6.4.2 clones in plants

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

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

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

• 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)

• 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 • explants sterilised using dilute bleach or alcohol to kill bacteria & fungi • 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 • once callus is formed, it divides producing larger number of small clumps of undifferentiated cells • 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 • once tiny platelets have formed, these are transferred to greenhouse to be grown in compost or soil & acclimatised to normal growing conditions

they would thrive in conditions needed for explant to grow

mass of undifferentiated, totipotent cells

• 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

• 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