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International Journal of Horticulture 2014, Vol.4, No.7, 32
-
39
http://ijh.biopublisher.ca
36
Table 5 Some anatomical parameters measured on the leaf of
Alternanthera maritima
after 12 weeks of exposure to salt spray
Level of salt spray
Stomata density (no./cm
2
)
Number of stomata/leaf)
Necrotic leaf area (%)
Visual ratings
CSS
165499.68
a
2987269.22
a
1.50
a
5.00
a
2SS
63653.72
b
836409.88
b
3.14
ab
4.72
a
4SS
59834.45
b
862812.77
b
3.18
ab
4.31
a
6SS
50922.98
b
573901.98
b
7.31
c
3.71
b
Note: Each value is a mean of 6 replicates. Means with the same letter(s) [in superscript] in the same column are not significantly
different at P≥0.05 (Turkey HSD); CSS=deionized water sprays (control), 2SS=two salt sprays per week, 4SS=four salt sprays per week,
6SS=six salt sprays per week. Visual ratings scale: 1=no green foliage, 2=25% green foliage, 3=50% green foliage, 4=75% green foliage
and 5=all green foliage
typically showed greater growth and reproduction
relative to those farther from shore (80~90 m) (Cheplick
and Demetri, 1999).
Reduction in leaf under salt stress in this study is similar
to that of
Pinus rigida
(Griffiths and Orians, 2004),
Crambe maritima
(De Vos et al., 2010),
Diodia
maritima
(Kekere and Bamidele, 2012) and
Commelina
erecta
subsp
maritima
(Kekere, 2013) following
exposure to salt sprays. Reduced leaf size
was due to
inhibition of leaf expansion and hence reduction of light
interception (De Vos et al., 2010). Interestingly, leaf size
was reduced but the general plant growth was enhanced.
Reduction in leaf area can therefore be an adaptation for
growth. Reduced leaf size provides decreased surface
for salt deposition and water loss through transpiration,
which are adaptations for water stress (Morant-Manceau
et al., 2004). Reduction in chlorophyll content can be
attributed to necrotic damage caused by Na
+
and Cl
-
ions toxicity. When there are necrotic spots on the leaf,
total photosynthesis and carbohydrate stored in the plant
decrease Chlorophyll reduction can also be due to the
deficiency of certain nutrients, some of which are
important for normal growth and are part of chlorophyll
ultrastructure (Touchette, 2009). Application of NaCl to
plant foliage induced fragmented cuticles, disrupted
stomata, collapsed cell walls, coarsely granulated
cytoplasm, disintegrated chloroplasts and nuclei, and
disorganized phloem thus reducing biomass (Touchette,
2009). Biomass increase in this study was as a result of
the increase in growth parameters. This study showed
that salt spray induced leaf and stem succulence. Also,
leaf succulence increased in
Crambe maritima
subjected
to air-borne seawater spray (De Vos et al., 2010).
Increased succulence in the presence of salt is an adaptive
mechanism for ion dilution (Rozema et al., 1985). In a
previous study, Griffiths and Orians (2003) reported a
significant reduction in xylem water potential in
Solidago puberula
,
Solidago rugosa
,
Gaylussacia
baccata
,
Myrica pensylvanica
,
Pinus rigida
and
Quercus ilicifolia
by salt sprays, indicating that salt
spray caused water stress and might be inhibiting
physiological processes in the plant. The increase of
some nutrients and accumulation of Na
+
and Cl
-
ions
indicated that high concentrations of seawater can
influence ions distribution, so that they can contribute to
the osmotic potential, and thereby increase the
protection against osmotic stress (Touchette, 2009).
Much of N contents under NaCl salinity were probably
used in synthesis of specific N compounds such as
amino acids (e.g. proline and aspartic acids), amides
(glutamine and asparagine) and the stress-related
proteins (Ashraf and Harris, 2004). Plants exposed to
salt usually absorb a large amount of Na
+
, which causes
a decrease in the contents of K
+
(Al–Karaki, 2000).
Most salt tolerant plants accumulate Na
+
in their shoots
whereas sensitive plants do not, and a more efficient K
+
uptake represents plant adaptation to salinity. Not only
Na
+
and K
+
contents, but also the Na: K ratio can be
used as phyto-physiological parameters for screening
less sensitive plants for NaCl stress (Al–Karaki, 2000).
A high Na: K ratio indicates metabolic disorders such as
a reduction in protein synthesis and enzyme activities
and an increase in membrane permeability (Al–Karaki,
2000). Moreover, elevated K
+
levels act osmotically,
preventing Na
+
influx into roots and shoots (Al–Karaki,
2000). Reduced stomata density and stomata
number/leaf under salt stress has also been reported on
Kandelia candel
(Hwang and Chen 1995). The fewer
stomata on the leaves were to reduce entry points to salt