Silicon Differently Affects Apoplastic Binding of Excess Boron in Wheat and Sunflower Leaves

Monocots and dicots differ in their boron (B) requirement, but also in their capacity to accumulate silicon (Si). Although an ameliorative effect of Si on B toxicity has been reported in various crops, differences among monocots and dicots are not clear, in particular in light of their ability to retain B in the leaf apoplast. In hydroponic experiments under controlled conditions, we studied the role of Si in the compartmentation of B within the leaves of wheat (Triticum vulgare L.) as a model of a high-Si monocot and sunflower (Helianthus annuus L.) as a model of a low-Si dicot, with the focus on the leaf apoplast. The stable isotopes ¹⁰B and ¹¹B were used to investigate the dynamics of cell wall B binding capacity. In both crops, the application of Si did not affect B concentration in the root, but significantly decreased the B concentration in the leaves. However, the application of Si differently influenced the binding capacity of the leaf apoplast for excess B in wheat and sunflower. In wheat, whose capacity to retain B in the leaf cell walls is lower than in sunflower, the continuous supply of Si is crucial for an enhancement of high B tolerance in the shoot. On the other hand, the supply of Si did not contribute significantly in the extension of the B binding sites in sunflower leaves.

Interactions of Silicon With Essential and Beneficial Elements in Plants

Silicon (Si) is not classified as an essential element for plants, but numerous studies have demonstrated its beneficial effects in a variety of species and environmental conditions, including low nutrient availability. Application of Si shows the potential to increase nutrient availability in the rhizosphere and root uptake through complex mechanisms, which still remain unclear. Silicon-mediated transcriptional regulation of element transporters for both root acquisition and tissue homeostasis has recently been suggested as an important strategy, varying in detail depending on plant species and nutritional status. Here, we summarize evidence of Si-mediated acquisition, uptake and translocation of nutrients: nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), iron (Fe), zinc (Zn), manganese (Mn), copper (Cu), boron (B), chlorine (Cl), and nickel (Ni) under both deficiency and excess conditions. In addition, we discuss interactions of Si-with beneficial elements: aluminum (Al), sodium (Na), and selenium (Se). This review also highlights further research needed to improve understanding of Si-mediated acquisition and utilization of nutrients and vice versa nutrient status-mediated Si acquisition and transport, both processes which are of high importance for agronomic practice (e.g., reduced use of fertilizers and pesticides).

The assessment of soil availability and wheat grain status of zinc and iron in Serbia: Implications for human nutrition

The deficiency of zinc (Zn) and iron (Fe) is a global issue causing not only considerable yield losses of food crops but also serious health problems. We have analysed Zn and Fe concentrations in the grains of two bread wheat cultivars along native gradient of micronutrient availability throughout Serbia. Although only 13% of the soil samples were Zn deficient and none was Fe deficient, the levels of these micronutrients in grain were rather low (median values of 21 mg kg(-1) for Zn and 36 mg kg(-1) for Fe), and even less adequate in white flour. Moreover, excessive P fertilization of calcareous soils in the major wheat growing areas strongly correlated with lower grain concentration of Zn. Our results imply that a latent Zn deficiency in wheat grain poses a high risk for grain quality relevant to human health in Serbia, where wheat bread is a staple food.

[Biogenesis of 6-aminopenicillanic acid (6-APA) and penicillin in Penicillium chrysogenum: effect of the biocatalyst chrysin]

The investigations were concerned with the examination of the effect of chrysin, a biocatalyst on the 6-APA and penicillin biogenesis in Penicillium chrysogenum (Thom), Panlabs P-5 strain. Chrysin, a natural plant biocatalyst was used to increase the large scale production of penicillin. The experiments were conducted on chemically defined media under conditions determined for this strain in shake flask fermentations. The production of 6-APA and penicillin G was checked and confirmed by HPLC. The level of free 6-APA in the germinating culture increased 12 hours after the inoculation of the P. chrysogenum conidiospores. With the addition of chrysin to the germinating culture the biogenesis of penicillin started in 14 hours but in the experiments without the chrysin addition it was observed 21 hours after the conidiospore inoculation. The origin of free 6-APA in the fermentation broth could be explained solely by the involvement of an independent metabolic pathway of the 6-APA and penicillin biogenesis i.e. N-acylation of free 6-APA. In the fermentation broth of P. chrysogenum it is necessary to distinguish between the primary 6-APA which is a product of the biosynthesis via L-cystine/D-valine and the secondary 6-APA which originates from isopenicillin N.