A General account of Plant Peroxisomes - Ultrastructure, Types :Leaf peroxisomes (Leaf -type peroxisomes), Peroxisomes for other special metabolism, unspecialized peroxisomes and Glyoxysomes ; Functions

1. PLANT PEROXISOMES
Dr. Saji Mariam George
Associate Professor (Retired)
Assumption College Autonomous
Changanacherry

2. PLANT PEROXISOMES
• Johannes Rhodin (1954) had observed small single
membrane bound organelles in the cytoplasm in
the electron micrographs of renal tubules of
mouse kidney and he coined the term microbody.
• Rouiller and Bernhard (1956) had observed
microbodies in liver cells.
• Christian de Duve and Baudhuin (1966) coined the
term Peroxisomes as they are actively involved in
hydrogen peroxide metabolism.
• In plants , microbodies were first isolated from
castor bean seedlings by Breidenbach and Beevers
(1967).

3. • Peroxisomes are closely
associated with other
organelles such as
endoplasmic reticulum
(ER) , mitochondria and
chloroplasts (in plants).
C, chloroplast; M, mitochondria; P,
peroxisome; N, nucleus.
© 2015 Bobik and Burch-Smith.

4. Ultrastructure of Peroxisomes
• Studied with an electron microscope.
• Small single membrane bound organelles.
• The size may range from 0.2 to 1.5 μm in diameter.
• The shape is generally round or ovoid.
• The number of peroxisomes vary from cell to cell.

5. • The matrix of peroxisome is finely granular with a
core which may be either amorphous or crystalloid
and contain many enzymes.
• The composition of enzymes in peroxisomes varies
in different organisms, tissues and cells.
• The peroxisomal enzymes include glycolate
oxidase, catalase, D-amino acid oxidase, urate
oxidase (uricase) etc.

6. Peroxisomes of higher plants are categorized into
four types based on metabolic functions. There are
variations in enzymatic content in each type.
i) Leaf peroxisomes (Leaf - type peroxisomes)
• Present in green and photosynthetically active
tissues. Commonly found in green leaves, green
cotyledons and other photosynthetic tissues.

7. • Leaf peroxisomes are closely appressed to the
chloroplasts and mitochondria.
• Generally round or ovoid - crystalline inclusions are
more common.
• Contain the enzymes like catalase, glycolate
oxidase, glyoxilate transaminase, serine – hydroxy
pyruvate transaminase, NADH- hydroxypyruvate
reductase, NAD malate dehydrogenase etc.

8. Function of Leaf peroxisomes
• Leaf peroxisomes play an important role in
photorespiration (in C3 plants) - contain enzyme
glycolate oxidase that oxidize and process glycolate
as part of the photorespiration process - Leaf
peroxisomes, chloroplasts and mitochondria
interact with each other in photorespiration.

9. Leaf peroxisomes in Tobacco leaf cells

10. ii) Peroxisomes for other special metabolism
• These peroxisomes are highly specialized to
perform certain physiological functions like
metabolism of urate, methanol, amines and
oxalate.
• Present in some higher plant tissues such as root
nodules and in many algal and fungal species.

11. Electron micrograph of Peroxisomes (P) in mature Cow pea root
nodule
Webb and Newcomb 1987 http://www.plantphysiol.org

12. • Peroxisomes for methanol oxidation, oxalate
synthesis and amine oxidation are found only in
fungi. Peroxisomes are abundantly present in
methanol-grown yeast cells.
• Methanol oxidase is present in methanol
metabolizing yeasts (methylotrophs).

13. Electronmicrographs of Pichia pastoris cells:
Normal yeast cell grown in glucose & Methanol metabolizing yeast
(methylotroph) grown in Methanol. Px – Peroxisomes.
Credit: acib/University of Graz
https://phys.org

14. iii)Unspecialized peroxisomes
• The enzymatic contents of these peroxisomes are
very limited - An unorganized form – Rare .
• Smaller in size than other types of peroxisomes.
• Present in plant cells that are inactive in
photosynthesis and that lack storage lipids such as
the roots of most plants - Often associated with the
division plate, tubers, stem etc.
• Contain catalase and hydrogen peroxide producing
oxidases.
• They do not carry out an active metabolism.
Specific role in cellular metabolism is unknown.

15. iv) Glyoxysomes
• These are specialized peroxisomes that are
abundant in germinating seeds which store fats as
reserve food material.
• First isolated by Breidenbach and Beevers (1967)
from Castor bean seedlings and they named them
Glyoxysomes since they contain the enzymes of the
Glyoxylate cycle (isocitrate lyase and malate
synthase ) and also catalase, glycolate oxidase and
urate oxidase.

16. • Glyoxysomes remain intimately associated with
lipid bodies, the spherosomes and contain the
enzymes for fatty acid metabolism and
Gluconeogenesis (formation of glucose from various
non-carbohydrate precursors such as succinate).
Functions of Glyoxysomes
• Glyoxysomes are the sites of β-oxidation of storage
fatty acids and glyoxylate cycle. β-oxidation - break
down of very long chain fatty acids to generate
acetyl-CoA, which in turn is metabolized by the
glyoxylate cycle to succinate bypassing the
decarboxylating steps of Kreb’s cycle. Succinate is
then used for gluconeogenesis or the synthesis of
other metabolic intermediates.

17. Glyoxysomes
uploaded by Ian A Graham
https://www.researchgate.net

18. • Peroxisomes play a significant role in hydrogen
peroxide metabolism. They are the site of synthesis
and degradation of the highly reactive and toxic
oxidizing agent hydrogen peroxide(H2O2) .
• A number of peroxisomal enzymes like urate
oxidase, glycolate oxidase, D- amino oxidase, α -
hydroxylic acid oxidase etc. produce highly toxic
hydrogen peroxide(H2O2) and the enzyme catalase
decompose it . Thus catalase act as a ‘safety valve’
to deal with peroxides that are dangerous to the
cell (Hydrogen peroxide detoxification).

19. THANK YOU