Bacteriophages

Bacteriophages

Viruses that attack bacterial cells are known as bacteriophages. Many results gained from studying bacteriophages have universal implications.

For example, the physical properties of DNA and RNA are remarkably identical in all organisms, and these are perhaps easiest to study in bacteriophage systems.

Bacteriophages, or phages for short, are viruses that parasitize bacteria. Viruses are an extra ordinarily diverse group of ultramicroscopic particles, distinct from all other organisms because of their noncellular organization.

Poisonous and Noxious Plants

Poisonous plants

Poisonous plants have evolved toxic substances that function to defend them against herbivores and thereby better adapt them for survival.

After evolving adaptations that facilitated colonization of terrestrial habitats, plants were confronted with a different type of problem.

This was the problem of herbivory, or the inclination of many different types of organisms, from bacteria to insects to four-legged herbivores, to eat plants. Pressures from herbivory drove many different types of plants, from many different families, to evolve defenses.

Resistance to Plant Diseases

Resistance to plant diseases

Plants have a number of defense mechanisms by which they can resist biotic or abiotic stresses that might cause their death or inhibit their growth. Such mechanisms are referred to as resistance.

Plants, the primary producers in all food chains, are besieged by a host of biological agents throughout their life cycles. Each species of plant is attacked by at least one hundred different kinds of mycoplasmas, viruses, bacteria, fungi, nematodes, and insects.

In addition, regional weather patterns change, and plants are often faced with unfavorable environmental conditions such as heat, drought, or cold. Plants must contend with the chemicals used by people to deal with unwanted plants. These herbicides are designed to kill the plant or to restrict its growth.

Rusts

Rust fungi

Rust fungi belong to the taxonomic class Teliomycetes within the basidiosporic phylum and include some seven thousand known species, all plant parasites, with many being extremely important plant pathogens.

Rust diseases have caused serious problems for centuries and continue to cost billions of dollars annually worldwide.

Important examples include: leaf, stem, and crown rusts of wheat, barley, and oats; the blister, fusiform, and gall rusts of pines; coffee rust; many field crop rusts, such as soybean, peanut, sunflower, and flax rusts; and rusts of many horticultural crops and ornamental plants, such as cedar-apple rust, bean rust, and rose rust.

Viruses and Viroids

Viroid

Viruses are extremely small parasites that have none of the structures characteristic of living cells. Many viruses are little more than a protein-coated and particle-containing DNA or RNA.

The protein coat is specifically adapted for breaching the plasma membranes of host organisms. Viroids are even simpler parasites comprising small, single-stranded molecules of RNA with no protein coat. They are the smallest known agents of infectious disease.

The concept of a virus dates back to the late nineteenth century investigations of the mosaic disease of tobacco by Dmitri Iosifovich Ivanovsky in Russia and Martinus Willem Beijerinck in Holland.