Growth in plants begins with the germination process. This happens after the seeds undergo a period of dormancy. The dormancy period is a resting event or inactive seeds for conducting growth activities.
In general, this event occurs in the dry season. That happens because plants lack water. Besides that, germination is an event of emergence of small plants or plantula from the seeds.
The event of seed germination begins with the process of water absorption by the seeds called imbibisi. The inclusion of water into the seeds stimulates the activity of the hormone gibberellins to stimulate the grains of aleuron. These grains are used to synthesize alpha amylase and protease enzymes.
The formation of alpha amylase and protease enzymes will stimulate the breakdown of starch and protein in endosperm into glucose and amino acids which will become substrates. The substrate will be used for metabolism or respiration.
The availability of enough substrate will encourage increased respiration to produce energy. So that enough energy is available for the division of embryonic cells in the seeds by mitosis.
This causes the seeds to rupture and the germination process is marked by the appearance of the plantula from inside the seed.
Factors that can stimulate germination are water, temperature, oxygen, and humidity. That is an external factor. While internal factors include enzymes and hormones that can affect the speed of germination.
Seeds can germinate to form plantula. Because there are embryos in the seeds. The embryo or plant institution has three parts, as follows: (a) the radicle or roots of the institution, (b) the cotyledons or leaves of the institution, and (c) the cauliculus or the trunk of the institution. Each of them can be explained below.
Radicles are candidates for roots that grow to form roots and will penetrate the seeds toward the pit. In poaceae or graminae, the root of the institution has the root of the institution called koleoriza.
Cotyledons are the first leaf candidates to grow in the germination process. The physical appearance of the institution leaves looks thick. This is due to function to hoard food reserves during the germination process.
Furthermore, this first leaf has a function also to carry out photosynthesis and as a food suction tool for embryos which is carried out in the form of a shield and in the form of a thin membrane called the skuletum.
Cauliculus or institutional stem is a prospective stem that will grow into a candidate for the upper trunk that is above the cotyledon called epicotyl. Whereas the candidate stem under the cotyledon is called hypocotyl.
The epicotyl will then grow to form stems and leaves. Unlike the hypocotyl which will grow to form the base of the stem and roots.
The tip of the epicotile that forms a leaf has an institution called the plumulae. Plumulae is covered by a membrane called coleoptilum.
Furthermore, based on the location of the cotyledons, at the time of natural germination, germination is divided into two, namely epigeal germination and hypogeal germination. Each can be explained as follows.
Epigeal germination . This type of germination is a germination marked by the lifting of the cotyledon above the soil surface. As a result, the hypocotyl portion can be seen above ground level. This type of epigeal germination can be found in green bean germination.
Hypogeal germination . This type of germination is a germination in which the cotyledons cannot be lifted above the ground. As a result, hypocotyl does not appear above ground level. This type of germination can be seen in peas and corn.
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Plant Growth and Development
The growth of living things can be interpreted as an increase in volume event that includes an increase in the number of cells, cell volume, cell types, or substances present in cells that are quantitative or can be calculated with numbers and irreversible or can not be returned to normal.
An example of a growth event is height and height increase in the stems of plants. Meanwhile, development is a process of specialization of cells leading to certain forms and functions that lead to the level of maturity that is qualitative and irreversible.
This qualitative trait is interpreted as not being stated in numerical order. Examples of developments in plants are plants that produce flowers as a means of reproduction.
Growth and development run simultaneously. It means walking together in parallel and supporting each other to reach the level of maturity.
The speed of growth in plants can be measured by an instrument called an auxanometer. The growth of plants based on the origin of the meristem can be divided into two, namely primary growth and secondary growth.
Primary growth is a growth caused by primary meristem activity and occurs at the primary growing point or in the active part of dividing and growing. This section is called the meristem network.
In the meristem tissue there is a root growing point and a stem growing point. Meanwhile, secondary growth is a growth caused by secondary meristem activity and occurs at the secondary growth point.
The point of growth can be interpreted as an area or part of the plant that experiences the fastest growth or increase in length. The primary growth point is at the tip of the stem and root tip.
Meanwhile, the secondary growth point is in cambium, cork cambium or phelogen. The primary growth point at the root tip is divided into three parts, namely the cleavage region, the elongation area, and the maturation area.
This cleavage area is called cleveage. Elongation area is called elongation. Meanwhile, this area of maturity is called differentiation.
Then, the growing point at the root tip will be divided into four parts, namely the root cap or caliptra area, cleavage area, elongation or elongation area, and the area of maturation or differentiation (Reaven Johson in Susilowarno).
Cleveage area has the following characteristics:
- The cells have the same shape and size as the compact arrangement
- Very actively splitting
- Less resistant to light radiation and chemicals.
This area requires large amounts of carbohydrates to build cell walls and protoplasms.
Elongation or elongation area has the following characteristics:
- The cells can extend to nine times longer. This is due to absorb a lot of water.
- Still actively splitting
- It is already resistant to radiation from light and chemicals
- Function to save food reserves.
The elongation of cells caused by absorbing water because in the cells that elongate formed large vacuoles so that the cell makes it possible to absorb large amounts of water.
Cell elongation in addition to being caused by the influence of water absorption, is also influenced by cell stretching hormones that can stimulate cell walls to stretch. Elongation of cells has a function to press the tip of the root to penetrate the soil.
Maturing areas have the following characteristics
- Cells with relatively varied shapes
- Already resistant to light radiation and chemicals
- Cell division activity is slow.
The area of differentiation is divided into three layers. These layers are protoderm, basic meristem, and prokambium.
Protoderm, will later develop to form the epidermis. Basic meristems, which will grow to form cortical parenchyma. Prokambium which grows into a central cylinder and beam transport, namely xylem and phloem.
The area of the root cap or caliptra consists of adult cells formed by calyprogen. In kaliptra cells there is a starch called columella. This column has a function as a food reserve.
Kaliptra has a function to protect the growing point of the root tip which is still weak and secrete polysaccharides to lubricate the soil. In order to be soft and able to be healed by the tip of the root and take water and minerals even in small amounts.
Furthermore, secondary growth is growth caused by the cleavage activity of the secondary meristem. Growth can result in an increase in stem and root diameters in dicotyledonous plants and gymnosperms.
In the monocotyledonous plants only a part of them experienced secondary growth as indicated by the increase in the diameter of the stem for the palmae or Arecaceae group.
Secondary meristems that cause secondary growth are generally known as cambium. The cambium in plants is divided into two types, namely vascular cambium and cork cambium.
Vascular cambium is the result of advanced differentiation or direct specialization of prokambium so that it is actually an adult tissue. However, it still has the ability to divide.
Cleavage from vascular cambium produces secondary tissue and results in a large increase in stem diameter. Therefore, this growth is called secondary growth.
The vascular cambium is a cambium that exists between the transport beams, that is, between the xylem and phloem. This cambium forms a circle on the stem and roots. Vascular cambium is divided into intravascular cambium and intervascular cambium.
Intravascular cambium is a cambium that separates the xylem and phloem and can divide outward to form a secondary phloem inward to form a secondary xylem.
Intervascular cambium is a cambium that exists between groups of carriers transporting one another. The cambium will split outward to form the skin element and to split inward to form the wood element.
The growth of vascular cambium will form a formation called the circle of the year.
Cork cambium or phelogenous tissue in the cortical stem tissue has the ability to divide outward to form phelemes and inward to form pheloderms.
Felids are dead cells that form cork cells. Whereas, feloderm are living cells that form secondary cortex.
Cleavage of cork cambium in this plant has a function to overcome the rupture of the epidermis and cortex as a result of vascular cambium activity in forming a year circle.
In some places on the stem there are gaps that are called lenticels. It has the function of exchanging oxygen and carbon dioxide.
The next discussion on the Effect of External Factors on Plant Seed Growth , see carefully.
Effect of External Factors on Plant Seed Growth
Since the making of plant seeds until they are ready to harvest is certainly influenced by many factors to determine the success of the growth and development of these plants.
In making seedlings when plants are experiencing primary growth, plants only need water and oxygen. While light, tends to be less needed.
After farmers move the seeds to paddy fields, of course the water and light requirements are different. That is because the plants are ready to hold secondary growth.
The factors that affect plant growth can be divided into two things, namely internal factors and external factors.
Internal factors include genes and hormones. Meanwhile, external factors include water, light, temperature, and humidity, pH, oxygen. Each factor can be explained as follows.
Water. For primary growth, soil growth media is not absolute. The important thing is the growing media that is easy to absorb water. Hard growing media will find it difficult to absorb water so the seeds cannot germinate.
Water is a compound that is very important to maintain the turgor pressure of cell walls. The function of water in plants is as follows:
- Circulating the results of photosynthesis to all parts of the plant.
- Determine the rate of photosynthesis
- For universal solvents in the process of plant growth and development
- Determine the nutrient transportation process contained in the soil.
Light. Basically direct sunlight greatly inhibits plant growth. This is due to the high light intensity which will evaporate the ground water in large amounts, so that the roots are not enough to absorb water.
In addition, light will be able to inhibit the work of the auxin hormone, where the auxin hormone will turn into compounds that inhibit growth if exposed to light. Sangay sunlight affects green leafy plants.
That is because sunlight determines the process of plant photosynthesis. Plant photosynthesis is a basic process in plants to produce food. The food produced will determine the availability of energy to produce food.
The food produced will determine the growth and development of plants. Sunlight also affects the growth of plants that grow in dark places that will grow faster.
The event of very rapid growth in a dark place is called etiolation. This situation occurs because there is no light that can maximize the function of auxin for elongation of plant cells.
As a result of these events, the body of the plant becomes abnormal. The leaves turn yellow, wide and thin. In addition, the trunk is small, very long, yellow, and weak.
This is different from plants that grow in bright places. Growth is slower with relatively short conditions, leaves develop well, and the color is green.
Humidity. Humidity is a total content of water vapor in the air. Conditions of high humidity and not much evaporation will help to keep water available around the plant so that the cells will be able to absorb large amounts of water and become longer.
pH The degree of acidity or basicity or pH that has an influence on the growth and development of plants is soil pH. The soil pH factor is determined by the type of soil. In order not to affect the growth and development of plants, the pH of the soil type is reduced by way of mixing.
Temperature. High temperatures and the amount of radiation intensity are always directly proportional so that for primary growth relatively low temperatures, high humidity, relatively sufficient amount of water, and little light are needed.
Sehu influences the action of enzymes that help to metabolize. Where metabolism supports growth. The temperature suitable for the growth and development of higher plants ranges from 0 0 C to 45 0 C.
Among these ranges, the temperature for growth and development of each type of plant varies. Actually, the optimum temperature for plant growth and development is related to the origin of the plant species.
Plants originating from the tropics require relatively higher temperatures compared to plants originating from sub-tropical or polar regions.
After sufficient germination, plants need to be transferred to media and soil that contains more organic matter. Then, placed in the sun for further growth or secondary growth.
Secondary growth requires direct sunlight to help photosynthesis. Some plants must be protected from low temperatures before germination and flowering.
Nevertheless there are some flowers that experience an increase in the speed of germination and flowering. This is as a result of low temperature stimulation in a certain amount of time.
The response to germination and flowering in plants due to low temperatures is called vernalization. Apple plants are more suitable for growing and producing more fruit in Batu Malang than in Kaliurang or Tawangmangu, due to low temperatures below 18 0 C.
Oxygen. Oxygen is a limiting factor in every organism. This condition also applies to plant growth and development. Oxygen concentration is largely determined by the medium in which the plant is located.
The roots of plants need good aeration to get enough oxygen. With this basis, farmers often loose their plants regularly. Good aeration can improve the process of root respiration to circulate nutrients in the soil to the leaves.
Mineral or nutritional salt. Plants need nutrients for survival. Nutrients needed in large quantities are called macro or macronutrient elements.
Macro elements include carbon, oxygen, hydrogen, nitrogen, sulfur, potassium, calcium, phosphorus, and magnesium. Conversely, the elements needed by plants in small amounts are called micro elements or micronutreins.
Examples of micro elements include chlorine, iron, boron, manganese, zinc, copper and nickel. Nutrient deficiencies in the soil or media where plants live can cause plants to not be able to grow and develop properly.
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Internal Factors That Influence Growth
Internal factors that affect growth can be divided into two, namely intracellular factors, in the form of genes and intercellular factors in the form of hormones.
Gene is a chemical substance that has the function to determine the nature of heredity. Genes are influential in determining plant growth patterns.
This means that the level of growth optimization, where the growth pattern of peanuts will not be the same as corn or more clearly in adulthood, peanuts will not have the same time and height and weight as corn.
Furthermore, genes can also regulate the speed of growth by regulating the speed of protein synthesis which produces enzymes that can be used to increase the speed of metabolism.
An increase in metabolic rate due to the presence of enzymes will increase the speed of supplying the components needed for growth. This means it also increases the speed of growth.
Hormones are chemical substances composed of proteins that have a function to stimulate growth. Hormones in plants are called phytohormones. Fitohormon has a function to help regulate growth.
This is due to the main role in regulating growth is the vitamins and minerals in the environment.
The role of phytohormons is to spur growth activities, where the growth patterns are determined by genes and the main regulation of growth is determined by vitamins and minerals. Types of fitohormon are as follows:
- Kalin Hormone. This phytohormone is produced in many meristem tissues throughout the plant body. Its function is to stimulate the growth of plant organs. The types of phytohormone are phylocalin (to stimulate leaf growth), kaulokalin (to stimulate stem growth), rhizokalin (to stimulate root growth), and anthokalin (to stimulate flower and fruit growth).
- Abscisic acid. Fitohormone is found in many stems, leaves and seeds. This abscisic acid has a function not to spur growth but actually inhibits growth. The functions of these growth inhibitors are as follows: (a) encourages seed dormancy so that they do not germinate, (b) encourages leaf shedding during the dry season to reduce water evaporation, (c) reduces the rate of division and elongation of cells in the growing point, and (d) helps close leaf stomata to reduce evaporation.
- Hormone wounds or wound cambium or traumalin acid. This phytohormone is produced by cambium on dicotyledonous stems. Traumalin acid stimulates cells in the injured area to become meristemic in nature again. This is intended to be able to hold cell division to cover the injured part. Wound closure tissue is called callus. Besides hormones, vitamins also affect growth and development. Examples of vitamins are ascorbic acid (vitamin C), riboflavin (vitamin B12), pyridoxine (vitamin B6), thiamine (vitamin (B1) and nicotinic acid. Vitamins play a role in the process of hormone formation and have a function as a cofactor or nonproton component to activate enzymes.
- Auxin hormone is found by Went. He found it at the coleptile end of Avena sativa or wheat. In addition, auxin is also at the tip of the stem buds of young leaves and fruit that are growing. Auxin can be made synthetically and is widely traded. Other names for auxin to be traded include indole acetic acid, indole butyric acid, naphthalene acetic acid, acid 2, 4 dichlorophenoxy asestate. Furthermore, it is also known as auxin a which can be found in animal and human urine. Auxin B in corn sprouts oil. Auxin physiologically exerts the following effects: (a) apical dominance and inhibits lateral dominance. This means that the auxin produced at the tip of the apical meristem is transported down in the armpit area to inhibit the emergence of axillary or lateral buds. If apical shoots are cut, lateral buds will develop; (b) cell elongation at the point where the stem grows. But in general, inhibitors root cell lengthening. Inhibition of root cells is caused by the concentration of auxin in the root is very low and influenced by the earth’s gravitational force; (c) stimulates cell division in the cambium region causing secondary growth; (d) leaf abscess or leaf decay is an event of the release or separation of leaves from the stem which is controlled by the concentration of auxin in the abscess area; (e) Parthenocarpy is an event without seed formation. Seedless fruit can be made by giving auxin to the pistil. Giving this induction will result in inhibition of pollen channel formation and inhibits fertilization because the ovary wall is swollen, causing fertilization to fail which will produce seeds; (f) phototropism, is a movement of plant growth towards the direction of the arrival of light. This can occur because auxin will shift to a place that is not exposed to light so that it will spur faster growth compared to areas exposed to sunlight. This condition causes the growth of plants to bend and appear to grow in the direction of light. The light that hits auxin activates the IAA oxidase enzyme so that the inactive IAA-aspartic acid complex is formed. This condition causes the growth of plants to bend and appear to grow towards the direction of light. The light that hits auxin activates the IAA oxidase enzyme so that the inactive IAA-aspartic acid complex is formed. This condition causes the growth of plants to bend and appear to grow towards the direction of light. The light that hits auxin activates the IAA oxidase enzyme so that the inactive IAA-aspartic acid complex is formed.
- This fitohormon was discovered by F. Kurusawa. Found in the fungus Gibberella fujikorol. The giberrelin hormone can be divided into various types, namely giberrelin A, Giberrrelin A2, and Gibberrelin A3 which have very specific molecular structures and functions. However, in its development can be found in various organs such as roots, stems, shoots, leaves, flower buds, root nodules, fruit, and callus and seed tissue. The physiological effects of Gibberellins are as follows: (a) inhibits seed formation, stimulates the growth of pollen channels, enlarges fruit size, and stimulates flowering; (b) stimulates fruit growth by parthenogenesis; (c) helps the germination process by stimulating the aleuron grains to synthesize the alpha amylase and protease enzymes so that they can inhibit seed dormancy;
- Fitohormon ini pertama kali ditemukan pada sel- sel batang tembakau. Sitokinin memiliki pengaruh fisiologis sebagai berikut: (a) memperkecil dominasi apikal; (b) merangsang pembelahan sel; (c) menunda pengguguran daun; (d) mengatur pembentukan untuk bunga dan buah; (e) menghambat proses penuaan dengan cara merangsang proses dan transportasi garam- garam mineral dan asam amino ke daun; dan (f) dalam teknik kultur jaringan memiliki fungsi untuk membantu pembentukan akar dan tunas.
- Ethylene gas. This phytohormone is found in old fruit. Ethylene gas is called because it is in the form of gas and has the function to damage the chlorope of the fruit that starts cooking. The function of ethylene gas in damaging chlorope in fruit peels is influenced by oxygen. The function of ethylene gas, among others, is as follows: (a) causes the stem growth to become sturdy and thick; (b) cause the fruit to ripen so that it generally changes color from green because chlorophyll is damaged; (c) together with gibberellins can adjust the ratio of female and male flowers in monoecious plants; and (d) together with auxin can stimulate flowering on mangoes and pineapples.
Implications of Technology for Growth and Development
- Utilization of auxin for parthenocarpi. Giving auxin to plants that are flowering can stimulate fruit growth without seed formation. Seedless fruit growth is known as parthenocarpy. The function of auxin in parthenocarpy is to block the process of pollination or pollination, fertilization, or fertilization.
- Utilization of gibberellins to increase the size of the fruit. The administration of gibberellins to fruiting plants can stimulate the formation of larger fruit sizes.
- Use of auxin for eradicating weeds. The synthesis of auxin hormone at a concentration of 0.1% by spraying can be used as an herbicide. Herbicides are killing wild weeds and weeds.
- Utilization of cytokines to prevent the loss of flowers and fruit. Giving cytokinin hormones in plants that are flowering and fruiting will be able to reduce the amount of flowers and fruit so that it can increase farmers’ income.
- Utilization of auxin and cytokines for fruit production throughout the season. Giving auxin to fruit-producing plants will stimulate plants throughout the year to produce flowers and fruit. Even though it’s not in the natural fruiting season.
- Utilization of physical and chemical techniques to solve seed dormancy. In order to accelerate the germination of seeds, especially those with hard seed skins can be done using physical and chemical techniques. The aim is to accelerate germination. Such techniques include sanding the seed coat or dampening with strong acids such as H2SO4 so that the seed coat becomes thin or soft. This allows the seed imbibition process to begin with the germination process.
- Manipulation of external factors of growth with hydroponic agriculture and green houses. In order to accelerate growth, it faces constraints related to land limitations. So the planting system was developed using a water medium called hydroponics. In addition, to anticipate the lack or excess of light, humidity, wind speed, and ambient temperature many agricultural systems are developed with mulch and in the green house.
- Utilization of cytokines for tissue culture. Tissue culture is a process of propagating plant tissue in certain media to produce seedlings in large quantities in a relatively short time. In the process of tissue culture, cytokinins are needed which will stimulate stem formation.
- Utilization of gibberellins and auction to regulate the number of male and female flowers. Administration of gibberellins and ethylene together in flowering plants can adjust the ratio of male and female flowers. The regulation of the number of male flowers and female flowers is intended to increase fruit yield for farmers.
- Utilization of auxin and ethylene to stimulate flowering. Provision of induction and ethylene together in mango and pineapple plants can stimulate the flowering process before it is premature.