Abdul Wakeel

Zinc nutrition in rice production systems: a review

BackgroundZinc (Zn) deficiency is one of the important abiotic factors limiting rice productivity worldwide and also a widespread nutritional disorder affecting human health. Given that rice is a staple for populations in many countries, studies of Zn dynamics and management in rice soils is of great importance.ScopeChanging climate is forcing the growers to switch from conventional rice transplanting in flooded soils to water-saving cultivation, including aerobic rice culture and alternate wetting and drying system. As soil properties are changed with altered soil and water management, which is likely to affect Zn solubility and plant availability and should be considered before Zn management in rice. In this review, we critically appraise the role of Zn in plant biology and its dynamics in soil and rice production systems. Strategies and options to improve Zn uptake and partitioning efficiency in rice by using agronomic, breeding and biotechnological tools are also discussed.ConclusionsAlthough soil application of inorganic Zn fertilizers is widely used, organic and chelated sources are better from economic and environmental perspectives. Use of other methods of Zn application (such as seed treatment, foliar application etc., in association with mycorrhizal fungi) may improve Zn-use efficiency in rice. Conventional breeding together with modern genomic and biotechnological tools may result in development of Zn-efficient rice genotypes that should be used in conjunction with judicious fertilization to optimize rice yield and grain Zn content.

Potassium Substitution by Sodium in Plants

Soil salinity is an ever-increasing constraint to crop productivity worldwide especially in countries with irrigated agriculture. In contrast to all the soil reclamation strategies to decrease salt concentrations in root zone, the use of sodium (Na+) in plant nutrition may be an interesting tactic. The roles of potassium (K+) and Na+ in plant nutrition suggest that K+ is the only monovalent cation which is essential for most higher plants and is involved in three important functions, i.e., enzyme activation, charge balance and osmoregulation. Plants need a small amount but high concentration of K+ for specific functions in the cytoplasm and a major portion (∼90%) of it is localized in vacuoles, where it acts as an osmoticum. Maintenance of osmotic potential in vacuoles, a nonspecific function of K+, can be achieved by other cations such as Na+. For decades an ample amount of work has been done on the substitution of K+ by Na+ in plant nutrition. In this regard, Na+ has the potential to replace K+ for some of its functions. In some plants, supplementation of Na+ in reduced amounts can eliminate K+ deficiency symptoms under limited K+ supply. Thus, the question of K+ substitution by Na+ in plant physiology is not only of academic interest but has considerable practical implications in relation to fertilizer management and plant growth in salt-affected environments. In this review, we discuss the possibilities of K+ substitution by Na+ under specific soil and environmental conditions.

Salt stress in maize: effects, resistance mechanisms, and management. A review

Maize is grown under a wide spectrum of soil and climatic conditions. Maize is moderately sensitive to salt stress; therefore, soil salinity is a serious threat to its production worldwide. Understanding maize response to salt stress and resistance mechanisms and overviewing management options may help to devise strategies for improved maize performance in saline environments. Here, we reviewed the effects, resistance mechanisms, and management of salt stress in maize. Our main conclusions are as follows: (1) germination and stand establishment are more sensitive to salt stress than later developmental stages. (2) High rhizosphere sodium and chloride decrease plant uptake of nitrogen, potassium, calcium, magnesium, and iron. (3) Reduced grain weight and number are responsible for low grain yield in maize under salt stress. Sink limitations and reduced acid invertase activity in developing grains is responsible for poor kernel setting under salt stress. (4) Exclusion of excessive sodium or its compartmentation into vacuoles is an important adaptive strategy for maize under salt stress. (5) Apoplastic acidification, required for cell wall extensibility, is an important indicator of salt resistance, but not essential for better maize growth under salt stress. (6) Upregulation of antioxidant defense genes and β-expansin proteins is important for salt resistance in maize. (7) Arbuscular mycorrhizal fungi improve salt resistance in maize due to better plant nutrient availability. (8) Seed priming is an effective approach for improving maize germination under salt stress. (9) Integration of screening, breeding and ion homeostasis mechanisms into a functional paradigm for the whole plant may help to enhance salt resistance in maize.

Proteome analysis of sugar beet (Beta vulgaris L.) elucidates constitutive adaptation during the first phase of salt stress.

Salinity is one of the major stress factors responsible for growth reduction of most of the higher plants. In this study, the effect of salt stress on protein pattern in shoots and roots of sugar beet (Beta vulgaris L.) was examined. Sugar beet plants were grown in hydroponics under control and 125 mM salt treatments. A significant growth reduction of shoots and roots was observed. The changes in protein expression, caused by salinity, were monitored using two-dimensional gel-electrophoresis. Most of the detected proteins in sugar beet showed stability under salt stress. The statistical analysis of detected proteins showed that the expression of only six proteins from shoots and three proteins from roots were significantly altered. At this stage, the significantly changed protein expressions we detected could not be attributed to sugar beet adaptation under salt stress. However, unchanged membrane bound proteins under salt stress did reveal the constitutive adaptation of sugar beet to salt stress at the plasma membrane level.

Hydrolytic and pumping activity of H+-ATPase from leaves of sugar beet (Beta vulgaris L.) as affected by salt stress

Cell wall extensibility plays an important role in plant growth. According to the acid-growth theory, lower apoplastic pH allows extension growth by affecting cell wall extensibility. A lowered apoplastic pH is presumed to activate wall-loosening enzymes that control plant growth. Plasma membrane (PM) H(+)-ATPases play a major role in the apoplastic acidification by H(+) transport from cytosol to the apoplast. A salt-induced decrease in H(+)-pumping activity of plasma membrane H(+)-ATPases in salt-sensitive maize plants has previously been found. This led us to formulate the hypothesis that salt-resistant plant species such as sugar beet (Beta vulgaris L.) may have a mechanism to eliminate the effect of higher salt concentrations on plasma membrane H(+)-ATPase activity. In the present study, sugar beet plants were grown in 1mM NaCl (control) or 150 mM NaCl in hydroponics. H(+)-ATPase hydrolytic and pumping activities were measured in plasma membrane vesicles isolated from sugar beet shoots. We found that plasma membrane H(+)-ATPase hydrolytic and pumping activities were not affected by application of 150 mM NaCl. Moreover, apoplastic pH was also not affected under salt stress. However, a decrease in plant growth was observed. We assume that growth reduction was not due to a decrease in PM-H(+)-ATPase activity, but that other factors may be responsible for growth inhibition of sugar beet plants under salt stress.

In vitro effect of different Na+/K+ ratios on plasma membrane H+-ATPase activity in maize and sugar beet shoot

Plant growth is impaired primarily by osmotic stress in the first phase of salt stress, whereas Na+ toxicity affects the plant growth mainly in the second phase. Salinity leads to increased Na+/K+ ratio and thus displacement of K+ by Na+ in the plant cell. Relatively higher cytosolic Na+ concentrations may have an effect on the activity of plasma membrane (PM) H+ -ATPase. A decreased PM-H+ -ATPase activity could increase the apoplastic pH. This process could limit the cell-wall extensibility and thus reduce growth according to the acid growth theory. To compare the effect of Na+ on PM H+ -ATPase activity in salt-sensitive maize (Zea mays L.) and salt-resistant sugar beet (Beta vulgaris L.) shoot, PM vesicles were isolated from growing shoots of both species and ATPase activity was determined by assaying the P(i) released by hydrolysis of ATP. The H+ pumping activity was measured as the quenching of acridine-orange absorbance. An increased Na+/K+ ratio decreased the PM H+ -ATPase activity in vesicles of maize as well as of sugar beet shoots. Nevertheless, the detrimental effect of increased Na+/K+ ratio was more severe in salt-sensitive maize compared to salt-resistant sugar beet. At 25 mM Na+ concentration, hydrolytic activity was not affected in sugar beet. However, a significant decrease in hydrolytic activity was observed in maize at pH 7. In maize and sugar beet, reduction in active H+ flux was 20% and 5% at 25 mM Na+ concentration in the assay, respectively. The active H+ flux was decreased to 80% and 60%, when 100 mM K+ were substituted by 100mM Na+. We conclude that PM H+ -ATPases of salt-resistant sugar beet and maize shoot are sensitive to higher concentration of Na+. However, sugar beet PM-H+ -ATPases are relatively efficient and may have constitutive resistance against lower concentration (25 mM) of Na+ as compared to that of salt-sensitive maize.

Seed priming improves early seedling vigor, growth and productivity of spring maize

Abstract Potential of seed priming treatments in improving the performance of early planted maize was evaluated against timely planting. Seeds of maize hybrid FH-810 were soaked in water (hydropriming), CaCl2 (2.2%, osmopriming), moringa leaf extracts (MLE 3.3%, osmopriming) and salicylic acid (SA, 50 mg L−1, hormonal priming) each for 18 h. Untreated and hydroprimed seeds were taken as control. Seeds primed with SA took less time in emergence and had high vigor in early planted maize. Amongst treatments, hormonal priming, reduced the electrical conductivity, increased the leaf relative and chlorophyll contents followed by osmopriming with CaCl2 at seedling stage. Likewise, plant height, grain rows and 1 000-grain weight, grain and biological yield and harvest index were also improved by seed priming; however hormonal priming and osmopriming with MLE were more effective in this regard. Improved yield performance by hormonal priming or osmopriming with MLE in early planting primarily owed to increased leaf area index, crop growth and net assimilation rates, and maintenance of green leaf area at maturity. In conclusion, osmopriming with MLE and hormonal priming with SA were the most economical treatments in improving productivity of early planted spring maize through stimulation of early seedling growth at low temperature.

Conservation Agriculture in South Asia

Conventional agriculture has put forth soil and crop sustainability to substantial soil degradation resulting in a concomitant decrease in the productivity of these systems. Conservation agriculture (CA) including minimum soil disturbance, permanent soil cover, and diversified crop rotations aimed to decrease and/or revert the effects of conventional farming practices like soil organic matter decline, soil erosion, soil physical degradation, and fuel use. However, in South Asia, the area under CA is very small compared to the rest of the world. The history of CA in South Asia starts when wheat plantation with zero tillage was first introduced in Indian and Pakistani Punjab in the 1980s. Currently, conservation tillage is being practiced on more than 5 M ha in Indo-Gangetic plains of South Asia. Conservation tillage reduced greenhouse gas emission and the production cost, and improved the soil health and crop yields. However, challenges like cultural and economic entrenchment of tillage agriculture in this region, weeds, insect pests, diseases, crop residue management, and reduced availability of suitable seeding and planting equipment are hindering its uptake. In this scenario, problem-oriented research and training, provision of conservation machinery at specific sites at proper time at affordable rates, and aggressive extension campaigns may help to boost up the uptake of CA in South Asia.

DIFFERENTIAL RESPONSE OF MAIZE AND MUNGBEAN TO TOBACCO ALLELOPATHY

Seedling emergence and stand establishment of crops following the allelopathic crops are often affected. When the crops are grown in rotation, they are influenced by allelopathy of preceding crop. In this study, consisting of three independent experiments, allelopathic effect of tobacco, rich in several allelochemicals, on the subsequent maize and mungbean crops was investigated. In first experiment, maize and mungbean were sown in field previously occupied by tobacco or was fallow. In second experiment, maize and mungbean were planted in pots after the harvest of tobacco. Whereas in third experiment, maize and mungbean seeds were soaked in water or 2 and 4 mM nicotine and were then sown in soil-filled pots. Stand establishment, leaf emergence and growth of maize were significantly improved when grown after tobacco, whereas in mungbean these characters were suppressed when grown after tobacco. Likewise external application of nicotine improved the emergence uniformity, seedling dry weight and chlorophyll contents in maize and suppressed these parameters in mungbean. Tobacco allelopathy also increased the total soil nitrogen, zinc, iron, nicotine and total phenolics. Nicotine-induced change in chlorophyll contents and α-amylase activity seems the possible reason of differential response of maize and mungbean to tobacco allelopathy. When grown in rotation with tobacco, stand establishment and growth of maize were improved, whereas mungbean stand and growth were suppressed. In crux, allelopathic nature of the crops must be considered while making the crop rotations.

Potash use in aerobic production system for basmati rice may expand its adaptability as an alternative to flooded rice production system

Direct seeded aerobic rice system has been developed and adopted as an alternative for medium-grain rice in many parts of the world, whereas efforts for aerobic basmati rice types are still in infancy. Among two major constraints for aerobic rice, weeds are progressively being eliminated to great extent through introduction of new herbicides; however, the issue of unfilled grains is still elusive. As potassium (K) deficiency produce sterile pollens in different crops, therefore possible K deficiency in aerobic rice production system may increase unfilled grains in rice. Therefore, it was hypothesized that K application may yield better by improving grain filling of basmati rice, especially, under aerobic conditions. Pot and field experiments were comprised of no K as control, K fertilization using 90 and 180 kg ha-1 keeping recommended N, P and Zn fertilization at the rate of 180, 125 and 25 kg ha-1. Two fine grain rice cultivars Basmati-515 and Super basmati were used due to their differential response to K fertilization. Results indicated that application of 180 kg K2O ha -1 significantly increased the K concentration in shoot, which increased the paddy yield. Highest chlorophyll contents were observed for Basmati-515 in aerobic rice and for Super basmati under flooded condition at 180 kg K2O ha -1. Decrease in number of un-filled grains may a contributory to paddy yield improvement in K fertilized treatments. The improvement in yield was more pronounced in Basmati-515 than Super basmati. Economic analysis showed higher benefit cost ratio for Basmati-515 with 90 kg Kg ha-1 under aerobic conditions. Net benefit of K fertilization was increased for both fertilizer rates and both cultivars except 180 kg K in Super basmati. As K fertilization increased the number of filled grains and improved the rice yield, therefore it is suggested to apply K fertilizers for better yield and expanded adaptability of aerobic rice production system for basmati rice. Availability of indigenous soil K under aerobic and flooded conditions should be quantified to develop precise K recommendations for both production systems of basmati rice.