Boron Concentrations (ppm)

Fig. 13.16 Comparison of radicle growth inhibition in tomato seedlings under different boron concentrations

I Root

Boron Concentrations (ppm)

Fig. 13.16 Comparison of radicle growth inhibition in tomato seedlings under different boron concentrations at the same locus in a sufficient number of cells (a minimum of 2% of mutations may be required to get a new PCR product visible on agarose gel) to be amplified by PCR. RAPD is likely to detect genomic instability as the newly growing and developing cells will produce a clone of dividing daughter cells. Thus the proportion of cells presenting the same genomic instability is high and easy to detect. In the field of genetic toxicology most RAPD studies describe changes such as differences in band intensity as well as a gain/loss of RAPD bands, defined as diagnostic RAPD.

Boron can result in the physiological and metabolic problems related to geno-toxicity thus limiting crop productivity. In some recent studies the genetic and epigenetic aspects of boron toxicity have been evaluated together with a reference to the mitotic index in some plant species where mitotic abnormalities have been recorded (Papadakis et al. 2004; Konuk et al. 2007). Konuk et al. (2007) has reported that boron inhibits mitosis in Allium cepa at doses of 100 mg L-1 and above. However, according to Karabal et al. (2003) and Cervilla et al. (2007) although boron causes oxidative damage, but its genotoxic effect is still unclear. In some recent studies, leaf cupping, a specific visible symptom of boron toxicity in some species, has been suggested to result from inhibition of cell wall expansion, through disturbance of cell wall cross-links (Loomis and Durst 1992). The nutritional importance and toxic effects of boron on plant growth have been investigated at length in different maize cultivars (Goldberg et al. 2003). These studies revealed that in general boron tolerance of cultivars varied from high to low and boron concentrations of low tolerant cultivars were higher than those of high boron tolerant cultivars. A considerable genotypic variation in susceptibility to boron toxicity has been identified for agronomic species like wheat and barley (Nable and Paull 1991; Paull et al. 1992). Donghua et al. (2000) investigated the effects of boron ions on root growth and cell division of broadbean. The results indicated that boric acid has a stimulatory effect on root growth at concentrations of 10-6 and 10-3 M, and an inhibitory effect at higher concentrations. Boric acid has toxic effects on the root tip cells during mitosis, forming chromosome bridges, chromosome fragments, chromosome stickiness, and micronuclei. Ayvaz (2002) investigated the genotoxic effects of 500, 750 and 1000 mg L-1 boron concentrations on barley. He recorded the germination percentage, root length, mitotic index and mitotic abnormalities. These findings point out that a decrease in the mitotic index level is due to mitode-pressive effect which leads to an inhibition of cell access to mitosis, stressing the fact that boron disrupts the normal cell cycle process by preventing biosynthesis of DNA and microtubule formation.

During oxidative stress, the excess production of reactive oxygen species (ROS) causes membrane damage that eventually leads to cell death. As in most ionic stresses, toxic levels of boron cause the formation of ROS. Karabal et al. (2003) observed in barley cultivars that its toxicity induced oxidative and membrane damage in leaves. Recently it has been reported in apple and grapevine that boron toxicity induces oxidative damage by lipid peroxidation and hydrogen peroxide accumulation (Molassiotis et al. 2006; Gunes et al. 2006). Cervilla et al. (2007) too found that high boron concentration in the culture medium provokes oxida-tive damage in tomato leaves and induces a general increase in antioxidant enzyme activity, in particular increasing ascorbate pool size. It also increases the activity of L-galactose dehydrogenase, an enzyme involved in ascorbate biosynthesis, and the activity of enzymes of the Halliwell-Asada cycle. This work therefore provides a starting point towards a better understanding of the role of ascorbate in the plant response against boron stress.

Takano et al. (2005) demonstrated that boron regulated endocytosis and degradation of BOR1, a plasma membrane transporter for boron in plant. They monitored BOR1 activity and protein accumulations in response to various boron doses. They found that the posttranscriptional regulation was a major regulatory mechanism in this connection. Their findings proved that endocytosis and degradation of BOR1 are regulated by B availability in order to avoid accumulation of toxic levels of boron in shoots under high-boron supply, while protecting the shoot from boron deficiency under limited boron supply.

9 Conclusion

In conclusion this overview on the interrelations of plants and boron stresses the following points; using plants for phytoremediation should possess (a) targeted metal(s) accumulating capability, preferably in aerial parts; (b) tolerance to the accumulated metal concentrations; (c) fast growth of the metal accumulating biomass; and (d) ease of cultivation and harvesting (Baker and Brooks 1989).

This study has also revealed that the boron concentrations in plants are 20 times more than in the soils around Bigadig-Balikesir. Polygonum equisetiforme appears as a hyperaccumulator of boron. Its wide distribution in the region implies that it can be used for restoration of desertified agricultural lands. Biochemical and molecular studies on this plant will enlighten the mechanisms of growth of hyper-boron accumulating species on boron rich soils. These findings can be used in the molecular and genetic studies in agricultural plants. This study stresses the fact that this plant can be used to evaluate the boron polluted agricultural soils irrigated by Simav stream which contains high boron levels. In this way more than 3 million ha of boron polluted soils can be again used for agricultural productivity. At the same time it can be used as a fertilizer in the boron poor soils.

Germination results indicate that some of the plants show sensitivity and some are tolerant. For example; in bean the inhibitory rate is (-) 19% at 10 mg L-1 boron whereas it is (-) 86% at 1000 mg L-1, indicating its sensitivity. In chickpea the inhibitory rate was (-) 23% at 10 mg L-1 boron and (-) 42% at 1000 mg L-1, depicting a high tolerance. Our data confirms the fact that maize is a semi-tolerant species. The inhibitory rate of maize is (-) 9% at 10 mg L-1 boron but (-) 82% at 1000 mg L-1. Barley has been reported as a semi tolerant species (Maas 1987) but in our studies it appears percent at 1000 mg L-1. Wheat also has been recorded as a sensitive species but it was reasonably tolerant and growth rate was 13% at 10 mg L-1 boron and (-) 87% at 1000 mg L-1. Finally tomato was highly sensitive, the inhibitory rate was (-) 31% at 10 mg L-1 boron and (-) 92% at 1000 mg L-1 (Fig. 13.17). Bean and tomato are sensitive, maize is semi tolerant, chickpea, wheat and barley are tolerant species on the basis of germination results.

Detox Diet Basics

Detox Diet Basics

Our internal organs, the colon, liver and intestines, help our bodies eliminate toxic and harmful  matter from our bloodstreams and tissues. Often, our systems become overloaded with waste. The very air we breathe, and all of its pollutants, build up in our bodies. Today’s over processed foods and environmental pollutants can easily overwhelm our delicate systems and cause toxic matter to build up in our bodies.

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