Morpho-physiological And Antioxidants Enzymes Response In Scented Rice Mediated By Mineral Element And Plant Growth Regulator Under Induced Cadmium(Cd) Stress

Pollution in paddy fields by Cd toxicity has attracted attention from global researchers due to the detrimental effects on growing plants and animals especially humans.Four independent but related researches have been undertaken to clearly understand the dynamics of varying soil Cd toxicity and how fragrant rice cultivars react to such toxicity under varying conditions.In the first research,an effort was made to evaluate cadmium influence on fragrant riceseedlings at vegetative stage.The experimental trials were laid out in a randomized complete block design comprising five varying fragrant rice cultivars?V1=Meixiangzhan 2,V2=Xiangyaxiangzhan,V3=Guixiangzhan,V4=Basmati and V5=Nongxiang 18?and four Cd levels(0,50,100 and 150 mg/kg^-1 soil).Antioxidant enzymes,lipid peroxidation?in terms of melanodialdehyde?MDA?and hydrogen peroxide?H₂O₂??,growth parameters?plant height,and total dry matter content?and Cd uptake in seedlings exposed to varying Cd levels were examined.The results revealed that,at increased levels of soil Cd toxicity,antioxidants enzymes were disrupted.lipid peroxidation was found released in Cd induced plants in higher toxic treatments.Concentration of Cd in roots and in shoots for the cultivars studied increased as the soil Cd concentrations was eleviated.Cadmium contents was found higher in the roots than in the stems and then leaves with V1and V5 cultivars showing maximum uptake in all plant parts.While V3 cultivar had less Cd accumulated in all plants organs.The results imply that,Cd toxicity have negative impacts on rice growth.Rice roots had higher Cd than shoots and uptake varies amongst cultivars.Conclusively,Cd toxicity impaired early growth in rice by affecting physio-biochemical rice seedlings attributes,however,cultivar V3 performed better than the other four cultivars with regards to Cd toxicity tolerance.In the second experiment,the focus was on examining Cd toxicity effects on fragrantrice genotypes and its consequences on yield,yield related parameters and rice grains quality traits.Randomized complete block design comprising five varying aromatic rice cultivars?V1=Meixiangzhan 2,V2=Xiangyaxiangzhan,V3=Guixiangzhan,V4=Basmati and V5=Nongxiang 18?and four Cd levels?0,50,100 and 150 mg/kg soil?were used.The findings revealed that,increased levels of soil Cd toxicity can also caused Cd uptake in roots and distribution to other organs increased.Cadmium was higher in roots compared to shoots with maximum uptake seen in Meixiangzhan 2 cultivar,followed by Nongxiang 18,Basmati,Xiangyaxiangzhan and Guixiangzhan cultivars.As Cd toxicity increased,yield and yield parameters were affected in all cultivars.Grain quality was also found affected under Cd stress condition.Antioxidants enzymes were found disrupted with more lipid peroxides released to higher induced Cd affected plants.The results manifested that soil Cd toxicity have negative impacts on rice performance and uptake varies amongst cultivars.Conclusively,Cd toxicity impaired rice yield formation and rice grain quality by altering yield components(panicles number,spikelet per panicles,spikelet setting?%?,however,Guixiangzhan variety performed better,while Meixiangzhan 2 performed less in terms of minimum Cd uptake and distribution to grains,yield and grain quality reduction under induced Cd stress condition.In the third research,the role of calcium(Ca²⁺)in preventing oxidative damage underinduced Cd²⁺toxicity in fragrant rice genotypes?Oryza sativa L.?grown in pots was examined.Trials were spread out in a randomized complete block design with two varying scented rice cultivars?Guixiangzhan and Meixiangzhan 2?.The results manifested that,as Cd toxicity increased,activities of antioxidant enzymes?Superoxide dismutase?SOD?,peroxidase?POD?,and Catalase?CAT??were disrupted at higher induced toxic level,but with Ca supplementation,antioxidant enzymes were augmented,plants osmolyte accumulation?proline,protein and soluble sugar?increased under Ca mediated growth while decreased under Cd stress condition,lipid peroxidation?in terms of melanodialdehyde?MDA?,Hydrogen peroxide?H₂O₂?and Electrolyte Leakage?EL??were all found increased in increased level of soil Cd,while in applied Ca treatments,a reduction of MDA,H₂O₂ and EL accumulation was observed,pigments of photosynthesis?chlorophyll a,b as well as carotenoids?were reduced in induced Cd treatments,while increased at treatments with applied Ca,yield and yield parameters were enhanced in Ca applied treatments and reduced under Cd treatment,Cd accumulation in plants parts as well as panicles and in grains for both cultivars increased with increased toxicity and reduced under Ca applied treatments.Cadmium uptake was more in roots than in shoots with Meixiangzhan 2 showing the highest uptake in roots,shoots,leaves and grains.The results showed that soil Cd toxicity have negative impacts on rice growth and Ca can serve as an amendment.Conclusively,Cd toxicity impaired rice growth by affecting physio-biochemical and morphological attributes,while Ca mitigates Cd toxicity by minimizing damage caused by oxidation in rice.The fourth experiment examined the possible role of exogenous application of MethylJasmonate on rice yield,rice grains quality and other essential elements in scented rice cultivars grown in induced cadmium stress conditions.Trials were arranged in a randomized complete block design with two different rice genotypes?Guixiangzhan and Meixiangzhan 2?.The findings revealed that,under Cd toxicity,rice yields,rice grains quality and mineral elements accumulation in grains were disrupted,but with Methyl Jasmonate supplementation,rice yields,grain quality and mineral elements accumulation were augmented,The results further manifested that Cd in roots,stems,leaves and in grains for both cultivars increased under induced soil Cd treatment only,while reduced under Methyl Jasmonate applied treatments.Uptake was more in roots than in shoots with Meixiangzhan 2 showing the maximum uptake in roots,shoots,leaves and grains as compared to Guixiangzhan culture under similar agronomic condition.The results suggested that soil Cd toxicity have negative consequences on rice yields,grain quality traits and mineral elements accumulation while Methyl Jasmonate can be used as an amendment.