Lecture 3 - Lecture 3 Plant Defences CAN BE PHYSICAL,...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Lecture 3 – Plant Defences CAN BE PHYSICAL, CHEMICAL , EVEN BEHAVIOURAL I. PHYSICAL DEFENCES : ALSO CALLED MECHANICAL PROTECTION a) BODY ARMOUR = TOUGH EPIDERMIS ("OUTER SKIN") Examples: WOODY STEMS ; TREES, SHRUBS b) OTHER ARMOUR - SPINES, THORNS, PRICKLES, STINGING HAIRS. Examples: RASPBERRY, BLACKBERRY, CACTUS, THISTLE, HAWTHORN c) TRICHOMES : SMALL HOOKED OR CLUBBED HAIRS = DENSE TANGLES IMPEDE SMALL ANIMALS such as MITES and small INSECTS. Example: MULLEIN SOME RELEASE STICKY GLANDULAR SECRETIONS = GLANDULAR HAIRS ONE TYPE - SEPARATELY STORED PHENOLS AND ENZYMES, WHEN ANIMAL BRUSHES THEM THEY,BEAK OPEN, CONTENTS MIX LIKE EPOXY , CREATE GLUE-LIKE OOZE THAT HARDENS , ALSO RELEASES REPULSIVE CHEMICALS Plants have many external structural defences that discourage herbivory. Plant structural defences on stems and leaves can deter, injure, or kill the grazer. Some defensive compounds are produced internally but are released onto the plant's surface For example, resins, ligning, silica, and wax cover the epidermis of terrestrial plants and alter the texture of the plant tissue. Example : The leaves of holly plants, for instance, are very smooth and slippery making feeding difficult. Some plants produce gummosis or sap (fluid transported in xylem cells (tracheids or vessel elements) or phloem sieve tube elements of a plant) that traps insects A plant's leaves and stem may be covered with sharp spines or trichomes – hairs on the leaf often with barbs, sometimes containing irritants or poisons. Plant structural features like spines and thorns reduce feeding by large ungulate herbivores (such as kudu, impala, and goats) by restricting the herbivores' feeding rate, or by wearing down the molars as in pears. The structure of a plant, its branching and leaf arrangement may also be evolved to reduce herbivore impact 2. DIGESTIBILITY REDUCERS (constitutive, most quantitative metabolites are digestibility reducers that make plant cell walls indigestible to animals) a) WHEN EATEN, MAKES IT HARD FOR THE ANIMAL TO DIGEST THE PLANT ; MOST HAVE DUAL PURPOSE = STRUCTURAL AND DEFENSIVE FUNCTIONS b) Condensed tannins, polymers composed of 2 to 50 (or more) flavonoid molecules, inhibit herbivore digestion by binding to consumed plant proteins and making them more difficult to digest, and by interfering with protein absorption and digestive enzymes. Examples : Silica and lignins, which are completely indigestible to animals, grind down insect mandibles (appendages necessary for feeding) c) For example , plants growing in nitrogen-poor soils will use carbon-based defences (mostly digestibility reducers), while those growing in low-carbon environments (such as shady conditions) are more likely to produce nitrogen-based toxins 3. STRUCTURAL ELEMENTS
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
a) PLANT TISSUES HAVE CELLS WITH STIFF WALLS THAT CAN BE THOUGHT OF AS REINFORCED CONCRETE - CEMENT WITH STEEL RODS STUCK IN FOR SUPPORT CELLULOSE = STRUCTURAL ELEMENT;
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 10

Lecture 3 - Lecture 3 Plant Defences CAN BE PHYSICAL,...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online