how plants respond to the environment

why plants respond to environment in terms of the need to avoid predation + abiotic stress

  • to cope w changing conditions + avoid abiotic stress

  • to maximise photosynthesis by obtaining more light, more water and more minerals

  • to avoid herbivory and grazing

  • to ensure germination of its seeds in suitable conditions

hormones

some have diff effects on diff tissues

  • some amplify each others effects - synergy

  • some cancel eachother out - antagonistic

  • some are commercially important and can be used to produce plants as ornaments or food

hormone

effects

auxins

associated w cell enlargement and differentiation. prevent leaf fall. maintains apical dominance. tropisms. stimulate ethene release

gibberellins

associated w cell enlargement + differentiation. germination. pollen tube growth

cytokinins

associated w cell division

abscisic acid

associated w dormancy + stomatal closure. cold protective response

ethene

associated w ageing. causes fruit ripening, promotes leaf fall (abscission)

responding to herbivory

physical

  • thorns, barbs, spikes, inedible tissues, hairy leaves, stings

chemical

  • tannins, alkaloids, terpenoid, pheromones

tannins

  • types of phenols

  • bitter taste deterring herbivory

  • toxic to insects

alkaloids

  • very bitter N compound.

  • act as drugs affecting animals metabolism e.g. caffeine, nicotine

  • can be toxic to insects and fungi

terpenoids

  • produced by plants as essential oils

  • toxic to insects and fungi

  • can be used as insect repellent e.g. lemongrass (citronella)

pheromones

  • chemical made by an organism which affects social behavior of other members of same species

examples of pheromones

  • maple trees, water stress, cabbages, apple trees, wheat seedlings

pheromone

effect

maple tree

Pheromone causes CALLOSE (polysaccharide/physical barrier) to form when the tree is under attack from insects.

Causes response in adjacent branches and on adjacent trees.

apple tree

When under attack from spider mites, pheromone released and attracts predatory mites to destroy apple tree pest.

cabbages

attacked by caterpillars of cabbage white butterfly. Pheromone released that attracts parasitic wasp. Wasp lays eggs in caterpillar which then gets eaten alive.

diff pheromones released by cabbage if under attack by different pest e.g. green fly and a different parasitic wasp is attracted.