REAL TREES 4 Kids! - In the Genes

In the Genes

Each year REAL TREE growers must replace the trees they harvest with a new crop of seedlings. Most of these new seedlings are replanted from nursery or seedbeds. When they are planted, they are about 3 to 5 years old.

You know, of course, that these seedlings just don't appear in the seedbeds. So, how do REAL TREES reproduce (or propagate)? There is some intense science going on behind the scenes!

The Genes

When you buy something that needs to be put together or built, one of the first things you do is find the instruction book, right? Well, REAL TREES (and other organisms) do the same thing. Their instruction book is found in each cell. These instructions are commonly referred to as genes or DNA.

REAL TREES and other plants are made up of cells. These cells are microscopic bundles that are responsible for all of the chemical processes of an organism. They are the basic units of life.

Inside every cell is a set of instructions. The instructions hold the genetic code for that organism and are usually found in the nucleus of the cell.

Here's how it works. Strands of chromosomes reside inside the nucleus. Chromosomes are made up of a chemical substance called DNA (deoxyribonucleic acid). DNA exists in long and twisted ladders. A gene is one section of that ladder. It holds a specific sequence of DNA.

All DNA is made up of four chemical bases - adenine, cytosine, guanine, and thymine. Each species contains the same DNA structure. Individuals in that species have individual differences because the order of the genes on the chromosomes is different.

When seeds are formed during pollination, they contain genes (DNA) from both the female parent cells and the male parent cells. The offspring gets half of its genes from the mother plant and half from the father. This gives each new plant a unique combination of genes — similar in many ways, but unique.

These differences are why REAL TREES (conifers) are different from broad-leafed trees, why a Colorado Blue Spruce is different from a Red Cedar, and why one Colorado Blue Spruce is different from another Colorado Blue Spruce! It's complicated and powerful stuff!

A Man Named Mendel

In the mid-1800s, Gregor Mendel was a monk living in the Abby of St. Thomas in what is now the Czech Republic. He was also a teacher interested in horticulture, meteorology, astronomy, and bees.

The farmers and horticulturists of Mendel's time used a method called selective breeding to produce better crops. They learned, through observation and experience, that by using seeds from plants that had the most desirable qualities (size, growth rate, hardiness, etc.) they could improve their crops.

After spending time in Vienna studying natural science and mathematics, Mendel began to experiment with pea plants. At that time, it was believed that the offspring of an organism would have blended qualities of each of its parents. As he worked, he discovered that this explanation was not accurate. Instead, he discovered that the genes or traits of the parent organism do not blend when combined. He found that the offspring of any two parents inherits one-half of its genes from each parent.

Using scientific methods, Mendel worked for many years. He theorized that heredity followed specific laws and that the outcomes of breeding could be predicted using mathematics.

Mendel's experiments and the discoveries he made created a science out of what farmers had been practicing in their fields. His experiments with pea plants were the starting point for the modern science of genetics.

Transfer of Genetic Information

During reproduction, the genes of each parent organism are transferred to the offspring. These genes contain the instructions for the development of a new organism. They determine which characteristics of the parent plant are seen in the offspring.

There are two main types of reproduction:

Sexual Reproduction

When a plant reproduces sexually, a male gamete joins with a female gamete through pollination and fertilization.

The offspring of a plant that reproduces this way is genetically similar to (and has characteristics of) each of it's two parents, but is not an exact copy.

Asexual Reproduction

Plants that reproduce asexually only have one parent. The offspring of a plant that reproduces this way is a genetic copy (clone) of its parent plant.

There are many ways asexual reproduction occurs:

vegetative reproduction
One part of the plant develops into a new plant. Examples: daffodils, garlic, potatoes, and strawberries

gemmation or budding
A group of cells grows out of the plant or animal and develops into a new individual Examples: hydra and coral

sporulation
Simple plants produce spores which are carried by wind or water and develop into new plants Examples: fungi and mosses

binary fission
Single-celled organisms use cell division as a way to reproduce. The splitting of the parent cells creates two daughter cells. Examples: amoeba, E coli, and paramecium

Seeds to Seedlings

Most REAL TREES get their start through sexual reproduction. In the life cycle of a gymnosperm, there are two phases: gametophyte and sporophyte. The plants you see are usually in the sporophyte stage. The gametophyte stage happens almost completely inside REAL TREE cones.

Sporophyte Stage

Mature REAL TREES are diploid sporophytes.

They are diploid because they have two sets of chromosomes (one from each parent).
They are sporophytes because they produce spores.

During this stage, most REAL TREES produce cones both male and female cones. Cones are the reproductive structures of conifer trees. They are also the location of most of the gametophyte stage in the REAL TREE life cycle.

Gametophyte Stage

The male cone is often called the pollen cone. It is in this structure that thousands of sporangia, called microspores, produce pollen grains. These are the male gametophytes and contain one set of chromosomes (haploid).

The female cone, or seed cone, contains megaspores. These develop into gametophytes which in turn produce ovules. Ovules produce egg cells. These are the female gametophytes and contain one set of chromosomes (haploid).

Gametophyte Stage

Pollen grains from male cones are carried on the wind to the female seed cones. Female cones are equipped with a sticky substance near the ovule. When pollen grains enter the pollen chamber of the ovule, a pollen tube begins to form. Sperm cells develop in the tube as it grows toward the egg cell in the ovule.

The sperm and egg cells are haploid at this point. Each cell contains one set of chromosomes.

Gametophyte Stage
to
Sporophyte Stage

When the pollen tube reaches the ovule, the one of the sperm cells fertilizes the egg. A zygote is created and develops into an embryo. The embryo now has two sets of chromosomes and is considered a sporophyte (diploid).

The ovule holding the embryo eventually develops into a seed. When the scales on the female cone open (either naturally or through harvesting processes*), the seeds will be dispersed. If conditions are right, the seed will grow and develop into a new mature sporophyte.

*Growers and nursery operators harvest the cones before they open. The harvested cones are dried. This causes the scales to open and release the seeds.

Sporophyte Stage

Fertile seeds are planted in nursery beds and cultivated for 3 to 5 years. They are then transplanted into fields for several more years before they are harvested.

A Crop from Cuttings

Not all REAL TREE species can reproduce sexually. The Leyland cypress, for example, does not produce viable seed. If not for artificial propagation techniques, the species would die out.

Those who grow and cultivate cultivars of Leyland cypress use a form of vegetative reproduction called cuttings to propagate the species. Using this technique, the grower produces trees that are genetically identical to the parent plant. On these operations, it's possible to have entire fields of REAL TREES that are genetically identical to each other!

The first step in the process is to select suitable trees to act as parent plants. The parent tree or trees are selected based on their characteristics. Growers look for a trees that are the right age and have the most traits that are most desired by their customers.

Once a parent tree is identified, a cutting is made. A stem is removed from the tree, prepared for planting, and immediately planted in pots or other small containers.

The cuttings are watered and cultivated in a greenhouse (or other temperature and humidity controlled area). After a period of time, roots begin to grow from the cuttings. They are then fertilized and transplanted into larger containers.

In 6 to 9 months, the new Leyland cypress seedlings are ready for planting in the fields.

Researchers continue to learn about the cycles of reproduction and the science behind inherited traits. Those who cultivate REAL TREES are putting that knowledge to work in their fields every day.