BIO153H5 Lecture Notes - Lecture 7: Gametophyte, Phragmoplast, Laminaria

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25 Jul 2018
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Plants I
What Adaptations are Necessary for life on Land?
- Water retention (if you’re a plant living in water, you don’t need to worry about water loss), can be done through:
1. the development of a root and shoot system (obtain water
from the environment)
2. the development of a cuticle (saving water and using water
effectively
- you need to be stable on land
- you need an effective way of transporting water and nutrients
throughout the plant body (transport system)
This is the Life Cycle of Laminaria, a Brown Algae
- the sporophyte and gametophyte are distinct structures that
exist for certain periods of time, and differ in diploidy (2n and n)
- both stages (haploid sporophyte and diploid gametophyte) must
be multicellular
- Laminaria has alternation of generation
The Closest Relative of Land Plants are the Charophytes
What Makes Charophytes Likely the Closest Living Relative of Land Plants?
- Rings of cellulose synthesizing proteins
- Peroxisomes enzymes (help reduce waste for photo-oxidation)
- Structures of flagellates sperms
- Formation of phragmoplast (when a plant cell divides, part of the division includes a structure of cells along the
dividing line, and this structure is called the phragmoplast)
- If these are commonly shared characteristics, the earliest ancestor between the
charophytes and land plants should also have these traits
- However, this is not the cast, meaning that the ancestral groups didn’t have
these traits. This means that these are shared derived traits (synapomorphy)
Does the Charophyte Life Cycle Include Alternation of generation?
- No, because there are no multicellular gametophyte and sporophyte stages
- The fact that the zygote is retained in the parent (which happens in land plants),
signifies that this is one of the first steps towards alternation of generation
What Does this Mean for the Evolution of Alternation of Generation?
- Alternation of generation must have evolved more than once, since brown algae
and land plants exhibit alternation of generation, but charophytes don’t
- However, sometimes characteristics get lost, so maybe it only evolves once
- If alternation of generation was evolved only once, we would need to incorporate
the charophytes losing alternation of generation into the phylogenetic tree
- Alternation of generation would need to evolve in all organisms prior to
charophytes, then be lost in charophytes
- The best tree is the one with the least steps; in this one, we have two
1. Alternation of generations at least twice
2. Alternation of generations once, but then lost in some organisms
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Document Summary

The closest relative of land plants are the charophytes. Formation of phragmoplast (when a plant cell divides, part of the division includes a structure of cells along the dividing line, and this structure is called the phragmoplast) If these are commonly shared characteristics, the earliest ancestor between the charophytes and land plants should also have these traits. Ho(cid:449)e(cid:448)er, this is (cid:374)ot the (cid:272)ast, (cid:373)ea(cid:374)i(cid:374)g that the a(cid:374)(cid:272)estral groups did(cid:374)"t ha(cid:448)e these traits. This means that these are shared derived traits (synapomorphy) No, because there are no multicellular gametophyte and sporophyte stages. The fact that the zygote is retained in the parent (which happens in land plants), signifies that this is one of the first steps towards alternation of generation. Alternation of generation must have evolved more than once, since brown algae a(cid:374)d la(cid:374)d pla(cid:374)ts e(cid:454)hi(cid:271)it alter(cid:374)atio(cid:374) of ge(cid:374)eratio(cid:374), (cid:271)ut (cid:272)haroph(cid:455)tes do(cid:374)"t. However, sometimes characteristics get lost, so maybe it only evolves once.

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