Research Progress of Suaeda Heteroptera and in Ecological

Restoration of Coastal Wetland

Yuting Wei

1,2

, Yubo Cui

1,2,*

, Peijing Kuang

1,2

, Junwen Ma

and Zhaobo Chen

1,2

Key Laboratory of Biotechnology and Bioresources Utilization, Ministry of Education, Dalian Minzu University, Dalian

116600, China

College of Environment and Resources, Dalian Minzu University, Dalian 116600, China

Keywords: Salt Stress, Phytoremediation Techniques, Suaeda Heteroptera.

Abstract: Coastal wetland ecosystems are important ecosystems linking freshwater and seawater. With the rapid

economic and social development, the total amount of pollutants discharged into the near-shore sea through

various ways and means remains high, with saline, heavy metal and antibiotic pollution. In order to gain a

comprehensive understanding of the salinity tolerance mechanism of the suaeda salsaand the mechanism of

soil improvement, this study summarises its salinity tolerance mechanism at the morphological, physiological

and biochemical levels as well as at the molecular level, and compares the research progress on the

management of heavy metals and antibiotics in soil. On the basis of this study, we suggest that more attention

should be paid to the exploitation of the key genes of saline alkali ponies, the role of saline alkali ponies in

the succession of saline plant communities, and the mechanism of how saline alkali ponies and

microorganisms can jointly improve the soil.

1 INTRODUCTION

Soil salinity is an ecological and environmental

problem faced worldwide and is one of the important

abiotic stressors affecting plant growth and

development and agricultural production. Coastal

wetlands are in the transition zone of evolution from

sea to land, with complex and fragile ecological

environment, and are high-risk ecosystems that are

highly vulnerable to damage. High soil salinity can

adversely affect photosynthesis, energy metabolism

and protein synthesis of plants (Parida AK, 2018).

Currently, soil salt stress has become one of the major

problems limiting agricultural production (cao 2018).

Therefore, researchers hope to solve the problem of

plant productivity limitation by soil salinity by

resolving plant salt tolerance mechanisms and

enhancing plant salt tolerance.

Suaeda salsa belongs to the genus Alkali poncho

of the family Laiidae as an annual herb and is a

pioneer plant in saline lands. Its fleshy leaves and

unique resilience mechanism make it extremely salt

and drought tolerant, and it is widely distributed in

China, making it an important wild planting resource.

Its above-ground parts can carry away a large amount

of salt, and it is currently widely used in the

improvement of saline agricultural and grazing fields

in Xinjiang, China. The adaptability of Suaeda salsa

on high concentration salt soils is of great importance

for the study of physiological mechanisms of salt

tolerance, molecular mechanisms of salt tolerance

and the breeding of salt-tolerant plants. It has a strong

salt tolerance and can significantly reduce soil salinity

and improve soil structure. It has been shown that it

has significant effect in remediation of organic and

heavy metal contaminated soil, especially in saline

soil conditions. However, there is still insufficient

research on the mechanism of salt tolerance and soil

improvement of Salicornia salina.

2 MORPHOLOGICAL STUDIES

ON THE SUAEDA

HETEROPTERA

Plants have been able to complete their life histories

and evolve a variety of survival strategies to adapt to

adversarial environments, and seed dimorphism is

one of these important strategies. Seed dimorphism

enhances the ability of plants to cope with

unpredictable environmental changes. It has been

220

Wei, Y., Cui, Y., Kuang, P., Ma, J. and Chen, Z.

Research Progress of Suaeda Heteroptera and in Ecological Restoration of Coastal Wetland.

DOI: 10.5220/0011196400003443

In Proceedings of the 4th International Conference on Biomedical Engineering and Bioinformatics (ICBEB 2022), pages 220-224

ISBN: 978-989-758-595-1

shown that the black and brown colored seeds of

Suaeda heteroptera have significant differences in

dormancy characteristics, salt tolerance, and

germination: the volume of brown seeds and ion

concentration in seed cells are higher than those of

black seeds; the water uptake rate, germination

potential, and salt tolerance of brown seeds are

significantly stronger than those of black seeds;

brown seeds can still achieve 30% seed germination

at a salt concentration of 0.78mol/L(Zhang, 2021).

The germination rate of brown seeds could still reach

more than 30% at a salt concentration of 0.78mol/L,

while black seeds could not germinate at a salt

concentration of 0.59mol/L. The higher ion

concentration in the cells of brown seeds may be a

major reason for the higher salt tolerance of their

seeds. In contrast, black seeds can remain dormant

under high salt concentration conditions, and after a

long period of storage, the seeds are still very

vigorous, thus broadening the time of seed

germination, reducing the risk of seeds germinating

out at once, and facilitating the completion of the

plant community of Suaeda heteroptera under

unfavorable environmental conditions (Xia, 2020).

Plant roots are the first organ to sense soil salinity

and are the first barrier to control soil salinity into the

plant. However, there are relatively few studies on the

response of the root system in salt stress, especially

on the mechanism of salt stress response of the root

system of saline plants. The root system of Suaeda

heteroptera is not fleshed out, and the roots are mainly

distributed in the 30cm soil layer, which is a shallow-

rooted functional root system that reduces the

accumulation of salts in the root system by rapid

upward transport of salts. The study showed that the

root system of Suaeda heteroptera showed obvious

salt aggregation under low salinity conditions and salt

rejection under high salinity conditions, and its root

depth increased with increasing salinity, which may

be related to the higher surface salinity. The salinity

of the soil between the roots of H. finasteri was

examined and found that the inter-root salt

concentration of H. finasteri was much higher than

the inter-root salt concentration of non-saline plants,

indicating that H. finasteri has a certain enrichment

function for salts. The root marginal cells are the first

to feel the salt stress in the soil and play an important

role in the signal perception and conduction of plant

stress tolerance, and their number is directly related

to the salt tolerance of plants. The number and

activity of root marginal cells of sweet-soil plants

decreased sharply under higher salt concentration,

while the number and activity of root marginal cells

of Suaeda heteroptera increased significantly without

any effect. The same mechanism may also exist in the

root system of the Suaeda heteroptera.

Suaeda heteropteraare dilute salt plants and their

above-ground parts are the main organs for salt

enrichment. Leaf fleshing is an important strategy for

saline plants to be able to grow and complete their life

history in saline environments. The fleshing of leaves

allows the plant cells to increase in number and

volume, allowing them to absorb and store large

amounts of water, which results in a significant

increase in water content per unit weight and volume

of tissue, thus diluting the salt ion concentration in the

leaf cells and maintaining the osmotic balance of the

leaf cells. The accumulation of Na

and Cl

in the leaf

is the main cause of leaf fleshing, which in turn leads

to an increase in the number of cells and the regional

isolation of large amounts of Na+ in the vesicles, thus

reducing the osmotic stress and ionic stress caused by

to the plant and facilitating the survival of Suaeda

heteropteraunder high salt concentration conditions.

3 PHYSIOLOGICAL AND

BIOCHEMICA RESPONSE OF

SUAEDA HETEROPTERA

UNDER SALT STRESS

Under salt stress, plants are harmed mainly from

osmotic stress and ion toxicity. High salt

concentrations can disrupt the metabolic pathways of

substances in plants as well as ion homeostasis, thus

affecting the growth activities of plants. To resist salt

stress, plants have evolved multiple pathways such as

osmoregulation, ion homeostasis systems, ROS

elimination systems, and hormone signaling to

counteract the damage caused by salt stress (Pan

2018).

Seed water uptake is critical for seed germination.

Higher external salt concentrations can cause osmotic

stress on seeds and thus affect plant seed uptake.

Under saline soil conditions, salinity is the main

factor affecting the germination of Suaeda

heteroptera. During the germination stage, seeds

resist salt stress mainly by regulating the osmotic

balance. Soluble sugars, soluble proteins and proline

are important osmoregulatory substances in the plant

body, and their contents are an important indication

of the plant's ability to maintain osmotic balance.

Within a certain range, the contents of soluble sugars,

soluble proteins, and proline generally increased in

the seeds of P. finasteri as the salt concentration

increased, indicating that P. finasteri maintained

osmotic balance mainly through the synthesis of

Research Progress of Suaeda Heteroptera and in Ecological Restoration of Coastal Wetland

221

osmoregulatory substances. However, as the salt

concentration continued to increase, the content of

proline began to decrease, while soluble sugars,

which are signal transduction substances, continued

to increase. In addition, it has been found that the Na

concentration in the seeds of Salicornia salina did not

increase with the increase of salt concentration in the

external environment, especially the Na

concentration. This may be an important reason for

the normal germination of the Suaeda heteroptera in

soils with higher salinity concentrations. When the

salt concentration in the external environment

increased to a certain value, the water uptake rate of

the seeds decreased significantly or even stopped.

This ensures that seeds do not initiate germination in

a high salt concentration environment, thus

maintaining seed activity.

The seedling stage is an important stage of plant

establishment, and vital activities such as energy and

material metabolism are strongly influenced by the

external environment. Studies have shown that the

uptake rate, stomatal conductance, and

photochemical reactions of the photosynthetic system

(PSII) of Suaeda heteroptera were not significantly

affected at a salt concentration of 400mmol/L.

Metabolites are directly related to plant life activities,

and under conditions of adversity, the plant body can

counteract adversity by regulating the synthesis of

metabolites. The most direct of these are changes in

primary metabolites: small molecules such as amino

acids, soluble sugars, and lipids play an important

role in resisting osmotic stress caused by adversity.

The synthesis of more complex secondary

metabolites: enzymes, flavonoids, ROS scavenging,

and signal transduction pathway substances are also

subject to change. A comparative analysis of the

metabolome of leaves of Suaeda heteroptera

seedlings under high versus low salt concentration

conditions revealed significant differences in the

intermediate substances of the secondary metabolite

synthesis pathways, including those of flavonoids,

polyphenols, and organic acids. This may be closely

related to the involvement of these substances in vital

activities such as cell membrane structure,

intracellular osmotic balance homeostasis and

scavenging of free radicals in plants under salt stress.

4 A STUDY OF THE

MOLECULAR MECHANISMS

OF SALT TOLERANCE IN THE

SUAEDA HETEROPTERA

The physiological and biochemical responses of the

plant body in response to adversity are fundamentally

determined by genes. Stress tolerance in plants is a

complex process involving multiple aspects of life

activities such as physiology, biochemistry, and

signaling. At present, the research on signal

perception, signaling and signal response of salt stress

is not very deep. However, the common signaling

pathways of adversity stress have been studied in

depth, and the functions of some key genes have been

studied in depth.

Under high salinity conditions, salt

regionalization is an important mechanism for salt

tolerance in plants, and the genes that have been

cloned to play important roles in Na ion

regionalization in Suaeda heteroptera: SeNHX1,

SeVHA-A and SeVP1, which encode Na

transport proteins, V-H

-ATPase enzyme and V-H

PPase enzyme, respectively, play important roles in

vesicle V-H

-ATPase and V-H

-PPase, respectively,

play important roles in vesicle Na ion regionalization.

The expression of SeNHX1 was significantly

increased in leaves under high concentration of salt

stress, and the transgenic results showed that

SeNHX1 was able to reduce the concentration of Na

ions in the leaf cytoplasm, increase the K/Na ion ratio,

and significantly increase the photosynthetic rate as

well as the chlorophyll II concentration in plants. The

up-regulated expression of SsVHA-H and SsVHA-B,

genes encoding H

-ATPase in the vesicles, provided

a proton gradient for Na ion translocation across the

membrane into the vesicles and reduced the ion

concentration in the cytoplasm, thus avoiding damage

to the organelles caused by high salt ion

concentrations. External salt concentration is too high

and plants are exposed to osmotic stress. Plants

generally maintain internal homeostasis through

organic small molecules and inorganic ions. Betaine

and proline are important osmoregulators in the

cytoplasm, and two important genes, SsBADH and

SsCMO, in the synthetic betaine pathway, and

SsP5CS, a key gene in the proline synthesis pathway,

have been successfully cloned. It was found that the

expression of these three genes was significantly

elevated under salt stress. High salt concentrations

cause oxidative stress in plants, and saline plants have

evolved a strong peroxide-clear system, which

reduces the damage caused by free radicals to the

ICBEB 2022 - The International Conference on Biomedical Engineering and Bioinformatics

222

plant body. The peroxide-clearing genes SsGST,

SsPrxQ, SsCAT1, SsCAT2, SsAPX, Ss.sAPX, and

SsTypA1 have been successfully cloned in Suaeda

heteropteraplants, and the overexpression of these

genes in plants showed a significant decrease in

hydrogen peroxide as well as MDA content,

indicating that these genes play an important role in

reducing oxidative damage to cell membranes.

With the development of high-throughput

sequencing technology, it has become possible to

study plant salt tolerance mechanisms from the

transcriptome level. Whole-transpringome

sequencing of roots and leaves of Suaeda heteroptera

treated with distilled water and high concentrations of

salt showed that genes related to the synthesis of

signaling substances such as growth hormone,

ethylene and jasmonic acid, which sense salt stress

signals and play important roles in transducing salt

stress signals, were up-regulated under high

concentrations of salt stress; K/Ca ion channels,

choline monooxygenase, and Na

transporters, V-

ATPase genes were up-regulated; Fe-SOD,

glutathione, L-ascorbic acid, and flavonoid-related

genes involved in free radical scavenging were also

up-regulated. This is consistent with the previous

findings: it indicates that Suaeda heteroptera resist

salt stress through a series of integrated responses

such as sensing adversity signals, transducing

adversity signals and resisting adversity stress.

5 RESEARCH ON THE

TREATMENT OF SALINE

CONTAMINATED SOIL BY

SUAEDA HETEROPTERA

Fig. 1. Cd uptake by the roots of the Suaeda salsa.

Figure 1 shows the uptake of Cd by Suaeda salsaat

different concentrations, which gradually increased

with increasing Cd concentration. Organic matter and

heavy metal pollution are two important types of soil

pollution, and a lot of results have been achieved in

the research of contaminated soil management.

Engineering measures are currently the main means

to carry out contaminated soil management, but have

certain limitations, so biological management has

gradually become a hot spot in contaminated soil

management research, especially the joint plant and

microbial management research. The special soil

properties of saline soils have limited the application

of many plants and microorganisms. As a pioneer

plant in saline soils, winged alkali poncho has a

relatively well-developed resilience mechanism, and

thus has a strong tolerance to survive under many

adversity conditions. And the plants have similarities

in physiological and biochemical responses, signal

sensing pathways, signal transduction pathways, and

stress-tolerant substances to resist different

adversities. This suggests that Suaeda heteroptera

may have some potential in saline soil pollution

management.

At present, the treatment of heavy metals in soil

mainly transforms heavy metals from activated state

to stable state by activator, and then extracts them

from soil by thermal desorption, electrochemical

method and extraction method (Zhu, 2005).

Activators have strict requirements on soil pH, etc. In

saline soils, activators may lose their activity.

Therefore, Suaeda heteroptera also play an important

role in the remediation of such contaminated soils.

Lead contamination is a common type of soil heavy

metal contamination. It has been shown that moderate

concentrations of NaCl can enhance the activity of

SOD, POD, and CAT in the peroxide scavenging

system of P. finasterides thereby reducing the damage

of Pb to P. finasterides; the inter-root uptake of Pb is

increased by about 35% at 1% NaCl compared to

0.1% NaCl. This indicates that salinity contributes to

the uptake and enrichment of Pb by Suaeda

heteroptera. The highest uptake rates of heavy

metals Cu, Zn, Pb, and Cd could be reached 31, 101,

34, and 62 mg/(kg-d) by Suaeda heteroptera. The

intercropping of H. alba and its inter-rooted

microorganisms was also able to abate the content of

heavy metals in the soil.

0(CK) 10μg/L 20μg/L

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Content of Cd in Suaeda salsa

(

μg·kg

-10

)

(μg·L

-10

)

14 days

Research Progress of Suaeda Heteroptera and in Ecological Restoration of Coastal Wetland

223

6 CONCLUSIONS AND

EXPECTATION

6.1 Mining and Utilization of Salt

Tolerance Genes in Suaeda

Heteroptera

The cloning and functional analysis of genes

controlling important traits such as yield, quality and

disease resistance in major food crops have been

basically completed. At present, the focus of research

is on the regulatory networks of genes controlling

important traits in major food crops and the

application of these key genes in breeding practice.

With the advent of the genomic era, molecular

breeding has become an important direction for future

breeding work. However, the progress of research on

plant resistance, especially the mining of resistance

genes, is still slow, partly due to the lack of resistance

plant resources, and partly due to the complexity of

plant resistance systems. As a pioneer species of the

saline plant community, the winged alkali poncho is

one of the few plants on earth that can tolerate 3%

salt, and the winged alkali poncho grows well under

a variety of adversities such as drought stress and

water stress. The ability to adapt to alternating

environments of salt stress, drought stress and water

stress suggests that Suaeda heteroptera may have

evolved mechanisms to adapt to most adversities.

Therefore, it is important for the breeding of salt-

tolerant plants to explore the salt-tolerance genes and

elucidate their salt-tolerance mechanisms.

6.2 Research on the Application of

Suaeda Heteroptera in Ecological

Restoration

The cloning and functional analysis of genes

controlling important traits such as yield, quality and

disease resistance in major food crops have been

basically completed. At present, the focus of research

is on the regulatory networks of genes controlling

important traits in major food crops and the

application of these key genes in breeding practice.

With the advent of the genomic era, molecular

breeding has become an important direction for future

breeding work. However, the progress of research on

plant resistance, especially the mining of resistance

genes, is still slow, partly due to the lack of resistance

plant resources, and partly due to the complexity of

plant resistance systems. As a pioneer species of the

saline plant community, the winged alkali poncho is

one of the few plants on earth that can tolerate 3%

salt, and the winged alkali poncho grows well under

a variety of adversities such as drought stress and

water stress. The ability to adapt to alternating

environments of salt stress, drought stress and water

stress suggests that Suaeda heteroptera may have

evolved mechanisms to adapt to most adversities.

Therefore, it is important for the breeding of salt-

tolerant plants to explore the salt-tolerance genes and

elucidate their salt-tolerance mechanisms.

ACKNOWLEDGEMENTS

The research was financed by the Natural Science

Foundation of Liaoning, China (2020-MZLH-02) and

Science and Technology Innovation Foundation of

Dalian, China (2018J12SN080).

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