Boron Supply and Water Deficit Consequences in Young Paricá (Schizolobium parahyba var. amazonicum) Plants

Boron (B) is a very important nutrient required by forest plants; when supplied in adequate amounts, plants can ameliorate the negative effects of abiotic stresses. The objective of this study was to (i) investigate gas exchange, (ii) measure oxidant and antioxidant compounds, and (iii) respond how B supply acts on tolerance mechanism to water deficit in young Schizolobium parahyba plants. The experiment employed a factorial that was entirely randomised, with two boron levels (25 and 250 µmol L-1, simulating conditions of sufficient B and high B, respectively) and two water conditions (control and water deficit). Water deficit induced negative modifications on net photosynthetic rate, stomatal conductance and water use efficiency, while B high promoted intensification of the effects on stomatal conductance and water use efficiency. Hydrogen peroxide and electrolyte leakage of both tissues suffered non-significant increases after B high and when applied water deficit. Ascorbate levels presented increases after water deficit and B high to leaf and root. Our results suggested that the tolerance mechanism to water deficit in young Schizolobium parahyba plants is coupled to increases in total glutathione and ascorbate aiming to control the overproduction of hydrogen peroxide and alleviates the negative consequences on electrolyte leakage and gas exchange. In relation to B supply, this study proved that sufficient level promoted better responses under control and water deficit conditions

Flúor: elemento potencialmente tóxico para plantas, animais e seres humanos.

The objective of this literature review demonstrates the negative action of fluoride as a toxic component in air, soil, plants and animals. Fluoride occurs naturally in the earth's crust, such as trace element in certain rocks and in the biosphere, with extreme reactivity. Some fluorine compounds such as elementary fluorine and hydrogen fluoride are much toxic and less found in the environment. One of the important aspects of this element is the F emission sources in the atmosphere, which are mainly aluminum industries, ceramics and fertilizers, the latter during the process of production of superphosphate. In soil it can be observed chemical effects caused by fluoride pollution before harming other organisms, thereby interfering indirectly on soil properties. The natural concentration of this element is 1m g kg-1. Fluoride is absorbed from the atmosphere by plants, especially by the leaves. In areas without emission of fluorine plants typically contain less than 10 mg kg-1 F in plant tissue. The gaseous fluoride penetrates the leaf tissue primarily through stomata, but also to a lesser extent through the cuticle and lenticels of branching. In mesophyll it migrates with the transpiration stream to the areas of leaf evaporation. In literature there are some reports on the behavior of F in the soil and the factors that influence its dynamics and how plants respond to certain concentrations of fluoride in their tissues, and some species that can be considered as bioindicators or pollution.Objetiva-se com esta revisão de literatura demostrar a ação negativa do flúor como componente tóxico na atmosférica, solo, planta e animais. O flúor ocorre naturalmente na crosta terrestre, como elemento traço em certas rochas e na biosfera, apresentando extrema reatividade. Alguns compostos de flúor, como flúor elementar e o fluoreto de hidrogênio, são muito tóxicos e menos encontrados no ambiente. Um dos aspectos importante sobre esse elemento são as fontes de emissão de F na atmosfera, que são principalmente as indústrias de alumínio, cerâmicas e fertilizantes, esta última durante o processo de produção dos superfosfatos. No solo são observados efeitos químicos causados pela poluição por flúor antes mesmo de ocorrer malefícios a outros organismos, interferindo assim de maneira indireta nas propriedades do solo. A concentração natural desse elemento encontra-se é 1m g kg-1 O flúor é absorvido da atmosfera pelas plantas, principalmente, pelas folhas. Em áreas sem emissão de flúor as plantas contêm, normalmente, menos de 10 mg kg-1 de F no tecido vegetal. O flúor em forma gasosa penetra no tecido foliar, sobretudo, através dos estômatos, mas também, em menor proporção, através da cutícula e lenticelas de ramificações. No mesofilo, migra com a corrente de transpiração para as zonas foliares de evaporação. Na literatura há alguns relatos sobre o comportamento do F no solo e os fatores que influenciam na sua dinâmica e como as plantas respondem a certas concentrações de flúor nos seus tecidos, assim algumas espécies que podem ser consideradas como plantas bioindicadoras ou de poluição