Date post: | 14-Jun-2015 |
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Light control of plant development : Seed germination and de-
etiolation
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Light in plant’s life
Light – major environmental factor
influencing the course of seedling
development
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Seed germination
• vulnerable / susceptible life stage in plant development
• sensor & mechanism respond to environmental condition (ex. light, water condition, gravity etc)
• transition between embryonic and postembryonic development
• Post embryonic shoot development Activation of SAM first true leaf
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Storage Protein
Amino Acids
Barley Seed Germination
Fruit+Seed Coat
Endosperm
Aleurone Layer
hydrolys
is
translat
ion
transcri
ption
hydrolys
is sugar
-amylase
RNA
DNA GA
imbibition
water
radicle apex
shoot apex
growth
cotyledon monocot
maltose
Embryo
exocytosis
starch
Amino Acids
Storage Protein
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Apa yang membedakan ?
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Etiolation
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Seedling development
• In the dark : etiolation - skotomorphogenesis– No chlorophyll production– Limited and/or abnormal organ
(root, stem, leaf) development
• When exposed to light : de-etiolation - photomorphogenesis– Chlorophyll synthesis– Proper development begins
• Why the difference?– Limited seed reserves– Efficient use of resources until
capable of Ps (i.e., chorophyll production).
De-etiolasi• Transformasi dari kondisi etiolasi ke kondisi
dengan pertumbuhan normal (green state)• Bisa terjadi beberapa saat setelah kecambah
yang mengalami etiolasi terpapar oleh cahaya.• Cahaya akan menginduksi pengurangan
kecepatan elongasi sel batang, pelurusan apical hook, inisiasi pembentukan atau perkembangan pigmen fotosintetik , energi bagi proses fotosintesis
• Sehingga fotosintesis bukanlah yang menginduksi de-etiolasi karena klorofil tidak terbentuk, akan tetapi cahaya 17
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De-etiolasi
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Photomorphogenesis• Sejumlah perubahan yang terjadi saat de-
etiolasi terjadi karena tanaman melakukan respon terhadap cahaya
• Photomorphogenesis ‘light form begins’• Pertumbuhan tanaman merupakan respon
terhadap cahaya yaitu terhadap perubahan jumlah, tipe, durasi dan arah datangnya cahaya.
• Membutuhkan Photoreceptors, yang membuat tanaman dapat mengintepretasikan cahaya
• Photoreceptor : phytochrome menyerap cahaya merah dan merah jauh (far red), serta reseptor cahaya biru
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Phytochrome
• Pigments that absorb red (665 nm) and far-red (730 nm) light.
• Ubiquitous in plants, role in most all plant development.
• Phytochrome can interconvert between Pr and Pfr
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Lettuce Seed Germination
660 nm
730 nmdark
Seed Coat
translat
ion
transcri
ption
hydrolys
is
starch
sugar
-amylase
RNA
DNA
imbibition
water
radicle apex
shoot apex
growth
dicot
photoreversibility Pfr Prphotoactiva
tion
Embryo
phytochromered and white light stimulate germination
cotyledons
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