Modulation of vacuolar H+ -pumps and aquaporin by phytohormones in rice seedling leaf sheaths

Comparative Transcriptome Profiling Provides Insights into Plant Salt Tolerance in Watermelon (Citrullus lanatus)

Salt stress seriously reduced the yield and quality of watermelon and restricted the sustainable development of the watermelon industry. However, the molecular mechanism of watermelon in response to salt stress is still unclear. In this study, 150 mmol·L^-1 NaCl was used to deal with the seedlings of salt-tolerant and salt-sensitive watermelon varieties. Physiological characteristics showed that salt stress significantly reduced the biomass of watermelon seedlings and the accumulation of K⁺ in roots and leaves and significantly increased the content of Na⁺, Cl^-, and malondialdehyde (MDA). Compared with the salt-sensitive variety, the salt-tolerant variety had higher K⁺ accumulation, lower Cl^-, Cl^- accumulation, and MDA content in roots and leaves. Then, RNA-seq was performed on roots and leaves in normal culture and under 150 mmol·L^-1 NaCl treatment. A total of 21,069 genes were identified by RNA-seq analysis, of which 1412 were genes encoding transcription factors (TFs). In the comparison groups of roots and leaves, 122 and 123 shared differentially expressed genes (DEGs) were obtained, respectively. Gene ontology (GO) annotation and KEGG enrichment results showed that there were many identical GO terms and KEGG pathways in roots and leaves, especially the pathways that related to sugar or energy (ATP or NADP⁺/NADPH). In addition, some DEGs related to salt tolerance were identified, such as plant hormone indole-3-acetic acid (IAA) and gibberellin (GA) signal transduction pathway-related genes, K⁺/Na⁺/Ca²⁺-related genes, lignin biosynthesis-related genes, etc. At the same time, we also identified some TFs related to salt tolerance, such as AP2-EREBP, bZIP, bHLH, MYB, NAC, OFP, TCP, and WRKY and found that these TFs had high correlation coefficients with salt tolerance-related genes, indicating that they might have a potential regulatory relationship. Interestingly, one TCP TF (Cla97C09G174040) co-exists both in roots and leaves, and it is speculated that it may be regulated by miR319 to improve the salt tolerance of watermelon.

Sheathing the blade: Significant contribution of sheaths to daytime and nighttime gas exchange in a grass crop

Despite representing a sizeable fraction of the canopy, very little is known about leaf sheath gas exchange in grasses. Specifically, estimates of sheath stomatal conductance, transpiration and photosynthesis along with their responses to light, CO₂ and vapour pressure deficit (VPD) are unknown. Furthermore, the anatomical basis of these responses is poorly documented. Here, using barley as a model system, and combining leaf-level gas exchange, whole-plant gravimetric measurements, transpiration inhibitors, anatomical observations, and biophysical modelling, we found that sheath and blade stomatal conductance and transpiration were similar, especially at low light, in addition to being genotypically variable. Thanks to high abaxial stomata densities and surface areas nearly half those of the blades, sheaths accounted for up to 17% of the daily whole-plant water use, which -surprisingly- increased to 45% during the nighttime. Sheath photosynthesis was on average 17-25% that of the blade and was associated with lower water use efficiency. Finally, sheaths responded differently to the environment, exhibiting a lack of response to CO₂ but a strong sensitivity to VPD. Overall, these results suggest a key involvement of sheaths in feedback loops between canopy architecture and gas exchange with potentially significant implications on adaptation to current and future climates in grasses.

Plasma membrane ATPase and the aquaporin HvPIP1 in barley brassinosteroid mutants acclimated to high and low temperature

The integral parts of the cell membranes are the functional proteins, which are crucial for cell life. Among them, proton-pumping ATPase and aquaporins appear to be of particular importance. There is some knowledge about the effect of the temperature during plant growth, including stress-inducing temperatures, on the accumulation of the membrane proteins: plasma membrane H⁺-ATPase and aquaporins, but not much is known about the effect of the phytohormones (i.e. brassinosteroids (BR)) on control of accumulation of these proteins. The aim of our study was to answer the question of how a BR deficit and disturbances in the BR perception/signalling affect the accumulation of plasma membrane H⁺-ATPase (PM H⁺-ATPase), the aquaporin HvPIP1 transcript and protein in barley growing at 20 °C and during its acclimation at 5 °C and 27 °C. For the studies, the BR-deficient mutant 522DK (derived from the wild-type Delisa), the BR-deficient mutant BW084 and the BR-signalling mutant BW312 and their wild-type Bowman were used. Generally, temperature of growth was significant factor influencing on the level of the accumulation of the H⁺-ATPase and HvPIP1 transcript and the PM H⁺-ATPase and HvPIP1 protein in barley leaves. The level of the accumulation of the HvPIP1 transcript decreased at 5 °C (compared to 20 °C), but was higher at 27 °C than at 20 °C in the analyzed cultivars. In both cultivars the protein HvPIP1 was accumulated in the highest amounts at 27 °C. On the other hand, the barley mutants with a BR deficiency or with BR signalling disturbances were characterised by an altered accumulation level of PM H⁺-ATPase, the aquaporin HvPIP1 transcript and protein (compared to the wild types), which may suggest the involvement of brassinosteroids in regulating PM H⁺-ATPase and aquaporin HvPIP1 at the transcriptional and translational levels.

Insights into the role of phytohormones regulating pAtNIP5;1 activity and boron transport in Arabidopsis thaliana

Aiming to counteract B deficiency impacts, plants have developed different strategies in order to reach an optimal growth in soils with limited B availability. These include B transport mechanisms that involves a facilitated transport, via channel proteins, and a high-affinity active transport driven by borate transporters. The AtNIP5;1 channel protein is a member of Major Intrinsic Protein family which facilitates B influx into the roots under low B supply. In order to explore the phytohormone-dependent regulation of AtNIP5;1, the effects of abscisic acid (ABA), ethylene, auxins and cytokinins on the activity of AtNIP5;1 promoter were evaluated using the reporter line pNIP5;1-GUS. The results show that ABA treatment increased pAtNIP5;1 activity. Besides, a larger B uptake was found following ABA treatment under B deficiency suggesting a role of ABA inducing B uptake. The ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) caused an induction of AtNIP5;1 expression although did not correlate with higher B concentrations nor with an improvement in root growth. On the contrary, auxins and cytokinins caused slight changes in pAtNIP5;1 induction. Altogether, these results show a regulatory role of phytohormones in AtNIP5;1 promoter what may affect B transport. The herein provided information may contribute to better understand the regulation of B transport in plants towards minimizing B deficiency impacts on agriculture.

Tonoplast of Beta vulgaris L. contains detergent-resistant membrane microdomains

The experiments conducted on tonoplast of Beta vulgaris L. roots were performed to identify detergent-resistant lipid-protein microdomains (DRMs, interpreted as lipid rafts).The presence of DRMs can be found when dynamic clustering of sphingolipids, sterols, saturated fatty acids is registered, and the insolubility of these microdomains in nonionic detergents at low temperatures is proven. The elucidation of tonoplast microdomains has been based on results obtained with the aid of high-speed centrifuging in the sucrose gradient. The experiments have shown that tonoplast microdomains are rich in sphingolipids, free sterols and saturated fatty acids (such a lipid content is also typical of lipid-protein microdomains of other membranes), while only few phospholipids are present in tonoplast microdomains. The presence of microdomains has been confirmed by fluorescence and confocal microscopy using filipin and Laurdan as fluorescent probes. The experiments with Laurdan have shown that tonoplast microdomains are characterized by a high order compared to characteristics of the rest of the tonoplast. Thus, the presence of detergent-resistant lipid-protein microdomains in the tonoplast has been demonstrated.

Repressing the expression of the SUCROSE NONFERMENTING-1-RELATED PROTEIN KINASE gene in pea embryo causes pleiotropic defects of maturation similar to an abscisic acid-insensitive phenotype

The classic role of SUCROSE NONFERMENTING-1 (Snf1)-like kinases in eukaryotes is to adapt metabolism to environmental conditions such as nutrition, energy, and stress. During pea (Pisum sativum) seed maturation, developmental programs of growing embryos are adjusted to changing physiological and metabolic conditions. To understand regulation of the switch from cell proliferation to differentiation, SUCROSE NONFERMENTING-1-RELATED PROTEIN KINASE (SnRK1) was antisense repressed in pea seeds. Transgenic seeds show maturation defects, reduced conversion of sucrose into storage products, lower globulin content, frequently altered cotyledon surface, shape, and symmetry, as well as occasional precocious germination. Gene expression analysis of embryos using macroarrays of 5,548 seed-specific genes revealed 183 differentially expressed genes in two clusters, either delayed down-regulated or delayed up-regulated during transition. Delayed down-regulated genes are related to mitotic activity, gibberellic acid/brassinosteroid synthesis, stress response, and Ca2+ signal transduction. This specifies a developmentally younger status and conditional stress. Higher gene expression related to respiration/gluconeogenesis/fermentation is consistent with a role of SnRK1 in repressing energy-consuming processes in maturing cotyledons under low oxygen/energy availability. Delayed up-regulated genes are mainly related to storage protein synthesis and stress tolerance. Most of the phenotype resembles abscisic acid (ABA) insensitivity and may be explained by reduced Abi-3 expression. This may cause a reduction in ABA functions and/or a disconnection between metabolic and ABA signals, suggesting that SnRK1 is a mediator of ABA functions during pea seed maturation. SnRK1 repression also impairs gene expression associated with differentiation, independent from ABA functions, like regulation and signaling of developmental events, chromatin reorganization, cell wall synthesis, biosynthetic activity of plastids, and regulated proteolysis.

Seasonal courses of maximum hydraulic conductance in shoots of six temperate deciduous tree species

The seasonal course of maximum hydraulic conductance of leaf laminae (K _lamina) of shoots correlated strongly with the seasonal course of the maximum hydraulic conductance of leaf laminae of HgCl₂-treated shoots (K _{lamina(HgCl2)}), and with the seasonal course of the difference (dK _lamina) between K _lamina and K _{lamina(HgCl2)}. However, it did not correlate strongly with the seasonal course of the hydraulic conductance of stem and petioles of the shoot (K _stpt) in six temperate deciduous tree species. The species ranked according to K _lamina as follows: Populus tremula L. > Salix caprea L. > Padus avium Mill. > Quercus robur L. > Tilia cordata Mill. > Acer platanoides L. The species-specific maxima of K _lamina correlated positively with the simultaneous values of K _{lamina(HgCl2)}, dK _lamina and K _stpt; the correlation was strongest with K _{lamina(HgCl2)}. It was concluded that the seasonal dynamics of maximum hydraulic conductance of leaf laminae was determined almost equally by the seasonal dynamics of the hydraulic conductance of foliar protoplasts and apoplast, but the inter-specific differences in K _lamina were mainly caused by the different apoplastic hydraulic conductance in leaves of these species. The relative contribution of dK _lamina (in K _lamina) was highest in slow-growing species (~55% in A. platanoides) and the lowest in fast-growers (~30% in S. caprea).

Tissue-specific expression and drought responsiveness of cell-wall invertase genes of rice at flowering

Drought stress near heading reduces grain yield in rice cultivars by inhibiting processes such as anther dehiscence and panicle exsertion. Because cell-wall invertases play an important role in carbon allocation to developing organs, we examined the tissue-specific expression and drought sensitivity of the corresponding genes (OsCIN1-9) at heading in the widely grown cultivar IR64. OsCIN1-5,8 were expressed to varying degrees in flag leaf, panicle, anthers and peduncle at 1 day before heading (1 DBH). When water was withheld for 2 days starting 3 DBH, anthesis and peduncle elongation were halted. At the same time, transcript levels for OsCIN1-5,8 genes were all markedly down-regulated in anthers and/or peduncles but were not affected in flag leaves. Re-watering allowed anthesis and peduncle elongation to proceed and restored expression of OsCIN1-5,8. We conclude that cell-wall invertase genes, as a class, respond rapidly to water deficit in anthers and peduncles and through a reduction in sink strength help to coordinate a delay in anthesis and heading. By contrast, vacuolar invertase OsVIN2 was up-regulated by drought stress in flag leaves, panicles, anthers and peduncles. Although OsCIN1-3,5,8 were active in the peduncle, only OsCIN2 was expressed strongly and preferentially at the base, where cell division and cell elongation occur. OsCIN2 was expressed principally in the primary and secondary vascular systems, consistent with a role in diverting sucrose from the phloem to the dividing and expanding cells of the peduncle, whereas the less abundant OsCIN1,3,5,8 transcripts were found principally in parenchyma cells. The OsCIN2 transcript levels in the base were highest at 1 DBH, when rapid peduncle elongation began. Drought stress halted peduncle elongation and reduced OsCIN2 transcript level to 8% of the control level. On re-watering, peduncle elongation was restored and OsCIN2 transcript level recovered to 24% of the control. The abscisic acid (ABA) level of peduncles increased 7-fold on drought stress and returned to the control level on re-watering. Detached peduncles floated on water elongated little and lost all OsCIN2 transcripts, but on 50-100 microM GA3 they elongated rapidly and maintained high OsCIN2 transcript levels. ABA antagonized both peduncle elongation and maintenance of OsCIN2 transcript levels. We conclude that this antagonism is a potential intervention point for breeding strategies directed at enhancing panicle exsertion during or after drought stress at heading.