Abstract
The greatest problems faced during the 21st century is climate change which is a big threat to food security due to increasing number of people. The increase in extreme weather events, such as drought and heat, makes it difficult to cultivate conventional crops that are not stress tolerant. As a result, increasing irrigation of arable land leads to additional salinization of soils with plant-toxic sodium and chloride ions. Knowledge about the adaptation strategies of salt-tolerant plants to salt stress as well as detailed knowledge about the control of transpiration water loss of these plants are therefore important to guarantee productive agriculture in the future. In the present study, I have characterized salt sensitive and salt tolerant plant species at physiological, phenotypic and transcriptomic level under short (1x salt) and long-time (3x) saline growth conditions. Two approaches used for long-time saline growth conditions (i.e increasing saline conditions (3x salt) and constant high saline conditions (3x 200 mM salt) were successfully developed in the natural plant growth medium i.e soil. Salt sensitive plants, A. thaliana, were able to survive and successfully set seeds at the toxic concentrations on the increasing saline growth mediums, with minor changes in the phenotype. However, under constant high saline conditions they could not survive. This was due to keeping low potassium, and high salt ions (sodium and chloride) in the photosynthetic tissue i.e leaf. Similarly, high potassium and low salt ions in salt tolerant T. salsuginea on both saline environments were the key for survival of this plant species. Being salt tolerant, T. salsuginea always kept high potassium levels and low sodium (during 1x) and chloride levels (during both 1x and 3x) in the leaf tissue. A strict control over transpirational water loss via stomata (formed by pair of guard cells) is important to maintain plant water balance. Aperture size of the stomata is regulated by the turgidity of the guard cells. More turgid the guard cells, bigger the apertures are and hence more transpiration. Under osmotic stress, the water loss is reduced which was evident in the salt sensitive A. thaliana plants under both short and long-time saline growth conditions. As the osmotic stress was only increased during long time saline growth conditions in T. salsuginea therefore, water loss was also decreased only under these saline conditions. Environmental CO2 assimilation also takes place via stomata in plants which then is used for photosynthesis. Stomatal apertures also influence CO2 assimilation. As the light absorbing photosynthetic pigments were more affected in A. thaliana, therefore photosynthetic activity of the whole plant was also reduced. Similarly, both short and long-time saline growth conditions also reduced the effective quantum yield of A. thaliana guard cells. Growth of the plant is dependent on energy which comes from photosynthesis. Reduced environmental CO2 assimilation would affect photosynthesis and hence growth, which was clearly observed in A. thaliana guard cells under long-time saline growth conditions. Major differences in both guard cells types were observed in their chloride and potassium levels. Energy Dispersive X-Ray Analysis (EDXA) suggested strict control of chloride accumulation in T. salsuginea guard cells as the levels remain unchanged under all conditions. Similarly, use of sodium in place of potassium for osmotic adjustments seems to be dependent on Na+/K+ rations in both guard cell types. Increased salt ions and reduced potassium levels in A. thaliana guard cells posed negative effect on photochemistry which in turn increased ROS metabolism and reduced energy related pathways at transcriptomic level in this plant species. Moreover, photosynthesis was strongly affected in A. thaliana guard cells both at transcriptomic and physiological levels. Similarly, global phytohormones induced changes were more evident in A. thaliana guard cells especially on 3x salt medium. Among all phytohormones, genes under the control of auxin were more differentially expressed in A. thaliana guard cells which suggests wide changes in growth and development in this plant species under salinity. Phytohormone, ABA is vital for closing the stomata under abiotic stress conditions. Increased levels of ABA during saline conditions led to efflux of potassium and counter anions (chloride, malate, nitrate) from the guard cells which caused the outward flow of water and hence reduction in turgor pressure. Reduced turgor pressure led to reduced water loss and CO2 assimilation especially in A. thaliana. Guard cells of both plant species synthesized ABA during saline conditions which was reflected from transcriptomic data and ABA quantification in the guard cells. ABA induced signaling in both plant species varied at the ABA receptor (PYL/PYR) levels where totally contrasting responses were observed. PYL2, PYL8 and PYL9 were specific to A. thaliana, furthermore, PYL2 was found to be differentially expressed only under 3x salt growth conditions thus suggesting its role during long term salt stress in this plant species. Protein phosphatases, which negatively regulate ABA signaling on one hand and act as ABA sensor on the other hand were found to be more differentially expressed in A. thaliana than T. salsuginea guard cells, which suggests their diverse role in both plant species under saline conditions. Differential expression of more ABA signaling players in long time saline conditions was prominent which could be because of darkness, as it is well known that rapid closure of stomata under dark conditions require ABA signaling. Moreover, representation of these components in dark also suggests that plants become more sensitive to dark under saline conditions which is also evident from the transpiration rates. Altogether, increased salt ions in A. thaliana guard cells and leaves led to pigment degradation and ABA induced reduction in transpiration which in turn influenced its growth. In contrast, T. salsuginea is the salt excluder and therefore keeps low levels of salt ions especially the chloride both in leaves and guard cells which mildly affects its growth. Guard cells of A. thaliana encounter severe energy problems at physiological and transcriptomic level. Main differences in the ABA signalling between both plant species were observed at the ABA receptor level.
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Claims 20
Claim · model-written summary
Increasing saline growth conditions were developed in soil.
- Taxon
- Arabidopsis
Arabidopsist0 - Outcome
- increasing saline conditions (3x salt)e0
- Value
- 3x salte0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Arabidopsis”
e0“Two approaches used for long-time saline growth conditions (i.e increasing saline conditions (3x salt) and constant high saline conditions (3x 200 mM salt) were successfully developed in the natural plant growth medium i.e soil”
Claim · model-written summary
Constant high saline growth conditions were developed in soil.
EutremaOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“Thellungiella”
e0“Two approaches used for long-time saline growth conditions (i.e increasing saline conditions (3x salt) and constant high saline conditions (3x 200 mM salt) were successfully developed in the natural plant growth medium i.e soil”
Claim · model-written summary
A. thaliana survived, set seed and showed minor phenotype changes under increasing saline conditions.
- Taxon
- A. thalianaArabidopsis thalianae0
- Treatment
- increasing saline growth mediumse0
- Outcome
- survive and successfully set seedse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Salt sensitive plants, A. thaliana, were able to survive and successfully set seeds at the toxic concentrations on the increasing saline growth mediums, with minor changes in the phenotype”
Claim · model-written summary
A. thaliana failed to survive constant high salinity.
- Taxon
- ArabidopsisArabidopsist0
- Treatment
- constant high saline conditionse0
- Outcome
- could not survivee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“However, under constant high saline conditions they could not survive.”
t0“Arabidopsis”
Claim · model-written summary
A. thaliana leaves retained low potassium and high sodium and chloride under constant high salinity.
- Taxon
- ArabidopsisArabidopsist0
- Organ / stage
- leafe0
- Outcome
- low potassium, and high salt ions (sodium and chloride)e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“This was due to keeping low potassium, and high salt ions (sodium and chloride) in the photosynthetic tissue i.e leaf”
t0“Arabidopsis”
Claim · model-written summary
T. salsuginea retained high leaf potassium and low salt ions in both saline environments.
- Taxon
- T. salsugineaEutrema salsugineume0
- Outcome
- high potassium and low salt ionse0
Verbatim
e0“high potassium and low salt ions in salt tolerant T. salsuginea on both saline environments were the key for survival of this plant species”
Claim · model-written summary
A. thaliana reduced water loss under short and long saline conditions.
- Taxon
- A. thalianaArabidopsis thalianae0
- Treatment
- short and long-time saline growth conditionse0
- Outcome
- water losse0
- Direction
- reducede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the water loss is reduced which was evident in the salt sensitive A. thaliana plants under both short and long-time saline growth conditions”
Claim · model-written summary
T. salsuginea reduced water loss only under long-term salinity.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“water loss was also decreased only under these saline conditions”
t0“Thellungiella”
Claim · model-written summary
Photosynthetic activity was reduced in A. thaliana.
- Taxon
- ArabidopsisArabidopsist0
- Outcome
- photosynthetic activity of the whole plante0
- Direction
- reducede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“photosynthetic activity of the whole plant was also reduced”
t0“Arabidopsis”
Claim · model-written summary
Salinity reduced effective quantum yield in A. thaliana guard cells.
- Taxon
- A. thalianaArabidopsis thalianae0
- Treatment
- short and long-time saline growth conditionse0
- Outcome
- effective quantum yield of A. thaliana guard cellse0
- Direction
- reducede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“both short and long-time saline growth conditions also reduced the effective quantum yield of A. thaliana guard cells”
Claim · model-written summary
T. salsuginea guard-cell chloride levels remained unchanged across conditions.
- Taxon
- T. salsugineaEutrema salsugineume0
- Organ / stage
- guard cellse0
- Outcome
- chloride accumulatione0
- Direction
- remain unchangede0
Verbatim
e0“chloride accumulation in T. salsuginea guard cells as the levels remain unchanged under all conditions”
Claim · model-written summary
A. thaliana guard-cell salt accumulation and potassium loss impaired photochemistry and increased ROS metabolism.
- Taxon
- A. thalianaArabidopsis thalianae0
- Outcome
- negative effect on photochemistrye0
- Qualifier
- Increased salt ions and reduced potassium levelse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Increased salt ions and reduced potassium levels in A. thaliana guard cells posed negative effect on photochemistry which in turn increased ROS metabolism”
Claim · model-written summary
A. thaliana guard cells showed reduced energy pathways at transcriptomic level.
- Taxon
- ArabidopsisArabidopsist0
- Outcome
- energy related pathways at transcriptomic levele0
- Direction
- reducede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“reduced energy related pathways at transcriptomic level in this plant species”
t0“Arabidopsis”
Claim · model-written summary
Phytohormone-related changes were more evident in A. thaliana guard cells, especially at 3x salinity.
- Taxon
- A. thalianaArabidopsis thalianae0
- Outcome
- global phytohormones induced changese0
- Direction
- more evidente0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“global phytohormones induced changes were more evident in A. thaliana guard cells especially on 3x salt medium”
Claim · model-written summary
Auxin-controlled genes were more differentially expressed in A. thaliana guard cells.
- Taxon
- A. thalianaArabidopsis thalianae0
- Gene
- genes under the control of auxine0
- Outcome
- differentially expressede0
- Direction
- moree0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“genes under the control of auxin were more differentially expressed in A. thaliana guard cells”
Claim · model-written summary
Both plant species synthesized ABA in guard cells during salinity.
- Taxon
- ArabidopsisArabidopsist0
- Organ / stage
- Guard cellse0
- Outcome
- synthesized ABAe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Guard cells of both plant species synthesized ABA during saline conditions”
t0“Arabidopsis”
t1“Thellungiella”
Claim · model-written summary
PYL2 was differentially expressed in A. thaliana only under 3x salinity.
- Taxon
- ArabidopsisArabidopsist0
- Gene
- PYL2e0
- Outcome
- differentially expressede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“PYL2 was found to be differentially expressed only under 3x salt growth conditions”
t0“Arabidopsis”
Claim · model-written summary
Protein phosphatases were more differentially expressed in A. thaliana than T. salsuginea guard cells.
- Taxon
- A. thalianaArabidopsis thalianae0
- Gene
- Protein phosphatasese0
- Outcome
- differentially expressede0
- Direction
- moree0
- Comparator
- T. salsugineae0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Protein phosphatases, which negatively regulate ABA signaling on one hand and act as ABA sensor on the other hand were found to be more differentially expressed in A. thaliana than T. salsuginea guard cells”
Claim · model-written summary
ABA-signaling components showed more differential expression under long-term salinity.
- Taxon
- ArabidopsisArabidopsist0
- Outcome
- Differential expression of more ABA signaling playerse0
- Direction
- moree0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Differential expression of more ABA signaling players in long time saline conditions was prominent”
t0“Arabidopsis”
Claim · model-written summary
T. salsuginea maintained low chloride in leaves and guard cells with mild growth effects.
- Taxon
- T. salsugineaEutrema salsugineume0
- Organ / stage
- leaves and guard cellse0
- Outcome
- low levels of salt ions especially the chloridee0
Verbatim
e0“T. salsuginea is the salt excluder and therefore keeps low levels of salt ions especially the chloride both in leaves and guard cells which mildly affects its growth”
The same questions in other papers
salinity · physiology: photosynthesis · Arabidopsis thaliana (thale cress)Results agree
1 paper in the same direction as this paper
- negative
Claims are grouped by organism, treatment and what was measured or targeted. A paper counts as positive when any of its claims in the group is positive.