**2.6 Heavy metal toxicity**

Many solutes are present in the rhizosphere required for the growth and development of plants. Plants uptake these solutes by roots and distribute them in the whole plant body. The successful plant life is ensured by up taking the other components with water from the rhizospheric soil by roots. The developmental plasticity and physiological activity in the plant roots is carried out by the water uptake with soluble elements. The distribution and uptake of these inorganic materials inside the plants is an intrinsic property of energy and material fluidity. In plant cells, a plethora of physiological and structural functions is supported by these essential ions but if these essential ions are present in the non-physiological concentrations, they can turn out as limiting factors. The cellular homeostasis is affected by their availability to plants, Inequalities in comparative abundance of these elements in soil and their rate of uptake. The defense system and adaption of plants is dependent on the developmental and physiological changes triggered by ion toxicity; but it can cause the permanent damage to the plant. In the rhizospheric soil, the ions of heavy metals are also present that can be absorbed by the roots with the water and nutrients and can be incorporated into the plant tissues. The zinc, iron, manganese, copper, aluminum, chromium, cadmium, cobalt, lead, arsenic, nickel and molybdenum are some toxic metals for plants [73].

The concentration of metal ions is excessive in polluted areas and plants growing in those areas suffer from metal toxicity. Some soils have high level of heavy metals

naturally like serpentine soils and the mining areas also have high heavy metal content due to activities of human beings. The environmental pollutants including high concentrations of heavy metals are becoming a major challenge for all organisms (plants, animals, microbes, etc.) across the globe. The ionic homeostasis is achieved in plants by maintaining the levels of essential and non-essential ions. Furthermore, this homeostasis in cells and tissues must be maintained in an organ specific manner. The risk of heavy metals can be mitigated by minimizing their uptake, avoiding their exposure and intracellular sequestering in the plants. The cellular structures, membranes structures, basic metabolism and transport processes are affected, if plant is not able to combat with the harmful effects and internalization of heavy metals. The stress reactions are triggered by the high levels of non-toxic and toxic metal ions that disturb the development at molecular, structural and physiological level. The defense mechanism is started in the plants upon the beginning of heavy metal toxicity [74]. The oxidative stress is caused by the heavy metal toxicity, so cells and sub-cellular compartments are protected by plant defense system. The plant growth and development are continued if the heavy metal ions are present in low or moderate concentrations. But, plants cannot survive during the long-term exposure of high level of heavy metal toxicity. The metal tolerance is a unique feature of some plant species in stress biology. The compartmentalization and of heavy metals, restriction of heavy metals in apoplast, extracellular attenuation and chelation of heavy metals and exclusion strategies are some mechanisms of achieving stress tolerance in the plants.

The most practical approach adopted by the plants to combat with the heavy metal toxicity is hyper accumulation and hyper tolerance of heavy metals inside the plant without effecting its viability [75]. The hyper accumulation of metal ions protects the plants from pathogens and herbivores in some conditions (Hörger et al. 2013). The contamination of heavy metals is present in the wide range of terrestrial habitats. In food chain, plants have vital importance, so heavy metal accumulation in plants causes severe contamination in the food chain. So, it is significantly important to know that how plants combat with the heavy metal exposure. The knowledge of these mechanisms is used in developing the practical biological methods to develop the tolerance against heavy metal toxicity [74]. Many promising and existing biotechnological approaches are used are used for this purpose [75]. Before concluding the major efforts used for making plant to heavy metal stress, it is necessary to understand the key factors involved in adjusting the heavy metal tolerance. The total cell protein study is called proteomics; it is a most valuable tool for understanding the basic procedures of development and stress responses in plants [73]. The sensing, transport and uptake of heavy metal, their sequestration in the vacuole and formation of phyto-chelating-heavy metal complex are some main procedures for influencing the plant susceptibility for the metal ions. These processes are controlled at transcriptional and post-transcriptional levels and the secondary process responsible for maintaining the plant during metal toxicity includes the defense reaction derived by the production of antioxidants to preserve the membrane lipid integrity. Diverse genes are responsible for controlling these processes. The heavy metal tolerance of the plants is achieved by the various biotechnological, molecular and genetic tools [74].

#### **3. Rice biotechnology under climate change conditions**

Due to climate change, the food availability is affected in 21st century to feed the population which is increasing day by day. Globally, climate change have bad effects on the human health, food security and water resources [76]. About 30-60% of rice

**13**

**4. Future prospects**

be affected.

*Introductory Chapter: Recent Advances in Rice Biotechnology for Abiotic Stress Tolerance*

of 26S proteasome and is involved in destruction of ubiquitinated protein.

The removal of cytotoxic degraded protein is done by OgTT1 (*Oryza glaberrima* thermo tolerant 1) maintain the cell from high temperature. Over expression of TT1 increase the ability of heat tolerant stress in rice. It helps to grow the rice in global warming [79]. To protect the food, production of heat tolerant varieties which can be grown in high temperature is a major challenge. In *Arabidopsis thaliana*, Dehydration responsive element binding protein 2A (DREB2A) is regulated by DNA polymerase subunit B3-1 (DPB3-1), is a transcriptional controller which regulate the growth of plant and increase the thermostability [80]. If temperature is round about 35°C in chamber trial at the time of flowering, then spikelet infertility occurs due to heat stress. When the temperature in Japan cities (Tokai, Kanto) was reached at 40°C in 2007, it induced extensive unproductiveness. The increase in world temperature is expected, that is why we need to develop techniques to protect the grain quality and production from heat damage [81]. During the ripening of rice, the high temperature causes the poor-quality grain production. Late transplanting and thermostable varieties are used in preventive measure. Deep-flood irrigation is a process which falling the rate of milky white seeds when the temperature is high and low. Adequate quantity of nitrogen is necessary to protect the grain from disease at reproductive stage [81]. In future, if water availability is less, yield of rice will badly

Due to climate change, the crop rotation time can be reduced. There are many positive and negative effects of climate change on crop, so scientist try to develop the verities which can be cultivated in harsh conditions to provide enough food to global population [82]. Galactinol synthase 2 gene from Arabidopsis is introduced in two rice verities and have ability to produce the good quality in waterless field environment. The biotechnologically advanced verities have greater intensity of galactinol as compared to non-transgenic verities. The drought resistance rice has greater ability of photosynthesis, recovering and plant growth. It is clear that AtGolS2 gene is beneficial which provide higher quantity of rice in drought stress [83]. Rice varieties which are better grown in anaerobic environment produce less yield in aerobic situation. To accurately measure the expression of different genes in a condition, it is necessary to find out the genes which have same output in aerobic and anaerobic systems [84]. Transcriptional reaction and ecological variation is affected by macroclimate and meadow type, then we identify the genes which are

In modern-day agriculture, biotechnology has a wide range of applications. It helps in understanding the genetics of important traits as well as in developing new cultivars. The transgenic crop deployment and the marker assisted breeding

involved in production and photosynthesis [82].

income is decreased per year because of different types of stresses [77]. The rice fields are susceptible due to climate change, expansion of urban area and ruined of cultivation field. Due to some cases, 100% rice production is destroy [78]. The rice yield is reduced due to increase in temperature by accumulation of carbon dioxide in environment. The production and quality of rice (*Oryza sativa* L.) is badly affected by climate change which is mainly abiotic stresses (heat, flood, salinity, cold and drought) and biotic stresses (pest, weeds and pathogens). Climate change cause the formation of unripe grains, white grains, and fractured grains. The grain damage is reduced by use of thermo-stable verities which are formed through conventional breeding and genetic engineering. Thermo tolerant 1 (TT1) is the most important (QTL) present in *Oryza glaberrima*, it codes α2 which is the subunit

*DOI: http://dx.doi.org/10.5772/intechopen.94036*

#### *Introductory Chapter: Recent Advances in Rice Biotechnology for Abiotic Stress Tolerance DOI: http://dx.doi.org/10.5772/intechopen.94036*

income is decreased per year because of different types of stresses [77]. The rice fields are susceptible due to climate change, expansion of urban area and ruined of cultivation field. Due to some cases, 100% rice production is destroy [78]. The rice yield is reduced due to increase in temperature by accumulation of carbon dioxide in environment. The production and quality of rice (*Oryza sativa* L.) is badly affected by climate change which is mainly abiotic stresses (heat, flood, salinity, cold and drought) and biotic stresses (pest, weeds and pathogens). Climate change cause the formation of unripe grains, white grains, and fractured grains. The grain damage is reduced by use of thermo-stable verities which are formed through conventional breeding and genetic engineering. Thermo tolerant 1 (TT1) is the most important (QTL) present in *Oryza glaberrima*, it codes α2 which is the subunit of 26S proteasome and is involved in destruction of ubiquitinated protein.

The removal of cytotoxic degraded protein is done by OgTT1 (*Oryza glaberrima* thermo tolerant 1) maintain the cell from high temperature. Over expression of TT1 increase the ability of heat tolerant stress in rice. It helps to grow the rice in global warming [79]. To protect the food, production of heat tolerant varieties which can be grown in high temperature is a major challenge. In *Arabidopsis thaliana*, Dehydration responsive element binding protein 2A (DREB2A) is regulated by DNA polymerase subunit B3-1 (DPB3-1), is a transcriptional controller which regulate the growth of plant and increase the thermostability [80]. If temperature is round about 35°C in chamber trial at the time of flowering, then spikelet infertility occurs due to heat stress. When the temperature in Japan cities (Tokai, Kanto) was reached at 40°C in 2007, it induced extensive unproductiveness. The increase in world temperature is expected, that is why we need to develop techniques to protect the grain quality and production from heat damage [81]. During the ripening of rice, the high temperature causes the poor-quality grain production. Late transplanting and thermostable varieties are used in preventive measure. Deep-flood irrigation is a process which falling the rate of milky white seeds when the temperature is high and low. Adequate quantity of nitrogen is necessary to protect the grain from disease at reproductive stage [81]. In future, if water availability is less, yield of rice will badly be affected.

Due to climate change, the crop rotation time can be reduced. There are many positive and negative effects of climate change on crop, so scientist try to develop the verities which can be cultivated in harsh conditions to provide enough food to global population [82]. Galactinol synthase 2 gene from Arabidopsis is introduced in two rice verities and have ability to produce the good quality in waterless field environment. The biotechnologically advanced verities have greater intensity of galactinol as compared to non-transgenic verities. The drought resistance rice has greater ability of photosynthesis, recovering and plant growth. It is clear that AtGolS2 gene is beneficial which provide higher quantity of rice in drought stress [83]. Rice varieties which are better grown in anaerobic environment produce less yield in aerobic situation. To accurately measure the expression of different genes in a condition, it is necessary to find out the genes which have same output in aerobic and anaerobic systems [84]. Transcriptional reaction and ecological variation is affected by macroclimate and meadow type, then we identify the genes which are involved in production and photosynthesis [82].

#### **4. Future prospects**

In modern-day agriculture, biotechnology has a wide range of applications. It helps in understanding the genetics of important traits as well as in developing new cultivars. The transgenic crop deployment and the marker assisted breeding

*Recent Advances in Rice Research*

stress tolerance in the plants.

biotechnological, molecular and genetic tools [74].

**3. Rice biotechnology under climate change conditions**

Due to climate change, the food availability is affected in 21st century to feed the population which is increasing day by day. Globally, climate change have bad effects on the human health, food security and water resources [76]. About 30-60% of rice

naturally like serpentine soils and the mining areas also have high heavy metal content due to activities of human beings. The environmental pollutants including high concentrations of heavy metals are becoming a major challenge for all organisms (plants, animals, microbes, etc.) across the globe. The ionic homeostasis is achieved in plants by maintaining the levels of essential and non-essential ions. Furthermore, this homeostasis in cells and tissues must be maintained in an organ specific manner. The risk of heavy metals can be mitigated by minimizing their uptake, avoiding their exposure and intracellular sequestering in the plants. The cellular structures, membranes structures, basic metabolism and transport processes are affected, if plant is not able to combat with the harmful effects and internalization of heavy metals. The stress reactions are triggered by the high levels of non-toxic and toxic metal ions that disturb the development at molecular, structural and physiological level. The defense mechanism is started in the plants upon the beginning of heavy metal toxicity [74]. The oxidative stress is caused by the heavy metal toxicity, so cells and sub-cellular compartments are protected by plant defense system. The plant growth and development are continued if the heavy metal ions are present in low or moderate concentrations. But, plants cannot survive during the long-term exposure of high level of heavy metal toxicity. The metal tolerance is a unique feature of some plant species in stress biology. The compartmentalization and of heavy metals, restriction of heavy metals in apoplast, extracellular attenuation and chelation of heavy metals and exclusion strategies are some mechanisms of achieving

The most practical approach adopted by the plants to combat with the heavy metal toxicity is hyper accumulation and hyper tolerance of heavy metals inside the plant without effecting its viability [75]. The hyper accumulation of metal ions protects the plants from pathogens and herbivores in some conditions (Hörger et al. 2013). The contamination of heavy metals is present in the wide range of terrestrial habitats. In food chain, plants have vital importance, so heavy metal accumulation in plants causes severe contamination in the food chain. So, it is significantly important to know that how plants combat with the heavy metal exposure. The knowledge of these mechanisms is used in developing the practical biological methods to develop the tolerance against heavy metal toxicity [74]. Many promising and existing biotechnological approaches are used are used for this purpose [75]. Before concluding the major efforts used for making plant to heavy metal stress, it is necessary to understand the key factors involved in adjusting the heavy metal tolerance. The total cell protein study is called proteomics; it is a most valuable tool for understanding the basic procedures of development and stress responses in plants [73]. The sensing, transport and uptake of heavy metal, their sequestration in the vacuole and formation of phyto-chelating-heavy metal complex are some main procedures for influencing the plant susceptibility for the metal ions. These processes are controlled at transcriptional and post-transcriptional levels and the secondary process responsible for maintaining the plant during metal toxicity includes the defense reaction derived by the production of antioxidants to preserve the membrane lipid integrity. Diverse genes are responsible for controlling these processes. The heavy metal tolerance of the plants is achieved by the various

**12**

are the two main areas. The remarkable progress has been made by the marker assisted rice breeding. Modern tools of biotechnology help in studying the functions of genes and mechanism of resistance through improved varieties via MAS. Exploitation of tissue culture techniques used as a vital mean or work as an assistant to other procedures together with recombinant DNA methods is at its frontline in plant improvement and modification for agriculture. The targeted genome editing methods like ZFNs, TALENs, CRISPR/Cas9 are implanted for the modification of non-operational alleles of the useful genes or to repress or knock out the non-useful alleles in plants without making the plant transgenic. The techniques and tools of biotechnology are a very sophisticated option for the rice breeders to develop the useful crop varieties.
