Week 4 Lecture 1
Plant Physical Defences continued;
Digestibility reducers –
are a common form
Plants usually contain a cocktail blend of chemicals, making it more difficult for herbivores to counterattack.
Toxins are found in most parts of a plant, especially vulnerable tissues not fortified with lignin or silica, such
as buds, young leaves, and unripe fruit
Chemicals often play dual roles in the plant, primary function metabolic
Other chemicals are produced solely for non-metabolic functions such as for pollination or defence; those are
. There are between 200,000 and 300,000 different secondary metabolites, many for
If a chemical defence is always present, even when a plant is not under attack, it is called a
. There are several major groups of constitutive toxins defined presence or absence of the element
Do not contain Nitrogen
, whose name reflects their initial discovery in turpentine. There are approximately 40,000
types of terpenoids and than 100,000 species of plants. While some secondary metabolites play non-
defensive as growth stimulation and pollinator attraction, others serve only to protect.
Many terpenoids are bitter tasting and defend through repulsion rather than by poisoning the animal that
ingests them. A few, however, can be deadly.
) are a major group of terpenoids. Milkweeds white
that oozes out is loaded with cardenolides
If you have ever sat on a conifer log or stump the gummy exudate is
(resin for short), a chemical
defence that is full of terpenoids. Many coniferous trees store resin special ducts or canals, and a few
special blisters on bark
Bark Beetle chews a resin canal, its contents forced out through the wound, overwhelming the insect and
encasing and killing it.
When turpentine component evaporates, the resin thickens and effectively seals off wound.
Some coniferous trees such as firs also manufacture oleoresin under attack.
Induced resin differs slightly in its chemical composition from the plant’s constitutive resin, and it often
accumulates in newly formed compartments called
traumatic resin ducts
that lie in wait, ready to defend
the tree against the next attack
The most famous (or infamous!) of all resins is likely
the one found in Poison Ivy.
All parts of the plant except pollen contain the resin and its active ingredient