Effect of Plant Growth Regulators on Chlorophyll Content and Relative Water Content of Green Gram under Salinity
Abstract
An investigation was carried out in green gram CO8. The objective of the experiment was standardization of NaCl to study the effects of salinity during seed germination of green gram and to study the response of green gram treated with plant growth regulators to salinity. In laboratory study, the standardization of NaCl was done first by using 75mM, 100mM, 150mM and 200mM NaCl. Among the four concentrations, 50% germination was observed in 150mM NaCl and it was standardized for further experiment. The plant growth regulators used were T3: NAA 100ppm, T4: NAA 200ppm, T5: kinetin 50ppm, T6: kinetin 100ppm, T7: GAᴣ 100ppm, T8: GAᴣ 200ppm along with T1: Absolute control and T2: Control (150mM NaCl). The experimental results showed a decrease in seedling growth due to salinity but with the seed treatment with the above mentioned PGRs showed an increased stress tolerance index, chlorophyll content and relative water content. The seeds treated with GAᴣ 200ppm recorded the maximum stress tolerance index (STI) (83.09) as well as higher relative water content (88.44%). While the seeds treated with kinetin 100ppm recorded the maximum chlorophyll content (1.22 gm/g). The whole study revealed that, in laboratory condition, with the imposition of salinity stress by 150mM NaCl, the seed treatment with GAᴣ 200ppm responded better compared to other treatments.
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Introduction
Green gram (Vigna radiata), also called Mungbean is a pulse crop from botanical family of Fabaceae. It is a warm season, frost-intolerant plant and suitable for being planted in temperate, sub-tropical and tropical regions. The most suitable temperature for mung bean'sgermination and growth is 15-18 °C. It has high adaptability to various soil types, while the best pH of the soil is between 6.2 and 7.2. Since, it is a short-day plant, long day condition will delay its flowering and podding. Salinity is one of the most important abiotic stress factors limiting plant growth and productivity (Flowers, 2004). Salinity affects almost every aspect of the physiology and biochemistry of plants and significantly reduces yield. High exogenous salt concentrations affect seed germination, induce water deficit, cause ionic imbalance of the cellular ions resulting inion toxicity and osmotic stress (Khan and Panda, 2009). Specific effects of salt stress on plant metabolism have been related to the accumulation of toxic Na+ and Cl-ions or to K+ and Ca2+ ions depletion (Sreenivasulu et al., 2000). As a consequence of ion imbalance and hyperosmotic stress, which are primary effects of salt stress, secondary stress such as oxidative damage may occur (Rahman et al., 2018). Plant hormones, also known as phytohormones, are small chemical messenger that are produced within the plant at extremely low concentrations and plays a crucial role in plant growth and development by co-ordinating their cellular activities. It control all aspects of plant growth and development, from embryogenesis, regulation of organ size, pathogen defence, stress tolerance and up-to reproductive development. Aziz Khan et al., (2009) concluded that phytohormones are known to play vital roles in the ability of plants to acclimatize to varying environments, by mediating growth, development, source/sink transitions and nutrient allocation.
Auxin plays an important role in cell elongation in the shoot, apical dominance, root initiation, prevention of abscission, induction of parthenocarpy, stimulation of respiration, activate cell division and induce callus formation, induce vascular differentiation in plants. NAA is a synthetic plant hormone in the auxin family and is an integral component in many commercial plant rooting horticultural products. It is a rooting agent and used for the vegetative propagation of plants from stem and leaf cuttings. It is also used for plant tissue culture. Kinetin is a cytokinin derivative which promotes cell division and plant growth. It has been shown to naturally exist in DNA of organisms including humans and various plants. While kinetin is used in tissue cultures to produce new plants, it is also found in cosmetic products as an anti-aging agent. Gibberllic acid, a plant hormone stimulating plant growth and development is a tetracyclic di-terpenoid compound. GAs stimulate seed germination, trigger transitions from meristem to shoot growth, juvenile to adult leaf stage, vegetative to flowering, determines sex expression and grain development along with an interaction of different environmental factors viz., light, temperature and water (Sivakumar R et al., 2018).
Conclusion
The objectives of the study were to find the effects of salinity during seed germination of Greengram and to study the effect of the plant growth regulators in response to salinity stress during the seed germination in Greengram (Figure 3). The NaCl solution was first standardized so that the resulting germination would be in the range of 50%. This is done with the trial of germinating the seeds with different concentrations NaCl solutions, such as 75 mM, 100 mM, 150 mM and 200 mM solutions. In these the 150 mM NaCl solution yielded the desired result and this solution was used for the study going forward. The seeds are treated by soaking the seeds with the 100 ppm (T3) and 200 ppm (T4) of NAA, 50 ppm (T5) and 100 ppm (T6) of Kinetin and 100 ppm (T7) and 200 ppm (T8) of GA3, for 8 hours. Then the treated seeds are places in the germination papers and are regularly saturated with the 150 mM NaCl solution except for the Absolute control which is saturated with normal irrigation water.
T1:Absolute control T5:Kinetin 50 ppm T7:GA3 100 ppm T8:GA3 200 ppm (Without salinity)
FIGURE 3: Effect of plant growth regulators on seedling growth of Greengran CO8 under salinity Stress tolerance index (STI) indicates the tolerant potential of the plants during stress. In this present investigation the STI of GA3 200ppm (T8) treatment noticed up to (70%) with high stress tolerance index compared to control followed by GA3 100ppm (T7) (6.8%). This increment may be due to GA3 200ppm (T8) induced germination, vigour index, shoot and root length under saline environment.
There was a decrease in the total chlorophyll content upto 92%, chlorophyll a upto 90% and chlorophyll bupto 93% compared to the control in response to the 150 mM NaCl treatment. The seeds treated with the Kinetin 100 ppm (T6) had a high chlorophyll content of 92%. Relative water content was decreased up to 26.59% by salinity stress. This might be due to high level of sodium chloride changed the water potential and decrease the water absorption of the plant, hence Relative water content is decreased. Reduction in relative water content was a common effect of salinity stress. GA3 200 ppm (T8) had increased the relative water content upto 26.59%.
