Rucete ✏ Campbell Biology In a Nutshell
Unit 6 PLANT FORM AND FUNCTION — Concept 38.2 Flowering Plants Reproduce Sexually, Asexually, or Both
Flowering plants have evolved flexible reproductive strategies. While sexual reproduction promotes genetic diversity, many angiosperms also reproduce asexually, allowing them to thrive in stable environments and a wide range of ecological conditions.
Asexual Reproduction in Angiosperms
- Asexual reproduction involves no gamete fusion; offspring are clones of the parent.
- Common in angiosperms, often the primary mode of reproduction.
- Vegetative reproduction via roots, stems, or leaves:
- Aspen groves: thousands of identical trees from one root system.
- Kalanchoë: produces plantlets on leaves.
- Apomixis: seeds formed without fertilization (e.g., dandelions)
- Diploid ovule cell forms embryo directly.
- Promising for producing uniform hybrid crops.
Sexual vs. Asexual Reproduction
Asexual reproduction advantages:
- No pollination required.
- Offspring inherit 100% of parent's genome.
- Efficient in stable environments.
- Avoids vulnerable seedling stages.
- Clonal offspring often more vigorous.
Sexual reproduction advantages:
- Generates genetic variation—key for evolution and adaptability.
- Allows seed dispersal and dormancy.
- Improves resistance to pathogens and environmental stress.
Drawbacks:
- Asexual plants risk extinction if conditions shift.
- Sexual reproduction consumes more energy and fewer offspring survive.
Mechanisms Preventing Self-Fertilization
To ensure genetic diversity, many angiosperms avoid selfing:
- Dioecious plants: separate male and female individuals (e.g., arrowhead).
- Heterostyly: floral structures discourage self-pollination (e.g., thrum and pin types).
- Self-incompatibility:
- Biochemical rejection of own pollen via S-genes.
- Two types:
- Gametophytic: based on pollen genotype.
- Sporophytic: based on parental plant genotype.
- Functions like an immune system in plants.
Application: Genetic engineering of self-incompatibility aids hybrid breeding without manual pollen removal.
Cloning and Propagation in Agriculture
- Totipotency: plant cells can regenerate into whole plants.
- Vegetative propagation: cloning from cuttings, commonly used in farming.
- Callus tissue can regenerate shoots and roots under proper conditions.
- Grafting:
- Combines:
- Stock: root system
- Scion: grafted shoot
- Unites disease resistance (stock) with desirable traits (scion).
- Combines:
- Tissue culture:
- Grows plantlets from small samples in media.
- Eliminates viruses in crops like strawberries.
- Supports genetic engineering and commercial cloning.
In a Nutshell
Flowering plants use both sexual and asexual reproduction. Asexual methods clone successful genotypes, while sexual reproduction boosts diversity and adaptability. Mechanisms like self-incompatibility prevent inbreeding, and humans harness plant regeneration for agriculture and biotechnology. This dual strategy underpins plant resilience and agricultural success.