Effect of elevated fluoride levels on hydrolysis of starch during seed germination and alteration in antioxidant system in wheat (Triticum aestivum L.) plants.
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Date
2022
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Department of Plant Physiology, Institute of Agricultural Sciences, Banaras Hindu University, Varanasi
Abstract
Experiments were conducted during rabi 2019-20 and 2020-21to examine the influence of increased fluoride concentrations in growth medium on hydrolysis of starch and starch hydrolysing enzymes during seed germination, and enzymatic and non-enzymatic anti-oxidant systems, bio-membrane stability, chlorophyll stability at different stages of growth and yield and yield attributes of wheat genotypes HUW-234.Germination related experiments were carried out at 0 (T1), 100 (T2), 200 (T3) and 300 (T4) ppm fluoride and pot culture experiments were carried out at 0 (T1), 100 (T2), 200 (T3) and 300 (T4) mg fluoride kg-1 soil.
It is nited that root and shoot lengths, fresh as well as dry weights of shoot and root reduced while root: shoot weight ratio increased with increased fluoride concentrations in germination medium. In germinating seeds increased fluoride concentrations decreased the activities of α-, β- and total amylases. Concentrations of soluble sugars in germinating seeds increased as fluoride levels in germination medium increased while starch and free amino acids concentrations decreased.Visible signs of fluoride toxicity were observed in the form of thinner stem and stunted growth.
Total chlorophyll content in leaves was the maximum at 60 days after sowing (DAS), after which it declined. Nevertheless, increased fluoride levels in the root zone resulted in decrease in chlorophyll content.As fluoride levels in soil increased, activities of superoxide dissimulate, peroxidase and polyphenol oxidase increased, however, activities of ascorbate peroxidase and catalase decreased.Proline and malondialdehyde (MDA) contents increased with increased fluoride toxcity.With advancement in growth and increase in fluoride concentrations in root zone chlorophyll stability index and membrane stability index declined.
Days required for 50% spike emergence and 50% anthesis increased as fluoride concentration in soil increased, whereas days for physiological maturity decreased resulting in reduced grain filling duration.Total dry matter plant-1, number of effective tiller plant-1, spikelets spike-1, spike length, grains spike-1, test weight and harvest index decreased as fluoride levels in the soil increased. Major reduction in yield plant-1 was due to reduction in productive shoots plant-1 followed by grains spike-1 and grain size (1000 grain weight). It is conclude that fluoride toxicity reduces seedling germination and vigour in wheat by decreasing seed hydration. F toxicity induces seed stored starch hydrolysis but decreases utilization of soluble sugars by developing seedlings resulting in poor seedling vigour. Fluoride toxicity imposes oxidative stress to plants and it causes variable effects on ROS scavenging enzymes. NaF induced fluoride toxicity reduces N, P and K contents in wheat straw and seeds. F toxicity reduces grain yield by reducing productive shoots plant-1, grains spike-1 and grain size. It is concluded that ROS scavenging system is not able to efficiently scavenge fluoride induced increased ROS in wheat, resulting in membrane damage and decrease in CSI and MSI. It is also concluded that decrease in germination and seedling vigour causes poor plant stand in F rich soils and oxidative stress causes deleterious effects on metabolic processes and cellular functions, resulting in reduction in growth, yield and yield attributes. It is suggested large number of wheat genotypes may be screened for their tolerance/susceptibility to F toxicity to visualize traits/parameters associated with F tolerance crop and to develop F tolerant high yielding wheat genotypes.
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wheat (Triticum aestivum L.)