THE EFFECT OF GIBBERELLIC ACID (GA₃) ON GROWTH, PHOTOSYNTHETIC PIGMENTS, AND METAL BIOSORPTION IN THE WATER FERN Salvinia natans (L.) All. UNDER ZINC STRESS

The response of plants to heavy metals involves phytohormones, particularly cytokinins, with zeatin being one of the active forms. Exogenous phytohormones are believed to induce plant resistance to heavy metals and enhance phytoextraction. We investigated the impact of exogenous zeatin on the morpho-physiological characteristics of young and mature sporophytes of Salvinia natans and their ability to extract zinc ions from the aquatic environment. It has been shown that zeatin mitigated the adverse effect of zinc sulfate on dry weight accumulation, but did not alleviate its negative impact on fresh weight accumulation in both young and mature sporophytes. During intensive growth and sori formation and spore maturation stages under zinc loading, exogenous zeatin (at 10–6 M concentration) led to 40% and 50% increase in the dry weight of young and mature sporophytes, respectively. In the presence of zinc sulfate, the total chlorophyll content decreased by 23% in the fronds of young sporophytes and by 44% in the fronds of mature sporophytes, while total carotenoids decreased by 21% in both cases. Zeatin addition alleviated the negative impact of the metal on the pigment complex in young sporophyte fronds but exacerbated it in mature sporophyte fronds. The pigment complex of the sporophyte was more susceptible to metal action during sori formation and spore maturation, resulting in frond browning and pronounced chlorosis. However, chlorosis was less intense and localized upon zeatin addition. The capacity of S. natans sporophytes to extract zinc ions from the aqueous medium was demonstrated, with zinc concentration decreasing by over tenfold from 10 mg·L–1 to 0.6 mg·L–1after 14 days of cultivation. The application of zeatin did not affect the efficiency of zinc ions extraction from water.

Rht4 is characterized as a GA-responsive dwarf gene in bread wheat (Triticum aestivum L.). The responsiveness of Rht4 to exogenous GA3 was characterized in seedlings, but the effects of exogenous GA3 on the important morphological and agronomic traits such as plant height, grain-filling rate, and yield components are unclear. In this study, the Rht4 responsiveness of exogenous GA3 on these traits was evaluated using the homozygous F4:5 and F5:6 lines derived from a cross between Jinmai47 and Burt ert937 (Rht4 donor). After exogenous GA3 application, the plant height of the dwarf lines was, on average, increased by 17.54%, about 7.92% more than that of the tall lines. Compared with the tall lines, application of exogenous GA3 significantly increased the kernel weight, maximum grain-filling rate (Gmax), average grain-filling rate (Gave) and kernel weight increment achieving Gmax (Wmax) in both superior and inferior grains, while the day on which the maximum grain-filling rate was reached (Tmax) in Rht4 dwarf lines was significantly earlier in the two generations. What is more, the grain number spike-1 , grain yield plant-1 , and 1000-kernel weight (TKW) of the dwarf lines notably increased after exogenous GA3 -treatment, while there was no significant change in the tall lines except for TKW. The quality traits of the dwarf lines with GA3 -treatment were greatly improved. Taken together, these results suggested that the application of GA3 could improve the grain-filling process of Rht4 and compensate for some negative influences, which may provide a reference for its application in wheat breeding and promote the characterization of its regulatory mechanisms.

The response of wheat plants ( Triticum aestivum L.) to a combined (consecutive) impact of low temperature (4 ° С) and cadmium sulphate (100 µM) was investigated. Pretreatment of the seedlings with cadmium for 1 day caused an increase in cold tolerance, which continued during the following exposure to the 4 ° С temperature, reaching a maximum after 1–2 days, but decreasing somewhat in the end of the experiment (7 d). At the same time cadmium did not prevent the accumulation of fresh and dry biomass of the shoots at subsequent exposure of the seedlings to 4 ° С temperature, although it negatively affected the total chlorophyll content in the leaves. Pretreatment of the seedlings by chilling during 1 day also caused an increase in their cold tolerance, which persisted for a few days at subsequent exposure to cadmium, but decreased significantly in 6–7 days. Moreover, the chilling pretreatment decreased the accumulation of fresh and dry biomass of wheat shoots as well as the total chlorophyll content in the leaves at the subsequent prolonged cadmium impact. It was concluded that the response of wheat plants to a prolonged impact (7 d) of a low non-freezing temperature or cadmium changed significantly if preceded even by a short-term (1 d) treatment with the other stress factor. In particular, exposure to cadmium before chilling partially ‘disrupted’ the programme of cold adaptation, wherefore the plants’ resistance did not reach the level typical for cold hardening at a temperature of 4 ° С, and cold pretreatment of the plants, in turn, aggravated the negative effects of cadmium on cold tolerance, biomass accumulation and the content of photosynthetic pigments in wheat leaves.

Water pollution is a global problem in recent times, and its remedy has become imperative to safeguard the health of ecosystems and humans. To solve the water pollution problem, detecting the presence of various pollutants in water is the first critical step. Although many physical and chemical techniques have been developed to date to measure the concentrations of different types of contaminants in the water, the biological methods are the most feasible due to their easy operational process and cost-effectiveness. The cyanobacteria, a unique group of photoautotrophs known to occupy various aquatic environments, are the potent candidates for detecting the presence of different types of pollutants in water. Due to their common occurrence in water bodies, toxicological responses of cyanobacteria have widely been investigated, which suggests that toxicological research on cyanobacteria may help us evaluate the levels of various contaminants in water bodies because they respond to different pollutants in distinct manners, either by modulating their morphological, ultrastructural, and physiological indices or by changing their community composition and altering molecular biological phenomena. However, water pollution is becoming very complex daily because new pollutants are being produced and discharged daily. Therefore, the toxicological responses of cyanobacteria must be assessed against both existing and emerging contaminants to be used as bioindicators for both kinds of pollutants. In the present chapter, we initially provided glimpses of the status of global water pollution and the types of major water pollutants, followed by discussing bioindicators’ advantages over other traditional methods in determining water pollution. Besides, the chapter also included information on the potential of cyanobacteria as bioindicators of water pollution and detailed descriptions of the cyanobacterial bioindicator characteristics for specific pollutants. Eventually, the chapter suggested that investigating the toxicological impacts of emerging contaminants like pharmaceuticals and aromatic pollutants on cyanobacteria and the selection of unique and distinct bioindicator characteristics will be helpful to better predict the presence of these pollutants in aquatic systems.

In a controlled environment, the effect of zinc deficiency on the photosynthetic apparatus (PSA) of 7-day-old winter wheat seedlings ( Triticum aestivum L.) cv. Moskovskaya 39 was studied. It was shown that in the early phases of seedling development, the zinc lack in the root environment does not clearly affect the plant shoot height and accumulation of dry biomass, but it has a negative effect on a number of PSA parameters. In particular, the leaf area of the 1-st leaf decreased and the photosynthetic pigments (chlorophylls and carotenoids) content and stomatal conductance declined. At the same time, with the microelement deficient, a redistribution of chlorophylls towards the light-harvesting complexes (LHC) of photosystems was noted, aimed at increasing light absorption. No significant changes in the ratio of chlorophylls ( a / b ) and the photosystem II (PS II) activity which was determined by the F v /F m parameter, characterizes the potential quantum yield of photochemical activity of PS II, were found. In addition, the rate of photosynthesis was maintained at a high level in seedlings deficient in zinc, and the integrity of cell membranes was maintained, which largely ensured their normal growth and accumulation of dry biomass. It has been suggested that the negative effect of zinc deficiency on a number of PSA parameters in seedlings may subsequently be one of the reasons for the decrease in wheat seed productivity indicated in the literature under these conditions.

Two pot experiments were conducted at the Experimental Station and in the Laboratory of Vegetable and Floriculture Department, Faculty of Agriculture, Mansoura University during the two successive seasons of 2005/2006 and 2006/2007 to study the effect of GA3 and ABA at different concentrations on vegetative growth, yield and chemical composition of khella plants growing under different potassium fertilization rates. The obtained results exhibited that khella plant height, shoot dry weight and content of photosynthetic pigments in the leaves as well as N, P and K concentrations in the shoots were increased with increasing potassium fertilization levels and the highest values were recorded when the plants received the high level of potassium (45 kg/fed.). GA3 and its interactions with potassium fertilization increased significantly the plant height, shoot dry weight and N, P and K concentrations in the shoots, while the content of photosynthetic pigments in the leaves was decreased. On the other hand, ABA and its interactions with potassium caused a decrease in the previous parameters except for the content of photosynthetic pigments in the leaves which was increased. Regarding number of umbels and fruit yield per plant as well as the content of khellin and visnagin (%), data showed that potassium fertilization and ABA as well as their interactions significantly increased these parameters. However, GA3 application alone caused a decrease in number of umbels and fruit yield per plant as well as the principle constituents (%). Meantime, GA3 with potassium fertilization at either 30 or 45 kg/fed. increased the fruits content of visnagin.

As a result of the performed investigations, it has been found that at the concentration of oil products, including petrol and diesel fuel, of 5.0 and 10.0 mg/L the content of photosynthetic pigments (chlorophylls <i>a</i> and <i>b</i> and carotenoids), and also (chlorophyll <i>a</i>/chlorophyll <i>b</i>) and (chlorophyll <i>a</i> + chlorophyll <i>b</i>)/carotenoids ratios significantly decreased, which is indicative of inhibiting the vital activity of macrophytes. It has been shown that the pigment system of <i>C. demersum </i>proved to be rather resistant to the influence of the concentrations of petrol and diesel fuel of 0.5 and 1.0 mg/L. This fact suggests that this species of higher aquatic plants can be used for phytoremediation of the aquatic environment moderately contaminated by oil products.

Effects on aquatic ecosystems

Selenium (Se) is considered a beneficial element for plants. It plays a fundamental role in several physiological processes that influence their growth, development, and productivity. However, the influence of Se depends on both the concentration used and the method of application. It was hypothesized that low concentrations of Se stimulate plant growth and development, and foliar applications are more effective as a method of application. For that reason, the objective of the present investigation was to evaluate the effectiveness of 5, 10, 25, and 50 µM of Se applied radically and foliarly in bell pepper crop employed in a soilless cultivation system. The presence of Se by both application methods stimulated plant production, dry biomass accumulation, and photosynthetic pigment content, as well as leaf concentration of nitrogen (N) and potassium (K), except for calcium (Ca), and phosphorus (P) which were influenced by the application method and Se concentration factor, respectively. Fruit size was favored by the Se concentration factor while shelf life was favored by the application method. Se concentration in fruit dry matter varied as a function of Se concentration and application method, being more effective for human consumption by foliar application. This demonstrates the potential of Se as a beneficial element and reinforces the importance of proper management of both the concentration and method of Se application in agricultural crop production.

Microplastics and heavy metals are the two main contaminants that are often found in aquatic environments and can lead to major issues for aquatic organisms. Polystyrene (PS) is a type of microplastic that is commonly found in aquatic environments. Hard clams are one of the organisms that are often used as a bioindicator of water pollution, and they can live in a certain salinity range. The objective of this study is to investigate the potential of PS particles as heavy metal vectors in M. lusoria influenced by differences in salinity. The result showed that the highest increase in concentrations of all heavy metals in hard clams was found in those placed at higher salinities. Hard clams that were placed at higher salinity required more water, allowing more PS particles to enter the clams’ bodies. Hard clams placed at salinity 30‰ always gathered significantly more PS particles (p<0.05) than hard clams placed at the other two salinities (20 and 25‰). This is also corroborated by water depletion at a salinity of 30‰, which is significantly higher (p<0.05) than the other two salinities. Our findings indicate that PS particles have the potential as vectors for heavy metal pollutants in hard clams in environments of varying salinity.

Ecotoxicological effects of TiO2 nanoparticulates and bulk Ti on microalgae Chaetoceros muelleri

Biosorption is a promising alternative method to treat industrial effluents, mainly because of its low cost and high metal binding capacity. In this work, Zinc and Chromium biosorption process by Sargassum sp. seaweed biomass was studied. The work considered the determination parameters of Zinc and Chromium sorption such as pH, temperature, agitation speed and biomass size. The optimum conditions were: pH3, temperature (303k) room temperature, biomass size 0.5mm and agitation speed 150rpm. The maximum uptake of Chromium and Zinc is 65% and 53% respectively. The kinetic study revealed that the adsorption of Chromium and zinc by Sargassum sp . fitted the Langmuir isotherm.

ABSTRACTIn the present study, the roles of foliarly applied 5-aminolevulinic acid (ALA) in photosynthetic parameters, ion contents and expression of several photosynthetic genes were investigated in rapeseed (Brassica napus L.) under well watered and drought conditions. Drought stress reduced relative plant growth rate and leaf water content (RWC), and contents of photosynthetic pigments, starch, soluble proteins and ions in roots. This type of stress, however, stimulated the accumulation of soluble sugars and free amino acids, as well as leaf proline contents. The transcript levels of photosynthetic genes were also down-regulated under drought stress. Exogenously applied ALA partially reduced growth inhibition and increased RWC and chlorophyll contents under drought conditions. The expression of photosynthetic genes was induced by ALA under both normal and drought conditions, which may contribute to an increased photosynthetic capacity. The ALA application further improved the accumulation of hexose and sucrose, accompanied by the maintenance of starch contents in the leaves and possibly relatively higher RWC under drought stress. Based on these results, we suggest that ALA promotes plant growth under drought stress via improving photosynthetic assimilation, increasing chlorophyll content and inducing the expression of several photosynthetic genes.

Physiological and biochemical effect of silver on the aquatic plant Lemna gibba L.: Evaluation of commercially available product containing colloidal silver

The Psychology of happiness: M. Argyle: Methuen, London (1987). 256 pages, £7.95.