Qaiser 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.

Physiological and biochemical changes in plants under waterlogging

Waterlogging usually results from overuse and/or poor management of irrigation water and is a serious constraint with damaging effects. The rapidly depleting oxygen from submerged root zone is sensed and plant adjusts expressing anaerobic proteins. Plant cells shift their metabolism towards low energy yielding anaerobic fermentation pathways in the absence of oxygen. Structural modifications are also induced as aerenchyma formation and adventitious rootings, etc. Studies at molecular and biochemical levels to facilitate early perception and subsequent responses have also been worked out to produce resistant transgenic plants. This review explores the sequential changes of plant responses at different levels regarding their defense strategies and efforts made to enhance them, tailoring crucial regulators so that they can withstand waterlogging stress.

Auxin Analogues and Nitrogen Metabolism, Photosynthesis, and Yield of Chickpea

ABSTRACT The impact of three auxins indole-3-acetic acid (IAA), 4-chloroindole-3-acetic acid (4-Cl-IAA), and indole-3-butyric acid (IBA) on nitrogen metabolism were investigated in chickpea (Cicer arietinum L.). Plants were raised from seeds soaked in water (control), 10−8 M of IAA, IBA, or 4-Cl-IAA, for 12 hours and were assessed for different parameters at 60 days after sowing. Observations showed that auxins, irrespective of the analogue significantly increased the nodulation, leghemoglobin content, nodule nitrogen content and the enzymes of nitrogen assimilation. Of the three auxins, 4-Cl-IAA was the most effective in increasing these parameters. The increase in seed yield was 27% higher than the water soaked control. The response to auxins followed the trend 4-Cl-IAA > IAA > IBA > control. It may be concluded from the present investigation that auxins, irrespective of the type, significantly improved the nitrogen metabolism, photosynthesis and yield of the chickpea. Of three auxins used, 4-Cl-IAA generated the best response.

Salicylic acid enhances the efficiency of nitrogen fixation and assimilation in Cicer arietinum plants grown under cadmium stress

The aim of this study was to determine the effect of salicylic acid (SA) on nitrogen fixation and assimilation under conditions of cadmium stress in chickpea plants. Chickpea seeds were sown in pots containing 0, 25, 50, or 100 mg of cadmium per kilogram of soil. The foliage of the 30-day-old plants was sprayed with 10−5 M SA, and the activities of nitrogenase, nitrate reductase, glutamine synthetase, glutamate synthase, and glutamate dehydrogenase were investigated. SA exposure increased the number of nodules, fresh and dry nodule masses, leghemoglobin content, and activity of the nitrogen-fixing enzyme nitrogenase compared with the control conditions. Furthermore, SA application enhanced the activities of the enzymes involved in nitrogen assimilation, in both the control and cadmium-stressed plants. The overall results indicate that SA increases the fixation and assimilation of nitrogen regardless of whether the plants are grown in the presence or absence of cadmium.

Cobalt stress affects nitrogen metabolism, photosynthesis and antioxidant system in chickpea (Cicer arietinum L.)

Abstract Plants of chickpea were exposed to varied levels of cobalt (Co) and sampled at the 60-day stage. Cobalt at concentration <100 µM significantly increased the number of nodules, their dry mass, leghemoglobin concentration and the activity of nitrogenase. Similarly, the activities of glutamate dehydrogenase, glutamine synthetase and glutamate synthase also exhibited an increase in the presence of Co <100 µM, in nodules and leaves, respectively. The various photosynthetic attributes in leaves and the activity of antioxidative enzymes both in nodules and leaves were inhibited by Co in a concentration-dependent manner. However, the lipid peroxidation and the content of proline exhibited a significant increase in response to Co and were at a maximum in the plants exposed to 250 µM concentration of cobalt. Since most of the parameters showed a significant increase in response to 50 µM cobalt, this concentration may be regarded as a threshold concentration.