6.4.2 clones in plants

Question 1

define micropropagation

Answer 1

growing large numbers of new plants from meristem tissue taken from sample plant

Question 2

define tissue culture

Answer 2

growing new tissues, organs or plants from certain tissues cut from sample plant

Question 3

how is a cutting made?

Answer 3

1. stem cut between two leaf joints (nodes) at 45 degree angle
2. cut end of stem dipped in rooting powder
3. cutting placed in moist soil

Question 4

other successful cuttings (besides stem)

Answer 4

• root cuttings = section of root buried just below soil surface & produces new shoots
• scion cuttings = dormant woody twigs
• leaf cuttings = leaf placed in moist soil & leaves develop new stems/new roots (some leaves may produce new plants from 1 cutting)

Question 5

6 steps for micropropagation

Answer 5

1. suitable plant material selected & cut into small pieces (explants)
   - explants are tiny pieces of leaf, stem, root or bud
   - meristem often used = free from viruses
2. explants sterilised using dilute bleach or alcohol to kill bacteria & fungi
3. explants placed on sterile growth medium (often agar gel) containing necessary nutrients (eg. glucose, amino acids, phosphates)
   - gel also contains high concentrations of auxin & cytokinin = stimulates cells of explants to divide by mitosis to form callus
4. once callus is formed, it divides producing larger number of small clumps of undifferentiated cells
5. small clumps of cells stimulated to grow, divide & differentiate into different plant tissues
   - achieved by moving cells to different growth media
   - each medium contains different ratios of auxin to cytokinin
   - roots = 100 auxin : 1 cytokinin
   - shoots = 4 auxin : 1 cytokinin
6. once tiny platelets have formed, these are transferred to greenhouse to be grown in compost or soil & acclimatised to normal growing conditions

Question 6

why are the explants sterilised to kill any bacteria or fungi during micropropagation

Answer 6

they would thrive in conditions needed for explant to grow

Question 7

define a callus

Answer 7

mass of undifferentiated, totipotent cells

Question 8

advantages of artificial cloning in plants

Answer 8

• relatively rapid method of producing new plants compared to growing from seed
• carried out when sexual reproduction isn’t possible & plants which have lost ability to breed sexually can be reproduced (eg. commercially grown bananas) or plants that are difficult to grow from seed
• plants selected will be genetically identical to parent plant & will display same characteristics eg. high yield, resistance to common pest or particular flower colour
• if original plant had unusual combination of characteristics due to selective breeding/genetic modification, the combination can be retained
• new plants uniform in phenotype, making them easier to grow/harvest
• using apical bud (meristem) as explant ensures new plants free from viruses

Question 9

disadvantages of artificial cloning

Answer 9

• tissue culture is labour intensive
• expensive to set up facilities necessary
• tissue culture can fail due to microbial contamination
• all cloned offspring are genetically identical & thus, susceptible to same pests/diseases (monoculture)
• no genetic variation