The Cannabis Breeder's Bible (13 page)

BASIC PLANT CELL STRUCTURES AND THE BASICS OF MOLECULAR GENETICS

Cells are the basic structural and functional units of which living organisms and tissues are composed. They are microscopic and consist of cytoplasm bounded by a membrane, with genetic material (DNA) contained in a nucleus.

Animals and plants have cells and so do all other living things. Animal cells look very different from those of plants but are very similar in appearance when you look at them using an electron microscope. Both animal and plant cells have a nucleus, mitochondria, endoplasmic reticulum, ribosomes, Golgi bodies and lysosomes.

Parts of the plant cell.

If one were to take these individual parts away from both the animal cell and the plant cell it would be very difficult to tell what type of organism these components came from unless you had a great deal of experience studying both structures. But as a whole unit, both types of cell structures have some major differences that would automatically help you identity which organism the cell came from. For instance, plant cells do not have centrioles or intermediate filaments, which may be seen in animal cells.

So now we know that plant cells appear differently than animal cells. Obviously that appearance has a lot to do with how these cells work. Let’s look briefly at how plant cells work.

Plant cells are eukaryotic, which means they are characterized by a discrete nucleus with a membrane, and other organelles. Plant cells have the following organelles.

• plasma membrane

• nucleus and nucleolus

• mitochondria

• ribosomes

• endoplasmic reticulum

• Golgi apparatus

• peroxisomes

• microtubules

Plant cells also have plastids, a cell wall and large vacuoles, which animal cells do not.

Chloroplasts

Chloroplasts are the most obvious plastids. They are usually round in shape and a typical cell has around 30, although there can be 10 more or less than that. Chloroplasts have a green pigment because they contain the chlorophyll that works with light during photosynthesis.

The Cell Wall

The cell wall is made of fibrils of cellulose, which are contained in polymers. The cellulose molecules work with intermolecular hydrogen bonding and build up this wall as a hard fibrils. There is a primary cell wall and a secondary cell wall.

1. The primary cell wall consists of the parenchyma and meristem. Both are roughly the same width. These primary walls are perforated to allow plasmodesmata to connect with nearby cells.

2. The secondary cell wall consists of a sclerenchyma, collenchyma and a xylem. They are basically supports to add stability to the cell.

Vacuoles

Vacuoles are encompassed by a membrane. Seedling plants contain lots of small vacuoles, but as the cells mature with age they come together to form a single large vacuole. Vacuoles store foods, wastes, acids and turgor. When your plant does not get enough water the turgor levels drop and the plant begins to wilt.

Plasma Membrane

The outer membrane of a cell is called the plasma membrane. The outer membrane contains other membranes within it. It is a thin, fluid, semipermeable lipid bilayer that includes proteins that form structures within the cell.

It serves the function of interfacing the extracellular fluid that encompasses all the cells in the plant. When the plasma membrane is covered in a liquid its phospholipids control this by forming a phospholipid bilayer.

Also contained in the plasma membrane are the integral membrane proteins.These proteins are firmly connected to it and allow the membrane a certain degree of movement.

Nucleus

The nucleus is covered in a number of membranes which contain tiny perforations. The perforations allow molecules to transfer in and out of the nucleus. The nucleus is important for the breeder to know about because it contains the chromosomes of a given cell. Each chromosome contains a single molecule of DNA and proteins. The entire unit—nucleus, DNA and proteins—is called the chromatin. Basically, the nucleus is the brain inside the cell.

Mitochondria

The mitochondria are involved in the conversion of food energy into molecules for cellular respiration. Cellular respiration is the procedure of oxidizing food molecules such as sugars into carbon dioxide and water.

Mitochondria have an outside membrane that encompasses the whole structure. They also have an inner membrane that sandwiches fluids between the two membranes. This space is called the inter-membrane.

Ribosomes

Ribosomes are particles found in the cytoplasm (the material inside a cell other than the nucleus) of cells.They can be free or attached to the endoplasmic reticulum, which binds messenger RNA and transfers RNA to synthesize polypeptides and proteins.

Endoplasmic Reticulum

This is a fine network of fibers found within the cytoplasm of a cell. These fibers are involved in a process called protein kinesis. Protein kinesis is essentially the movement, division and transport of proteins in a cell to specific locations.

Golgi Apparatus

The Golgi Apparatus is a series of complex membranous vesicles in the cytoplasm. It is involved in secretion and intracellular transport and works with the endoplasmic reticulum in protein kinesis.

Peroxisomes

A peroxisome is a cytoplasmic organelle that contains the reducing enzyme catalase. The Golgi apparatus manufactures peroxisomes and these are used in protein kinesis.

Microtubules

These are protein filaments found in the cytoskeleton and used mainly in cell motion, although they do provide some other smaller tasks.

These are the basic organelles and their components. Further discussion explaining exactly what kind of movement and protein kinesis goes on would be too complex for the nature of this book. If you want to learn more about plant cells then you may want to pick up a science book on the subject. What we’ve outlined above are some elements of the plant cell that are directly responsible for sharing the plant’s genetic code. Here we briefly discussed the nucleus of the cell and how it contains the chromosomes that are the genetic material that we are manipulating. We will look more closely at chromosomes later.

PLANT GROWTH

It is easy for most growers to mistake plant height for an increase in growth. Although this may seem to be the case it actually is not quite as simple as this. To be more precise, plant growth actually corresponds to the increase of plant cell numbers which are, by their nature, irreversible without pruning or cutting the plant back. Areas of the plant which grow are called “Meristems.” Meristems come in two types:

Apical Meristems

Apical Meristems are mostly found at the shoot and root tips. In their initial stages of development the cells are not specialized or designed to carry out specific tasks, but they gradually become elongated and go through vacuolation. After this they are specialized to carry out various tasks and become stable plant tissue.

Lateral Meristems

Lateral meristems are called lateral because they are found growing out from the side of the plant. They usually perform tasks like stem, branch and root thickening. They also form the phloem and xylem.

In order for meristems to be produced the plant must be growing in near optimal conditions for photosynthesis to occur. Nutrients will also contribute to their development. If the conditions are less than optimal, the production of meristems decreases or even stops. This is especially noticeable in cold growing conditions or where photosynthesis is not working. The lack of meristems being produced is more commonly known as “growth stunting.”

Hormones

Hormones are organic compounds produced by plants that regulate growth and other physiological activities. Plants have five classes of hormones.

Auxins

Auxins promote stem cell elongation and have some function in controlling yields. Auxins are mainly produced in the stem, bud and roots. Auxins play an active part in
phototropism
. Phototropism occurs when a plant bends toward the light. Auxins also work with apical dominance. When auxins are present they prevent lateral growth. When you prune back the shoot tip of a plant auxins are no longer present to prevent lateral growth. This is known as apical dominance. Auxins also stimulate cell division in the cambium, stimulate differentiation of phloem and xylem, and stimulate root initiation on stem cuttings. Auxins also delay leaf aging and stimulate flowering. They are also known to promote females. Auxins can both inhibit and increase growth depending on how the plant uses them.

Barmac Auxinone is an auxin-based hormone that is available from most good grow stores. It is used to stimulate root growth.

SensaSpray is another auxin-based hormone and is used to promote females. It also contains ethylene (see below), another plant hormone.

Gibberellins

Gibberellins are very similar to auxins, however gibberellins do not seem to inhibit growth (unless introduced in large amounts) except possibly in root growth. Gibberellins promote cell division and stem elongation. They are also involved in the production of a seed’s embryo and can help seeds to germinate faster. Gibberellins can speed up growth but they can also promote more males.

Bonza Bud is an anti-gibberellins-based hormone that is available from most good grow shops. It will help keep internode lengths short and promote female flowers.

Ozi Tonic contains tricantanol, gibberellic acid, propolis and vitamin B. The gibberellic acid can promote male growth, and females that grow from Ozi Tonic treated plants may have increased yields.

Cytokinins

Cytokinins promote cell division and leaf expansion, are responsible for morphogensis in tissue culture and are involved in the stimulation of chlorophyll synthesis. They are mostly produced at the tip of a shoot. They work very closely with auxins for plant growth.

Acadian Seaweed Extract is a common cytokinin product. It contains the cytokinin BAP and is used to prevent transplant shock.

Nitrozyme is another cytokinin product. It is easier to find than Acadian Seaweed Extract and is also used to treat transplant shock.

Abscisic Acid

Abscisic acid promotes seed dormancy by inhibiting cell growth. It helps seeds to synthesize storage proteins. It also slows down cell division and bud production. Abscisic acid inhibits shoot growth but does not seem to affect the roots. It is also involved in the processes of leaf wilt. Abscisic acid is an antagonist of gibberellic acid, auxine and cytokinine. It also plays a role in pathogen defense.

Ethylene

Ethylene is a gaseous hormone closely regulated by the plant. It stimulates shoot and root growth and promotes flowering maturation. It also controls leaf aging. For ethylene products see SensaSpray above.

HORMONE CHART

ADDITIONAL HORMONE PRODUCTS

Here is a list of additional hormone products that we have not covered already.

Am inogro

Aminogrow contains L form amino acids and is used to help improve plant vigor and increase resistance to stress, pest attacks, mold and fungi.

Checking your bud for mold is important. Immediately clip away any moldy bud. Humidity promotes mold. Fresh air is the solution to mold problems. Prevention is better than using fungicides.