Review Of Literature

Review of Literature

2

Rice is a member of grass family. It belongs to genus Oryza of Gramineae family. The genus posses about 24 species out of which 22 are wild and two species namely Oryza sativa and Oryza glaberrima are cultivated. While Oryza glaberrima was grown in the tropical and subtropical Asia but center of domestication is a matter of discussion. Some believes that simultaneous domestication in various center extending from the plains below eastern hills of Himalayas.

Another view postulates a more limited center of

origin. Notably inland valleys in Thailand, Burma and Laos ,Oryza glaberrima is generally considered as a wild specie .It is commonly found in West Africa in a few secondary centers. As far as production is concerned China is the top producer with 166,000.000 metric tonnes, followed by India with 133,513,000metric tonnes. Brazil posses

lowest

of

production

with

10,219,300

metric

tonnes

( Anonymous,2009) From the initial point or points of cultivation, Oryza sativa has spread over a considerable part of the earth and has become a major food crop for a larger part of world’s population. Varieties adaptation generally includes development of the main subspecies i.e “Indica” and “Japonica” and the improvement of land and water management practices, which changed and optimizes rice edaphic and climatic Review of Literature

environment. Rice is essentially a crop of sub-tropic and on the higher elevations up to 6000 feet above sea level. Rice need abundant supply of fresh water for irrigation followed by high temperatures and high atmospheric humidity .Rice thrives over a wide range of soils ranging from 4.5 to 8.5 pH. Only a few rice varieties posses tolerance to saline and alkaline condition. Rice is a staple food for 17 countries and at present it is grown over more then 100 countries. Archaeological evidences indicated that the sophisticated rice cultivation system existed in China over 7,000 years ago. Rice is grown in all the continents except Antarctica. It is grown in 15.294m millions ha . Today rice produces food for nearly 2/3 of world population about 4/5 of rice is produced by small scaled farmers and is an source of income for 100 millions households of Asia and Africa RICE IN INDIA :-

In India, rice is an important staple food for more

than 2/3rd of population. Rice provides a vital role in our national food security and is a mean of livelihood for millions of rural households. In India, a number of festivals such as Bihu, Pongal, Onam are associated with rice harvest . There is a considerable increase in productivity of rice in India during the recent past. The productivity of rice was 668 kg/ha in 1950-51 has reached to 2,066 kg/ha during 2000-02. During the period of 1961 to 2005, the cultivation of rice has increased from 35 m ha to 44m ha followed by increase in production from 54 million tonnes to 124 million tonnes and productivity from 1.54 tonnes to Review of Literature

2.93 tonnes/ha. This increase is basically due to cultivation of the hybrid rice varieties in major areas with advanced rice production technologies and mechanization ( Fairhust and Doberman, 2002 b). In India rice is the major staple food for 65% of total population. The rice cultivation area extends

throughout India. Rice

cultivation can be taken up in areas lying below sea level (Kerala) and up to altitude of 2000m (Kashmir) . During last 45 years (1967 – 2008), the rice area has increased by one half times from 115-50 million ha to about 153.26 million hectares. It is estimated that the rice demand in 2025 will be 140 million tonnes in India. The demand for food grain is expected to rise not only as a function of population growth but also as more and more people crosses poverty line. Rice ranks second in position in terms of area harvested and cultivated. In terms of importance as a food crop or in terms of calorific value rice crop occupies first place amongst cereal crops. The nutritive composition varies with environmental condition, the germ, pericarp of aleurone layer are rich in endosperm. Carbohydrate of rice is starch constituting about 72% to 75% with fiber content of hemicellulose of pentose, Arabinose and Xylose. Protein “Glutelin”, is also known as “Oryzenin”, rice also contains albumin, globulin and prolamines. Rice is however , deficient in Lysine and Threonine. Rice: Improvement Via Tissue Culture. Plant tissue culture has become thrust area in all areas of crop improvement programmes. The beginning of the plant tissue culture Review of Literature

was made early in 1898, when a German botanist, G. Haberlandt successfully cultured fully

differentiated individual plant cells,

isolated from the different tissues in several plant species. During 1934 to 1939, due to discovery of the important hormones auxins and B vitamins, the were

laid

down

by

like

foundations of the plant tissue culture

three

scientists

(Gautheret,

White

and

Nabecourt.). In vitro culture of rice begin in the early 1950 s, it was “Fujiwara” and “Ojima” (1954) who first of all reported successful culture of rice roots excised from seedlings germinated aseptically. However, a major realization in this course of practice is the genetic variability. This variation in tissue culture raised plants is proving to be an rich source of crop improvement. Among the techniques anther culture, protoplast fusion, leaf culture, root culture, immature embryo culture

and

seed

culture

are

important

in

course

of

crop

improvement. Rate of callus induction generally depends upon various factors that includes culture environment genotype, media composition,type of explant and partial dessication. ( Vasil and Hildebrandt, 1965) For

the

rice,

the

seeds

derived

embryogenic

calli

are

considered as most appropriate source of genetic variation (De Datta et al., 1990). Embryogenic calli are convenient and large quantity can be made with absolute uniformity in physiological characters. They are now widely used for experimental purposes. Review of Literature

The genotype plays a very crucial role in callusing ability of seeds (Abe and Futsuhara,1986) that requires different types of medium i.e MS (Murashige, and Skoog,1962 ), N6 ( Chu, 1975), B6 with different composition of growth hormone. However, for the rice 2,4-D

is found to be only growth regulator for callusing . In

addition to this there are various other chemical like casein hydrosylate for Japonica rice

and Indica Rice. Proline addition in the

medium also induces the callusing in various varieties. Sucrose concentration however, plays an important role in callusing from the anther (Guha and Mukherjee., 1964). Variations induced in Culture :- The variation observed in tissue culture is due to physiological changes induced by the culture condition. However, sometimes these variations are temporary and disappear when culture conditions are removed. However, sometimes it persists for longer period. The first reports of morphological variation observed in plants were published by Heinz and Mee (1971).Since then, several useful variants of sugarcane resistant to salt stress fungal and viral diseases have now been released. This variation so produced through tissue culture could be useful for the development of new cultivars ( Larkin and Scowcroft., 1981) Genetic variants selected through tissue couture are referred to as calli clones, protoclones from protoplast cultures. Somaclonal variations are used to describe genetic variation regenerated from the cell cultures . Plants regenerated from cell culture of gametic origin are termed as “Gametoclones”. Review of Literature

To be of agronomic use, a somaclone must fulfill the basic requirements i.e It must involves useful characters, it should be superior from the parent, must be combined with all other desirable characters of parents and

the variations must be inherited stably

through successive generations. Underlying principle behind the somaclonal variations lies in quantitative

phenotypic

variations,

activation

of

transposable

elements and high frequency of sequence changes (Bayliss ,1980). The

“DNA

methylation”

have

been

suggested

as

a

possible

mechanism (Kaepler and Phillips, 1993) and patterns of DNA methylation have been charaterised for many varieties (Selker and Stevens,1985). The DNA methylation leads to chromatin changes that ultimately cause disturbed replication timing and base changes. Essential Role of Phosphorus (P) in plant Phosphorus is an essential nutrient both as a part of several key plant structural compound and as a catalyst in the conversion of numerous

key

biochemical

processes.

Phosphorus

is

a

vital

component of DNA, the genetic “Memory unit” of all living things. It is also a component of RNA, which reads genetic code. The structures of both DNA and RNA are liked together by phosphorus bonds. Phosphorus is highly mobile in plant and when deficiency occurs it may be translocated from old plant tissue to young actively growing areas. Thus, early vegetative responses to phosphorus are often observed .As the plant matures, phosphorus is translocated into Review of Literature

the fruiting areas of the plant where high energy compounds are needed for the formation of the seeds and fruits. The percentage of total amount of the each nutrient taken up is higher for phosphorus late in growing season than for either nitrogen or potassium.The total phosphorus content of soils is generally very low i.e 0.6%

this compares

to an average soil content of 0.14%

nitrogen and 0.83% potassium ( Hoford ,1997) , many factors influence the content of soil phosphorus. Some of these are : (1) Type of parent material from which soil is deserved ; (2) Degree of weathering (3) Climatic conditions. In addition, soil phosphorus levels are affected by erosion,crop removal and phosphorus fertilization (Kirk et al., 1998). Soil phosphorus is classified in two broad groups (1) Organic phosphorus, found as plant residues, manure and microbial tissues. In phosphorus rich soils 50% or more of the phosphorus is in organic form compaired to 3% in deficient solis (2) Inorganic forms consists of the apatite i.e original source of all phosphorus. Soluble phoshorus either in the form of fertilizer or natural weathering reacts with clay, iron and aluminium

compound in the

soil and is converted readily to less available form by process called “phosphorus fixation”. Due to fixation, the phosphorus moves little in the soil (less then an inch ) a crop absorbs more then 20% of fertilizer as a result the phosphorus is lost by “Leaching”.

Review of Literature

N

P

K

Ca

Fig.1 Relative movement of nutrients in the soil Precipitation of the phosphorus as slightly soluble calcium phosphate occurs in calcareous soils with pH values around 8.0 under the acidic condition, phosphorus is precipitated as Fe or Al phosphates of low solubility, maximum availability generally occurs in a pH range of 6.0 to 7.0 and this pH provide phosphorus as H2PO4that is readily absorbed by plant than HPO4-

(9.0) Tricalcium phosphates unavailable

7.0 Mono and dicalcium phosphates maximum available

( 5.5) Fe , Al phosphates unavailable

Fig.2 Effects of pH on phosphorus availability

Review of Literature

Phosphorus Deficiency : Effects on CropThe plant obtains phosphorus from the soil. It occurs in both organic and inorganic forms. It is the most limiting element after the nitrogen

(Jungk , 2001) due to it's fixation in the

soil. About 5-7 billion ha soil worldwide lacks the sufficient plant available phosphorus (Bates, 1973) and almost 50% of rice soils are currently phosphorus deficient. Phosphorus deficiency is widespread in all major rice ecosystems and is major limiting factor in arid upland soils

where

soil

P

fixation

capacity

is

often

very

large.

( Raghothama, 1999). The common causes of P deficiency are: low indigenous soil – P supply, insufficient supply of mineral P fertilizers, low efficiency of applied

fertilizer, P immobilization ( Kirk et al, 1999), excessive

use of N fertilizers, crop establishment methods ( more likely in direct- seeded rice where plant density is high and root system are shallow). Moderate P deficiency is generally different to recognize. In the field, P deficiency is often associated with other nutrient disorders. (Bagyarj and Verma, 1995). Phosphors deficient plants are stumped with greatly reduced tillering. leaves are narrow, short, very erect and dirty dark green. Stems are thin and spindly and plant elongation is retarded. The number of leaves, panicles and grain per panicle is also reduced red

Review of Literature

and purple colors formation occurs if

variety posses property of

anthocynin production (Doberman and Fairhost,2000b). Other effects include delayed maturity, large production of empty grain, no response to application of fertilizer. Plant mechanism, adaptation for low phosphorus stress Plant have developed several mechanism to counter the problem of low phosphorus availability, so as to acquire more phosphorus from the surrounding rhizosphere. Such adaptations are generally at the physiological biochemical and morphological levels. Morphological adaptation for countering low P stress General diffusion rates of phosphorus is very low because soil particles easily binds the phosphorus .If P doesn’t move freely in the rhizosphere, plant may increase P uptake by the expanding the root system, thereby exploring more soil volume .The size of root system is considered as an important factor of plant that deficiency

tolerate P

( Wissuwa,2002). Tolerance however, could be

achieved by the increase in the external P uptake efficiency, defined as the phosphorus uptake per unit root size (RSA) (Raghothama., 1999). Alternatively, plant generally capable of releasing soil bound phosphorus by excreting the organic compound, P solublization due to organic ions ( anions) were responsible for the bulk of P uptake by rice from P deficient soil ( Kirk et.al. 1999). Another response to low Review of Literature

phosphorus

availability

is

the

symbiotic

association

with

the

mycorrhiza. The fungus and plant show symbiosis where fungus helps in aquitisation of phosphates (Bagyaraj and Verma,1995) . Fungus so extends the phosphorus depletion zone (Harrison and Van Burren ,1995. Generally genotypes with the more P uptake efficiency are highly associated with higher relative root growth. This is due to fact that additional P allows further biomass accumulation, including root growth ,this is considered as primary factor for the genotypic differences in P uptake ( Wissuwa, 2002). It is also reported that under low phosphorus availability the root to shoot ratio generally increases followed by increase in root diameter with

increase in absorptive

surface

area. The

root

assimilates more root hairs as to enhance uptake of Pi. (Gahhonia and Nielson. 1998). Molecular and Biochemical mechanisms phosphorus limited environment :-

involved

under

Efforts have been directed for improvement of tolerance to low phosphorus stress. Since, there is considerable variation at genotypic level for the ability to take up P from a highly fixing soil exists in gene bank accession. Genetic studies on tolerance to P deficiency in rice have identified a major quantitaitve trait locus ( QTL) for Pi uptake (Senanayake, 1984) which has small marker interval

subsequently been mapped to a

on the long arm of chromosome 12.

( Wissuwa et al., 1998). Review of Literature

Two OsPHR genes from rice Oryza sativa .L were isolated and designated as OSPHR-1 and OSPHR-2 based on the amino acid sequences homology to AtPHR 1 ( Bari et.al., 2006) that plays an crucial

role

during

the

Pi

starved

condition

in

Arabidopsis

(Hamberger et al ,2002). OsPHr – 1 and 2 are involved in Pi starvation signaling pathway by regulation of the express of Pistarvation. In E.coli there exists a high affinity phosphate transporter Pst CAB – this is generally active transport system, more specifically on ATP binding cassette ( ABC) transporter. It is generally activated under the low phosphate levels. Similarly, OSP-11 have been characterized adaptation

to

(Wasaki et al., 2003 ). It is responsible for the early

stages

environment

of

adaptation

to

low

phosphorus

( Liu et al., 1997 ).

Recently OSPTF–1 (transcriptional factor) was introduced into Nipponbare i.e a phosphorus deficiency sensitive, derived from Kasalth (Keke et. al, 2005). The transformed cultivars showed an (over expressing OSPTF–1) considerable tolerance to phosphorus deficiency.

Possibility

of

manipulation

of

the

expression

of

phosphorus transported gene may be involved in the mobilization of phosphorus within soil. In E.coli and Brewer's yeast there are reports of some groups that are activated under phosphorus starved condition

(Torriani

and Ludtke, 1990). Psi genes are useful in the enhanced uptake of pi from soil under p starved condition. The PHO-regulon is now well Review of Literature

known aggregation of gene ( Sacchromycese cerevisiae) that helps in scavenging any available Pi from soil under starving condition ( Abel et al, 2002).

Review of Literature

The PHO regulon is generally regulated by the two component system. namely PHO. B – Pho- R. Pho R

(Autophosphorylation under P starved condition)

PhoB

Enhanced uptake

Binds Pho–Box of Pho- regulon

Activation of operon

Fig . Mechanism of Pho -regulon working (Torriani, 1990) Similar to Pho ragulon of sacchromycese cerevisae, Pho.1 and Pho. 2 and also Pho.3 have been isolated (Hamberger et al.,2002). During the phosphorus starved state the common enzymes associated with phosphate metabolism gets activated, (Green, 1994). This includes transporters

“Phytase ”, RNAase” and some phosphate (Raghothama, 1999). These enzymes plays

crucial role in phosphate nutrition during the stress by performing phosphorylation and dephosphorylation thereby causing activation and deactivation of many proteins specially transporters necessary for phosphorus uptake ( Liu et. al., 1997). Acid phosphatase is the most crucial enzyme that is involved in the release of the Pi from organic compounds, ions, soils and tissues Review of Literature

( Tabatabai and Bremner,1969). The activity of acid phosphatase generally increase under the low phosphorus stress state. Acid phosphatase is responsible for moblisation of Pi from phosphate esters. It is now well know that the low phosphorus stress leads to accumulation of the polyamines specially “putrescine” ( Bertoldi et al, 2004). It was found that common precursor of putrescin i.e. Argenine decarboxylase complex (ADC) generally increases in various stresses including P. This in turn increases synthesis of the putrescin production. The decarboxylated form of SAM i.e S. adenosyl methionine is precursor of the putrescin and ethylene. Thus, under low P condition ethylene production is also elevated. Polyamines are general indication to stresses like acid stresses and somatic stresses ( Flores and Galston, 1982).

Review of Literature