Flowering, reproduction and
Terminator technology
Plant Physiol Biotech 3470
Lecture 14
Thurs 15 March 2006
Angiosperms and gymnosperms are the two
major groups of land plants
• Vascular plants (a/k/a “higher” plants) include
– Ferns and relatives
– Cycads and rare gymnosperms
– Conifers (common gymnosperms) – Flowering plants (angiosperms)
• Monocotyledons (monocots; grasses)
• Dicotyledons (dicots)
• Angiosperms and gymnosperms both reproduce through the
production of seeds and pollen
– They are seed plants
gymnosperms
angiosperms
• Angiosperms and gymnosperms differ by the location of their female plant parts
(ovules, which contain the eggs)
• In gymnosperms these are often located inside cones on modified leaves (bracts) • Angiosperms by definition have ovules
borne inside fleshy structures called
ovaries
• Ovaries are flower parts; flowers are unique to angiosperms
• Angiosperms dominate the earth’s vegetation
• Almost all crop plants, orchard trees, garden plants and ornamentals are flowering plants
Rost et al., “Plant biology”, 2nd edn
• Angiosperm flowers can be
perfect or imperfect
• Perfect flowers are bisexual and have both male
(stamens) and female (pistils or carpels) parts
– This includes the vast majority of flowering plants
– We are familiar with many of them!
– Wheat, rice, potatoes
• Imperfect flowers have
either stamens or pistils but
not both
• Imperfect flowers can be further subclassified
Most angiosperm species produce bisexual,
or perfect flowers
♀
♂
– Monoecious
• Stamens and pistils on different parts of the same plant
• Maize, cucurbits, oaks
– Dioecious
• Male and female flowers on different plants!
What do perfect and imperfect flowers
have to do with farming and plant
reproduction?
• The type of flowers produced by a crop species influences how it is grown
– This is because crop products are (almost) all seeds (fruits) !
• Perfect flowers often reproduce by self-pollination
[a/k/a selfing] (pollen that fertilizes the ovule comes from the same flower or plant)
• This means that the alleles in the selfed seed will be the same as in the parent plant
– There are usually 2 alleles available to heterozygotes (A and a) – However different phenotypes may result depending on
whether the offspring possess the dominant (AA or Aa) or recessive (aa) alleles
Breeding is the control of pollen flow in crop
plants to produce a desired offspring
• Ensuring that different pollen pollinates female flower parts can be done by removing male sexual organs
(anthers) before the pollen is mature
• This is what Mendel did when he crossed pea plants
• For imperfect flowers,
crossing between plants can be controlled in the field and greenhouse by covering
female plant parts and dusting them with pollen of choice
• e.g., for a monoecious species like maize, place
glassine envelopes over maize silks (female flowers)
Scientific American, August 2004
This technique is widely used for both traditional and
Let’s get to the Source article
• It states that “agrochemical” companies like
Monsanto can tell farmers which seeds to plant
(T or F?)
• It specifically alleges that these companies are
targeting small scale farmers who only grow what
they eat (
subsistence farming
)
• It also states that large plant biotech companies
are acquiring other seed companies (for their
g_____ stocks) at a rapid rate to improve their
seed (T or F?)
• It also alleges that genetically modified food is
The truth…
• Subsistence farming is not particularly “noble” or “natural” as implied in the article
• It is practiced by the poorest people in the world • It consists of intense labor for meager yields
• Farmers do not want to work hard for nothing
• They would love to plant higher yielding seed varieties • The real problem preventing them from doing this is
poverty:
– They cannot afford inputs to maximize yield
• Seed
• Chemicals / fertilizer • Fuel
• Irrigation
Heritage crop plant varieties are living
gene banks
Important observation:
• These seeds are potentially sources of new alleles allowing plants to grow well under biotic and abiotic stress
• This is especially important given the single varieties of crop plants that dominate markets
– Bananas desperately need new disease resistance alleles
– Potatoes are susceptible to fungal infection (e.g., by Phytopthera)
• Preserving heritage varieties is thus very important!
• Seed banks perform this role for many crops (tomatoes,
wheat, corn, etc.)
Replanting monoecious plants dilutes
their desirable combination of allelles
• No farmer can be “forced or coerced by a corporation or their government to grow patented seed”
– They are small businessmen!
– They can buy whatever seed they like
• For monoecious plants like maize, the yield increase seed in hybrids means that the parentage of these plants is very important
– Remember that specific combinations of inbred parents give
heterozygotic offspring that are much bigger (a/k/a h_________ )
• We have seen that planting selfed monoecious seed is undesirable agronomically for farmers because it
Terminator technology is copy
protection for seeds
• This technology makes seed unable to regrow
• In these seeds, embryos may germinate but do not survive
• There are many ways to do this
Ask: what genes are important for permitting embryos to grow?
• These are potential targets for preventing germination
– Genes for proteins that mobilize stored photoassimilate (e.g., starch hydrolyzing enzyme in endosperm a/k/a a______ )
– Genes for structural proteins important for shoot and root growth
– Genes for proteins of photosynthesis and energy metabolism
• Expression of these genes can be shut down in embryos by several methods
Terminating embryo growth requires
careful control of gene expression
Key question: Is the gene whose expression you wish to shut down only expressed in the embryo?
• A thorough understanding of metabolism is required prior to interfering with the expression of a gene
• e.g., you do not want to prevent starch hydrolysis everywhere in the plant: where is it important?
• Targeting shutting down the gene properly in time and
place requires selection of the right elements within genes that control their expression
– These are part of the gene upstream from the coding sequence and are called p_______s
Consider the benefits of seeds that
cannot sprout
• The
frequency of outcrossing
of transgenes to
wild populations of related plants would decline
– No viable seeds would be left behind in the field that could crossbreed with wild relatives
• Seeds could be stored for
longer periods of
time
without affecting their physiology and
chemical makeup
– An advantage for farmers and food processors
•
Patent protection
for seed companies
Any “unnatural” change to crop
plants is greeted skeptically
• The article appeals to
passion
without
explaining why it is a good idea to ban
Terminator technology
• No elaboration is made on the “
growing body
of evidence
” that GM food has harmful effects
in animals that consume it
– This is highly dependent on the transgene
– Different plants can modify proteins in novel ways that can precipitate immune responses in humans
