18: Angiosperm Life Cycle and Diversity

ANGIOSPERMS

  • Have vascular tissue, seeds, AND flowers

  • Sporophyte is the dominant generation

  • Most diverse phylum with 300,000+ known living species (in addition to those in the fossil record)

Angiosperm Life Cycle

Angiosperm Diversity

  • >300 families

  • Humans consume a relatively narrow range of species

    • estimated that 20,000-30,000 plant species are edible

    • humans have historically eaten about 2,500 species with some regularity

    • current world food supply depends on only 150 species

Food plant diversity is usually on display during holiday meals like Thanksgiving.

Plant Domestication

  • Domestication - growing a plant and selecting for favorable characteristics

  • Causes plant populations to change genetically over time, such that it is more useful or desirable for humans

Some Production Traits/Characteristics Important in Domestication

  • Faster growth

  • Increased biomass

  • Shift in carbohydrate content

  • Ability to withstand abiotic stress

  • Disease resistance

  • Wider growth range

Changes in Sclerification/Fibrosity

Decrease in toxic metabolites & anti-nutrients

  • Alkaloids are found in several plant families

  • Glucosinolates in Brassicaeceae (bitterness)

  • Lectins in legumes

  • Amylase inhibitors in kidney beans, wheat, and rye

Enhanced and Variable Carbohydrate Content

  • Change in carbohydrate profiles, where starches are either stored or converted to mono- and disaccharides (sweeter fruits).

  • Members of the Musa genus have been cultivated in part to produce a higher percentage of simple carbohydrates.

Developed or increased variability in pigment

  • Plastids contribute to most fruit color variation, as in bell pepper (Capsicum annum). Selection has occurred for more variation.

  • Anthocyanins and betacyanins are stored in vacuoles and have anti-oxidant properties. Natural variation occurs in potato—domestication has actually reduced some variability.

Increased biomass & water content

Zea, a genus of grasses, has several edible members

Where on Earth did our modern food plants evolve?

Tracing crop plants to their centers of origin usually involves looking for:

  • High varietal diversity

    • different traits based on variations in genetic composition & expression

  • Co-occurrence of wild ancestors with domesticated

  • Long history of crop use

Tomatoes originated in northern regions of South America.

Germplasm: preserving diversity

  • Term used to describe the variety of genetic composition of a particular species

  • Seeds are usually how germplasm is collected and stored

  • US germplasm collections are maintained by the USDA —National Germplasm System

Preserving Crop Plant Germplasm

  • Some large-scale commercial crops have relatively homogeneous germplasms to ensure that plant quality and yield is consistent

  • Homogeneity increases production but also can reduce the rate of survival when exposed to pests, diseases, and environmental stressors

  • Conserving the germplasm of known variations in a species allows for a more complete genetic inventory, which could be useful in plant breeding

Svalbard Global Seed Vault

  • A seed bank with deposits made by countries

  • Countries must also have backup collections of their own

  • The vault provides a germplasm reserve should a regional or global crisis occur

  • Located on the island of Spitsbergen, Norway

  • Ideal location due to no tectonic activity, permafrost, and elevation above sea level

  • Opened February 2008

  • Capacity to store 4.5 million samples