Shamsul Hayat

Role of proline under changing environments: A review

When exposed to stressful conditions, plants accumulate an array of metabolites, particularly amino acids. Amino acids have traditionally been considered as precursors to and constituents of proteins, and play an important role in plant metabolism and development. A large body of data suggests a positive correlation between proline accumulation and plant stress. Proline, an amino acid, plays a highly beneficial role in plants exposed to various stress conditions. Besides acting as an excellent osmolyte, proline plays three major roles during stress, i.e., as a metal chelator, an antioxidative defense molecule and a signaling molecule. Review of the literature indicates that a stressful environment results in an overproduction of proline in plants which in turn imparts stress tolerance by maintaining cell turgor or osmotic balance; stabilizing membranes thereby preventing electrolyte leakage; and bringing concentrations of reactive oxygen species (ROS) within normal ranges, thus preventing oxidative burst in plants. Reports indicate enhanced stress tolerance when proline is supplied exogenously at low concentrations. However, some reports indicate toxic effects of proline when supplied exogenously at higher concentrations. In this article, we review and discuss the effects of exogenous proline on plants exposed to various abiotic stresses. Numerous examples of successful application of exogenous proline to improve stress tolerance are presented. The roles played by exogenous proline under varying environments have been critically examined and reviewed.

Salicylic Acid Influences Net Photosynthetic Rate, Carboxylation Efficiency, Nitrate Reductase Activity, and Seed Yield in Brassica juncea

Aqueous solutions of salicylic acid (SA) were applied to the foliage of 30-d-old plants of mustard (Brassica juncea Czern & Coss cv. Varuna). The plants sprayed with the lowest used concentration (10−5 M) of SA were healthier than those sprayed with water only or with higher concentrations of SA (10−4 or 10−3 M). 60-d-old plants possessed 8.4, 9.8, 9.3, 13.0 and 18.5 % larger dry mass, net photosynthetic rate, carboxylation efficiency, and activities of nitrate reductase and carbonic anhydrase over the control, respectively. Moreover, the number of pods and the seed yield increased by 13.7 and 8.4 % over the control.

Salicylic acid : a plant hormone

Preface. Contributors. 1. Salicylic acid: Biosynthesis, metabolism and physiological role in plants S. Hayat, B. Ali and A. Ahmad 2. Effects of salicylic acid on the bioproductivity of plants A. Larque-Saavedra and R. Martin-Mex 3. Effect of salicylic acid on solute transport in plants M.S. Krasavina 4. Role of hormonal system in the manifestation of growth promoting and antistress action of salicylic acid F.M. Shakirova 5. Role of salicylic acid in the induction of abiotic stress tolerance T. Janda, E. Horvath, G. Szalai and E. Paldi 6. The role of salicylates in Rhizobium-legume symbiosis and abiotic stresses in higher plants F. Mabood and D. Smith 7. Stress and antistress effects of salicylic acid and acetyl salicylic acid on potato culture technology H.A. Lopez-Delgado, I.M. Scott and M.E. Mora-Herrera 8. Salicylic acid and reactive oxygen species in the activation of stress defense genes L. Holuigue, P. Salinas, F. Blanco and V. Garreton 9. The interplay between salicylic acid and reactive oxygen species during cell death in plants J.F. Dat, N. Capelli, F. van Breusegem 10. Salicylic acid as a defense-related plant hormone: Roles of oxidative and calcium signaling paths in salicylic acid biology T. Kawano and T. Furuichi 11. Salicylic acid and local resistance to pathogens I.V. Maksimov and L. G. Yarullina 12. Salicylic acid in plant disease resistance R. Chaturvedi and J. Shah 13. Transcriptomic analysis of salicylic acid-responsive genes in tobacco BY-2 cells I. Galis and K.Matsuoka Index.

Nickel: An Overview of Uptake, Essentiality and Toxicity in Plants

Nickel even though recognized as a trace element, its metabolism is very decisive for certain enzyme activities, maintaining proper cellular redox state and various other biochemical, physiological and growth responses. Study of the aspects related with uptake, transport and distributive localization of Ni is very important in various cellular metabolic processes particularly under increased nitrogen metabolism. This review article, in core, encompasses the dual behavior of Ni in plants emphasizing its systemic partitioning, essentiality and ill effects. However, the core mechanism of molecules involved and the successive physiological conditions required starting from the soil absorption, neutralization and toxicity generated is still elusive, and varies among the plants.

Growth of tomato (Lycopersicon esculentum) in response to salicylic acid under water stress

Abstract Plants of Lycopersicon esculentum L. cv. K-25 were subjected to water stress by withholding water for 10 days at 20 (WS I) and 30 (WS II) days after sowing (DAS). Seedlings were sprayed with double distilled water (DDW) or 10−5M salicylic acid (SA) at 45 DAS. The water stress at earlier stage of growth (20 day stage) was more inhibitory as compared to the later stage (30 day stage). The plants exposed to water stress exhibited a significant (p<0.05) decline in photosynthetic parameters, membrane stability index (MSI), leaf water potential, activity of nitrate reductase (NR), carbonic anhydrase (CA), chlorophyll and relative water content (RWC). A follow-up treatment with SA protected against the stress generated by water and significantly improved the above parameters. However, proline content and antioxidant enzymes increased under drought as well as under SA treatments.

24-Epibrassinolide protects against the stress generated by salinity and nickel in Brassica juncea.

The plants of Brassica juncea (L) were grown in the presence of NaCl and/or NiCl2 and were sprayed with 1muM of 24-epibrassinolide (EBL) at 15 days after sowing (DAS) and were sampled at 30 DAS. The plants exposed to NaCl and/or NiCl2 exhibited a significant decline in growth, the level of pigments and photosynthetic parameters. However, the follow up treatment with EBL detoxified the stress generated by NaCl and/or NiCl2 and significantly improved the above parameters. The NaCl and/or NiCl2 increased electrolyte leakage and lipid peroxidation, and decreased the membrane stability index (MSI) and relative water content. However, the EBL treatment in absence of the stress improved the MSI and relative water content but could not influence electrolyte leakage and lipid peroxidation. The antioxidative enzymes and the level of proline exhibited a significant increase in response to EBL as well as to NaCl and/or NiCl2 stress.

Effect of Salicylic Acid on Salinity-induced Changes in Brassica juncea

Seeds of Indian mustard (Brassica juncea (L.) Czern. et Coss.) were exposed to 0, 50, 100 and 150 mmol/L NaCl for 8 h and seeds were sown in an earthen pot. These stressed seedlings were subsequently sprayed with 10 micromol/L salicylic acid (SA) at 30 d and were sampled at 60 d to assess the changes in growth, photosynthesis and antioxidant enzymes. The seedlings raised from the seeds treated with NaCl had significantly reduced growth and the activities of carbonic anhydrase, nitrate reductase and photosynthesis, and the decrease was proportional to the increase in NaCl concentration. However, the antioxidant enzymes (catalase, peroxidase and superoxide dismutase) and proline content was enhanced in response to NaCl and/or SA treatment, where their interaction had an additive effect. Moreover, the toxic effects generated by the lower concentration of NaCl (50 mmol/L) were completely overcome by the application of SA. It was, therefore, concluded that SA ameliorated the stress generated by NaCl through the alleviated antioxidant system.

Effect of 28-homobrassinolide treatment on nickel toxicity in Brassica juncea

Plants of Brassica juncea L. cv. T-59 were supplied with 50 or 100 µM nickel (Ni50, Ni100) at 10 d after sowing (DAS), and sprayed with 28-homobrassinolide (HBR) at 20 DAS. The plants treated with Ni alone exhibited reduced growth, net photosynthetic rate, content of chlorophyll, and the activities of nitrate reductase (E.C.1.6.6.1) and carbonic anhydrase (E.C. 4.2.1.1) at observed 40 DAS, whereas, the contents of peroxidase (PER), catalase (CAT), and proline were increased. However, the spray of HBR partially neutralized the toxic effect of Ni on most of the parameters. Moreover, the treatment of HBR in association with either of the Ni concentration boosted the contents of PER and CAT in leaves and that of proline both in leaves and roots.

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.

Physiological changes induced by chromium stress in plants: an overview

This article presents an overview of the mechanism of chromium (Cr) stress in plants. Toxic effects of Cr on plant growth and development depend primarily on its valence state. Cr(VI) is highly toxic and mobile whereas Cr(III) is less toxic. Cr-induced oxidative stress involves induction of lipid peroxidation in plants that cause severe damage to cell membranes which includes degradation of photosynthetic pigments causing deterioration in growth. The potential of plants with the adequacy to accumulate or to stabilize Cr compounds for bioremediation of Cr contamination has gained engrossment in recent years.