Boron essential plant nutrient

Boron, chlorine, copper, iron, manganese, molybdenum (for N-fixation), and zinc are considered essential plant micronutrients. These elements are needed by plants only at very low levels and frequently are toxic at higher levels. There is some chance that other elements will be added to this list as techniques for growing plants in environments free of specific elements improve. Most of these elements function as components of essential enzymes. Manganese, iron, chlorine, and zinc may be involved in photosynthesis. Though not established for all plants, it is possible that sodium, silicon, and cobalt may also be essential plant nutrients. 

Boron is an essential trace plant nutrient. Although its exact function has not yet been established, deprivation of boron alfects plant growth and in boron-poor soils, crop yields are diminished. An important application of borax is in borate fertilizers. In contrast, the toxicides of boric acid and borax to animal life are sufficient for them to be used as insecticides,... 

Non-metallic trace nutrients include boron (for plants only), iodine and fluorine (for vertebrates), selenium, and silicon. Selenium forms an essential part of the important mammalian enzyme glutathione peroxidase which, in mammals, protects membranes from oxidation and is one of the microbiocidal enzymes in phagocytes (Stadtman, 1980). A selenium, iron, and molybdenum enzyme was described above under molybdenum . Silicon is thought to contribute to the architecture and resiliance of connective tissues of vertebrates. In rats, silicon is essential for growth and development. It seems to be present as a silanolate, with Si-O-R bridges to such polysaccharides as heparin and hyaluronic acid (Schwarz, 1973). 

Soil pH is easily tested for and determines the availability of nutrients and the success of white clover. Very acid soils (below pH 5.0) will cause a deficiency of the trace elements iron, boron, copper and molybdenum and conversely will cause injury to plant growth by increasing the availability of aluminium and manganese to toxic levels. Over-liming, on the other hand, which can raise the pH above 6.5, will reduce the availability of certain essential elements such as phosphorus, manganese and boron. 

Boron and arsenic are natural components of soil and are both present as oxyanions. Boron is present as boric acid or borate polymers, and arsenic is present as arsenate. While boron is weakly held by soil, arsenic is similar to phosphate in its interactions with soil constituents. Boron is an essential nutrient for plants however, it is also toxic to plants at relatively low levels. Arsenic is toxic. The laboratory chemistry of both of these elements is well understood, but their environmental chemistry, speciation and movement, is less well understood [23-27],... 

The plants that were the precursors of the coal required a range of elements as nutrients or for stmctural support. Elements essential to plant metabolism include phosphoms, potassium, sulfur, calcium, and magnesium. Some plants also require boron, chlorine, copper, iron, manganese, molybdenum, and zinc (Severson and Shacklette, 1988). Plants may contribute inorganic constituents... 

Both macro- and micro-elements are nutrients that are necessary for the growth and normal development of organisms and whose function cannot be taken on by any other element. They are therefore termed essential . For this reason, macro- and microelements are also called macro- or micro-nutrients. A division into essential and non-essential elements is not always appropriate, since there are numerous exceptions that become apparent when, for example, higher and lower plants are compared. We now know that calcium, boron and chlorine are not essential to some bacteria and fungi, and that sodium and silicon are not essential to higher plants (Marschner, 1983). 

In 1923, boron was accepted as being an essential nutrient initially for broad beans (Viciafaba) and subsequently for all plants. Boron is required for the development of zebraflsh (Danio rerio) (Rowe and Eckert, 1999) and for reproduction and development in frogs (Xenopus laevis) (Fort et al 1999). Experimental studies suggest that boron is a potentially essential nutrient for humans also (WHO, 1996 Nielsen, 2008). The aim of the present review is to assess the literature on dietary sources and intake of boron in humans and to evaluate the impact of boron on metabolism in health and disease. 

From evidence published so far, it appears that soil conditions and agricultural methods have limited effect on the boron composition of plant foods. This suggests that plants have effective mechanisms for maintaining homeostasis of boron, possibly mediated by specific boron transporters (Takano et al., 2002). The lack of a clear effect of agricultural methods on the plant composition of boron is consistent with the limited impact of agricultural methods on other nutrients (Dangour et al., 2009), and may well reflect the essentiality of boron for the integrity of the cell wall in plants (O Neill et al., 1996). 

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