Plant growth, boron

Boron and Borates. Boron is an essential element for plant growth however, concentrations >2 mg/L are harmful to some plants. 

For all natural waters, boron is one of their constituents with varying concentrations from minute traces to several ppm (parts per million). It is essential for plant growth but is exceedingly toxic at concentration slightly above optimum. Boron tolerances vary depending upon climate, and crop varieties. Relative boron tolerances of agricultural crops are presented in Table 3 [12]. 

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 is essential for plant growth and development. In medicinal chemistry its main use is related to that of coupling reagent. The most important employment of boron as drug relies upon the treatment of certain tumors by Boron Neutron... 

In arid conditions a soil content of boron > 30 ppm leads to boron toxicity for plants and animals. We can consider this value as the maximum permissible concentration (standard). Physiological and morphological alterations of plant growth are typical forms of boron toxicity. The animal toxicity is related to the decrease... 

Micronutrients are elements such as Boron, Zinc, Copper, Cobalt, Iron, Magnesium etc. which are required in trace amounts. The addition of extra trace elements has no effect on plant growth but a deficiency of any or all of these can cause serious disturbance of plant growth, leading to a loss of active chemical. Since plants can be cultivated in areas with different soils of varying fertility, it follows that the site of cultivation could influence quality, indicating again the need for assays for chemical content. 

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,... 

Tso, T.C., J.E. McMurtrey Jr, and R.N. Jeffrey Mineral deficiency and organic constituents in tobacco plants. III. Plant growth and alkaloid contents related to gradual development of calcium or boron deficiency symptoms Plant Physiol. 37 (1962) 804—808, see 3984. 

Although the exact role of boron in plants is unknown, several physiological and biochemical activities associated with tissue boron content have been supported experimentally. This review covers some recent work on the role of boron in (1) organic translocation in plants, (2) enzymatic reactions, (3) plant growth regulator response, (4) cell division, (5) cell maturation, (6) nucleic acid metabolism, (7) phenolic acid biosynthesis, and (8) cell wall metabolism. 

The confusion surrounding the metabolic role of boron in plants has resulted in a searcK" for the initial physiological effect of removing boron from the plant environment or, in some cases, adding boron to the plant growth medium or to excise tissue culture. Early plant responses to boron or to its deficiency and other types of experiments have helped clarify borons role in plant metabolism. 

Adsorbed Boron. Boron precipitated and adsorbed on surfaces of soil particles is probably of greater importance to plant growth because of equilibria existing between adsorbed and soluble boron. A substantial proportion of the boron added to soil either as a component of fertilizers or in irrigation water is adsorbed by certain soil materials, the balance remaining in the soil solution. This soil solution concentration is especially important to plant nutrition because of its immediate availability to plants. Plants respond primarily to the soil solution boron, independently of the amount of boron adsorbed by soil (ii). Consequently, conditions affecting equilibria between adsorbed and soluble boron are highly rele-... 

Plant growth is retarded or injured by soluble salts because these salts interfere with the uptake of water, and the effect is largely independent of the kinds of soluble salts present. Retardation of growth increases directly with salt concentration. Sometimes elements, such as boron, may be present in solution and produce a direct toxic effect other than the usual soluble salt effect. 

It is generally agreed that in addition to major elements necessary to support plant growth, the elements boron, manganese, copper, zinc, molybdenum, and iron are required in trace quantities. In addition to these essential elements, some 40 other elements have been detected in plant tissue. Spectroscopic methods have been used to detect most of the above list of elements and quantitative data have been obtained in most cases. 

Sodium, chlorine, boron and many other salts in higher levels in iirigation water and soil are detrimental to plant growth and development since they rupture and destroy plant cells. Calcium from gypsum has a significant role in preventing the uptake of Na by plants. 

Arreola, J.A., Castillo Gonzalez, A.M., Valdez Aguilar, L.A., Colinas Leon, M.T., Pineda, J. Avitia Garcia, E. (2008). Effect of calcimn, boron and molybdenum on plant growth and bract pigmentation in poinsettia. Revista Fitotecnia Mexicana, 31,165-172. 

Plants require several micronutrients, largely elements that occur only at trace levels, for their growth. These include boron, chlorine, copper, iron, manganese, molybdenum (for N fixation), and zinc. Some of these are toxic at levels above those required for optimum plant growth. Most of the micronutrients are required for adequate function of essential enzymes. Photosynthetic processes use manganese, iron, chlorine, and zinc. Since the micronutrients are required at such low levels, soil normally provides sufficient amounts. 

In this case, the mean garden level (1.81 ppm) is only about two and a half times as great as the rural arable level (0.70 ppm), but the difference is perhaps more serious since some of the levels encountered could have deleterious effects on plant growth. The range of concentration of water-extractable boron in soils over which plants will grow normally is unusually narrow because of the ease with which water-soluble boron is taken up by plants [131]. On the other hand, available boron is largely present in the soil as soluble borates, so that contaminant boron is readily leached out of the soil. 

An extended series of pot experiments in the greenhouse has been carried out at the Edinburgh School of Agriculture since 1964, with a view to providing information (i) on the relationship between the available levels of the elements, boron, copper, lead, zinc and cadmium in the soil and uptake of these elements by oats, clover, radishes and lettuces, and (ii) on the effects on yield of these plants of increasing soil concentrations of these elements. Since the levels of all these elements are markedly enhanced in urban and industrial areas, it has become important to determine the level of contamination above which plant growth is restricted, and the threshold toxicity levels above which no effective growth is possible. 

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