PLANT PHYSIOLOGY

1. HIGH IRRADIATION
RESPONSES
PRESENTED BY-
Rashmi Jalan

2. The role of light in the life of plants
CHLOROPHYL
L
PHOTOSYNTHESI
S
PHYTORECEPTORS
QUALITY QUANTITYDIRECTION PERIODICITY
PHOTOMORPHOGENESIS

3. PREREQUISTE
A. FLUENCE - total number of photons impinging on a unit surface area (micromoles/m2).
B. FLUENCE RATE -number of photons impinging on unit surface area per unit time
(micromoles/m2/s).
C. IRRADIANCE – the amount of energy that falls on flat sensor.
D. LAW OF RECIPROCITY- The reciprocal relationship between fluence rate and time.
E. ROLE OF PHYTOCHROMES IN PLANTS-
1. Relatively rapid turgor responses involving ion fluxes.
2. Slower, long-term processes associated with photomorphogenesis, involving alterations in
gene expression.
3. Some of early biochemical reactions affects lateral developmental responses.

4. HIGH
IRRADITION is
brought by
continues or
prolonged
exposure to light
having
wavelength
more than >600.

5. High-Irradiance Responses
Photochromic responses of the third type are termed High Irradiance Responses(HIRs).
HIRs require prolonged or continuous exposure to light of relatively high irradiance, and the response
is proportional to the irradiance within a certain range >1000 mol photons/m2.

6. High-Irradiance Responses Properties
• HIR are Proportional to the Irradiance and the Duration.
• HIRs require prolonged or continuous exposure to light of relatively high irradiance.
• HIRs saturate at much higher fluences than LFRs—at least 100 times higher and are not photo
reversible.
• Neither continuous exposure to dim light nor transient exposure to bright light can induce HIRs.
• HIRs do not obey the law of reciprocity.
• HIRs do not show photo reversibility.

8. The HIR Action Spectrum of Etiolated Seedlings Has
Peaks in the Far-Red,Blue,and UV-A Region
Arabidopsis and Brassica rapa plants grown in prolonged irradiation of both
high and low R : FR ratios.

9. o Synthesis of anthocyanin in various dicot seedling
and in apple skin segments.
o Inhibition of hypocotyl elongation in mustard, lettuce,
and petunia seedlings.
o Induction of flowering in henbane(Hyoscyamus).
o Plumular hook opening of lettuce.
o Enlargement of cotyledons in mustard.
o Production of ethylene in Sorghum.
Some plant photomorphogenic
responses induced by High Irradiance

10. REFERENCES
• PLANT PHYSIOLOGY, 3rd EDITION, byTAIC & ZEIGER.
• SLIDESHOW .COM
• http://6e.plantphys.net/