Lecture'14'Bio'200''Plants:''• Polyploidy'• Hybridize'easily'• Mostly'hermaphroditic,'(but'can'find'male'or'female)'• Successful'without'being'able'to'move'• Around'a'billion'years'ago,'a'species'similar'to'the'more'primitive'gene'algae'like'Chlamydomonas,'arises'and'accounts'as'its'descendants'all'the'green'plants'it'followed.''• About'500'MYA,''the'first'land'plants'arise,'Land'plants'mark'a'break'from'the'species'that'we'have'been'talking'about'so'far.'Almost'all'plants'are'multicellular'• This'is'the'first'group'of'organisms'that'really'conquers'size.''• Few'plants'are'unicellular,'ex:'green'algae'(many'don’t'consider'plants,'but'rather'protsits).'• As'we'move'through'plant'evolution,'we'see'bigger'and'bigger'plants'until'we'reach'some'of'the'largest'plants.''• Ex:'Bristle'cone'pine'(Pinus'Longaeva)R'5,000'years'old'• Some'of'the'longest'life'span,'and'some'of'the'tallest'organisms'on'earth.'• California'Redwood'trees'(Sequoia'Sempervirens)'R'tallest'tree'• All'ancient'plants'were'aquatic'• Inherently'different'from'animals''The'invasion'of'land:'• The'more'complex'feats'in'evolutionary'history,'whether'you'are'a'plant'or'and'animal'• Exposure'to'air'presents'aquatic'organisms'with'some'seriously'complexities.''• Plants'must'find'a'way'to'survive'long'term'in'air,'which'means'not'to'dry'out.''• Also'they'must'find'a'way'to'be'able'to'stand'without'the'support'of'an'inRcompassing'water'column.''• Also,'aquatic'plants'are'dependent'on'water'to'transport'their'gametes'around.'Which'means'land'plants'must'discover'new'ways'to'reproduce'and'spread'their'gametes.''• This'really'comes'down'to'survival'and'reproduction'• As'we'move'through'plant'evolution'and'look'at'the'different'groups'of'plants,'we'see'different'and'increasing'complex'and'successful'means'with'dealing'with'the'above'issues.''''''Land'Plant'Adaptions:''I. Embryophytic:''o Land'plants'first'become'this'o All'have'some'structure'to'protect'the'developing'embryo'to'prevent'it'from'drying'out.'''II. Cuticle:'o Plants'also'needed'a'way'for'themselves'not'to'dry'out'o They'do'this'by'secreting'a'waxy'substance'called'the'Cuticle'o It'traps'water'inside'the'plant'o Once'you'have'a'cuticle,'its'hard'to'get'air'in,'air'contains'CO2,'that'is'necessary'for'photosynthesis.'o Land'plants'have'to'develop'stomata'for'CO2'intake.'/''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' ''III. Stomata:'o Little'holes'of'pores'that'are'found'on'the'epidermis'of'the'leaves,'steams,'and'other'organs.''o They'open'to'let'air'in,'and'then'they''close'to'keep'the'plants'from'drying'out'''IV. Pigmentation:'o Most'land'plants'have'special'pigmentation'that'will'block'out'mutagenic'UV'radiation'from'the'sun.''o Previously,'the'water'for'aquatic'plants'blocked'out'these'radiations.''V. Fungal'Relationship:'o Land'plants'developed'a'relationship'soil ' dwelling'fungi'that'will'help'them'absorb'nutrients'rather'than'aquatic'plants'that'have'access'to'freeRfloating'nutrients'in'the'water.'''VI. Tracheid'Cells:'o Elongated'cells'that'will'allow'for'transport'of'water'and'mineral'salts'through'the'plants'body.''o Also'provide'structural'support'and'will'allow'plants'to'become'these'large'organisms.'''VII. Thick'Spore'Walls:'o Will'protect'the'spores'from'drying'out'on'land.'''VIII. Seeds:'o Ultimate'form'of'embryo'protection'''''Life'Cycle'Differences:'Humans'o Humans'and'most'animals'have'a'diplontic'life'cycle,'it'means'only'the'diploid'stage'is'multicellular.'Our'gametes'that'are'haploid'and'always'unicellular'o Only'the'diploid'stage'undergoes'Meiosis.''''''''''''''''''''' Plants'o Haplodiplontic'Life'CycleR'both'the'haploid'and'diploid'stages'are'multicellular'in'meiosis.'o Plants'have'two'forms;'have'a'haploid'gametophyte'that'produces'gametes'and'a'diploid'sporophytic'that'produces'haploid'spores.''o A'gametophytic'generation'alternates'with'a'sporophytic'generation'in'the'plants.''o This'leads'to'alternation'of'generations.'It'describes'the'plant'life'cycle.''o Multicellular'Sporophyte'produces'specialized'structures'that'called'Sporangia.''o The'sporangia'are'where'meiosis'occurs.''o Inside'the'sporangia,'the'diploid'spore'mother'cell'will'undergo'meiosis'and'produce'haploid'spores.'o This'meiotic'event'represents'a'transition'from'diploid'to'the'haploid'generation.'Everything'above'that'point'is'1N'(haploid)'o The'spores'divide'by'mitosis'to'grow'into'mature'haploid'gametophyte.''o Now'we'have'a'multicellular'haploid'gametophyte.'o This'gametophyte'produces'gametes'via'mitosis.''o This'happens'on'specialized'structures'depending'on'plant'groups.'o The'gametes'will'then'fuse'into'Syngamy,'aka'fertilization.''o The'fertilized'cell'is'a'single'diploid'cell,'this'represents'the'transition'from'haploid'to'the'diploid'stage.'Everything'below'this'point'is'2N'(diploid)'o The'zygote'will'grow'via'mitosis'until'it’s'a'mature'sporophyte.''o The'process'repeats.'''''''''''''''''''''Two'important'points'for'plant'life'Cycle:'o Spores'swim'and'so'do'gametes.'This'requires'a'lot'of'adaption'for'land'plants.'This'is'easier'for'aquatic'plants'o The'two'generations,'the'sporophytic'and'the'gametophyte'vary'greatly'among'the'different'plant'groups.''a. For'example,'in'the'mosses…'the'gametophytic'stage'(in'blue)'gets'smaller'and'smaller'as'plants'evolve.''b. As'we'move'into'the'seed'plants,'we'see'a'change'in'dominance,'from'the'haploid'gametophytic'stage'being'the'dominant'one,'to'the'sporophytic'becoming'the'dominant'one.''c. We'think'this'trend'is'due'to'the'fact'that'that'the'haploid'phases'are'very'sensitive'to'recessive'mutations.'They'are'masked'by'the'second'allele'in'the'diploid'generation,'but'this'is'not'the'case'in'the'haploid'generation'd. Haploid'generations'are'much'more'sensitive'due'to'the'mutations'from'the'UV,'not'blocked'by'water'on'land.''''''''''''Plant'Phylogeny:''o All'scientist'classify'land'plants'as'plants'o Some'people'include'green'algae'as'plants,'while'some'only'include'some'of'the'green'algae'o Some'people'even'consider'red'and'brown'algae'to'be'plants.'o But'closely'related'green'algae'are'more'plant'like'than'not.''o The'closest'specie'to'the'plants'and'green'algae'and'the'red'algae'aka'an'outRgroup'on'the'phylogeny.''o
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