potential (Ψ) and osmotic potential (Ψπ) from the middle of the second youngest fully developed leaf blade will be measured. Turgor pressure (Tp) will be estimated from the difference between Ψπ and Ψ. For the determination of chlorophyll contents hand held SPAD-502 meter will be used. Relative water contents (RWC), membrane stability index (MSI) in leaves will also be determined.

Statistical analysis:

Statistical analysis will be also done by using some reliable statistical package.



Growth conditions:

A pot culture experiment will be conducted to study the effect of boron supply on growth and yield of sunflower in salt-affected soils, using four sunflower genotypes screened from the first experiment (Two tolerant and two sensitive) in the wire house of Saline Agriculture Research Centre, University of Agriculture Faisalabad. Soil will be collected from the soil surface (0-15 cm) and analyzed for physiochemical properties. The soil will be air dried and passed through 2 mm sieve and thoroughly mixed. Glazed pots will be filled with 12 kg soil per pot. Six seeds of each genotype will be sown in each pot and thinning will be done fifteen days after germination to maintain two plants per pot. The recommended doses of N, P and K will be applied.

The desired level of salinity (140 mM NaCl) and Boron (5ppm) will be developed by adding calculated amount of NaCl and H3BO3.


At final harvest shoot length, shoot fresh and dry weight will be determined.

Na+, K+, Cl- and B contents will be determined with flame photometer, chloride analyzer and spectrophotometer respectively. For the determination of chlorophyll contents hand held SPAD-502 meter will be used. Proline in leaves will also be determined. At maturity data regarding 1000 achene's weight, number of achene's per head. Head diameter and oil contents will be recorded. Data will be subjected to reliable statistical package.


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