Dormansi
Sasi Gendro Sari
Fisiologi Tumbuhan
1. Dormansi
Adalah periode terjadinya hambatan pertumbuhan
 Secara alami, merupakan sinkronisasi pertumbuhan dan
perkembangan dengan kondisi lingkungan yang diinginkan
(seperti tanaman atau bagian tanaman yang dorman selama
periode dingin atau kering)
 Dalam periode pascapanen, kondisi dormansi sering
dimanipulasi
 Ada 3 macam dormansi berdasarkan tempat atau penyebab
hambatan pertumbuhan:

1.
2.
3.
Ekodormansi (jika 1 faktor lingk. tdk mendukung)
Endodormansi (terdapat mekanisme internal) dimana signal yg
diterima terjadi pada struktur dimana dormansi dimulai)
Paradormansi (sama dengan endodormansi, tetapi signal yg
diterima oleh suatu struktur diluar dari terjadinya tempat
dormansi)
Why dormancy?
ENVIRONMENT
(season)
METABOLISM
DORMANCY
favorable
active
non-dormant
unfavorable
inactive
dormant
To survive (prolonged) periods of unfavourable conditions
What happens to a seed after dispersal?
The soil seedbank
seeds incorporated in soil
seedling emergence
seedling death
in situ germination
non-dormant seed
dormant seed
non-viable seed
Germination
100
0
January
April
July
October
January
Seeds in the soil go through successive cycles of
dormancy to survive unfavorable periods and to
germinate in the right season
Primary vs. secondary dormancy:
Dormancy cycling
Environment
GERMINATION
NONDORMANT
DORMANT
Genotype
After-ripening
Chilling
Light
Temperature
Nitrate
Breaking of dormancy and induction
of germination
• Temperature
• Light
• Nitrate
Factors that influence germination
• Temperature
• T1 long-term, (AR, cold strat.) sensitizes seeds;
• T2 short term controls germination;
• Light
• Nitrate
T1: when?
T2: how much and how fast?
Dual role of temperature
How do these factors interact in the field and what is their ecological
relevance?
Seasonal emergence
Mean monthly
temperature
Germination in the
light
Germination in the
dark
Chenopodium album
Germination at prevailing
field temperature +/- nitrate
Germination at 20 °C in the
light +/- nitrate
Germination at 20 °C in the
dark +/- nitrate
Dormancy cycling: summer and winter annuals
Winter annual
Field temperature
Summer annual
Seasonal temperatures determine overlap of germination window with field temperature,
light- and nitrate thresholds
40
30
20
Min
Pfr/Ptot
Tfield
10
0
Oct
Jan
Apr
Jul
Oct
Time
Hilhorst, 2007
Nitrate content
[nitrate]
Light quality
Field temperature, °C
Max
Roles of light and nitrate
The role of light: phytochrome
Pr
red
660 nm
Pfr
Germination
730 nm
far-red
inactive
active
The extent of germination is
determined by:
Pfr
Pr + Pfr
=
Pfr
Ptot
=φ
© Peter v. Sengbusch - b-online@botanik.uni-hamburg.de
Pfr
Ecological relevance of
Ptot
=φ
φ
Spectral distribution of light
under leaf canopy
Neighbor detection and avoidance of
competition
Decrease of φ (and germination) with
increasing LAI
Of the 5 known phytochromes, PhyA, PhyB and PhyE are involved in light-induced
germination...
Henning et al. Plant Phys. 2002
Penetration of light in the soil is very low
So, how can light-requiring seeds in the seed bank be induced to
germinate when they are buried at lower depths?
Germination may be induced by disturbance of the soil, allowing the seeds to perceive a
short exposure to light.
Cultivated in the dark
2% coverage
Cultivated in the light
80% coverage
The role of nitrate
Neighbour detection and avoidance of
competition;
Indicator of soil fertility;
Relationship between nitrate content of
soil and seed and germination
Bouwmeester, 1990
Hilhorst and Karssen, 1990
Light and nitrate act on the GA/ABA balance
nitrate
Oh, E., et al. Plant Cell 2007;19:1192-1208
Copyright ©2007 American Society of Plant Biologists
Pages in text book Lambers:
Pp. 329-330 What is phytochrome?
Pp. 375-385 Seed dormancy and germination