small plants

The Eighteenth Session of the FAO European Inland Fisheries Commission (EIFAC) held in Rome from 17 to 25May 1994, noted with satisfaction that high quality freshwater fish products are becoming increasingly popular, especially in the more affluent countries. It recommended technologies with emphasis on cyprinids, and the provision of support for further research into new technologies for high quality fish products.

This study was undertaken following the recommendations of the above session and is based on the situation of the freshwater fish processing sector in Poland.

Bykowski, P.; Dutkiewicz, D.

Freshwater fish processing and equipment in small plants.

FAO Fisheries Circular. No. 905. Rome, FAO. 1996. 59p.

ABSTRACT

This document provides a brief review of the inland fisheries situation in Europe followed by the consideration of freshwater fish as raw material for processing. The document also reviews the equipment used in freshwater fish processing, taking into account the different processing methods such as chilling, preserving, smoking and fish silage production. Information on different forms of packaging and labelling requirements is also provided. Finally, the requirements for fish processing plants, hygiene and sanitary regulations, location of premises, cleaning and disinfection, water quality, public health hazards (with particular reference to the European Union regulations) and fish quality criteria are discussed.

A reference list records the publications consulted in the preparation of this study and indicates further reading.

Cleistogamy

It occurs in bisexual flowers which are always closed. Such closed flowers can perform only self pollination. Cleistogamy is generally accompanied by geocarpy when the fruits are formed underground, e.g., Groundnut, The phenomenon of having both open and closed flowers is called chasmocleistogamy.
Advantage of self pollination
1. Self-pollination can preserve parental characters indefinitely. Therefore, a useful variety, once evolved in a homozygous form, can be preserved.
2. It helps in maintaining pure lines for experimental hybridization.
3. It is more economical. The plants do not consume more energy in the production of large number of pollen grains.
4. It ensure seed production. The flowers do not take chances. Some flowers (e.g., Oxalis) utilize self-pollination for seed production when cross-pollination fails.
Disadvantage of self pollination
1. Useful characters can not be introduced by this method.
2. The undesirable or defect characters do not get eliminated from a plant.
3. The immunity of race towards infection decreases and ultimately the plant race become susceptible to many diseases.
4. Continuous self-pollination can lead to the death of the species
5. Self-pollination does not cause any verities. Hence, plants become less adapted to the changes in environment.
Cross pollination
Cross pollination is the transfer of pollen grains from the anther of one flower to the stigma of a genetically different flower. It is also known as allogamy or xenogamy (Gk. Xenos-strange, gamos-marriage). Cross pollination is accomplished with the help of an external agencies like wind (anemophily), water (hydrophily) and animals (zoophily). It is artificial carried out by plant breeders for maintaining races of cultivated plants and producing new varieties. On the basis of external agencies, cross pollination is performed by the following modes.
1. Anemophily
2. Hydrophily
3. Zoophily
Anemophily – In this type, pollination is brought about by wind. Wind picks up the pollen grains from the dehisced. Anthers of a flowers and drops them on the stigmas of other flowers. Example of wind pollination plants are Maize, Poplar, Birch, Oak, Urtica. These pants show the following characteristic.
i. Anemophilous plants grow in large groups. This ensures the pollination of flowers of all the plants.
ii. In many herbaceous plants the flowers are produced above the foliage (e.g., Plantago). This ensures the exposure of flowers to the wind.
iii. In deciduous anemophilous trees, flowers are produced before leaves (peach, apple)
iv. A high proportion of pollen grains is wasted in wind pollination. Therefore, plants produced large quantities of the pollen. A tassel of maize gives rise to 20-25 million pollen grains.
v. Pollen grains are small, light or dusty and can be blown to distances of upto 1300 km. Pollen grains of some plants have air sacs for making them light (e.g., Pine)
vi. Pollen grains are dry and unwettable.
vii. Stigmas are sticky, hairy, feathery (e.g., grasses) or branched in order to increases surface are for catching pollen grains.
viii. In wind pollination flowers, the non-essential floral oranges are either absent or reduced. This makes the flowers small, inconspicuous and devoid of colour, nectar or smell.

Pollination

The transference of the pollen grains from the anther to the stigma is called pollination. It is of two types –
1. Self pollination 2. Cross pollination
Self pollination
Self pollination is the transference of pollen grains from the anther of a flower to the stigma of either the same or genetically similar flower. It is generally not dependent on any external agency for pollination. It is of two types:
a) Autogamy – It is the transfer of pollen grains from anther of a bisexual flower to its stigma. Both stamens and carpel mature at the same time. It occurs in several cereals (wheat, rice) some peas and flowers which do not open.
b) Geitonogamy – It is kind of self pollination where flowers could be bisexual or unisexual but are borne on the same plant. It may required an external agency like insects or wind.
Self pollination may occurs when the flowers are open (chasmogamy) or closed (elesistogamy). Chasmogamous self pollination occurs only when their anthers and stigma mature at the same time (homogamy).
The self pollinated flower are generally small, inconspicuous, colourless, odourless and nectaorless. Self pollination occurs by following methods:
1. Homogamy – In this case the anther and stigmas of a bisexual flower mature simultaneously. The pollen grains reach the mature stigma either by contact, wind, gravity, rain drop or even insects. Self pollination brought about by contact is called direct autogamy and remaining agencies perform indirect autogamy.
I. Direct autogamy – It is accomplished by the movement of floral parts on account of growth, bending or folding, in convolvulus lxoza, catharanthus and Gardenia the anthers are borne at the mouth of the corolla tube. With the growth of style the stigma comes in contact with ripe anthers and pollination occurs. Pollination takes place in Cotton when the stigma in being pushed out of the staminal tube due to the growth of the style.
In Mirabilis ( four o’clock plant) the filaments of ripe anthers bend and bring in contact with stigma. A similar curling of style takes place in Potato. The stigma of Sunflower has brushing hair which helps in pushing the pollen grains from the synantherous tube. The stigma curls back and receives the pollen grains present on the brushing hair. The closing of flowers at night performer self pollination in Argemone Mexicana.
II. Indirect autogamy – It occurs without coming contact of anthers and stigmas. The pollen grains reach the stigma by rain (e.g., Caltha) or gravity (e.g., Lilac). In Lilac the anther lie exactly above the stigmas. The pollen grains of the dehisced anther fall over the low lying stigmas under the influence of gravity.
In sanicula male and female flowers grow side by side. The long style of the female flowers bends over the male flowers to get pollinated.

VEGETATIVE REPRODUCTION

Flowering plants reproduced by two methods; sexual and vegetative. By sexual method, seeds are produced which on germination form new plants. whereas vegetative reproduction is the formation of new plants from some vegetative part of plants like root, stem, leaf or bud. A vegetative part, capable of forming a new plant, always possesses a growing point or a bud. It also must have sufficient food for the early growth of new plants. Vegetative reproduction is seen in several plants. It is only method of reproduction in plants which do not flower and seed naturally, e.g., Pineapple, Banana, Sugarcane, etc. It is also being used by farmers to propagate the desired verieties quickly.
Types of vegetative reproductionI. Natural vegetative reproductionII. Artificial vegetative reproductionNatural vegetative reproductionVegetative reproduction is found mostly in the perennial plants. These plants propagate and reproduce naturally. Any part of the plants may accomplish vegetative reproduction. The various parts of the plants used for natural vegetative propagation are as follows:1. Root – Roots of some plants like Shisham, Guava, Poplar, Rose, etc. develop adventitious buds on them. On being separated from the parent plants or the removal of the aerial part, these roots develop into new plants. Some tuberous adventitious roots besides possessing adventitious buds contain sufficient quantities of food, e.g., Sweet potato, Dahlia, Asparagus. If sown in the soil these roots produce several leafy shoots which are known as slips. These slips develop their own roots. These roots are separated out into pieces and then planted in the soil.2. Underground stems – Underground stems are also capable of showing vegetative reproduction and form new plants. Vegetative propagation in some underground stems are discussed below.a) Suckers – A number of short underground stem branches known as suckers arise at the base of an aerial shoot. They grow into aerial branches which develop adventitious roots and new suckers at their bases. When these suckers are separated, a number of independent plants are developed, e.g., Mint, Chrysanthemum.b) Rhizomes – Rhizomes are the modified stems which have may buds and sufficient stored food. A piece of rhizomes containing a bud can give rise to a new plant. This method is adopted in agriculture in the propagation of plant like Banana, Ginger, Turmeric, etc. The rootstock rhizome of banana is very large and bears a number of buds. For vegetative propagation, the rhizome is cut into large pieces and planted into soil.c) Corms – Like rhizomes, the corms also have sufficient amount of stored food. They also bears many buds in the axils of scales present on the nodes. Under favourable conditions, all or several buds produce new shoots using the food stored in the corm. Each new shoot stores food at its base and produces a new corm. Examples are colocasia, crocus, freesia, etc.d) Bulb – A bulb is underground stem which has a number of buds. On being separated and planted, these buds give rise to new plants e.g., Garlic, Narcissus. Onion can also be propagated by bulb but multiplication by seeds is more economical.e) Tubers – A stem tuber is a swollen apical part of an underground stem branch which is known as sucker. It bears a number of nodes called eyes. Each eye possesses few buds. If the whole tuber is sown in the soil, only the terminal buds sprout because of apical dominance. Therefore, a tuber is cut into pieces, with each having one or more eyes. These pieces are then planted in the soil. New plants are produced from the buds presents on the eyes. Example – Potato

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Bacteriophage life cycle

Bacerophage, named T4- virus attacks Escherichia coli. It completes its lifecycle inside the bacterial cells. Virus exhibits two types of life cycles –

1. Lytic life cycle –

In lytic life cycle, virus multiplies in host cell, which stages:

a) Adsorption – The bacteriophage attaches itself over the surface of host cell (bacteria) by means of tail fibers.

b) Penetration (Injection) – Tip of tail possesses an enzyme called lysozyme which dissolved cell wall of the host. The nucleic acid of bateriophage passes into host through tube. However, capsid and tail sheath remain outside, as they have no role in multiplication.

c) Formative phase – After entering into bacterium, the viral nucleic acid takes over all the cellular activity of host. Viral genome replicates itself and codes for new types of proteins which are viral lysozyme, internal proteins and coat proteins.

d) Mutation – The coat proteins wrap itself over the viral genomes to produces a new virus. The period between the entry of phage genome inside bacterium upto formation of first new virus is called eclipse period. It is about 13 min in T4 bacteriophage.

e) Lysis – Soon after maturation, host cell wall ruptures, probably by the presence of some free lysozyme. The newly formed bacteriophages are released. They repeat the cycle again when they come in contact with another bacteria.

2. Lysogenic life cycle – In this cycle, the host does not undergo death and virus does not multiply in the hot cell. In case of some bacterio-phage, its genome does not take over the control of cellular machinery of host. Viral genome is integrated with host DNA. Stage is called prophage. Viral genime replicates along with host DNA.

When it breaks from host DNA, it may carry some host genes along with, which may be transferred to other cells on being infected. Such a mode of division of the prophage is called lysogey. The host bacterium is termed as lysogenic bacterium.

Retro-virus and Reverse transcription

Some DNA viruses (retroviruses) have a gene which codes for the enzyme reverse transcriptase. It helps in the synthesis of double stranded DNA from its original single RNA strand. This phenomenon is called reverse transcription.

RNA viruses capable of reverse transcription are called retrovirus. This phenomenon was described by D. Baltimore in 1970. Tumor causing virus and AIDS causing HIV are the example of retrovirus exhibiting reverse transcription.

About 20 viral gene have been identified which are responsible for triggering cancer cells which are known as oncogenes. Upon activation of oncogenes, cells divide abnormally and uncontrolled causing diseases cancer. However, the origin of cancer is a complex phenomenon.

GENETIC EXPRESSION AND ITS REGUALTION

Biochemically, a gene is a segment of DNA with a specific sequence of nitrogenous base. Functionally, genes are segment of DNA which controls the cellular functions by controlling the synthesis of a protein. Thus genes express itself in the form of a protein or enzyme that controls the development of specific character or a specific function.

In other way, expression refers to the molecular mechanism by which genes show its potential in the phenotype of an organism.

One gene one enzyme theory

Regarding the gene expression, the theory “one gene one enzyme” was proposed by Beadle and Tatum of California which working biochemical mutation on red mold Neurospora crassa. They were awarded Nobel Prize in 1958 for this work. Based on their work, they proposed a concept called “one gene one enzyme” hypothesis. It means that in a biosynthetic pathway several steps are involved each step is controlled by a specific enzyme which is synthesized under the control of specific gene. This hypothesis was later modified as one gene one polypeptide theory. Since it was found that the function unit at the genetic level is a polypeptide.

Viral gene expressions

Important characters of a virus

Virus (L. position) is a nucleoprotein entity which uses host machinery for its multiplication. The first virus to be discovered was Tobacco Mosaic Virus (TMV). The characteristic features of a virus are –

I. Virus is the smallest organism known so far.

II. It dose not have cellular structure.

III. It is obligate properties as it multiplies inside the living cells only.

IV. It exhibits properties of both living and non-living things. It has no metabolic activity of its own. It becomes active and multiply when it infects a living host cell.

V. Virus is capable of exhibiting mutation and recombination.

VI. It exhibits high degree of host specificity.

VII. It has very few enzymes like lysozyme, reverse transcriptase, etc.

Classification of viruses

Viruses are highly specific in nature and they have been classified into three categories on the hosts they live in –

I. Plant virus – virus that infects plants. e.g. Potato mosaic virus (PMV), Tobacco mosaic virus (TMV), etc.

II. Animal virus – virus that infects animals. e.g. Polio-myelitis virus, Infuenza virus. Small pox virus, Hepatitis virus, Mumps virus.

III. Bacterial viruses or bacteriophages – virus that infect bacteria.

There are different types of viruses containing DNA or RNA as a hereditary material. Depending on the type of the nucleic acid contained, viruses are placed in two groups –

I. Deoxyvira – virus that possesses DNA as the genetic material, also called as DNA virus. Majority of the animals viruses is DNA virus except polio virus, Rabies virus, Herps, etc.

II. Ribovira – virus that possesses RNA as the genetic material, also called as RNA virus. Majority of the plant viruses is RNA virus, Mumps, Influenza, and Rabies.

Structure of a virus

Structurally, a virus is made up of two components

a) Nucleoid – it is also called core. It is made up of a strand of highly coiled nucleic acid which is either DNA (in DNA virus) or RNA (in RNA virus).

b) Capsid – Capsid forms a covering around the nucleoid. It is made up of proteins or polypeptides. Its proteins are protective in function. They are resistant to proteolytic enzymes of the host. They have enzymatic properties. These also help the viruses in adsorption and penetration inside the host.

Some viruses like influenza or herpes have an additional lipoprotein membrane called enveloped made of lipoproteins.

Structure of bacteriophage

• A bacteriophage has two parts – head and a tail.

• Head is icosahedral and tail cylindrical.

• Head bears genetic material (DNA or RNA)

• Tail contains a hexagonal basal flat plate which bears six long tail fibres.

• These tail fibres remain coiled inside tail but spread out at the time of infection.

Genes expressions in eukaryotes

The genome of higher eukaryotes is very complex. Eukaryotes genome contains DNA many times as compared to prokaryotic genome. For example, drosophila has 5,000 to 10,000 genes. Human haploid genome seems to have at least 23,000 to 1,00,000 genes. In eukaryotes, most of the DNA is non functional or inactive and known as excess DNA or repetitive DNA. The diploid organism has two sets chromosomes. The genome in eukaryotes controls various function such as; growth and division of cells, differentiation and specialization of tissues such as muscles, liver, or heart in animals and parenchyma, chlorenchyma, Xylem and phloem in plants. As the eukaryotic genomes is very large, the genes expression and its regulation become very complex.
Genes regulation
In prokaryotes and eukaryotes, genes are regulated by various factors.
Following terms are used in genes regulation:
a) Exons and introns – In eukaryotes, some of the nitrogenous based do not code for amino acids. They are inserted between those segments of bases that normally code for amino acids. The coding segments of genes are called exons and non-coding segments are called introns.
b) Splicing – When the unwanted introns are removed and functional regions (exons), responsible for coding, are again joined, it is called as splicing.
c) Inducible genes and Inducer – All the genes present on the chromosome are not expressed simultaneously. The genes that remain inactive or repressed (i.e. an inducer) is present in the medium, are called inducible genes. The phenomenon of the action of these genes is called enzyme induction and substrate is called inducer.
For example, E. coli grown in a medium without lactose, does not produce enzymes required for lactose metabolism. But when the same bacteria is placed in a lactose supplemented medium, it starts producing enzyme like ß-galactosidase required for converting lactose to glucose and galactose. Therefore, since lactose is used to induce this enzyme, it is called inducer and this phenomenon is called enzyme induction.
d) Repressible genes and repression – When E. coli is supplied with certain metabolite more than required, the action of some genes, responsible for formation of some specific enzymes, can be inhibited or repressed. Repression may take place in the case even if the metabolite is being provided from outer source. As a result certain genes are repressed and do not produce enzymes. Such inactivated genes are known as repressible genes and phenomenon is called enzyme repression.
e) Co-repressor – Molecules that binds with the repressor protein to from a function repressor complex is called co-repressor.
In a tryptophan opero, tryptophan acts as a co-repressor by binding with the repressor protein to form a complex which on binding with the promoter switches it off and hence no transcription take place.
f) Constitutive genes – These refer to prokaryotic genes whose expression is not regulated. The products of these genes are produced at a constant, often low rate. Such genes are called constitutive genes and their expression is said to be constitutive. Such genes are involved in photosynthesis and respiration.
g) Structural genes – Genes that contains the information to determine the sequence of amino acid is called structural genes.
h) Regulatory genes – These genes codes for the product that regulates the level of expression of the structural genes. Although it is located at site away from the structural genes, it is called key element of operon. It forms repressor protein to make repressor complex.
i) Promoter genes – Genes that form the binding site of RNA polymerse is called promoter genes. Each genes may be regulated by a specific promoter.
j) Operator genes – Genes that operates the activity of structural genes, is called operator genes. It lies adjacent to the promoter site. Structural genes are expressed or not expressed depending upon whether the operator genes are on or off.
k) Operon genes – Genes are genetic unit consisting of an operator, a promoter and one or more structural genes whose activity is influenced by operator genes.

Operon concept
In order to study genes regulation or induction, Jacob and Monad (1961) proposed Operon concept in prokaryote (E. coli). An opron is a group of coordinately regulated genes, the products of which typically catalyze a multi-enzyme metabolic pathway and its controlling elements. Controlling elements include promoter genes, operator genes and regulatory genes.
Although there are many operons in bacterial cells, but the lactose or Lac operon discovered by Jacob Monad is classic example of all operons.

1. Structure of the lac operon – Two classes of genes are needed to named Z, Y, and A that code for three enzymes mentioned below.
• Z genes that codes for ß-galactosidase.
• Y genes that codes for galactoside permease.
• A genes that codes for thiogalactoside transacetylase.
These genes are located in a row adjacent to each other and hence they are called linked. They are known as polycistronic. Structural genes are regulated by operator genes and promoter genes.
a) Operator genes – Operator genes lies between the promoter genes and the structural genes. The operator genes act as a switch. Structural genes are expressed or not expressed depending upon whether operator genes are on or off. Single operator genes regulate all the three structural genes.
b) Promoter genes – Single promoter genes direct proper initiation of transcription. The lac Z, lac Y and lac A genes are expressed as a polycistronic message from a common promoter. The binding of DNA dependent RNA polymerase and promoter initiates the transcription of structural genes.
2. Regulatory genes – Regulatory genes are located away from structural genes. Hence regulatory genes are often not considered as part of operon. However, regulatory genes are the key element of operon. In codes for product that regulates the level of expression of structural gene. The regulatory genes constantly transcribe mRNA to produce the repressor protein.
Regulation of Lac operon expression
The absence and presence of lactose (inducer) switch on or off the transcription of mRNA and protein synthesis. This phenomenon can be described in following steps:
I. When E. coli is grown in a medium in absence of lactose, the regulator genes produce a repressor protein that bind the operator genes and block its activity. RNA polymerase can not move from promoter to structural genes. It stops the transcription of mRNA from structural genes and thus protein synthesis is switched off. Hence the enzyme is produced.
II. When the lactose is introduced in the medium, lactose binds to the repressor protein. In this way, repressor protein fails to bind to the operator genes. Then the operator genes remain active and hence switch is turned on. Operator genes induce RNA polymerase to bind to promoter mRNA corresponding to all three enzymes; Z genes code for ß-galactosidase, Y genes for galactoside permease and A genes for thiogalactosede transcetylase. With the expression of these three enzymes metabolism of lactose beings
Synthesis of enzymes is continued unless and until all the lactose molecules are consumed. When the last molecules of lactose bound to repressor is consumed, the inactive repressor becomes active and thus binds to operator site to switch off the operon as normal.

Role of repression and constitutive enzymes
When a substrate required by bacterium is supplied in excess amount from the outside, bacterium stops or inhibits the production of substance. In other way, we can say that the genes are being inactivated. These inactivated genes are thus called repressible genes and the phenomenon is called repression.
However, some of the cellular activities are functioning normally and constantly such glycolysis. The genes, that constantly expressed to take care of normal cellular activity such as glycolysis, are known as constitutive genes. The expressions of these genes are not regulated. The enzymes produced by bacterium for above function are known as constitutive enzymes. The constitutive enzymes are dehydrogenases.