Agriculture Reference
In-Depth Information
actively accumulated in the vacuole or be excreted into apoplast. Sodium compartmentation
in the vacuole is an adaptation mechanism typical of halophytes [118]. Ottow et al. [118]
observed that P. euphratica could tolerate increasing sodium concentration by apoplastic
accumulation of salt in the leaves' cell wall regions but not in the vacuole. A similar mechanism
for apoplastic localization of sodium could operate in P. alba and accounts for the different
behavior observed among the cultivars studied. These hypotheses need to be tested by further
studies to determine the exact site of sodium localization at histological, cellular, and subcel‐
lular levels.
The results of our previous study suggest that seedlings of different walnut cultivars differ in
tolerance to salinity and drought stress. Results demonstrated variability in germination ability
and seedling growth in saline and drought habitats, implying that it might be possible to select
walnut seedlings for salt and drought tolerance in germination stage [180; 212-213]. Salinity
treatments caused a net K + uptake, which is likely to be the result of osmotic adjustment in
tolerant cultivars. Net Na + uptake by sensitive cultivars was noticeably higher than in tolerant
cultivars. Interestingly, in control plants, the sodium content in shoots of cultivars that belong
to the sensitive groups was significantly higher than in the shoots of the other halfsib progeny.
This suggests a constitutive ability of these cultivars to accumulate more sodium in the leaves.
This feature could contribute to osmotic adjustment in response to salinity or drought as has
also been observed in P. euphratica plants exposed to salt stress, in which the osmotic adjust‐
ment was mainly resulted from sodium accumulation [118]. In the tolerant and semi-tolerant
groups, roots had higher potassium contents than shoots. This could reflect differences in the
membrane transport properties of cells in different stress-tolerant groups [119]. The amount
of calcium accumulation was increased by increase in salinity stress levels, especially in shoots
of tolerant and semi-sensitive cultivars. Calcium is an essential plant nutrient that is required
for its structural roles like in membrane integrity, as a counterion for inorganic and organic
anions in the vacuole, as an intracellular messenger in the cytosol, and as an enzyme activator
[120]. In conclusion, different strategies for adaptation to salinity or drought have been
observed in seedlings of walnut cultivars with different climatic origins when grown in a
greenhouse trial. Thus, a different genetic basis underlies the different behaviors observed
under salt and drought stress. The degree of variation in salinity and drought tolerance in these
cultivars could be linked to their different abilities in sodium exclusion at the root level or to
different regulation of ion transport across shoot cell membranes. Our results suggest that the
cultivars Chandler and Panegine20 could also be suitable models to be used for the study of
the physiology and genetics of abiotic stress tolerance in walnut [212].
The higher content of seed nutrients is of vital importance for germination, but salinity and
drought suppresses their role in the metabolism of seeds and the production of seedlings [144].
During germination of walnut seeds, a higher content of potassium, calcium, phosphorus, and
nitrogen was partitioned into the plumule and radicle as a strategy of tolerance to salinity
[213]. Guerrier [145] attributed the reduced salt tolerance of tomato to its inability to accumu‐
late and transport lower amounts of calcium and potassium. The SOS pathway (salt overly
sensitive) is triggered by a transient increase of cytosolic Ca 2+ as a first effect of salt stress. The
increase in Ca 2+ concentration is sensed by a calcium binding protein (SOS3) [212].
Search WWH ::




Custom Search