The soil salinity is a dominant abiotic problem in arid and semi-arid region of the world. In these areas it occurs natural due low rainfall to leech salts from soil, aided by human activities due to excessive irrigations, over-use of fertilizers and poor drainage. The purpose of this research was to elaborate the toxic effect of salt stress to pea plants and to determine mitigating role of exogenously applied Moringa olifera leaf extract (MLE) under salinity stress. The variety of pea known as "Pea-2009" was put under salt stress at concentrations of 0 and 100 mM NaCl and treated with MLE extract at concentrations of 0 and 3% as a priming and foliar approach. Under salinity stress, the results of this study showed a decrease in plant growth (fresh and dry biomass of shoot and root s), leaf relative water contents, chlorophyll a and b, carotenoid, TFAAs, proline, K+, and antioxidants (POD, APX, and CAT), whereas the application of MLE either (seed priming/foliar spray) enhanced all studied attributes under both checked and control conditions. On the other hand, with salinity stress, the levels of Na+, MDA, and H2O2 rose, but the MLE treatment decreased the levels of Na+, MDA, and H2O2 particularly under salt stress. Salt treatment resulted in a substantial decrease in yield (number of pods plant-1, pod weight, and seed weight), while MLE fertigation increased the production of pea plants. Therefore, exogenous application of MLE potentially enhance growth of yield of economically important crops grown under stressful environmental conditions like salinity by maintaining better physio-biochemical indices.
Zinc as a micronutrient is highly essential for animals and plants to attain optimum growth and development. Zinc-deficient soils result in stunted and abnormal growth of plants. Three wheat varieties, i.e., Zincol-2016 (biofortified), Galaxy-2013, and Punjab-2011 (both non-biofortified), were sown in pots containing fertile soil in a completely randomized design with four replicas. The seedlings were sprayed with four zinc solutions (Control, 0.03%, 0.06%, and 0.09% of Zn as ZnSO4.7H2O) 40 days after sowing. It was observed that the impact of 0.06% zinc spray was more pronounced on wheat plants as compared to that of 0.03% and 0.09%. More pronounced improvement in growth, chlorophyll content, total soluble proteins, and sugars was observed in cv. Zincol-2016 as compared to that in the other two varieties, Galaxy-2013 and Punjab-2011. Similarly, Zn foliar spray significantly enhanced root, straw, and grain K+, Cu2+, Zn2+, and Fe2+ contents in all three cultivars. In contrast, grain phytate contents were reduced with increased supplementation of Zn. Data revealed that grain yield was improved significantly by exogenous application of zinc, especially at 0.06% in all three wheat varieties, but being more promising in Zincol-2016. Furthermore, Zincol-2016 accumulated higher zinc contents in grains as compared to that in Galaxy-2013 and Punjab-2011. Foliar application of zinc resulted in higher uptake and accumulation of this element from soil to seeds, thereby resulting in improved vegetative growth.
Salt stress obstructs plant's growth by affecting metabolic processes, ion homeostasis and over-production of reactive oxygen species. In this regard silicon (Si) has been known to augment a plant's antioxidant defense system to combat adverse effects of salinity stress. In order to quantify the Si-mediated salinity tolerance, we studied the role of Si (200 ppm) applied through rooting media on antioxidant battery system of barley genotypes; B-10008 (salt-tolerant) and B-14011 (salt-sensitive) subjected to salt stress (200 mM NaCl). A significant decline in the accumulation of shoot (35-74%) and root (30-85%) biomass was observed under salinity stress, while Si application through rooting media enhancing biomass accumulation of shoots (33-49%) and root (32-37%) under salinity stress. The over-accumulation reactive oxygen species i.e., hydrogen peroxide (H2O2) is an inevitable process resulting into lipid peroxidation, which was evident by enhanced malondialdehyde levels (13-67%) under salinity stress. These events activated a defense system, which was marked by higher levels of total soluble proteins and uplifted activities of antioxidants enzymatic (SOD, POD, CAT, GR and APX) and non-enzymatic (α-tocopherol, total phenolics, AsA, total glutathione, GSH, GSSG and proline) in roots and leaves under salinity stress. The Si application through rooting media further strengthened the salt stressed barley plant's defense system by up-regulating the activities of enzymatic and non-enzymatic antioxidant in order to mitigate excessive H2O2 efficiently. The results revealed that although salt-tolerant genotype (B-10008) was best adopted to tolerate salt stress, comparably the response of salt-sensitive genotype (B-14011) was more prominent (accumulation of antioxidant) after application of Si through rooting media under salinity stress.
Chlorophyll-a fluorescence is an efficient tool to determine the photosynthetic capacity of plants and the health status of plants under normal or stress conditions including salinity stress. This study was aimed to elucidate changes in the efficiency of photosystem II (PSII) in barley genotypes differing in degree of salt tolerance, which can be used for phenotyping in the breeding program for developing salt-tolerant cultivars. Twelve barley (Hordeum vulgare L.) genotypes were subjected to salt stress and salt stress reduced the growth of all barley genotypes, which is associated with a decline in chlorophyll and K+ contents (roots and leaves) and increase in Na+. Of the 12 barley genotypes, one salt-tolerant (B-10008) and one salt-sensitive barley genotype (B-14011) was selected to further investigate the structural stability of PSII using fast chlorophyll a kinetic analysis under salinity stress. The shape of OJIP transients changed due to salt stress in both salt-sensitive and salt-tolerant barley genotypes indicating a disturbance in structural stability at various points of PSII. The detailed analysis of JIP-test parameters suggested that salt stress caused photoinhibition of PSII due to enhanced inactive reaction centers, reduced absorption flux (ABS/RC), low transfer of electrons per reaction center (ETO/RC) and enhanced accumulation of QA¯ (VJ) thus reducing primary photochemistry (TRO/RC, ɸPO). These changes in PSII resulted in the reduction of the maximum quantum yield of PSII (Fv/Fm) and performance index (PIABS). Moreover, salinity stress enhanced dissipation energy flux per reaction center (DIO/RC) as a protective measure to save PSII from photooxidative damage in thylakoid membrane. The appearance of positive K and L-bands supported the idea that salt stress dissociated the light-harvesting complex from core proteins of PSII, damaged oxygen-evolving complex and reduced the structural stability of PSII by disturbing the electron transfer between acceptor and donor sides of PSII especially in salt sensitive genotype (B-14011). Moreover, such an adverse effect of salt stress on PSII was less in salt-tolerant barley genotype (B-10008). Thus, some JIP-test parameters can be used as potential phenotype marker for screening salt-tolerant genotypes.
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