Saddam Hussain

Phytohormones and plant responses to salinity stress: a review

Plants are exposed to a variety of abiotic stresses in nature and exhibit unique and complex responses to these stresses depending on their degree of plasticity involving many morphological, cellular, anatomical, and physiological changes. Phytohormones are known to play vital roles in the ability of plants to acclimatize to varying environments, by mediating growth, development, source/sink transitions and nutrient allocation. These signal molecules are produced within the plant, and also referred as plant growth regulators. Although plant response to salinity depends on several factors; nevertheless, phytohormones are thought to be the most important endogenous substances that are critical in modulating physiological responses that eventually lead to adaptation to salinity. Response usually involves fluctuations in the levels of several phytohormones, which relates with changes in expression of genes involved in their biosynthesis and the responses they regulate. Present review described the potential role of different phytohormones and their balances against salinity stress and summarized the research progress regarding plant responses towards salinity at physiological and molecular levels. We emphasized the role of abscisic acid, indole acetic acid, cytokinins, gibberellic acid, salicylic acid, brassinosteroids, jasmonates, ethylene and triazoles in mediating plant responses and discussed their crosstalk at various baseline pathways transduced by these phytohormones under salinity. Current progress is exemplified by the identification and validation of several significant genes that enhanced crops tolerance to salinity, while missing links on different aspects of phytohormone related salinity tolerance are pointed out. Deciphering mechanisms by which plant perceives salinity and trigger the signal transduction cascades via phytohormones is vital to devise salinity related breeding and transgenic approaches.

Potential role of phytohormones and plant growth-promoting rhizobacteria in abiotic stresses: consequences for changing environment

Plants are sessile beings, so the need of mechanisms to flee from unfavorable circumstances has provided the development of unique and sophisticated responses to environmental stresses. Depending on the degree of plasticity, many morphological, cellular, anatomical, and physiological changes occur in plants in response to abiotic stress. Phytohormones are small molecules that play critical roles in regulating plant growth and development, as well as stress tolerance to promote survival and acclimatize to varying environments. To congregate the challenges of salinity, temperature extremes, and osmotic stress, plants use their genetic mechanism and different adaptive and biological approaches for survival and high production. In the present attempt, we review the potential role of different phytohormones and plant growth-promoting rhizobacteria in abiotic stresses and summarize the research progress in plant responses to abiotic stresses at physiological and molecular levels. We emphasized the regulatory circuits of abscisic acid, indole acetic acid, cytokinins, gibberellic acid, salicylic acid, brassinosteroids, jasmonates, ethylene, and triazole on exposure to abiotic stresses. Current progress is exemplified by the identification and validation of several significant genes that enhanced crop tolerance to stress in the field. These findings will make the modification of hormone biosynthetic pathways for the transgenic plant generation with augmented abiotic stress tolerance and boosting crop productivity in the coming decades possible.

Phytoremediation strategies for soils contaminated with heavy metals: Modifications and future perspectives

Presence of heavy metals in agricultural soils is of major environmental concern and a great threat to life on the earth. A number of human health risks are associated with heavy metals regarding their entry into food chain. Various physical, chemical and biological techniques are being used to remove heavy metals and metalloids from soils. Among them, phytoremediation is a good strategy to harvest heavy metals from soils and have been proven as an effective and economical technique. In present review, we discussed various sources and harmful effects of some important heavy metals and metalloids, traditional phytoremediation strategies, mechanisms involved in phytoremediation of these metals, limitations and some recent advances in phytoremediation approaches. Since traditional phytoremediation approach poses some limitations regarding their applications at large scale, so there is a dire need to modify this strategy using modern chemical, biological and genetic engineering tools. In view of above, the present manuscript brings both traditional and advanced phytoremediation techniques together in order to compare, understand and apply these strategies effectively to exclude heavy metals from soil keeping in view the economics and effectiveness of phytoremediation strategies.

Rice management interventions to mitigate greenhouse gas emissions: a review

Global warming is one of the gravest threats to crop production and environmental sustainability. Rice, the staple food of more than half of the world’s population, is the most prominent cause of greenhouse gas (GHG) emissions in agriculture and gives way to global warming. The increasing demand for rice in the future has deployed tremendous concerns to reduce GHG emissions for minimizing the negative environmental impacts of rice cultivation. In this review, we presented a contemporary synthesis of existing data on how crop management practices influence emissions of GHGs in rice fields. We realized that modifications in traditional crop management regimes possess a huge potential to overcome GHG emissions. We examined and evaluated the different possible options and found that modifying tillage permutations and irrigation patterns, managing organic and fertilizer inputs, selecting suitable cultivar, and cropping regime can mitigate GHG emissions. Previously, many authors have discussed the feasibility principle and the influence of these practices on a single gas or, in particular, in the whole agricultural sector. Nonetheless, changes in management practices may influence more than one gas at the same time by different mechanisms or sometimes their effects may be antagonistic. Therefore, in the present attempt, we estimated the overall global warming potential of each approach to consider the magnitude of its effects on all gases and provided a comprehensive assessment of suitable crop management practices for reducing GHG emissions in rice culture.

Drought induced changes in growth, osmolyte accumulation and antioxidant metabolism of three maize hybrids

Consequences of drought stress in crop production systems are perhaps more deleterious than other abiotic stresses under changing climatic scenarios. Regulations of physio-biochemical responses of plants under drought stress can be used as markers for drought stress tolerance in selection and breeding. The present study was conducted to appraise the performance of three different maize hybrids (Dong Dan 80, Wan Dan 13, and Run Nong 35) under well-watered, low, moderate and SD conditions maintained at 100, 80, 60, and 40% of field capacity, respectively. Compared with well-watered conditions, drought stress caused oxidative stress by excessive production of reactive oxygen species (ROS) which led to reduced growth and yield formation in all maize hybrids; nevertheless, negative effects of drought stress were more prominent in Run Nong 35. Drought-induced osmolyte accumulation and strong enzymatic and non-enzymatic defense systems prevented the severe damage in Dong Dan 80. Overall performance of all maize hybrids under drought stress was recorded as: Dong Dan 80 > Wan Dan 13 > Run Nong 35 with 6.39, 7.35, and 16.55% yield reductions. Consequently, these biochemical traits and differential physiological responses might be helpful to develop drought tolerance genotypes that can withstand water-deficit conditions with minimum yield losses.

A biochar application protects rice pollen from high-temperature stress.

The influences of high temperature and fertilization with biochar and phosphorus (P) on the pollen characteristics of two rice cultivars (IR-64 and Huanghuazhan) were examined in controlled growth chambers. Temperature treatments included high daytime temperature (HDT), high nighttime temperature (HNT) and ambient temperature (AT). The fertilization treatments were control, biochar alone, P alone and biochar + P. High temperature severely reduced pollen fertility, anther dehiscence, pollen retention and pollen germination of both rice cultivars, with HNT more destructive than HDT. The Huanghuazhan cultivar performed better than IR-64 under high temperature, with higher pollen fertility, better anther dehiscence and greater pollen retention and germination rates. In both cultivars, the pollen of plants treated with biochar + P were more resistant to heat induced stress. Further studies are needed to test the ability of biochar to ameliorate the effects of different abiotic stresses in rice and other crops.

Lead toxicity in rice: effects, mechanisms, and mitigation strategies—a mini review

Lead (Pb) is a major environmental pollutant that affects plant morpho-physiological and biochemical attributes. Its higher levels in the environment are not only toxic to human beings but also harmful for plants and soil microbes. We have reviewed the uptake, translocation, and accumulation mechanisms of Pb and its toxic effects on germination, growth, yield, nutrient relation, photosynthesis, respiration, oxidative damage, and antioxidant defense system of rice. Lead toxicity hampers rice germination, root/shoot length, growth, and final yield. It reduces nutrient uptake through roots, disrupts chloroplastic ultrastructure and cell membrane permeability, induces alterations in leaves respiratory activities, produces reactive oxygen species (ROS), and triggers some enzyme and non-enzymatic antioxidants (as defense to oxidative damage). In the end, biochar amendments and phytoremediation technologies have been proposed as soil remediation approaches for Pb tainted soils.

A combined application of biochar and phosphorus alleviates heat-induced adversities on physiological, agronomical and quality attributes of rice.

Present study examined the influence of high-temperature stress and different biochar and phosphorus (P) fertilization treatments on the growth, grain yield and quality of two rice cultivars (IR-64 and Huanghuazhan). Plants were subjected to high day temperature-HDT (35 °C ± 2), high night temperature-HNT (32 °C ± 2), and control temperature-CT (28 °C ± 2) in controlled growth chambers. The different fertilization treatments were control, biochar alone, phosphorous (P) alone and biochar + P. High-temperature stress severely reduced the photosynthesis, stomatal conductance, water use efficiency, and increased the leaf water potential of both rice cultivars. Grain yield and its related attributes except for number of panicles, were reduced under high temperature. The HDT posed more negative effects on rice physiological attributes, while HNT was more destructive for grain yield. High temperature stress also hampered the grain appearance and milling quality traits in both rice cultivars. The Huanghuazhan performed better than IR-64 under high-temperature stress with better growth and higher grain yield. Different soil fertilization treatments were helpful in ameliorating the detrimental effects of high temperature. Addition of biochar alone improved some growth and yield parameters but such positive effects were lower when compared with the combined application of biochar and P. The biochar+P application recorded 7% higher grain yield (plant(-1)) of rice compared with control averaged across different temperature treatments and cultivars. The highest grain production and better grain quality in biochar+P treatments might be due to enhanced photosynthesis, water use efficiency, and grain size, which compensated the adversities of high temperature stress.

Silicon Application Increases Drought Tolerance of Kentucky Bluegrass by Improving Plant Water Relations and Morphophysiological Functions

Drought stress encumbers the growth of turfgrass principally by disrupting the plant-water relations and physiological functions. The present study was carried out to appraise the role of silicon (Si) in improving the drought tolerance in Kentucky bluegrass (Poa pratensis L.). Drought stress and four levels (0, 200, 400, and 800 mg L−1) of Si (Na2SiO3·9H2O) were imposed after 2 months old plants cultured under glasshouse conditions. Drought stress was found to decrease the photosynthesis, transpiration rate, stomatal conductance, leaf water content, relative growth rate, water use efficiency, and turf quality, but to increase in the root/shoot and leaf carbon/nitrogen ratio. Such physiological interferences, disturbances in plant water relations, and visually noticeable growth reductions in Kentucky bluegrass were significantly alleviated by the addition of Si after drought stress. For example, Si application at 400 mg L−1 significantly increased the net photosynthesis by 44%, leaf water contents by 33%, leaf green color by 42%, and turf quality by 44% after 20 days of drought stress. Si application proved beneficial in improving the performance of Kentucky bluegrass in the present study suggesting that manipulation of endogenous Si through genetic or biotechnological means may result in the development of drought resistance in grasses.

Benefits of rice seed priming are offset permanently by prolonged storage and the storage conditions

Seed priming is a commercially successful practice, but reduced longevity of primed seeds during storage may limit its application. We established a series of experiments on rice to test: (1) whether prolonged storage of primed and non-primed rice seeds for 210 days at 25°C or −4°C would alter their viability, (2) how long primed rice seed would potentially remain viable at 25°C storage, and (3) whether or not post-storage treatments (re-priming or heating) would reinstate the viability of stored primed seeds. Two different rice cultivars and three priming agents were used in all experiments. Prolonged storage of primed seeds at 25°C significantly reduced the germination (>90%) and growth attributes (>80%) of rice compared with un-stored primed seeds. However, such negative effects were not observed in primed seeds stored at −4°C. Beneficial effects of seed priming were maintained only for 15 days of storage at 25°C, beyond which the performance of primed seeds was worse even than non-primed seeds. The deteriorative effects of 25°C storage were related with hampered starch metabolism in primed rice seeds. None of the post-storage treatments could reinstate the lost viability of primed seeds suggesting that seeds become unviable by prolonged post-priming storage at 25°C.