Response of Wheat Seeds Grown under NaCl and ZnCl₂ Stress

Aisha Auwal, Jibrin Ashiru Ibrahim, Vimlendu Bhushan Sinha*

Department of Biotechnology, School of Engineering and Technology, Sharda University, Greater Noida, Uttar Pradesh - 201306, India

*Corresponding Author E-mail: vimlendusinha@gmail.com; vb.sinha@sharda.ac.in

Abstract:

The study was undertaken to study the effect of salt (NaCl) and heavy metal (ZnCl₂) stress on germination of selected wheat cultivar. Seeds were subjected to salt stress (0, 25, 50, 75, and 100 mM) for NaCl and heavy metal stress (0.05, 0.5, 5, and 50 µg/ml) for ZnCl₂which elucidated their physiological response towards them. About 100 % germinaton was obtained for all the salt treatments except 100 mM concentration, where 40 % germination was obtained which indicate a significant decrease in the germination percentage, germination rate, and appearance of leaves as the concentration increases with an increase in the salt concentration. For ZnCl₂, results for these parameters increased as the concentration was increased. However, highest average fresh weight, dry weight and shoot length were observed in 75 mM (NaCl) treatment concentrations and lowest in 25 mM and 100 mM concentration. For ZnCl₂, highest average fresh weight, dry weight and shoot length were observe in 5 µg/ml, 0.5 µg/ml and 5µg/ml concentrations respectively and the lowest were found in 0.05, 5 and 0.5 µg/ml concentrations respectively. The seedling when accessed for RWC, then it was observed that those having high RWC are more resistance against salinity stress.

KEY WORDS: Germination, Wheat, Abiotic stress, physiology, RWC

Introduction:

Wheat is an annual crop belonging to Gramineae family and has originated from South Western Asia. It is reported to be the major agricultural commodity since, and grown as both spring and winter crop. It has been used as food by plants and animals as it provides more calories than any other food crop (Hanson et al. 1982; Cheftel et al. 2002). Wheat is known to grow in wide environmental ranges including temperate areas, less and high rainfall areas, warm and humid climatic conditions and also extreme low temperatures (Paliwal et al. 2012).

Wheat and other plants are exposed to unavoidable environmental regimes conditions, such as heat, flooding, drought, cold, salinity, heavy metals, UV radiations etc, which are collectively known as abiotic stresses. Seed germination represents the most crucial or the most sensitive stage of a plants growth especially in the presence of environmental stresses (Keys et al. 1975). Success of seed germination under stress provide the agriculturists to study the outcome till the complete growth and development cycles that easily cope up together with the environmental stresses. Abiotic stress leads to deterioration of the environment, affects optimum germination of seeds and cause crop loss and thus, reduces the overall average yields (Mizoi et al. 2013; Roy et al. 2011). Salinity is among the most important factor limiting the productivity of agricultural crops affecting germination, plant vigor and crop yields (Munns and Tester, 2008). Photosynthesis, protein synthesis, energy and lipid metabolism are the processes which affect the onset and development of salt stress within a plant, (Parida and Das, 2005). Initially, when plants are exposed to long term salinity, they experiences water stress, which in turn leads to a reduction in expansion of leaves. The osmotic effects of salinity stress can be observed after salt application and continue for the complete time of exposure, leading to distorted cell expansion, inappropriate cell division, and uneven stomatal operations may be due to reduction in photosynthetic area (Flowers, 2004; Munns, 2002; Cramer and Nowak, 1992). In a nut shell, excess sodium and chloride ion affects plant enzymes which causes swelling of the cell, leading to a decrease in the amount of energy being produced together with some physiological changes. Ionic stress results in senescence of older leaves and shows some toxicity symptoms such as necrosis and chlorosis, which appears in mature leaves due to high Na⁺ which affects the plant by disrupting protein synthesis and interfering with the major enzyme activities by disturbing physiological and biochemical processes like photosynthesis, antioxidant phenomenon, and nitrogen metabolism (Hasegawa et al. 2000; Munns, 2002; Verslues et al. 2006; Fan et al. 2015). An important abiotic factor limiting plant germination and early seedling stages is water stress which is brought about by drought and salinity and are wide spread problems in the world (Al Mansouri et al. 2001); Soltani et al. 2006). Factors such as: delay in the onset, reduction in the rate and increase in the dispersion of germination events, and finally crop yield are caused by salinity stress (Ashraf and Foolad, 2005). Interestingly, salinity and drought have been reported to affect the plant in a similar way as both results into the reduced water potential as a common consequence (Legocka et al. 2005). Different palnt species behave differently for germination rate and seedling growth when they are subjected to salt stress and this has contributed towards differences in germination characteristics of different plant species (Besma and Mounur, 2010). Interestingly, for breeding purposes, the resistance to various stresses may be combined and may create opportunities for better yield of wheat varieties (Shpiler and Blum, 1986; O’Toole and Stockle, 1991). Heavy metals stress causes stunted growth, blockage of key metabolic enzymes for various processes, increased toxicity, ecosystem disturbance and industrial pollution (Kaur et al. 2012; Sharma and dubey, 2005). The present study was undertaken with the objective to study morphological and physiological effects of heavy metal and salinity on the studied wheat variety.

MATERIAL AND METHODS:

Procurement and viability testing of of seeds:

The seed of wheat cultivar (PBW550) was procured from Tarai Agri Seeds, Pantnagar, Uttarakhand, India. The procured cultivars was checked for viability by germinating about three hundred seeds in controlled conditions.

Determination of seeds with maximum frequency of occurrence:

About 4000 seeds were randomly weighed on weighing balance for determining the weight of the seeds corresponding to maximum frequency of occurrence.

Effect of salt stress and ZnCl₂ on wheat seeds:

A laboratory experiment was conducted to examine the effect of saline solutions on germination qualities of seeds. The cultivars were washed with deionized water and dispersed in petridishes (25 seeds per petridish) on a wet filter paper. The solutions used to moisten the filter paper contained NaCl (0, 25, 50, 75, 100 mM) and ZnCl₂ (50, 5, 0.5 and 0.05 µg/ml). Seeds were germinated at room temperature of 25±2 °C. Radicle emergence to a length of 2-5mm was the criterion for seed germination. Germination was recorded everyday continuously for 15days at every 24 h interval.

Calculation of Timson’s index efficiency:

Germination efficiency and Timson’s index was calculated using standard statistical procedures and method described by (Patade, et al. 2011).

Determination of RWC in treated seedling:

The fresh weight samples were weighed, submerged in distilled water and finally were dried at 48^oC for 72h (after weighing) and weighed again. RWC was calculated according to (Dhopte and Manuel, 2002) formulae

RWC= ((FW-DW)/(TW-DW))×100

Where, FW is fresh weight, DW is dry weight and TW is turgor weight of plant sample.

RESULTS:

Determination of modal weight of the seeds:

The seeds corresponding to 42 mg weight were found to have the highest occurring frequency and thus, were selected as the sample seeds for experimental set up.

Germination of wheat cultivars under differential NaCl and ZnCl₂stress conditions:

Germinated seeds were recorded every 24 hours for 10 days. Result for control showed that germination of all seeds. For NaCl, the result showed that 100 % seeds germinated at 25, 50 and 75 mM concentrations whereas only 40 % seeds germinated at 100 mM concentration under salt stress. However, the seeds grown under ZnCl₂ stress were able to depict 100 % germination rate (Fig 1).

Emergence of radical, plumule and their survival till the opening of cotyledonary leaves:

The seeds when observed for radical, plumule and cotyledonary leaves emergences depicted that out of 100 % germination obtained for NaCl under varying conditions produced a variable result of a maximum of 45 % survival in 20 mM stress condition and a minimum of 25 % in 100 mM stress condition as compared to that of control (Table 1). Under heavy metal stress the lowest survival rate was obtained for 50 µg/ml concentration and the highest was obtained for 0.05 µg/ml treatment (Table 2).

Table.1. No of radicle, plumule and leaves

Development germination of plants	Control	20mM	50mM	75mM	100mM
No of radicle	25	25	25	25	10
No of plumule	25	25	25	25	10
No of cotyledonary leaves	25	11	10	9	6

Table.2. Effect of Zncl₂ on wheat seeds at different concentrations of heavy metals.

Development germination of plant/ ZnCl₂ (µg/ml)	Control	0.05µg/ml	0.5µg/ml	5µg/ml	50µg/ml
No of radicle	25	25	25	25	25
No of plumule	25	25	25	25	25
No of leaves	25	18	12	12	8

Determination of average weight, dry weight of plants and RWC:

Highest RWC was observed in control condition. However, initially for both salt and heavy metal stress solution corresponding to 38.25%, whereas in NaCl the RWC was quite low as compared to the control set but showed gradual increase with increasing stress level (Fig 2 and 3).

DISCUSSION:

The study was carried out with the objective to study the effect of salt stress and heavy metal stress which affects the germination potential of studied wheat cultivar. Salinity stress limits plant germination and early seedling stages and has become a widespread problem of the world (Almansouri et al. 2001; Soltani et al. 2006; Misra and Dwivedi 2004). In this study seeds with highest frequency of occurrence were selected as the seeds to be used for precisely studying the effect of stress, which was done in order to maintain the same cotyledonary content for the experimental set up. In general, the highest germination percentage occurs in non salty conditions and it decreases depending on the ascending salt concentrations. Salinity in the study might have affected the seed germination by decreasing the ease with which the seeds take up water and also might have reduced the intake of toxic ions by changing various enzymatic/hormonal activities of the seeds.

The plumule and radicle growth represents an important aspect for salt and heavy metals stress due to their close association with soil for absorbing water from the soil and supply to various parts of the plants. Hence it can be deduced from the work that increasing salinity concentrations causes osmotic and/or specific toxicity reducing the germination percentage and higher concentration produces toxic effects on the embryo which leads to delay and decrease in germination (Majid and Jabad, 2013). Heavy metal stress such as (Zn) is hazardous to human health as well as detrimental to microorganisms, plants and animals. In the experiment carried out, seed germination gradually decreased with an increase in concentration of sodium chloride and also number of leaves decreases with increase in concentration of zinc chloride which happened due to the toxicity of ZnCl₂on root growth and shoot length (Akbari et al. 2011). The RWC are also affected because the plants may have developed negative mechanism for dealing with salinity and heavy meatl stress on cumulative germination and plant growth which may be cultivar specific. However, results of germination percentage/ssed growth/RWC etc. may be due to the ability of these cultivars to tolerate or avoid salinity and heavy metal stress through active salt extrusion, passive salt exclusion or dilution and modified impor/export channels.

CONCLUSION:

Considering the experiment carried out, the effect of salinity stress for all traits was significant. By increase of salinity stress, germination percentage, shoot length, radicle, plumule, leaves were significantly reduced. Stress is minimum at control and lower concentrations but increases as concentration become higher and higher. However, some mechanisms have to be developed to withstand the toxic effects caused by ion accumulation in plants since salinity and heavy metal stresses are significant problems affecting agriculture worldwide causing an osmotic stress, ionic toxicity, thereby disturbing the uptake and translocation of mineral nutrients and are predicted to become a larger problem in the coming decades.

ACKNOWLEDGEMENTS:

The authors are thankful to Sharda University for providing funds for this research.

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Received on 09.05.2016 Modified on 21.05.2016

Research J. Science and Tech. 2016; 8(2):77-82

DOI: 10.5958/2349-2988.2016.00010.3