Cyanide Toxicity in plants, Mechanism and examples from different plant families. Cyanide resistant respiration and it's significance.

1. Presented to:
Dr. Mansoor Hameed
Presented By:
Ayesha Siddiqui
Cyanide toxicity in plants

2. What is cyanide?

5. Organic Cyanides
 Organic cyanides are usually called nitriles; in these,
the CN group is linked by a covalent bond to a carbon-
containing group, such as methyl (CH3) in methyl
cyanide (acetonitrile).
 In nature, substances yielding cyanide are present in
certain seeds, such as the pit of the wild cherry and the
seeds of apples.

6. Toxicity of Cyanide Ions
 Toxicity resides in the release of Cyanide ion,
CN-
 Inorganic Cyanides are potentially toxic as they
have capability of removal of ion when in a
medium
 Organic nitriles do not readily release cyanide
ions, and so have low toxicities. By contrast,
compounds such as trimethylsilyl
cyanide (CH3)3SiCN readily release HCN or the
cyanide ion upon contact with water

8. Cyanogenic glycosides in edible plants

9. Mechanism of release of CN-
 Cyanogenic glycosides in plants are stored in
the vacuole, but, if the plant is attacked, they are
released and become activated by enzymes in the
cytoplasm. These remove the sugar part of the
molecule and release toxic hydrogen cyanide.
 Storing them in inactive forms in the vacuole
prevents them from damaging the plant under normal
conditions.

10. Occurrence of Cyanogenic
glycosides in plants
Family Plant name Cyanogenic
glycoside
Rosaceae
Peach (Prunus persica) Amygdalin
Plum (Prunus domestica ) Amygdalin
Bitter Almond
(P. amygdalus var.amara)
Amygdalin
Apricot
(Prunus armeniaca)
Amygdalin
Prunus serotina Prunasin
Prunus laurocerasus Prulaurasin

11. Cyanogenic glycosides in different
plants
Family Plant name Cyanogenic
glycoside
Euphorbiaceae Cassava
(Manihot esculenta )
Linamarin &
Lotaustralin
Linaceae Flax
(Linum usitatissimum )
Linamarin
Leguminosae Beans
(Phaseolus beans)
Phaseolunatin
Gramineae Sorghum vulgare Dhurrin

12. Natural occurrence of cyanide
in Plants

13. substances
yielding
cyanide are
present in
seeds of
apples
I have
Cyanide in
me

14. Cassava
(Manihot esculenta)

15. Sorghum
vulgare
Sorghum vulgare
Dhurrin

16. Almond
(Prunus amygdalus)
The bitter almond emyzne eht sniatnocnislume which,
in the presence of water, acts on amygdalin, yielding 2
glucose, cyanide and the essential oil of bitter almonds,
which is nearly pure benzaldehyde.

18.  Cyanogenic glycosides might
serve as nitrogen storage
compound esp. in seeds (e.g.
linamarin, linustatin etc)
 Plant protection against
herbivores, pathogens, and
competitors

20. 3 Stages of Respiration
1. Glycolysis
 cytoplasm
 with or without oxygen present
 breaks glucose (6C) into 2 pyruvates (3C)
2. TCA Cycle
 mitochondrial matrix
 only if oxygen present
 converts pyruvate via acetyl CoA into CO2; generates
NADH and FADH2
3. Electron Transport Chain
 mitochondrial membranes = cristae
 transfers electrons from NADH and FADH2 to
reduce O2 to H2O and generate ATP

23. Cytochrome c oxidase
 It receives an electron from each of
four cytochrome c molecules, and transfers them
to one oxygen molecule, converting molecular
oxygen to two molecules of water. In the process,
it binds four protons from the inner aqueous
phase to make water, and in addition translocates
four protons across the membrane, helping to
establish a transmembrane difference of
proton electrochemical potential that the ATP
synthase then uses to synthesize ATP.

26. The binding of cyanide to this enzyme
prevents transport of electrons from
cytochrome c to oxygen. As a result,
the electron transport chain is
disrupted, meaning that the cell can
no longer aerobically produce ATP for
energy.

28. An “alternate path” (aka, the cyanide resistant path) de-couples
respiratory electron transport from ATP production. This
pathway produces O2, but not ATP. It can serve as an “energy
overflow valve” when supply exceeds demand – but it results in a
net loss of energy from the plant. Is this a relic “error” or an
important physiological function?
An “alternative
oxidase” (AOX)
accepts electrons
coming from
complex II,
preventing them from
getting to complex III

29. Importance of Cyanide Resistant
Respiration
 Its plays important role in the growth of roots.
 In fungi, the ability of the alternative oxidase to
bypass inhibition of parts of the electron
transport chain can contribute
to fungicide resistance.
E.g. This is seen in the strobilurin fungicides that
target complex III, such as azoxystrobin,
picoxystrobin and fluoxastrobin. However, as the
alternative pathway generates less ATP, these
fungicides are still effective in
preventing spore germination, as this is an
energy-intensive process.

30. When it flowers, the
Philodendron flower
heats to as high as
46 C (115 F). The
heat protects the
flowers from freezing
at night and
disperses compound
that attract
polinators
Light energy —> Heat
Energy is captured from light
by Philodendron leaves and
used for life processes and
growth