EFFECT OF Cu AND Mn TOXICITY ON CHLOROPHYLL FLUORESCENCE AND GAS EXCHANGE IN RICE AND SUNFLOWER UNDER DIFFERENT LIGHT INTENSITIES

Copper (Cu) and manganese (Mn) are essential micronutrients for plants, but toxic at high concentrations. Responses of rice (Oryza sativa L.) and sunflower (Helianthus annuus L.) to toxic concentrations of Mn and Cu (up to 100 μM) were studied under three light intensities including low (LL, PPFD=100), intermediate (IL, PPFD=500) and high (HL, PPFD=800) light intensities in hydroponic medium. Rice plants showed higher susceptibility than sunflower to both heavy metals concerning dry matter of shoot and root. Growing under higher light intensity strengthened the effect of Cu toxicity while ameliorated that of Mn, the latter was attributed to the lower Mn accumulation of HL plants in both shoot and root. Chlorophyll content of leaves was influenced negatively only by Cu treatment and that at the highest concentration in the medium (100 μM). Similar with growth results, reduction of net assimilation rate (A) was higher in HL than LL plants treated by excess Cu, but in contrast to growth response, reduction was more prominent in sunflower than rice. Excess Mn-induced reduction of A was similar between LL and HL plants and was greater in sunflower than rice. Reduction of A was partly attributable to stomatal limitation, but non-stomatal mechanisms were also involved in this reduction. Copper and Mn treatment did not change the optimal quantum efficiency of PSII in dark-adapted chloroplasts (Fv/Fm ratio), but Fv/F0 was influenced particularly by Cu treatment, the reduction was higher in rice than sunflower and in HL compared to LL plants. Regarding excess Cu and Mn-mediated alterations in chlorophyll concentration, Fv/F0 and Tm values, it was suggested that, Cu and Mn toxicity depress the leaf photosynthetic capacity primarily by causing a significant alteration of the composition and functional competence of the photosynthetic units rather a reduction in the number of photosynthetic units (PSUs) per unit leaf area

Photosynthesis, Nitrogen Metabolism and Antioxidant Defense System in B-Deficient tea (Camellia sinensis (L.) O. Kuntze) Plants

Response of tea plants to B deficiency was studied in hydroponic medium under environmentally controlled conditions. Plants height, number of leaves and dry matter production of shoot and root were significantly decreased by B deficiency. Concentration of chlorophyll, carotenoids, anthocyanins and flavonoids was not affected by B deficiency in the young leaf, while a significant reduction of Chl a/b ratio and increase of carotenoids concentration was detected in the old leaf. Among leaf chlorophyll fluorescence parameters, only non-photochemical quenching (qN) increased in parallel to increase of carotenoids in the old leaves of B-deficient plants. Net assimilation (A) and transpiration (E) rate and stomatal conductance (gs) were decreased significantly under B deficiency conditions only in the young leaf. Activity of nitrate reductase increased in the young and decreased in the old leaf slightly, but was not influenced by B deficiency in the roots. Nitrate concentration diminished while nitrite concentration increased in the young leaf under B starvation. Data of antioxidant enzymes activity implied that ascorbate peroxidase was likely important for the protection of old leaf and peroxidase for roots, while superoxide dismutade contributed to the protection of all three organs against oxidative stress provoked by B deficiency conditions. H2O2 content of leaves and roots did not increase or even decreased under B deficiency conditions, that was associated with accumulation of proline. Our evidences suggest a protective role for proline against free radicals that may contribute significantly to the higher tolerance of tea plants to B deficiency

Bound Putrescine, a Distinctive Player under Salt Stress in the Natrophilic Sugar Beet in Contrast to Glycophyte Tobacco

The influence of salinity on the different polyamine fractions (free, conjugated, and bound) was compared in a natrophilic halophyte (Beta vulgaris L. cv. IC) and a salt sensitive glycophyte (Nicotiana rustica L. cv. Basmas). Low-level salinity (25 mM NaCl) and high salinity (150 and 50 mM NaCl for sugar beet and tobacco, respectively) were supplied in hydroponics. Under low salinity shoot dry weight increased in sugar beet, but decreased in tobacco. Under high salinity growth reduction in sugar beet and tobacco were similar. However, sugar beet accumulated higher Na and Cl in roots and shoots than tobacco. Low salinity caused an increase (22%) in the rate of net CO2 assimilation in sugar beet. This parameter was depressed in both species under high salinity. Sugar beet had constitutively higher free spermine levels in roots and shoots than tobacco. Spermidine levels were constitutively higher in shoots of sugar beet and in roots of tobacco. Under salt stress tobacco plants tended to increase free polyamine levels. The most important salt–induced rise in polyamine titer, however, was found in roots and shoots of sugar beet. In sugar beet roots the bound putrescine fraction increased 9.3-fold under growth- stimulating salt supply (25mM) and 20-fold under salt stress (150 mM). In tobacco roots this fraction only increased 2.3 and 3.8-fold under mild (25 mM) and high salt stress (50 mM), respectively. Our results provide support to the view that bound putrescine contributes to the protection against salt stress in the natrophilic sugar beet

Influence of Si Supplementation on Growth and Some Physiological and Biochemical Parameters in Salt-Stressed Tobacco (Nicotiana rustica L.) Plants

Tobacco is a salt-sensitive glycophyte crop species. In this work effect of silicone (Si) supplementation (1 mM as Na2SiO3) was studied in Nicotiana rustica L. cv. Basmas grown hydroponically in growth chamber under control, low (25 mM) and high (75 mM) NaCl concentration for two weeks. Dry matter production of leaves was depressed by salinity level as low as 25 mM and higher salt concentration decreased plants dry weight by 52-82%. Si supplementation alleviated salt stress effect as could be judged by higher dry weight of shoot and roots in +Si plants compared with –Si counterparts. Leaf chlorophyll a and carotenoids concentrations and net assimilation rate were higher in Si-treated plants not only in salt-affected but also in control plants. Si treatment resulted in higher concentration of soluble carbohydrates but not proline. Leaf transpiration rate, unexpectedly, was not diminished by Si and water use efficiency was rather lowered by Si in salt-treated plants. Si application caused a slight reduction of Na concentration while increased that of K and Ca significantly and resulted in higher K:Na ratio in the leaves, stem and roots. Our results suggested that Si application improved tolerance to salt stress in tobacco due to an enhancement of photosynthesis, accumulation of organic osmolytes as well as improvement of K:Na selectivity but not limiting water loss. In addition, greater dry matter production of Si-supplemented plants in the absence of salt was associated with elevated photosynthesis rate, higher K and Ca uptake and proline content

Stressed out symbiotes:hypotheses for the influence of abiotic stress on arbuscular mycorrhizal fungi

Abiotic stress is a widespread threat to both plant and soil communities. Arbuscular mycorrhizal (AM) fungi can alleviate effects of abiotic stress by improving host plant stress tolerance, but the direct effects of abiotic stress on AM fungi are less well understood. We propose two hypotheses predicting how AM fungi will respond to abiotic stress. The stress exclusion hypothesis predicts that AM fungal abundance and diversity will decrease with persistent abiotic stress. The mycorrhizal stress adaptation hypothesis predicts that AM fungi will evolve in response to abiotic stress to maintain their fitness. We conclude that abiotic stress can have effects on AM fungi independent of the effects on the host plant. AM fungal communities will change in composition in response to abiotic stress, which may mean the loss of important individual species. This could alter feedbacks to the plant community and beyond. AM fungi will adapt to abiotic stress independent of their host plant. The adaptation of AM fungi to abiotic stress should allow the maintenance of the plant-AM fungal mutualism in the face of changing climates. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s00442-016-3673-7) contains supplementary material, which is available to authorized users

Salinity tolerance in cotton

Cotton is the chief crop and main pillar of textile industry. Its fiber and seed have significant economic importance. However, salinity interferes with the normal growth functioning and results in halted growth and declined yield of fiber and seed. Salinity effects are more obvious at early growth stages of cotton, limiting final yield. Salt decreases boll formation per plant which ultimately gives decreased fiber yield and poor lint quality. Salinity is a global issue increasing every year due to uncontrolled measures and improper land management. Application of saline irrigation water is adding increments to already existing salts and deteriorating the productive soil. Arid regions are totally dependent upon rain for growth of cotton. Salt problem is more in arid regions due least availability of moisture and water for flushing salts from cotton root zone. Moreover, higher temperature favors excessive evaporation under arid conditions and leaving salt on the upper surface of soil. Salts at the surface soil impede cotton seed germination. In this chapter, we discussed formation of saline soils and their sources which deter cotton growth. Physiological changes, oxidative stress caused due to salinity, role of molecular transporters involved in detoxification and specific gene expression is also illuminated. © Springer Nature Singapore Pte Ltd. 2020. All rights reserved

The effects of selenate and sulphate supply on the accumulation and volatilization of Se by cabbage, kohlrabi and alfalfa plants grown hydroponically

The effect of Selenium (Se) supplementation at five levels of 0 (control), 5, 10, 15, 20 ìM in plants supplied with one of four concentrations of sulphur (S) including 0.05, 0.25, 0.5 and 1.0 mM was investigated in two varieties of Brassica oleracea (cabbage and kohlrabi) and alfalfa (Medicago sativa L.) in a hydroponic experiment. In severely S deficient plants (0.05 mM), Se acted as a toxic element, alfalfa was the most susceptible plant that died at this treatment. However, in plants supplied with near adequate (0.5 mM) or adequate (1.0 mM) S, Se acted as a growth promoting element. The most pronounced stimulation of growth was observed in cabbage and the lowest in alfalfa. Increasing S concentration in the medium, reduced Se uptake and transport. In contrast, S uptake and transport increased in response to Se addition. Se volatilization was higher in alfalfa than cabbage and kohlrabi when expressed on unit shoot dry weight or leaf area basis, but not when expressed per plant. Results suggested that Se supplementation of plants supplied with adequate S, not only had beneficial effects on plants growth but also can have application in enrichment of livestock fodder and human food.