Agriculture Reference
In-Depth Information
gymnorhiza
, salt-responsive mRNA expression of lipoic acid synthase (LAS)
was reported [29]. LAS catalyzes the synthesis of the ROS scavenger lipoic
acid [47] and may play a role in salt tolerance by removing ROS produced by
salt stress.
Compatible solutes such as sorbitol, mannitol, myo-inositol and proline
were reported to be effective hydroxyl radical scavengers [48-50] and free
proline accumulated in plant tissues during abiotic stresses would contribute to
scavenging of surplus free radicals produced under a variety of abiotic stresses
[50].
Mangroves also appear to be highly tolerant to heavy metals [51-53]. An
increase in SOD, CAT, and POD enzyme activities in the roots of heavy
metal-stressed
K. candel
and
B. gymnorhiza
has been reported [54]. On the
other hand, EST analysis of
Heritiera littoralis
demonstrated that the
metallothionein 2a, which is a Cys-rich cytoplasmic metal-binding protein able
to protect cells against the toxic effects of metals, was returned 487 times,
despite normalization [55]. Recently, it has been reported that the cotton
metallothionein GhMT3, a reactive oxygen species scavenger, increased
tolerance to abiotic stress including salt stress in transgenic tobacco and yeast
[56]. Thus, it is possible that the accumulation of metallothionein during
defense signaling could diminish ROS damage and increase the tolerance of
mangroves to salt stress. It has also been suggested that variations in the
morphology and function of nutritive root and glandular tissues, which play a
role in the management of excess cations in saline environments, may have
significantly different effects among species with respect to metal
accumulation, transport, partitioning and excretion. Taken together, the above
findings indicate that salt tolerance mechanisms in mangroves are partially
explained by the scavenging activity of antioxidative proteins induced by salt
stress [57].
2.4. Genome-Wide Studies of Mangrove Salt Tolerance
2.4.1. Functional Screening of Salt Tolerance-Related Genes from
Mangroves
The salt tolerance of mangroves can be partially explained by known
physiological and biochemical features. However, the mechanisms described
thus far are insufficient to explain the intensive salt tolerance observed in
mangroves.
