This document discusses plant stresses caused by salt. It begins by explaining that salt can accumulate to injurious levels in soils where irrigation water contains high salt concentrations and there is no drainage system. Approximately one-third of irrigated land worldwide is affected by salt. The document then classifies plants as halophytes, which are native to saline soils, or glycophytes, which are less tolerant of salt. Among crops, maize, onion, and citrus are highly sensitive, while cotton and barley are moderately tolerant and sugar beet and date palms are highly tolerant. The effects of salt include reduced osmotic potential of soil water, disruption of plant water balance, and specific ion toxicity that can damage cells and inhibit

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