• 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
• 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 .
• 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
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
, 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+
• 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
• 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
15. • Ion toxicity – disruption of enzyme activity at
• Ion imbalance: High Cl-
concentrations - NO3-
• High Na+ replace Ca2+
in root cell membranes –
loss of K+
16. • Mechanisms to deal with salinity:
• - anatomical, morphological, physiological and
• - adaptations - two categories:
• - exclusion
• - inclusion
• 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-
• excretion – high energy cost – decreased
• 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