Comparative Leaf Anatomy and Pressure-Volume Analysis in Plants of Ipomoea pes-caprae Experimenting Saline and/or Drought Stress

A Medicinal Halophyte Ipomoea pes-caprae (Linn.) R. Br.: A Review of Its Botany, Traditional Uses, Phytochemistry, and Bioactivity

Ipomoea pes-caprae (Linn.) R. Br. (Convolvulaceae) is a halophytic plant that favorably grows in tropical and subtropical countries in Asia, America, Africa, and Australia. Even though this plant is considered a pan-tropical plant, I. pes-caprae has been found to occur in inland habitats and coasts of wider areas, such as Spain, Anguilla, South Africa, and Marshall Island, either through a purposeful introduction, accidentally by dispersal, or by spreading due to climate change. The plant parts are used in traditional medicine for treating a wide range of diseases, such as inflammation, gastrointestinal disorders, pain, and hypertension. Previous phytochemical analyses of the plant have revealed pharmacologically active components, such as alkaloids, glycosides, steroids, terpenoids, and flavonoids. These phytoconstituents are responsible for the wide range of biological activities possessed by I. pes-caprae plant parts and extracts. This review arranges the previous reports on the botany, distribution, traditional uses, chemical constituents, and biological activities of I. pes-caprae to facilitate further studies that would lead to the discovery of novel bioactive natural products from this halophyte.

Type 17 immunity promotes the exhaustion of CD8+ T cells in cancer

Background

Multiple types of immune cells producing IL-17 are found in the tumor microenvironment. However, their roles in tumor progression and exhaustion of CD8⁺ tumor-infiltrating lymphocytes (TILs) remain unclear.

Methods

To determine the role of type 17 immunity in tumor, we investigated the growth of B16F10 melanoma and the exhaustion of CD8⁺ TILs in Il17a^−/− mice, Il17a^CreR26^DTA mice, RORγt inhibitor-treated mice, or their respective control mice. Adoptive transfer of tumor-specific IL-17-producing T cells was performed in B16F10-bearing congenic mice. Anti-CD4 or anti-Ly6G antibodies were used to deplete CD4⁺ T cells or CD11b⁺Gr-1^hi myeloid cells in vivo, respectively. Correlation between type 17 immunity and T cell exhaustion in human cancer was evaluated by interrogating TCGA dataset.

Results

Depletion of CD4⁺ T cells promotes the exhaustion of CD8⁺ T cells with a concomitant increase in IL-17-producing CD8⁺ T (Tc17) cells in the tumor. Unlike IFN-γ-producing CD8⁺ T (Tc1) cells, tumor-infiltrating Tc17 cells exhibit CD103⁺KLRG1⁻IL-7Rα^hi tissue resident memory-like phenotypes and are poorly cytolytic. Adoptive transfer of IL-17-producing tumor-specific T cells increases, while depletion of IL-17-producing cells decreases, the frequency of PD-1^hiTim3⁺TOX⁺ terminally exhausted CD8⁺ T cells in the tumor. Blockade of IL-17 or RORγt pathway inhibits exhaustion of CD8⁺ T cells and also delays tumor growth in vivo. Consistent with these results, human TCGA analyses reveal a strong positive correlation between type 17 and CD8⁺ T cell exhaustion signature gene sets in multiple cancers.

Conclusion

IL-17-producing cells promote terminal exhaustion of CD8⁺ T cells and tumor progression in vivo, which can be reversed by blockade of IL-17 or RORγt pathway. These findings unveil a novel role for IL-17-producing cells as tumor-promoting cells facilitating CD8⁺ T cell exhaustion, and propose type 17 immunity as a promising target for cancer immunotherapy.

Plant Responses to Salt Stress: Adaptive Mechanisms

This review deals with the adaptive mechanisms that plants can implement to cope with the challenge of salt stress. Plants tolerant to NaCl implement a series of adaptations to acclimate to salinity, including morphological, physiological and biochemical changes. These changes include increases in the root/canopy ratio and in the chlorophyll content in addition to changes in the leaf anatomy that ultimately lead to preventing leaf ion toxicity, thus maintaining the water status in order to limit water loss and protect the photosynthesis process. Furthermore, we deal with the effect of salt stress on photosynthesis and chlorophyll fluorescence and some of the mechanisms thought to protect the photosynthetic machinery, including the xanthophyll cycle, photorespiration pathway, and water-water cycle. Finally, we also provide an updated discussion on salt-induced oxidative stress at the subcellular level and its effect on the antioxidant machinery in both salt-tolerant and salt-sensitive plants. The aim is to extend our understanding of how salinity may affect the physiological characteristics of plants.

Salt tolerance of Beta macrocarpa is associated with efficient osmotic adjustment and increased apoplastic water content

The chenopod Beta macrocarpa Guss (wild Swiss chard) is known for its salt tolerance, but the mechanisms involved are still debated. In order to elucidate the processes involved, we grew wild Swiss chard exposed to three salinity levels (0, 100 and 200 mm NaCl) for 45 days, and determined several physiological parameters at the end of this time. All plants survived despite reductions in growth, photosynthesis and stomatal conductance in plants exposed to salinity (100 and 200 mm NaCl). As expected, the negative effects of salinity were more pronounced at 200 mm than at 100 mm NaCl: (i) leaf apoplastic water content was maintained or increased despite a significant reduction in leaf water potential, revealing the halophytic character of B. macrocarpa; (ii) osmotic adjustment occurred, which presumably enhanced the driving force for water extraction from soil, and avoided toxic build up of Na(+) and Cl(-) in the mesophyll apoplast of leaves. Osmotic adjustment mainly occurred through accumulation of inorganic ions and to a lesser extent soluble sugars; proline was not implicated in osmotic adjustment. Overall, two important mechanisms of salt tolerance in B. macrocarpa were identified: osmotic and apoplastic water adjustment.

Comparison of individual and combined effects of salinity and deficit irrigation on physiological, nutritional and ornamental aspects of tolerance in Callistemon laevis plants

The effect of water deficit, salinity and both applied simultaneously on several physiological and morphological parameters in the ornamental plant Callistemon laevis was studied to identify the tolerance mechanisms developed by this species to these sources of stress and to evaluate their adaptability to such conditions. C. laevis plants were grown in pots outdoors and subjected to four irrigation treatments lasting ten months: control (0.8 dS m(-1), 100% water holding capacity), water deficit (0.8 dS m(-1), 50% of the amount of water supplied in control), saline (4.0 dS m(-1), same amount of water supplied as control) and saline water deficit (4.0 dS m(-1), 50% of the water supplied in the control). Water and saline stress, when applied individually, led to a reduction of 12% and 39% of total biomass, respectively, while overall plant quality (leaf color and flowering) was unaffected. However, saline water deficit affected leaf color and flowering and induced an excessive decrease of growth (68%) due to leaf tissue dehydration and a high leaf Cl and Na concentration. Biomass partitioning depended not only on the amount of water applied, but also on the electrical conductivity of the water. Water stress induced active osmotic adjustment and decreased leaf tissue elasticity. Although both Na and Cl concentrations in the plant tissues increased with salinity, Cl entry through the roots was more restricted. In plants submitted to salinity individually, Na tended to remain in the roots and stems, and little reached the leaves. However, plants simultaneously submitted to water and saline stress were not able to retain this ion in the woody parts. The decrease in stomatal conductance and photosynthesis was more marked in the plants submitted to both stresses, the effect of which decreased photosynthesis, and this together with membrane damage delayed plant recovery. The results show that the combination of deficit irrigation and salinity in C. laevis is not recommended since it magnifies the adverse effects of either when applied individually.

Co-ordination among leaf water relations and xylem vulnerability to embolism of Eucalyptus trees growing along a depth-to-groundwater gradient

The importance of groundwater resources in arid and semi-arid areas for plant survival is well documented. However, there have been few studies examining the importance and impacts of groundwater availability in mesic environments. The aim of this study was to determine how depth-to-groundwater (DGW) impacts on leaf water relations, leaf structure and branch xylem vulnerability to embolism in a mesic environment. We hypothesize that increasing DGW results in increased resistance to drought stress and that this will be manifested across leaf and branch attributes pertaining to water relations. We further investigate whether there is co-ordination across leaf and branch-scale level responses to increased DGW. Four species were used in this study: Eucalyptus globoidea Blakely, E. piperita Sm., E. sclerophylla (Blakely) L.A.S.Johnson & Blaxell and E. sieberi L.A.S.Johnson. Six sites were chosen along an 11 km transect to span a range of average DGW: 2.4, 4.3, 9.8, 13, 16.3 and 37.5 m. Leaf water relations of trees showed less sensitivity to drought stress as DGW increased. This was reflected in significantly lower leaf turgor loss point and maximum osmotic potential, increased maximum turgor and a reduced leaf relative water content as DGW increased. At shallow DGW sites, minimum diurnal leaf water potentials were generally more negative than leaf water potential at zero turgor, but the reverse was observed at deep sites, indicating a larger growth potential safety margin at deep sites compared with shallow sites. Leaf cell wall elasticity varied independently of DGW. Xylem vulnerability to embolism was quantified as the water potential associated with 50% loss of conductance (P 50). In both summer and winter P 50 was significantly and negatively correlated with DGW. Co-ordination between leaf- and branch-level responses to increase in DGW was apparent, which strongly supports the conclusion that groundwater supply influenced woodland structure and functional behaviour.

A comparative study of the early osmotic, ionic, redox and hormonal signaling response in leaves and roots of two halophytes and a glycophyte to salinity

Salt stress is one of the most important abiotic stress factors affecting plant growth and productivity in natural ecosystems. In this study, we aimed at determining possible differences between salt tolerant and salt sensitive species in early (within 72 h) salt stress response in leaves and roots. To this purpose, we subjected three Brassicaceae species, namely two halophytes-Cakile maritima and Thellungiella salsuginea--and a glycophyte--Arabidopsis thaliana- to short-term salt stress (400 mM NaCl). The results indicate that the halophytes showed a differential osmotic and ionic response together with an early and transient oxidative burst, which was characterized by enhanced hydrogen peroxide levels and subsequent activation of antioxidant defenses in both leaves and roots. In addition, the halophytes displayed enhanced accumulation of abscisic acid, jasmonic acid (JA) and ACC (aminocyclopropane-1-carboxylic acid, the precursor of ethylene) in leaves and roots, as compared to A. thaliana under salt stress. Moreover, the halophytes showed enhanced expression of ethylene response factor1 (ERF1), the convergence node of the JA and ethylene signaling pathways in both leaves and roots upon exposure to salt stress. In conclusion, we show that the halophytes C. maritima and T. salsuginea experience an early oxidative burst, improved antioxidant defenses and hormonal response not only in leaves but also in roots, in comparison to the glycophyte A. thaliana. This differential signaling response converging, at least in part, into increased ERF1 expression in both above- and underground tissues seems to underlay, at least in part, the enhanced tolerance of the two studied halophytes to salt stress.