Muhammad Amjad

Transcription factors as tools to engineer enhanced drought stress tolerance in plants

Plant growth and productivity are greatly affected by abiotic stresses such as drought, salinity, and temperature. Drought stress is one of the major limitations to crop productivity worldwide due to its multigene nature, making the production of transgenic crops a challenging prospect. To develop crop plant with enhanced tolerance of drought stress, a basic understanding of physiological, biochemical, and gene regulatory networks is essential. In the signal transduction network that leads from the perception of stress signals to the expression of stress‐responsive genes, transcription factors (TFs) play an essential role. Because TFs, as opposed to most structural genes, tend to control multiple pathways steps, they have emerged as powerful tools for the manipulation of complex metabolic pathways in plants. One such class of TFs is DREB/CBF that binds to drought responsive cis‐acting elements. Transgenic plants have been developed with enhanced stress tolerance by manipulating the expression of DREB/CBF. Recently the functions of an increasing number of plant TFs are being elucidated and increased understanding of these factors in controlling drought stress response has lead to practical approaches for engineering stress tolerance in plants. The utility of the various TFs in plant stress research we review is illustrated by several published examples. The manipulation of native plant regularity networks therefore represents a new era for genetically modified crops. This review focuses on the recent understanding, latest advancements related to TFs and present status of their deployment in developing stress tolerant transgenic plants.

Beyond osmolytes and transcription factors: drought tolerance in plants via protective proteins and aquaporins

Mechanisms of drought tolerance have been studied by numerous groups, and a broad range of molecules have been identified to play important roles. A noteworthy response of stressed plants is the accumulation of novel protective proteins, including heat-shock proteins (HSPs) and late embryogenesis abundant (LEA) proteins. Identification of gene regulatory networks of these protective proteins in plants will allow a wide application of biotechnology for enhancement of drought tolerance and adaptation. Similarly, aquaporins are involved in the regulation of water transport, particularly under abiotic stresses. The molecular and functional characterization of protective proteins and aquaporins has revealed the significance of their regulation in response to abiotic stresses. Herein, we highlight new findings regarding the action mechanisms of these proteins. Finally, this review also surveys the current advances in engineering drought tolerant plants, particularly the engineering of protective proteins (sHSPs and LEA) and aquaporins for imparting drought stress tolerance in plants.

Exogenous Application of Polyamines Improves Germination and Early Seedling Growth of Hot Pepper

Las poliaminas son compuestos organicos de bajo peso molecular implicados en numerosos procesos biologicos en todos los organismos vivos. El acondicionamiento de semillas es una tecnica que mejora el comportamiento de las semillas respecto a una germinacion mas rapida y uniforme, con plantulas normales y vigorosas. Se realizo un estudio de laboratorio para explorar los beneficios del acondicionamiento de semillas con poliaminas sobre la germinacion y el crecimiento de plantulas de aji (Capsicum annuum L.) Las semillas de aji fueron colocadas en solucion acuosa aireada de putrescina, espermina o espermidina (25, 50, 75 y 100 mM), durante 48 h a 25 ± 2 °C. Se observaron resultados significativos (P < 0,05) para los diferentes atributos de germinacion de semillas y crecimiento de plantulas. El acondicionamiento con poliaminas adelanto la germinacion y sincronizo el porcentaje final de germinacion, tiempo hasta 50% de germinacion, tiempo medio de germinacion, energia de germinacion, velocidad de germinacion, e indice de germinacion en comparacion con el control. El mejoramiento de longitud de tallo y raiz, peso fresco y seco de plantulas, tasa de crecimiento de plantulas y el indice de vigor de las plantulas fue claramente indicativo de los efectos positivos de la imprimacion de semillas con poliamina. De todas las poliaminas, putrescina demostro ser mejor a bajas concentraciones (es decir 25 y 50 mM) para la mayoria de los rasgos relacionados con emergencia de semillas y crecimiento de plantulas.

Arsenic Uptake, Toxicity, Detoxification, and Speciation in Plants: Physiological, Biochemical, and Molecular Aspects

Environmental contamination with arsenic (As) is a global environmental, agricultural and health issue due to the highly toxic and carcinogenic nature of As. Exposure of plants to As, even at very low concentration, can cause many morphological, physiological, and biochemical changes. The recent research on As in the soil-plant system indicates that As toxicity to plants varies with its speciation in plants (e.g., arsenite, As(III); arsenate, As(V)), with the type of plant species, and with other soil factors controlling As accumulation in plants. Various plant species have different mechanisms of As(III) or As(V) uptake, toxicity, and detoxification. This review briefly describes the sources and global extent of As contamination and As speciation in soil. We discuss different mechanisms responsible for As(III) and As(V) uptake, toxicity, and detoxification in plants, at physiological, biochemical, and molecular levels. This review highlights the importance of the As-induced generation of reactive oxygen species (ROS), as well as their damaging impacts on plants at biochemical, genetic, and molecular levels. The role of different enzymatic (superoxide dismutase, catalase, glutathione reductase, and ascorbate peroxidase) and non-enzymatic (salicylic acid, proline, phytochelatins, glutathione, nitric oxide, and phosphorous) substances under As(III/V) stress have been delineated via conceptual models showing As translocation and toxicity pathways in plant species. Significantly, this review addresses the current, albeit partially understood, emerging aspects on (i) As-induced physiological, biochemical, and genotoxic mechanisms and responses in plants and (ii) the roles of different molecules in modulation of As-induced toxicities in plants. We also provide insight on some important research gaps that need to be filled to advance our scientific understanding in this area of research on As in soil-plant systems.

Characterization of Capsaicinoids and Antioxidants in Hot Peppers as Influenced by Hybrid and Harvesting Stage

Studies were conducted to investigate the accumulation pattern of capsaicinoids and antioxidants such as carotenoids, ascorbic acid and phenolic compounds in three hot pepper hybrids at five different harvesting stages: immature green, mature green, color break, red ripe and dried fruit. Capsaicin and dihydrocapsaicin contents were maximum at mature green stage in both Sky Red (61.30 and 43.76xa0mg/100xa0g) and Wonder King (43.93 and 26.16xa0mg/100xa0g) hybrids, whereas Maha hybrid reached top values at color break stage (39.13 and 24.20xa0mg/100xa0g). The accumulation of total carotenoids showed an 8-fold increase from red ripe (12xa0mg/100xa0g) to dried fruit stage (96xa0mg/100xa0g), while a noticeable decline by 76xa0% was observed for ascorbic acid at same harvesting stages (150 vs. 36xa0mg/100xa0g, respectively). The three hot pepper hybrids showed great variations in the evolution of total phenolic contents during harvesting stages. Overall, the mature green stage was ideal to acquire maximum pungency due to capsaicinoids, while peppers at red ripe stage were best sources of ascorbic acid and dried fruits contained higher levels of total carotenoids.

Assessment of hot peppers for aflatoxin and mold proliferation during storage.

Aflatoxin contamination and mold proliferation in three hot pepper hybrids (Sky Red, Maha, and Wonder King) were studied during 5 months of storage at three temperatures (20, 25, and 30°C) and under different packaging conditions (low-density polyethylene bags and jute bags). The presence of aflatoxins in hot pepper samples was determined by high-performance liquid chromatography with a UV-Vis detector. Sampling for analysis of aflatoxins, total mold counts, and Aspergillus counts was carried out at 0, 50, 100, and 150 days of storage. Hot peppers packed in jute bags were more susceptible to aflatoxin contamination than those packed in polyethylene bags; aflatoxin concentrations were 75% higher in peppers stored in jute bags. The effect of storage temperature resulted in aflatoxin concentrations that were 61% higher in hot peppers stored at 25 and 30°C than in those stored at 20°C. Of the three pepper hybrids, Wonder King was more susceptible to aflatoxin contamination, with a maximum of 1.50 μg/kg when packed in jute bags and stored at 25°C for 150 days. However, no sample exceeded the maximum permitted level for total aflatoxins in spices established by European Union regulations (10 μg/kg). Total mold counts and Aspergillus counts increased with storage duration, but all counts were significantly lower in peppers stored in polyethylene bags. A gradual increase in temperature during prolonged storage of hot peppers in combination with aeration may be the main reasons for increases in fungal biomass and Aspergillus proliferation with the subsequent aflatoxin production.

Mold and aflatoxin reduction by gamma radiation of packed hot peppers and their evolution during storage.

The effect of gamma radiation on moisture content, total mold counts, Aspergillus counts, and aflatoxins of three hot pepper hybrids (Sky Red, Maha, and Wonder King) was investigated. Whole dried peppers packed in polyethylene bags were gamma irradiated at 0 (control), 2, 4, and 6 kGy and stored at 25°C for 90 days. Gamma radiation proved to be effective in reducing total mold and Aspergillus counts in a dose-dependent relationship. Total mold counts in irradiated peppers immediately after treatments were significantly lowered compared with those in nonirradiated samples, achieving 90 and 99% reduction at 2- and 4-kGy doses, respectively. Aspergillus counts were significantly reduced, by 93 and 97%, immediately after irradiation at doses of 2 and 4 kGy, respectively. A radiation dose of 6 kGy completely eliminated the population of total molds and Aspergillus fungi. The evolution of total molds in control and irradiated samples indicated no further fungal proliferation during 3 months of storage at 25°C. Aflatoxin levels were slightly affected by radiation doses of 2 and 4 kGy and showed a nonsignificant reduction of 6% at the highest radiation dose of 6 kGy. The distinct effectiveness of gamma radiation in molds and aflatoxins can be explained by the target theory of food irradiation, which states that the likelihood of a microorganism or a molecule being inactivated by gamma rays increases as its size increases.

Morpho-physiological evaluation of tomato genotypes under high temperature stress conditions

BACKGROUNDnTomato (Solanum lycopersicum L.) is an important but heat-sensitive vegetable crop. The losses in tomato production associated with heat stress are aggravating further under a global warming scenario. The present study was designed to investigate the comparative performance of tomato genotypes under high temperature stress. Tomato genotypes (191) were exposed to the controlled conditions of high temperature (40/32u2009°Cu2009day/night temperature). Different morphological (shoot length, root length, shoot fresh weight, root fresh weight, shoot dry weight, root dry weight and number of leaves), physiological (photosynthetic rate, transpiration rate, water use efficiency, stomatal conductance to water, sub-stomatal CO2 and leaf temperature) and SPAD value (chlorophyll content) were recorded to check the diversity among genotypes against heat stress.nnnRESULTSnAll the genotypes showed a significantly variable response in almost all the attributes under high-temperature conditions. Correlation among the variables provided a clear understanding of the phenomena involved. Based on all the attributes studied, genotypes L00090 and L00091 were found to be the most heat tolerant compared to other genotypes, whereas CLN1462A and CLN 1466E were found to be comparatively sensitive.nnnCONCLUSIONnIt was concluded that the studied attributes were genotype dependent, and significant diverse performance was noted. The findings of this study pave the way towards the selection of tolerant genotypes, not only for use under high-temperature conditions but also to employ them in breeding programs to produce heat-tolerant hybrids.

DAIRY MANURE AND NITROGEN FERTILIZER EFFECTS ON RESIDUAL NITRATE AND PHOSPHATE, AND WHEAT YIELD IN A SANDY CLAY LOAM SOIL

Dairy manure (DM) rates of [0 (DM0), 30 (DM30)), 60 (DM60) Mg ha−1] and three nitrogen (N) rates [0 (N0), 125 (N125), 250 (N250) kg ha−1] were tested in a sandy clay loam, to evaluate their effects on growth and yield of wheat crop (Triticum aestivum L.), residual nitrate nitrogen (NO3-N) and phosphorus (P) concentrations in the surface soil, and selected soil physical measurements [saturated hydraulic conductivity (Ksat), and bulk density (BD)]. Increasing N and DM rates gave higher wheat yields, increased concentrations of residual NO3-N and P in the surface soil and improved Ksat and BD. Highest grain yield of 3.8 Mg ha−1 (70.3% more than the control) was observed in DM60 × N250 treatment. Residual accumulation of N-NO3 and P in the surface soil at high N and/or DM application rates suggests the need to carefully manage N and DM inputs on farm fields to avoid environmental contamination.

Salicylic acid confers salt tolerance in potato plants by improving water relations, gaseous exchange, antioxidant activities and osmoregulation

BACKGROUNDnPotato is an important vegetable; however, salt stress drastically affects its growth and yield. A pot experiment was therefore conducted to assess salicylic acid efficacy in improving performance of potato cultivars, grown under salt stress (50u2009mmolu2009L-1 ). Salicylic acid at 0.5u2009mmolu2009L-1 was sprayed on to potato plants after 1 week of salinity application.nnnRESULTSnSalt stress effects were ameliorated by salicylic acid effectively in both the studied cultivars. N-Y LARA proved more responsive to salicylic acid application than 720-110 NARC, which confirmed genetic variation between cultivars. Salicylic acid scavenged reactive oxygen species by improving antioxidant enzyme activities (superoxide dismutase, catalase, peroxidases) and regulating osmotic adjustment (proline, phenolic contents), which led to enhanced water relation and gaseous exchange attributes, and thereby increased potassium availability and reduced sodium content in potato leaves. Moreover, potato tuber yield showed a positive correlation with potassium content, photosynthesis and antioxidant enzyme activities.nnnCONCLUSIONnSalt tolerance efficacy of salicylic acid is authenticated in improving potato crop performance under salt stress. Salicylic acid effect was more pronounced in N-Y LARA, reflecting greater tolerance than 720-110 NARC, which was confirmed as a susceptible cultivar. Hence salicylic acid at 0.5u2009mmolu2009L-1 and cultivation of N-Y LARA may be recommended in saline soil.