Seed germination

1

Light control of plant development : Seed germination and de-

etiolation

2

Light in plant’s life

Light – major environmental factor

influencing the course of seedling

development

Iriawati, SITH - ITB 3

Iriawati, SITH - ITB 4

5

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

6

Iriawati, SITH - ITB 7

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

Iriawati, SITH - ITB 8

9

Iriawati, SITH - ITB 10

Iriawati, SITH - ITB 11

Iriawati, SITH - ITB 12

Iriawati, SITH - ITB 13

Apa yang membedakan ?

14

Iriawati, SITH - ITB 15

Etiolation

Iriawati, SITH - ITB 16

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

Iriawati, SITH - ITB 18

Iriawati, SITH - ITB 19

De-etiolasi

20

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

21

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

22

Iriawati, SITH - ITB 23

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

24

Iriawati, SITH - ITB 25

Iriawati, SITH - ITB 26