Natural Clones in Plants (OCR A Level Biology)

• Many plants can reproduce asexually using meristem cells, in a process called vegetative reproduction
• Vegetative organs of plants include:
  • Root and shoot tips
  • Axillary buds (where leaves and the stem meet)
  • Vascular cambium (between xylem and phloem)

• Naturally, over time a young, miniature plant (a plantlet) forms at these locations and remains attached to its parent plant
• These plantlets are clones of their parent (as no other DNA has been introduced)
• At maturity, the plantlet becomes detached from its parent and can live independently, when it is capable of photosynthesizing by itself
• The new plants all have the same phenotype, so are uniform, making growing and harvesting easier
  • Plants that are hard to grow from seeds can be propagated, eg. orchids for the horticulture industry

• Some plants have horizontal stems or runners that form over the soil surface, pointing sufficiently far away so that a new plant at that location will not be overshadowed by its parent, or in competition for water or soil nutrients
  • Roots form under the nodes of runners, called adventitious roots
  • The runner dies when the plantlet is self-sustaining
  • Strawberries, peppermint and spider plants reproduce in this way

An example of asexual reproduction in plants with runners that form adventitious roots

Propagation techniques using vegetative reproduction

• Many methods of propagation do not require seeds as it is not sexual reproduction that is occurring, it is asexual reproduction

• A well as runners, plants can propagate asexually using tubers, rhizomes, bulbs, suckers, and offsets
• All modes of vegetative propagation contain modified stems that can generate meristematic tissue
• Potato tubers are swollen modified roots that form eyes on their surface
  • Eyes can sprout new growth (called 'chitting')
  • The starch stored in the tuber fuels the early growth of the new plant

• Ginger forms rhizomes, a modified stem that grows horizontally underground
  • New growth stems from nodes in the rhizome, forming new stems and adventitious roots
  • The section used in cookery is the rhizome

• Onions and garlic form bulbs that can grow adventitious roots underground and leafy shoots above ground
• Suckers are growths that appear from the root systems of many trees and shrubs, which can provide meristematic tissue for vegetative propagation
  • Examples are poplars, cherries and plums

• Offsets are small, virtually complete daughter plants that have been asexually produced on the mother plant
  • Examples are tulips and lilies

• Gardeners and horticulturalists can use these techniques to propagate desirable species asexually, effectively and at less cost than utilising sexual reproduction techniques
  • This is done by taking cuttings and dividing up plants into different clumps or sections