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In the present study the ameliorating effects of Si nutrition supplied as 1 mmol L−1 sodium silicate were proved on the seedling growth of canola (Brassica napus L.) seedlings under salinity stress (i.e. 0, 30, 60, 90 and 120 mmol L−1sodium chloride). Salinity obviously disrupted cellular homeostasis, something was evident in the decreased percent of scavenging HO-free radical and Metal chelating %, and hence reduction in photosynthetic pigments contents (chl.a and carotenoids). Silicon nutrition, however, enabled canola cells to balance between the steady-state levels of different ROS through improving the detoxification of the excess ROS. This was prevalent in higher scavenging percent of HO- and metal chelating. In addition, Si maintained membranes integrity through improved levels of lipid peroxidation inhibition %. Si buffered oxidative stress through sustaining the enzymatic and non-enzymatic scavenging capacity of reactive oxygen species in salt-stressed plants. Enzymatic antioxidants such as (CAT, SOD, APX, and POS) activities as well as non-enzymatic antioxidants such as carotenoids contents phenolics contents increased at 120 mmol L−1 sodium chloride. Thus, silicon nutrition alleviated the deleterious effects of salinity on the growth of canola plants through increased reactive oxygen species scavenging capacity (enzymatically and non-enzymatically), maintaining the membrane integrity of seedling cells as evidenced by raising the reducing power contents, sustained higher levels of chlorophyll. Consequently, enhance seedlings growth observations.

Co-deprivation of some photosynthetic electron transport mineral pairs is sought for enhancing antioxidant accumulation in a local isolate of Arthrospira (Spirulina) platensis, to improve their nutritional value and economic feasibility. The omitted element pairs were iron and sulfur (‑FeS), manganese and iron (‑MnFe) and nitrogen and sulfur (‑NS); chosen on the basis of their strong mediation in redox activities (Fe, Mn or S) or as sinks (N or S) of photosynthetic electrons. Antioxidant contents were estimated in 15 days old cells as growth of Arthrospira was not deteriorated by depriving the studied mineral pairs on the one hand and older cells tend to accumulate secondary compounds than younger ones whose bioenergetics are diverted into vegetative growth on the other hand. Iron‑sulfur, followed by iron‑manganese deprivation, induced the highest rates of photosynthtic oxygen evolution and respiratory oxygen uptake. Nitrogen‑sulfur starved cells, however, seem just survived as the increment of their dry mass relative to the inoculum was insignificant; they exhibited the lowest rates of photosynthesis with significantly enhanced respiration. A positive correlation between dry mass allocation and antioxidant accumulation can be deduced in the following order: ‑FeS > ‑FeMn > ‑NS. Vitamins A and tocopherols exhibited significant rise per unit dry mass (about fourfold that of the control) at ‑FeS while total antioxidants, reducing power and phenolics were more than doubled. FeMn pair deprivation sustained growth but did not enhance the accumulation of the targeted antioxidants. Under NS deprivation, neither Vitamin A nor tocopherols was enhanced although total antioxidants, reducing power and total phenolics were significantly higher than in control cultures. Soluble carbohydrates and free amino acids did not exhibit significant alterations in response to the imposed deprivations, indicating that enhancing the antioxidant accumulation did not take place at the expense of growth or primary metabolism in Arthrospira.

Boron (B) toxicity often limits crop yield and the quality of production in agricultural areas. Here, we investigated the effects of calcium (Ca), silicon (Si) and salicylic acid (SA) on development of B toxicity, B allocation in canola (Brassica napus cultivar Sarw 4) and its role in non-enzymatic antioxidants in relation to yield of this cultivar under B toxicity. Canola seedlings were subjected to four B levels induced by boric acid in the absence or presence of Ca, Si and SA. The results showed that Ca, Si and SA addition ameliorated the inhibition in canola growth, water content (WC), and improved siliqua number, siliqua weight and seed index. The B content in shoots and roots and total B accumulation in the whole plant were increased in control plants under B-toxicity-stress, and these parameters were significantly decreased by addition of Ca, Si and SA. The shoot ascorbate pool (ascorbate, AsA, and dehydroascorbate, DHA), α-tocopherol and phenolics (free and bound) were increased under B toxicity, and were significantly decreased in most cases by addition of Ca, Si and SA, except α-tocopherol, which increased at low B levels (0, 25 and 50 mg kg soil-1). The glutathione content did not obviously change by B stress, while added Ca, Si and SA inhibited its accumulation under B stress. In addition, B toxicity reduced the shoot flavonoids content; however, this reduction was not alleviated by the use of Ca, Si and SA treatments. It could be concluded that growth and yield of canola plants grown under high B concentration improved after external application of Ca, Si or SA.

AMELIORATION with silicon (1mM sodium silicate Na2SiO3) or humic acid (50mg L-1 HA) was tested in counteracting the phytotoxicity of copper oxide nanoparticles (CuONPs) at 50, 100 and 150mg L-1 on Safflower plants (Carthamus tinctorius). Si sustained seed growth at (150mg L-1 CuO NPs). The application of HA increased copper concentration in seedling by about 5 to 10 fold, relative to the control at 50 and 100mg L-1. Fresh weight of safflower seedlings were reduced significantly at 100mg L-1 CuO NPs. Si enhanced fresh and dry matter gain under 100 and 150mg L-1 CuO NPs, also HA improved dry matter at 100mg L-1 CuO NPs. Chlorophyll a and carotenoid contents reduced by about 60% and 50% at CuO NPs (100mg L-1), respectively as compared to control. Chlorophyll a and carotenoid contents reduced by about 60% and 50% at CuO NPs (100mg L-1), respectively as compared to control. Si or HA sustained Chl.a content unchanged and improved carotenoids contents at 100mg L-1 CuO NPs.Phenolics contents significantly increased under CuO NPs phytotoxicity. External application of HA provoked more phenolics content. Nano-CuO phytotoxicity reduced H2O2 scavenging and lipid peroxidation inhibition %. Si or HA enhanced significantly lipid peroxidation inhibition % and H2O2 radial scavenging %. Si or HA reflected significant enhancement of SOD and CAT enzymes under elevating concentrations of CuO NPs. Si enhanced significantly POD activity at (50, 100 and 150mg L-1) CuO NPs levels.

Boron (B) toxicity is an important environmental constraint that limits crop productivity. Salicylic acid (SA) and thiamin participate in the processes underlying plant adaptations to certain types of abiotic and biotic stress. This study aimed to investigate the individual and combined effects of SA or thiamin and B on physiological attributes of wheat under normal and B-toxicity conditions. Seeds were soaked in SA or thiamin and excess B was applied for 10-day after planting the seedlings. Growth parameters, photosynthetic pigments, B and some elements concentrations, hydrogen peroxide (H2O2), proline, other free amino acids, soluble proteins and carbohydrates were measured. Application of SA or thiamin showed an increase in tolerance towards high B as indicated by H2O2, amino acids, soluble proteins and carbohydrates contents. The results support the conclusion that SA and thiamin alleviate B toxicity not at the level of B content but by affecting other elements and osmo-protective metabolite.

This study investigates the response of two wheat cultivars to boron toxicity stress. Plants were cultivated in sand culture and boron was applied to the culture for 10-day. Symptoms, tiller number, boron concentration, soluble sugars, proteins and other free amino acids than proline were studied. The differences between the cultivars were apparent from higher boron and the chlorosis in tolerant cultivar was about 7% compared to the sensitive one 70%. Tiller number gradual decreased in tolerant-cultivar, while in sensitive one a dramatic reduction was exhibited by increasing boron level in culture media. In most boron levels, although the accumulation of soluble carbohydrates was significantly stimulated in shoot of B-sensitive cultivar (Gemmeza 9; S), there were no appreciable differences in the production of carbohydrates in shoot of B-tolerant cultivar (Sakha 93; T). However, the soluble proteins production did not affect by most boron levels in both cultivars. The presence of boron at various concentrations induced a production of free amino acids in shoots of each of the two test cultivars. Tiller number (yield index) decreased in the two test cultivars and was in range 50-59 and 84-92% less than control plants for tolerant and sensitive cultivar, respectively. DOI: http://dx.doi.org/10.5281/zenodo.200373

Concerns about the vulnerability of agricultural production to climate change are increasing. The establishment of seedlings at early growth stages of crop plants, one of the most important determinants of high yield, is severely affected by extreme temperatures. Therefore, efforts must be made to achieve high germination rate and vigorous early growth under extreme temperature conditions.Alfalfa is a perennial forage crop with high yield, good quality and high protein content, but is frequently exposed to extreme temperature conditions. The primary purpose of this investigation was to test the hypothesis that L-ascorbic acid (AsA) and pyridoxine (B6) pretreatment can completely or partially alleviate the effect of extreme temperature stress on seed germination and other physiological activities of alfalfa seedlings. Such treatment could be of importance for the establishment of alfalfa seedlings under temperature conditions colder or hotter than the optimum.Several parameters were studied in alfalfa seedlings primed before germination with 50 ppm ascorbic acid or 50 ppm pyridoxine for 6 h and then subjected to various temperatures (10, 15, 20, 25, 30, 35 and 40°C) for 7 days.The germination percentage of alfalfa seeds was negatively affected by extreme temperature. The vitamin treatments failed to alleviate the depressive effect of extreme temperature stress on seed germination. Extreme temperature also induced a reduction in the growth, total water content and respiration rate of alfalfa seedlings. Seed soaking in vitamins modified the stress-induced changes in respiration rate and growth criteria. Temperatures above or below the optimum stimulated the accumulation of soluble carbohydrates in alfalfa seedlings. Treatment with AsA or B6partially or completely retarded the stimulatory effects of extreme temperature on soluble carbohydrate accumulation in the seedlings except in the case of 40 °C, where a significant stimulation was detected. However, extreme temperature stress and its interactive effects with AsA or B6induced an inhibitory effect on the accumulation of free amino acids and soluble proteins in the test seedlings.