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Team:Cambridge-JIC/Background on Byrophytes
From 2014.igem.org
Intro to Bryophytes and how to get in their clang
Primitive plants are everywhere and together are called Bryophytes. Bryophytes are divided into three lineages. In evolutionary order these are:- Marchantiaphyta or Liverworts (that's Poly!)
- then came Mosses (bryophyta)
- and finally the newer Hornworts or Anthocerotophyta.
- then came all the rest.
What makes Bryophytes special: Role-Reversal Plants and Nature's strange ways
Bryophytes are united by unique features. These include:- Sexual reproduction by spores - a fine line between bacteria, yeast and these plants
- No cumbersome flowers or energy absorbing seeds
- No lignin (what makes plants tough) or vascualture and last but not least
- a reversed life cycle!
bryophytes are indeed often referred to as 'Up-Side-Down' or 'Role-Reversal' plants. Their life cycle is the opposite of most: We and other organisms spend our life as diploids: two sets of chromosomes, one from Dad, one from Mother. We specialize a set of cells in our reproductive organs which undergo meiosis (splitting of cells to form 2 cells with 1 copy of each gene), forming a haploid egg or sperm. When the sperm and the egg come together, they form a haploid organism which grows. And the cycle starts again.
bryophytes live most of their life as haploids (only have one copy of their genes!). A set of cells differentiate to become the ova and the sperm. When the haploid sperm reaches the haploid ova, they fuse, become diploid for a short time, and then undergo meiosis (split genome) to form two haploid plants! Intrigued by this oddity? Go to 'Marchantia's Life Cycle' to find out more.
But let's not underestimate them...
Close up on Mar-cam-tiophytes (liverworts)
Primitve does not mean frail; quite the contrary.
Looks, Location and Loveliness
Poly can be found found worldwide from tropical and arctic climates to your backyard! She likes moist soil or rocks in damp habitats. Her favourite hide-outs include banks of pools and rivers, bogs, fens and dune slacks. You can easily find her in man-made habitats such as gardens, paths and greenhouses. Some even dare calling her a horticultural weed! After fires, she rapidly colonizes the burnt ground, restoring an eco-stystem.
Morphology
Liverworts are wither of the leafy or thalose variety. Marchantia Polymorpha is a thallose one. Thallus means simply undifferentiated plant tissue. (not very descriptive)
The Dilemma: Food or Water?
Being thin, flat with a large surface area is great to maximise sunlight absorption and to photosynthesise lots; this comes at a cost: water evaporation. Plants that thrive have evolved to an optimum intermediate. Poly exhibits a beautiful simple morphological adaptation: air pores, the ancestors of the current stomata that most plants now have.
Rosette growth and Splash cups
Poly grows out in a rosette shape. If a thallus reaches the soil, it can become the start of a new plant. However this doesn't get her very far. At ___- weeks of development, a gemma cup appears at the centre of a thallus. The cup contains loose cells. As rain drops into the cup, the loose cells are propulsed out to find new ground to conquer. This allows simple rapid asexual isogenic reproduction
Reproductive Organs
Sexual reproduction, which allows gene mixing between two plants is another matter. Upon maturation at ___ weeks, the haploid Poly grows a reproductive stem at the centre. For the males, this is called a __ and resembles a flat disc on a stem. It bears the spores that will disperse. In females,an Umbrella appears.Underneath it is the protected Ova. With wind, rain or a researchers hand, the sperm is let loose and flies to collect under the sticky surface of the umbrella. Magic occurs: sperm and ova fuse. The diploid result undergoes recombination (gene mixing), divides multiple times and undergoes meiosis. The product is over ___ of haploid potential progeny with genomic diversity.
The reproductive organs can be stimulated to appear by exposure to infra-red light!
