Phytoecdysteroids: Distribution, Structural Diversity, Biosynthesis, Activity, and Crosstalk with Phytohormones.

Phytoecdysteroids (PEs) are naturally occurring polyhydroxylated compounds with a structure similar to that of insect molting hormone and the plant hormone brassinosteroids. PEs have a four-ringed skeleton composed of 27, 28, 29, or 30 carbon atoms (derived from plant sterols). The carbon skeleton of ecdysteroid is known as cyclopentanoperhydrophenanthrene and has a ß-sidechain on C-17. Plants produce PEs via the mevalonate pathway with the help of the precursor acetyl-CoA. PEs are found in algae, fungi, ferns, gymnosperms, and angiosperms; more than 500 different PEs are found in over 100 terrestrial plants. 20-hydroxyecdysone is the most common PE. PEs exhibit versatile biological roles in plants, invertebrates, and mammals. These compounds contribute to mitigating biotic and abiotic stresses. In plants, PEs play a potent role in enhancing tolerance against insects and nematodes via their allelochemical activity, which increases plant biological and metabolic responses. PEs promote enzymatic and non-enzymatic antioxidant defense systems, which decrease reactive oxygen species in the form of superoxide radicals and hydroxyl radicals and reduce malondialdehyde content. PEs also induce protein biosynthesis and modulate carbohydrate and lipid synthesis. In humans, PEs display biological, pharmacological, and medicinal properties, such as anti-diabetic, antioxidant, anti-microbial, hepatoprotective, hypoglycemic, anti-cancer, anti-inflammatory, antidepressant, and tissue differentiation activity.

Phytoremediation of Cadmium Contaminated Soil Using Brassica juncea: Influence on PSII Activity, Leaf Gaseous Exchange, Carbohydrate Metabolism, Redox and Elemental Status.

Phytoremediation is an ecologically and economically feasible technique to remove heavy metal from soil. The aim of the study was to examine cadmium (Cd) toxicity and phytoremediation aptitude of Brassica juncea. In the present study, plants survived when exposed to different levels of Cd (0, 25, 50 and 100 mg/kg soil) and accumulated a large amount of Cd in its root and shoot. Translocation factor (TF) of Cd from root to shoot was > 1 at both 45 and 60-day stage of growth suggesting that B. juncea is a hyperaccumulator and strong candidate for phytoextraction of Cd. Alongside, Cd impaired photolysis of water, PSII activity, nutrient uptake, photosynthesis and sugar accumulation in the plant. Cd-generated oxidative stress restricts the growth of B. juncea. The toxic effect of Cd was more pronounced at 45-day stage of growth signifying the drifting of plant towards acquirement of exclusion strategy.

Effect of cadmium on the growth and antioxidant enzymes in two varieties of Brassica juncea.

Increasing contamination and higher enrichment ratio of non-essential heavy metal cadmium (Cd) induce various toxic responses in plants when accumulated above the threshold level. These effects and growth responses are genotype and Cd level dependent. An experiment was conducted to analyze the effect of Cd toxicity in Brassica juncea [L] Czern and Coss by selecting its two varieties Varuna and RH-30. Cadmium (0, 25, 50 or 100 mg CdCl2 kg(-1) of soil) fed to soil decreased the values of growth characteristics, activity of nitrate reductase and leaf water potential, whereas activities of antioxidant enzymes and proline content increased with the increasing concentration of Cd, observed at 30 and 60 day stages of growth, in both the varieties. Moreover, Cd uptake by the roots was higher in RH-30 than Varuna. Also the activity of antioxidant enzymes and proline accumulation were higher in Varuna with increasing soil level of Cd. Out of the two varieties, Varuna was more tolerant than RH-30 to Cd stress.

Regulation of growth and photosynthetic parameters by salicylic acid and calcium in Brassica juncea under cadmium stress.

Cadmium, a non-essential and toxic metal, negatively affects plant growth and productivity, and alters the plant's physiological processes necessary for its survival. The present study was designed to explore the individual and combined effects of calcium and salicylic acid (SA) on the morphology and physiology of Brassica juncea L. cv. Varuna under cadmium stress. The application of calcium (2 mM) through the soil and/or SA (10-5 M) as foliar spray enhanced the growth, photosynthetic parameters, and proline content determined after 45 days of treatment. The application of cadmium (6 mg kg-1) through the soil was toxic and decreased both growth and the photosynthetic parameters. The application of calcium and SA in combination was most effective in alleviating the harmful effects of cadmium on growth and photosynthesis. Calcium and SA clearly induced plant protection mechanisms by enhancing proline and chlorophyll accumulation in the leaves.

Protection of growth in response to 28-homobrassinolide under the stress of cadmium and salinity in wheat.

This study examines the impact of 28-homobrassinolide (HBL) in alleviating the effects of cadmium (Cd) and salinity (NaCl) on wheat plants solely and against the synergy. The surface sterilized seeds of Triticum aestivum cv. PBW-373 were sown in the soil amended either with salinity or cadmium or both. The foliage in was sprayed at 20d after sowing (DAS) both in stressed and non-stressed plants. The spray of HBL at 20 DAS increased almost all the parameters while decreased the H2O2 content and lipid peroxidation in the leaves. The presence of cadmium and/or salinity decreased the values for all the growth and photosynthetic parameters but improved the activity of antioxidant enzymes and proline content in 30d old plants. However, the ill effects observed under NaCl and/or Cd treatment were completely overcomed by the spray of HBL to the plants at 20d stage. The spray of HBL to stressed plants further increased the antioxidant enzyme activities and proline content thereby giving tolerance to the plants against the stress.

Soil cadmium enrichment: Allocation and plant physiological manifestations.

Cadmium (Cd) in soil is enriched through several leaky management agricultural practices and natural resources. Cd enriched soil is inevitable cause of nutritional stress besides Cd induced toxicity symptoms and physiological malfunctions. Redox signals shift toward oxidative stress which accelerates cellular damage and elicits defense mechanism at the cost of growth. Plants get enriched with this toxic, abundant and undesirable element through 'mineral uptake system' non-specifically. Different components and pathways have been marked cooperating in cellular sequestration and systemic localization of Cd, escaped from avoidance and efflux. Cd induced metabolic alteration led to electron leakage as ROS, reduced photosynthesis and carbon fixation. Compromised primary metabolism negatively feedbacks the plant growth, result into loss of potential crop yield.

Foliar spray of brassinosteroid enhances yield and quality of Solanum lycopersicum under cadmium stress.

The presence of cadmium in the soil above a particular level is proposed to check not only plant growth but also productivity and fruit quality. Therefore, in the present study investigations are directed to evaluate the effect of four levels of cadmium (3, 6, 9, 12 mg kg(-1)) in interaction with two analogs of brassinosteroids on the growth, fruit yield and quality of tomato. Under greenhouse conditions plants were analyzed for antioxidant system activity and photosynthetic assimilation efficiency. Cd stressed plants exhibited poor growth and biological yield. The metal also had a negative impact on the antioxidant system of the resulting fruits. However, the follow up application of BRs (10(-8) M) neutralized the damaging effects of the metal on the plants.

Brassinosteroids protect photosynthetic machinery against the cadmium induced oxidative stress in two tomato cultivars.

The present study was conducted with an aim to gain better insight of brassinosteroid generated response on the effects of cadmium on photosynthetic machinery and active oxygen metabolism in two tomato cultivars (K-25 and Sarvodya). These tomato cultivars were subjected to graded cadmium levels in soil (0, 3, 6, 9 or 12 mg kg(-1) soil) with their foliage being sprayed with 0 or 10(-8) M of 28-homobrassinolide/24-epibrassinolide (HBL/EBL) at 59 d stage. The results suggested that photosynthetic parameters, leaf water potential and activity of several enzymes (nitrate reductase and carbonic anhydrase) decreased significantly in both the cultivars, to a lesser extent in K-25 than Sarvodya with the increasing levels of cadmium in the soil. However, the activity of antioxidant enzymes and proline content increased in response to metal treatment as well as the application of brassinosteroids (HBL/EBL). Overall, exogenous application of brassinosteroids improved the activity of photosynthetic machinery and that of antioxidant defense system in both the cultivars, and also nullified the damaging effect of metal on these parameters.

Protective response of 28-homobrassinolide in cultivars of Triticum aestivum with different levels of nickel.

Seeds of five wheat (Triticum aestivum) cultivars (PBW-373, UP-2338, DL-LOK-01, DL-373, and HD-2338) were sown in earthen pots and 10-day-old seedlings were exposed to 0, 50, and 100 µM of nickel (Ni) in the form of nickel chloride. At the 20-day stage, seedlings were sprayed with 0.01 µM of 28-homobrassinolide (HBL). The results of the experiment at the 30-day stage revealed a decline in the dry mass per plant, leaf area, leaf water potential, and net photosynthetic rate with concomitant decline in the activities of various enzymes (viz. carbonic anhydrase and nitrate reductase) with an increasing concentration of Ni. However, an increase in proline content and the activities of catalase, peroxidase, and superoxide dismutase was observed as a result of an increase in Ni concentration. Moreover, the treatment of these stressed plants with HBL enhanced the activities of carbonic anhydrase and nitrate reductase, catalase, peroxidase, and superoxide dismutase. The proline content in the leaves also increased, which is known to act as an osmolyte and reactive oxygen species scavenger. The toxic effects generated by Ni were ameliorated by HBL through an improved antioxidant system and osmolyte. Moreover, improvement of photosynthetic parameters and growth characteristics further strengthen our belief that HBL acted as a potent stress alleviator.

Brassinosteroids protect Lycopersicon esculentum from cadmium toxicity applied as shotgun approach.

Surface-sterilized seeds of two tomato cultivars (cv. K-25 and Sarvodya) were soaked in 100 microM CdCl(2) for 8 h (shotgun approach). The resulting 59-day-old seedlings were sprayed with 10(-8) M of 28-homobrassinolide (HBL) or 24-epibrassinolide (EBL) to their foliage. Both cultivars showed significantly different response to Cd stress. Cadmium severely restricted the growth, photosynthetic efficiency, and activity of nitrate reductase (E.C. 1.6.6.1) and carbonic anhydrase (E.C. 4.2.1.1) in Sarvodya as compared to K-25. However, the activities of antioxidative enzymes were significantly higher in K-25. This result may be considered an indication of better tolerance of the K-25 cultivars to Cd stress. Moreover, the spray of both the brassinosteroids (HBL/EBL) were found very effective in neutralizing the adverse effects generated by metals that reflect in better photosynthetic performance by the cultivars. An interesting aspect of this study is that HBL or EBL spray caused a further increase in proline content and antioxidative enzyme activities, which were already enhanced by Cd stress. This effect of brassinosteroids (HBL/EBL) was more pronounced in K-25 than in Sarvodya, representing the tolerance and adoptable behavior of K-25.