1. PLANT STRESSES: SALT

3. INTRODUCTION
• When irrigation water contains a high
concentration of solutes and when there is no
opportunity to flush out accumulated salts to
a drainage system, salts can quickly reach
levels that are injurious to salt-sensitive
species.
• It is estimated that about one-third of the
irrigated land on Earth is affected by salt.

4. CLASSIFICATION OF PLANTS
• Halophytes are native to saline soils and
complete their life cycles in that environment
• Glycophytes (literally “sweet plants”), or
nonhalophytes, are not able to resist salts to
the same degree as halophytes.

5. CLASSIFICATION OF PLANTS
• Among crops,
• maize, onion, citrus and bean are highly
sensitive to salt;
• cotton and barley are moderately tolerant;
• sugar beet and date palms are highly tolerant .

6. Effects
• Dissolved solutes in the rooting zone generate
a low (more negative) osmotic potential that
lowers the soil water potential.
• The general water balance of plants is thus
affected

7. • most plants can adjust osmotically when
growing in saline soils.
• Such adjustment prevents loss of turgor
(which would slow cell growth)

8. Specific ion toxicity effects
• Injurious concentrations of ions—particularly
Na+
, Cl–
, or SO42–
— accumulate in cells.
• An abnormally high ratio of Na+ to K+ and
high concentrations of total salts inactivate
enzymes and inhibit protein synthesis.

9. • Photosynthesis is inhibited when high
concentrations of Na+
and/or Cl–
accumulate in
chloroplasts.
• photophosphorylation may be affected.

10. • Plants minimize salt injury by excluding salt
from meristems, particularly in the shoot, and
from leaves that are actively expanding and
photosynthesizing.
• In plants that are salt sensitive, resistance to
moderate levels of salinity
• in the soil depends in part on the ability of the
roots to prevent potentially harmful ions from
reaching the shoots.

11. • Sodium ions enter roots passively (by moving
down an electrochemical-potential gradient,
so root cells must use energy to extrude Na+
actively back to the outside solution.

12. • have salt glands at the surface of the leaves.
• The ions are transported to these glands,
where the salt crystallizes and is no longer
harmful

13. • Salt effects:
– Plant Growth
– Production
– Survival

14. Salts:
• - Humid areas – NaCl dominant
• - Dry areas: sulfates – CaSO4
• Na2SO4
• MgSO4
• - alkaline (pH = 8 – 10)

15. • Ion toxicity – disruption of enzyme activity at
high salinities
• Ion imbalance: High Cl-
concentrations - NO3-
uptake inhibited
• High Na+ replace Ca2+
in root cell membranes –
loss of K+
from roots

16. • Mechanisms to deal with salinity:
• - anatomical, morphological, physiological and
biochemical
• - adaptations - two categories:
• - exclusion
• - inclusion

17. Exclusion
• Trait of most glycophytes – maintain low salt
levels in roots:
• - filtration – salts filtered out at plasmalemma
of root parenchyma cells
• - high levels of phospatidyl choline in
plasmalemma restrict Cl-
uptake –
• excretion – high energy cost – decreased
growth

18. Inclusion
• Once salt enters root – mechanisms to resist
or tolerate salinity – missing in glycophytes:
• Transport prevention – salts kept in roots –
stopped from entering xylem
• active reabsorption of salts from xylem to
older root cells
• high energy (ATP) cost