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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.

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