Nudrat Aisha Akram

Improving salinity tolerance of plants through conventional breeding and genetic engineering: An analytical comparison

The last century has witnessed a substantial improvement in yield potential, quality and disease resistance in crops. This was indeed the outcome of conventional breeding, which was achieved with little or no knowledge of underlying physiological and biochemical phenomena related to a trait. Also the resources utilized on programs involving conventional breeding were not of great magnitude. Plant breeders have also been successful during the last century in producing a few salt-tolerant cultivars/lines of some potential crops through conventional breeding, but this again has utilized modest resources. However, this approach seems now inefficient due to a number of reasons, and alternatively, genetic engineering for improving crop salt tolerance is being actively followed these days by the plant scientists, world-over. A large number of transgenic lines with enhanced salt tolerance of different crops can be deciphered from the literature but up to now only a very few field-tested cultivars/lines are known despite the fact that considerable resources have been expended on the sophisticated protocols employed for generating such transgenics. This review analytically compares the achievements made so far in terms of producing salt-tolerant lines/cultivars through conventional breeding or genetic engineering.

Role of transgenic plants in agriculture and biopharming

At present, environmental degradation and the consistently growing population are two main problems on the planet earth. Fulfilling the needs of this growing population is quite difficult from the limited arable land available on the globe. Although there are legal, social and political barriers to the utilization of biotechnology, advances in this field have substantially improved agriculture and human life to a great extent. One of the vital tools of biotechnology is genetic engineering (GE) which is used to modify plants, animals and microorganisms according to desired needs. In fact, genetic engineering facilitates the transfer of desired characteristics into other plants which is not possible through conventional plant breeding. A variety of crops have been engineered for enhanced resistance to a multitude of stresses such as herbicides, insecticides, viruses and a combination of biotic and abiotic stresses in different crops including rice, mustard, maize, potato, tomato, etc. Apart from the use of GE in agriculture, it is being extensively employed to modify the plants for enhanced production of vaccines, hormones, etc. Vaccines against certain diseases are certainly available in the market, but most of them are very costly. Developing countries cannot afford the disease control through such cost-intensive vaccines. Alternatively, efforts are being made to produce edible vaccines which are cheap and have many advantages over the commercialized vaccines. Transgenic plants generated for this purpose are capable of expressing recombinant proteins including viral and bacterial antigens and antibodies. Common food plants like banana, tomato, rice, carrot, etc. have been used to produce vaccines against certain diseases like hepatitis B, cholera, HIV, etc. Thus, the up- and down-regulation of desired genes which are used for the modification of plants have a marked role in the improvement of genetic crops. In this review, we have comprehensively discussed the role of genetic engineering in generating transgenic lines/cultivars of different crops with improved nutrient quality, biofuel production, enhanced production of vaccines and antibodies, increased resistance against insects, herbicides, diseases and abiotic stresses as well as the safety measures for their commercialization.

Drought Tolerance: Roles of Organic Osmolytes, Growth Regulators, and Mineral Nutrients

Abstract Drought, the occurrence of a substantial water deficit in the soil or in the atmosphere, is an alarming constraint to crop productivity and yield stability worldwide. It is the leading environmental stress in world agriculture, causing losses in crop yield probably exceeding losses from all other causes combined. Drought stress adversely affects a variety of vital physiological and biochemical processes in plants, leading to reduced growth and final crop yield. Some plant species have evolved mechanisms to cope with the stress, including drought avoidance, dehydration avoidance, or dehydration tolerance. Such adaptive mechanisms are the results of a multitude of morphoanatomical, physiological, biochemical, and molecular changes. Osmoregulation is the most common physiological adaptation, which takes place by reducing cellular water potential via accumulation of a variety of organic and inorganic solutes in the cell. As a consequence, such plants are capable of taking up water from a low water potential medium to sustain normal or near normal physiological processes necessary for growth and development. However, most economically important crop species lack the capability of coping with this type of drought stress, precluding their cultivation under water-limited conditions. Various strategies have been proposed to facilitate crop production under drought conditions, in particular, development of new crop varieties with enhanced drought tolerance. Genetic improvement of crop plants for drought tolerance is a long-term endeavor, which requires, among other things, the availability of genetic sources of tolerance, knowledge of the physiological mechanisms and genetic controls of tolerance traits at different developmental stages, and employment of suitable germplasm screening and breeding protocols. An alternative and quicker strategy to promote plant drought tolerance is exogenous application of various compounds, including organic solutes (organic osmolytes and plant growth regulators) and mineral nutrients. Recently, this strategy has gained considerable attention because of its efficiency, feasibility, and cost- and labor-effectiveness. In this chapter, we review the roles of organic osmolytes, plant growth regulators, and mineral nutrients in plant response to drought stress and discuss their exogenous application in enhancing plant drought tolerance and alleviating the damaging effects of drought stress.

Salt-induced modulation in growth, photosynthetic capacity, proline content and ion accumulation in sunflower (Helianthus annuus L.)

Salt-induced changes in growth, photosynthetic pigments, various gas exchange characteristics, relative membrane permeability (RMP), relative water content (RWC) and ion accumulation were examined in a greenhouse experiment on eight sunflower (Helianthus annuus L.) cultivars. Sunflower cultivars, namely Hysun-33, Hysun-38, M-3260, S-278, Alstar-Rm, Nstt-160, Mehran-II and Brocar were subjected to non-stress (0xa0mM NaCl) or salt stress (150xa0mM NaCl) in sand culture. On the basis of percent reduction in shoot biomass, cvs. Hysun-38 and Nstt-160 were found to be salt tolerant, cvs. Hysun-33, M-3260, S-278 and Mehran-II moderately tolerant and Alstar-Rm and Brocar salt sensitive. Salt stress markedly reduced growth, different gas exchange characteristics such as photosynthetic rate (A), water-use efficiency (WUE) calculated as A/E, transpiration rate (E), internal CO2 concentration (Ci) and stomatal conductance (gs) in all cultivars. The effect of 150xa0mM NaCl stress was non-significant on chlorophyll a and b contents, chlorophyll a/b ratio, RWC, RMP and leaf and root Cl−, K+ and P contents; however, salt stress markedly enhanced Ci/Ca ratio, free proline content and leaf and root Na+ concentrations in all sunflower cultivars. Of all cultivars, cv. Hysun-38 was higher in gas exchange characteristics, RWC and proline contents as compared with the other cultivars. Overall, none of the earlier-mentioned physiological attributes except leaf K+/Na+ ratio was found to be effective in discriminating the eight sunflower cultivars as the response of each cultivar to salt stress appraised using various physiological attributes was cultivar-specific.

Alleviation of adverse effects of drought stress on growth and some potential physiological attributes in maize (Zea mays L.) by seed electromagnetic treatment.

Effects of varying preseed magnetic treatments on growth, chlorophyll pigments, photosynthesis, water relation attributes, fluorescence and levels of osmoprotectants in maize plants were tested under normal and drought stress conditions. Seeds of two maize cultivars were treated with different (T0 [0u2003mT], T1 [100u2003mT for 5u2003min], T2 [100u2003mT for 10u2003min], T3 [150u2003mT for 5u2003min] and T4 [150u2003mT for 10u2003min]) electromagnetic treatments. Drought stress considerably suppressed growth, chlorophyll a and b pigments, leaf water potential, photosynthetic rate (A), stomatal conductance (gs) and substomatal CO2 concentration (Ci), while it increased leaf glycinebetaine and proline accumulation in both maize cultivars. However, pretreated seeds with different magnetic treatments significantly alleviated the drought‐induced adverse effects on growth by improving chlorophyll a, A, E, gs, Ci and photochemical quenching and nonphotochemical quenching, while it had no significant effect on other attributes. However, different magnetic treatments negatively affected the gs and Ci particularly in cv. Agaiti‐2002 under drought stress conditions. Of all magnetic treatments, 100 and 150u2003mT for 10u2003min were most effective in alleviating the drought‐induced adverse effects. Overall, preseed electromagnetic treatments could be used to minimize the drought‐induced adverse effects on different crop plants.

Salt‐induced modulation in inorganic nutrients, antioxidant enzymes, proline content and seed oil composition in safflower (Carthamus tinctorius L.)

BACKGROUNDnSafflower (Carthamus tinctorius L.) has gained considerable ground as a potential oil-seed crop. However, its yield and oil production are adversely affected under saline conditions. The present study was conducted to appraise the influence of salt (NaCl) stress on yield, accumulation of different inorganic elements, free proline and activities of some key antioxidant enzymes in plant tissues as well as seed oil components in safflower. Two safflower accessions differing in salt tolerance (Safflower-33 (salt sensitive) and Safflower-39 (salt tolerant)) were grown under saline (150 mmol L(-1) ) conditions and salt-induced changes in the earlier-mentioned physiological attributes were determined.nnnRESULTSnSalt stress enhanced leaf and root Na(+) , Cl(-) and proline accumulation and activities of leaf superoxide dismutase, catalase and peroxidase, while it decreased K(+) , Ca(2+) and K(+) /Ca(2+) and Ca(2+) /Na(+) ratios and seed yield, 100-seed weight, number of seeds, as well as capitula, seed oil contents and oil palmitic acid. No significant effect of salt stress was observed on seed oil α-tocopherols, stearic acid, oleic acid or linoleic acid contents. Of the two safflower lines, salt-sensitive Safflower-33 was higher in leaf and root Na(+) and Cl(-) , while Safflower-39 was higher in leaf and root K(+) , K(+) /Ca(2+) and Ca(2+) /Na(+) and seed yield, 100-seed weight, catalase activity, seed oil contents, seed oil α-tocopherol and palmitic acid. Other attributes remained almost unaffected in both accessions.nnnCONCLUSIONnOverall, high salt tolerance of Safflower-39 could be attributed to Na(+) and Cl(-) exclusion, high accumulation of K(+) and free proline, enhanced CAT activity, seed oil α-tocopherols and palmitic acid contents.

Salt-induced modulation in some key gas exchange characteristics and ionic relations in pea (Pisum sativum L.) and their use as selection criteria

A glasshouse experiment was conducted to assess the influence of salt stress on some key physiological attributes of nine genetically diverse cultivars of a potential vegetable crop, pea (Pisum sativum L.). The nine pea cultivars (2001-20, 2001-35, 2001-40, 2001-55, 9800-5, 9800-10, 9200, Tere-2 and Climax) were exposed to four levels (0, 40, 80, and 120u2009mm) of NaCl in sand culture. Salt stress reduced the shoot and root dry weights, chlorophyll concentration, gas exchange and water relation parameters, leaf and root K, Ca and Ku2009:u2009Na ratio, while it enhanced concentrations of proline, leaf and root Na and Cl contents. Of all cultivars, 9800-10, 2001-20, 2001-55 and 2001-35 were higher in plant dry biomass, chlorophyll concentrations as well as in photosynthetic rate than the other cultivars at the highest salt regime whereas cvv. 2001-40, 9800-5 and 9200 were the lowest in these attributes. Overall, the genetically diverse cultivars of pea showed varying degree of salt tolerance. As the expression of different biochemical and physiological attributes differed in different cultivars under saline conditions, most of the attributes could be used as selection criteria for salt tolerance of pea. Thus, chlorophyll a, b and photosynthetic rate have great practical importance as effective physiological selection criteria for the selection of salt-tolerant pea cultivars.

A Study on the Transfer of Cadmium from Soil to Pasture Under Semi-Arid Conditions in Sargodha, Pakistan

The study was conducted on the cadmium (Cd) transfer from soil to pasture at Khizerabad Livestock Farm, District Sargodha (falling under semi-arid conditions), Pakistan. The concentrations of Cd in the soil and forage ranged from 2.80 to 6.74xa0mg/kg and 1.14 to 4.20xa0mg/kg, respectively, in different sampling periods. The higher values of Cd in pasture suggested the possible risk of entering Cd into higher food chain as these concentrations of Cd can potentially be transported from soil to different animals rearing on the farm pastures, and they should be taken into account in risk assessment of chemical toxicity. Providing region-specific mineral mixture having highly bioavailable forms of other trace elements to the ruminants like Zn, Fe, and Mn, which are known to antagonize Cd, would help in overcoming the Cd toxicity. There is an urgent need of permanent monitoring of cadmium content in the feed used in animal nutrition at livestock farm.

A study on the transfer of iron in soil-plant-animal continuum under semi-arid environmental conditions in Sargodha, Pakistan.

The present investigation on the iron (Fe) transfer from soil to plant and in turn to animal (cows), as a function of sampling periods was conducted at the Livestock Experimental Station Sargodha, Pakistan which falls under semi-arid conditions. Although the iron transfer from soil to forage increased consistently, the forage Fe content decreased progressively with increase in sampling period. Highest Fe transfer from forage to cow blood plasma was observed during October and lowest during January. The transfer of Fe from forage to animal milk was maximum during the months of October and January and minimum during December. The transfer of Fe to plasma and milk was found to be dependent variably on the growth stage of forage in this investigation. Based on the findings of the present study, it is evident that mineral supplementation with higher Fe availability is urgently warranted to the animals particularly during the months of December and January to enhance plasma Fe in the cows being reared at that livestock farm during the entire grazing period. Thus, obligatory supplementation of Fe to the ruminants is highly recommended. Since the processes involved in iron management system in humans, animals, and plants are basically similar, appropriate elemental management must be provided to the living organisms, otherwise deficient or excessive levels of iron may deteriorate the developing cells of the organisms.