ACTA PHYSIOLOGIAE PLANTARUM Vol. 28. No. 2. 2006: 137-147
Effect of CaCl2 on growth performance, photosynthetic efficiency and nitrogen assimilation of Cichorium intybus L. grown under NaCl stress Anjum Arshi, Malik Zainul Abdin1 and Muhammad Iqbal* Department of Botany and Centre for Biotechnology1, Jamia Hamdard, Hamdard Nagar, New Delhi-110 062 * corresponding author e-mail:
[email protected]
Key words: CaCl2, chlorophyll, Cichorium intybus, NaCl, nitrogen assimilation, photosynthesis and stomatal conductance
Abstract Pot culture experiments were conducted to assess the extent of growth, photosynthetic efficiency and nitrogen assimilation of chicory (Cichorium intybus L.) as affected by NaCl and CaCl2 alone as well as in combination. Six treatments, i.e., 80 mM and 160 mM NaCl, 5 mM and 10 mM CaCl2 and 80 mM + 10 mM and 160 mM + 10 mM of NaCl + CaCl2 were given to the growing plants separately at three developmental stages, viz., the pre-flowering (30 DAS), flowering (120 DAS) and post-flowering (150 DAS) stages. Each NaCl treatment caused a significant reduction in total plant biomass, photosynthetic rate, stomatal conductance, total chlorophyll content, soluble protein content, NR activity and nitrogen content, although nitrate content increased. On the contrary CaCl2 treatment gave a favorable effect, compared to the control. The effect of combined treatments was similar to that of NaCl but less in magnitude. Thus, the application of CaCl2 may mitigate the adverse effect caused by NaCl.
List of abbreviations: Chl = chlorophyll content; DAS = days after sowing; NR = Nitrate reductase activity; PN = photosynthetic rate; gs = stomatal conductance
Introduction
The phenomena of plant growth and development are variously influenced by environmental factors such as temperature, freezing, water, salinity and nutrients availability (Levitt 1980). Salinity is a common environmental stress that influences plant growth and places major limits on plant productivity in cultivated areas worldwide. Salinity can seriously alter plant metabolic activities such as assimilation of mineral nutrients (Munns et al. 2000, Arshi et al. 2002), stomatal conductance (Brugnoli and Lauteri 1991, Ouerghi et al. 2000), mesophyll conductance (Delfine et al. 1998), carbon metabolism, and/or efficiency of photosynthetic enzymes (Brugnoli and Björkman 1992). Salinity inhibits plant growth via osmotic and ionic effects, and different plant species have developed different mechanisms to cope with these effects (Munns 2002). Osmotic adjustment, i.e. reduction of cellular osmotic potential by net solute accumulation, has been considered an important mechanism of salt tolerance in plants. Reduction in osmotic potential in salt-stressed plants can stem from inorganic ion (Na+, Cl- and K+) accumulations (Hasegawa et al. 2000). The osmotic adjustment in both leaves and roots contributes to the maintenance of water up-
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take and cell turgor, allowing physiological processes, such as stomatal opening, photosynthesis, and cell expansion (Serraj and Sinclair 2002). In addition to their role in cell water relations, organic solute accumulations may help in maintenance of ionic homeostasis and the C/N ratio, and in removal of free radicals and stabilization of macromolecules, such as proteins, protein complexes and membranes (Bohnert and Shen 1999, Bray et al. 2000).
Calcium, an essential plant nutrient useful in stabilization of membranes, signal transduction and control of enzyme activity (Kirkby and Pilbeam 1984, Helper and Wayne 1985), is also reported to be helpful in remediating the adverse effect of salinity on plants. It helps in maintaining membrane integrity and ion-transport regulation and is considered essential for K+/Na+ selectivity and membrane integrity (Hanson 1984). Addition of calcium salts to a complete nutrient solution may alleviate suppression of root growth under high salinity level (Kent and Lauchli 1985).
Given
the above, this study was undertaken to eval u ate the ef fect of CaCl 2 on growth, photosynthetic efficiency and nitrogen assimilation of chicory (Cichorium intybus L.: Asteraceae) grown under salt stress.
Materials and Methods Experimental Set up
Pot culture experiments were conducted at the experimental site of Botany Department in Hamdard University, New Delhi. Seeds of chicory, procured from the Herbal Garden of the University, were sown in earthen pots of (12″ x 12″) in the second week of October. The crop duration was between 180-190 days. The pots were filled with 12.0 kg of soil with pH 7.2, electrical conductivity 0.207 mmhos·cm-1 and farmyard manure (FYM) in the ratio of 2:1. The basal dose of NPK was applied as recommended for chicory crop at the time of pod filling and 20 days after sowing. Four plants per pot were maintained at seedling stage, whereas one plant per pot at pre-flowering, flowering and post-flowering stages. Treatments of NaCl and CaCl2 alone and in combination (NaCl + CaCl2) were given to the growing plants in the form of so-
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lution prepared in double distilled water at the three phenological stages. The controls as well as the treated plants were watered similarly. Care was taken to avoid drainage of solution or water. Sampling and Plant Analysis
Observations were made at 30 days interval from the time of treatments till harvest for each developmental stage i.e. pre-flowering (30 DAS), flowering (120 DAS) and post-flowering ((150 DAS) stages. The number of replicates in each sampling and treatment was five. For the measurement of NR activity, contents of chlorophyll and soluble protein, leaves were taken from the pots in ice bucket. Biomass of the Plant
The plants were dried in oven at 80 °C ± 2 °C. The dry weights of samples, recorded with the help of electronic top pan balance (Eagle, New Delhi, India), were expressed in g. Measurement of Photosynthetic Rate and Stomatal Conductance
Photosynthetic rate (PN) and stomatal conductance (gs) of fully expanded leaves were recorded at each sampling time by using a portable Infra Red Gas Analyser (LI-6200, LICOR Inc., Lincoln, USA) and expressed as µmol CO2·m-2·s-1 and mol·m2·s-1, respectively. The measurements were taken on sunny days at 9:00 to 11:00 a.m. at ambient temperature. Estimation of Chlorophyll Content
Total chlorophyll (chl) content of leaves was estimated according to the method of Hiscox and Israelstam (1979), using Dimethyl sulphoxide (DMSO). The absorbance of the reaction mixture was recorded at 645 and 663 nm with a Beckman DU 640 B spectrophotometer (Fullerton, USA). Estimation of Soluble Protein Content
The total soluble protein content of leaves was estimated by the Bradford’s method (1976). 1.0 g of plant material was homogenized in 5 ml of 0.1 M phosphate buffer (pH 7.5) at 4 °C using pre-chilled mortar and pestle. The homogenate was centrifuged at 5,000 rpm for 10 min at 4 °C. The
EFFECT OF CACL2 ON GROWTH PERFORMANCE, ...
supernatant was mixed with equal amount of chilled 10 % Trichloro acetic acid. This was again cen tri fuged at 3,300 rpm for 10 min. The supernatant was discarded and the pellet was dissolved in 1 ml of 0.1 N NaOH after washing with acetone.
To 0.1 ml of aliquot, 5 ml Bradford’s reagent was added and mixed by vortexing. Absorbance was measured at 595 nm on a spectrophotometer (Beckman 640 B, Fullerton, USA). Protein content was calculated using the standard curve of bovine serum albumin and expressed in mg·g-1 f. w. In Vivo Assay of Nitrate Reductase Activity
The maximum decline in the total biomass (60 %, 54 % and 56 %) was recorded at 180 DAS with 160 mM NaCl treatments given at three growth stages (Fig. 1). Thus the effect of pre-flowering treatment was most profound.
On
the contrary, CaCl2 treatments enhanced the biomass. The enhancement was maximum with 10 mM CaCl2 treatment (up to 18 % with the pre-flowering, 21 % with flowering and 15 % with post-flowering treatments) (Fig. 1). The combined treatments (NaCl + CaCl2) reduced significantly (p
