Do leaf surface characteristics affect Agrobacterium infection in tea [Camellia sinensis (L.) O Kuntze]?

Enhancing water stress tolerance of bread wheat during seed germination and seedling emergence: caffeine-induced modulation of antioxidative defense mechanisms

Better crop stand establishment, a function of rapid and uniform seedling emergence, depends on the activities of germination-related enzymes, which is problematic when there is insufficient soil moisture. Different ways are in practice for counteracting this problem, including seed priming with different chemicals, which are considered helpful in obtaining better crop stand establishment to some extent through improved seed germination and seedling emergence. In this growth room experiment, caffeine was used as a seed priming agent to improve germination under moisture scarcity. Polyethylene glycol-8000 (18%) was added to Hoagland's nutrient solution to create drought stress (-0.65 MPa). The experiment was arranged in a completely randomized design (CRD), having four replications of each treatment. A newly developed wheat genotype SB-1 was used for the experimentation. Different doses of caffeine, i.e., 4 ppm, 8 ppm, 12 ppm, and 16 ppm, including no soaking and water soaking, were used as seed priming treatments. Water deficit caused oxidative stress and adversely affected the seed germination, seedling vigor, activities of germination enzymes, photosynthetic pigments, and antioxidative defense mechanism in roots and shoots of seedlings. Caffeine seed priming ameliorated the negative effects of water deficit on seed germination and seedling vigor, which was attributed to the reduction in lipid peroxidation and improvement in the activities of germination-related enzymes like glucosidase, amylase, and protease. Conclusively, seed priming with 12 ppm caffeine outperformed the other treatments and hence is recommended for better crop stand establishment under conditions of soil moisture deficit.

Establishment of an efficient transformation system and its application in regulatory mechanism analysis of biological macromolecules in tea plants

Tea (Camellia sinensis), one of the most important beverage crops originated from China and is now cultivated worldwide, provides numerous secondary metabolites that account for its health benefits and rich flavor. However, the lack of an efficient and reliable genetic transformation system has seriously hindered the gene function investigation and precise breeding of C. sinensis. In this study, we established a highly efficient, labor-saving, and cost-effective Agrobacterium rhizogenes-mediated hairy roots genetic transformation system for C. sinensis, which can be used for gene overexpression and genome editing. The established transformation system was simple to operate, bypassing tissue culture and antibiotic screening, and only took two months to complete. We used this system to conduct function analysis of transcription factor CsMYB73 and found that CsMYB73 negatively regulates L-theanine synthesis in tea plant. Additionally, callus formation was successfully induced using transgenic roots, and the transgenic callus exhibited normal chlorophyll production, enabling the study of the corresponding biological functions. Furthermore, this genetic transformation system was effective for multiple C. sinensis varieties and other woody plant species. By overcoming technical obstacles such as low efficiency, long experimental periods, and high costs, this genetic transformation will be a valuable tool for routine gene investigation and precise breeding in tea plants.

Leaf surface traits contributing to wettability, water interception and uptake of above-ground water sources in shrubs of Patagonian arid ecosystems

BACKGROUND AND AIMS

The ecohydrological significance of leaf wetting due to atmospheric water in arid and semiarid ecosystems is not well understood. In these environments, the inputs of precipitation or dew formation resulting in leaf wetting have positive effects on plant functioning. However, its impact on plant water relations may depend on the degree of leaf surface wettability. In this study we evaluated leaf wettability and other leaf traits and its effects on foliar water uptake and canopy interception in plant species of a Patagonian steppe. We also studied how leaf traits affecting wettability vary seasonally from growing to dry season.

METHODS

Contact angle of a water droplet with the leaf surface, water adhesion, droplet retention angle, stomatal density, cuticular conductance, canopy interception and maximum foliar water uptake were determined in six dominant shrub species.

KEY RESULTS

All species increased leaf wettability during the dry season and most species were considered highly wettable. The leaf surface had very high capacity to store and retain water. We found a negative correlation between foliar water uptake and leaf hydrophilia.

CONCLUSIONS

Despite the diversity of life forms, including cushion shrubs and tall shrubs, as well as phenological variability, all species converged in similar seasonal changes in leaf traits that favour wettability. Intercepted water by crowns and the extremely high capacity of retention of droplets on leaf surfaces can have a significant impact on eco-hydrological process in water limited ecosystems where most of water sources during the growing and the dry season may be small rainfall events or dew, which do not always increase soil water availability.

Leaf surface characteristics affect the deposition and distribution of droplets in rice (Oryza sativa L.)

We studied the effects of leaf surface characteristics on canopy droplet behaviour using two rice cultivars with similar leaf shapes but significantly different leaf surface characteristics: Jia58 (glabrous rice; smooth leaf surface and no burrs) and Yongyou12 (hairy-leaved rice; rough leaf surface covered with burrs). The plants were subjected to spray tests with different spray pressures and nozzle apertures. The results showed that the deposition amount per unit leaf area was significantly higher in the Yongyou12 canopy than in the Jia58 canopy. The diameter, volume median diameter, number median diameter, and coverage of droplets were significantly higher in Yongyou12 than in Jia58, while the coverage density of droplets was significantly lower. The proportion of small droplets of Jia58 is higher than that of Yongyou12. Thus, a larger amount of large-sized droplets could retain on the leaf surface of hairy-leaved rice, and a larger number of small-sized droplets were retained on the leaf surface of glabrous rice. Smaller pressure and larger flow nozzle were conducive to the retention of the Jia58, while Yongyou12 required larger pressure and larger flow nozzles. Ultrastructural analyses revealed that the leaf surface of glabrous rice had no trichomes and more wax than hairy-leaved rice, and the critical surface tension was lower, resulting in the retention of mainly small droplets on its leaf surface and a lower deposition amount. Therefore, in order to increase the deposition of pesticide droplets on the leaf surface in production, glabrous rice should choose nozzles with smaller spray pressure and large flow rate.

Acid or base? How do plants regulate the ecology of their phylloplane?

Plants interface with and modify the external environment across their surfaces, and in so doing, can control or mitigate the impacts of abiotic stresses and also mediate their interactions with other organisms. Botanically, it is known that plant roots have a multi-faceted ability to modify rhizosphere conditions like pH, a factor with a large effect on a plant's biotic interactions with microbes. But plants can also modify pH levels on the surfaces of their leaves. Plants can neutralize acid rain inputs in a period of hours, and either acidify or alkalinize the pH of neutral water droplets in minutes. The pH of the phylloplane-that is, the outermost surface of the leaf-varies across species, from incredibly acidic (carnivorous plants: as low as pH 1) to exceptionally alkaline (species in the plant family, Malvaceae, up to pH 11). However, most species mildly acidify droplets on the phylloplane by 1.5 orders of magnitude in pH. Just as rhizosphere pH helps shape the plant microbiome and is known to influence belowground interactions, so too can phylloplane pH influence aboveground interactions in plant canopies. In this review, we discuss phylloplane pH regulation from the physiological, molecular, evolutionary, and ecological perspectives and address knowledge gaps and identify future research directions.

Phytochrome Mediated Responses in Agrobacterium fabrum: Growth, Motility and Plant Infection

The soil bacterium and plant pathogen Agrobacterium fabrum C58 has two phytochrome photoreceptors, Agp1 and Agp2. We found that plant infection and tumor induction by A. fabrum is down-regulated by light and that phytochrome knockout mutants of A. fabrum have diminished infection rates. The regulation pattern of infection matches with that of bacterial conjugation reported earlier, suggesting similar regulatory mechanisms. In the regulation of conjugation and plant infection, phytochromes are active in darkness. This is a major difference to plant phytochromes, which are typically active after irradiation. We also found that propagation and motility were affected in agp1⁻ and agp2⁻ knockout mutants, although propagation was not always affected by light. The regulatory patterns can partially but not completely be explained by modulated histidine kinase activities of Agp1 and Agp2. In a mass spectrometry-based proteomic study, 24 proteins were different between light and dark grown A. fabrum, whereas 382 proteins differed between wild type and phytochrome knockout mutants, pointing again to light independent roles of Agp1 and Agp2.

Advances in Surfactants in Foliar Application of Agrochemicals on Mango Leaf Surfaces

The surface tension, pH and contact angle of the wetting liquid as well as the complex composition of the leaf surface are important parameters to describe the spreading, wettability and absorption of agrochemicals on the leaf surfaces. The contact angle of aqueous solutions of agrochemicals (multi-micronutrient fertilizers, growth regulator and insecticides) with/without Leaf guard, bis(2-ethylhexyl) sulfosuccinate sodium salt (AOT) and Sapindus mukorrossi (Ritha) were measured over the surface of mango leaves. The order of contact angle (mean) values was found to be AOT < Ritha < Leaf guard, which implies that AOT is a better wetting agent, but Ritha has a higher range of adhesion work because of its acidic nature (low pH). The wetting free energy was found to be more negative in the presence of Leaf guard, Ritha and AOT than in water, which indicates that wetting is more spontaneous in the presence of surfactants. The adaxial surface of mango leaves had a higher surface free energy than the abaxial part and hence showed higher wettability than the abaxial part.

Metabolite Profiling and Transcriptome Analysis Revealed the Chemical Contributions of Tea Trichomes to Tea Flavors and Tea Plant Defenses

Tea trichomes contain special flavor-determining metabolites; however, little is known about how and why tea trichomes produce them. Integrated metabolite and transcriptome profiling on tea trichomes in comparison with that on leaves showed that trichomes contribute to tea plant defense and tea flavor and nutritional quality. These unicellular, nonglandular, and unbranched tea trichomes produce a wide array of tea characteristic metabolites, such as UV-protective flavonoids, insect-toxic caffeine, herbivore-defensive volatiles, and theanine, as evidenced by the expression of whole sets of genes involved in different metabolic pathways. Both dry and fresh trichomes contain several volatiles and flavonols that were not found or at much low levels in trichome-removed leaves, including benzoic acid derivatives, lipid oxidation derivatives, and monoterpene derivatives. Trichomes also specifically expressed many disease signaling genes and various antiherbivore or antiabiotic peptides. Trichomes are one of the domestication traits in tea plants. Tea trichomes contribute to tea plant defenses and tea flavors.

Effects of the leaf functional traits of coniferous and broadleaved trees in subtropical monsoon regions on PM2.5 dry deposition velocities

Plants can intercept airborne particulate matter through deposition. Different types of plants exhibit different functional leaf traits, which can affect the dry deposition velocity (V_d). However, the most crucial leaf traits of coniferous and broadleaved trees remain unidentified. In this study, we selected 18 typical plants from the subtropical monsoon regions, where PM_2.5 (fine particulate matter with a diameter of ≤2.5 μm) concentrations are relatively high, and classified them into coniferous and broadleaved categories. Subsequently, we analyzed the relationships between V_d and leaf surface free energy (SFE), single leaf area (LA_s), surface roughness (SR), specific leaf area (SLA), epicuticular wax content (EWC), and width-to-length ratio (W/L). The results indicated that most coniferous trees exhibited a high V_d. The correlation analysis revealed that SFE, SR, LA_s, and W/L were the key factors that affected the V_d of all the tested species. SFE and SLA had the strongest influence on the V_d of broadleaved trees, whereas LA_s and SLA had the strongest effect on that of coniferous trees. Most coniferous trees had a high SLA, which can reduce water loss and hinder particle deposition. However, the stiff leaves of coniferous trees fluttered less, resulting in a larger leaf area that enhanced the capture efficiency. The leaf structure of broadleaved trees is more flexible, resulting in erratic flutter, which may impede deposition and lead to high resuspension. Coniferous and broadleaved trees may have different dominant leaf traits that affect particle deposition.

Tea plant genomics: achievements, challenges and perspectives

Tea is among the world's most widely consumed non-alcoholic beverages and possesses enormous economic, health, and cultural values. It is produced from the cured leaves of tea plants, which are important evergreen crops globally cultivated in over 50 countries. Along with recent innovations and advances in biotechnologies, great progress in tea plant genomics and genetics has been achieved, which has facilitated our understanding of the molecular mechanisms of tea quality and the evolution of the tea plant genome. In this review, we briefly summarize the achievements of the past two decades, which primarily include diverse genome and transcriptome sequencing projects, gene discovery and regulation studies, investigation of the epigenetics and noncoding RNAs, origin and domestication, phylogenetics and germplasm utilization of tea plant as well as newly developed tools/platforms. We also present perspectives and possible challenges for future functional genomic studies that will contribute to the acceleration of breeding programs in tea plants.

Influence of Multiple Factors on the Wettability and Surface Free Energy of Leaf Surface

The wettability of plant leaves directly reflects leaf hydrophilicity, which is the key factor that influences the adhesion of liquid pesticide as well as affects plant protection products (PPP) efficacy. Generally, the wettability of leaf surface is quantified by the contact angle and surface free energy (SFE), which are mainly dependent on leaf surface properties, liquid properties and other spraying parameters. Therefore, the aim of this paper was to investigate the SFE of rice and rape leaves with the variation of leaf status, leaf surface, and probe liquid as well as the influence of droplet falling height, solid surface, and PPP concentration on the wettability. The results showed that: (1) the dispersive components of SFE of rice and rape account for a large proportion which are closely related to their hydrophobicity—the abaxial of rape new leaf and the adaxial of rape old leaf are easier to wet comparing with rice and rape leaves in other statuses; (2) the increase of droplet falling height had a significant effect on improving the wettability between wax surface and adjuvant solution, while it had little improving effect on the wettability between wax surface and water; (3) the wettability of different solid surface varied greatly, and the order of wettability from good to bad is water-sensitive paper (WSP), wax, rape leaf, and rice leaf; (4) the effect of PPP concentration on the leaf surface wettability is significant, the contact angle decreased with the increase of PPP concentration, and the wettability of microemulsion is better than that of suspending agent and wettable powder. In conclusion, the SFE and wettability of crop leaf surface determine the suitable type of PPP, studying the influence of multiple factors on leaf surface wettability can provide a reliable reference for providing scientific guidance as well as improving the effective utilization of PPP.

Development of Multifunctional Avermectin Poly(succinimide) Nanoparticles to Improve Bioactivity and Transportation in Rice

Avermectin (AVM) as a nonsystemic pesticide possesses a low effective utilization rate. Studies of the multifunctional pesticide delivery system for improving biological activity are developing prosperously. In this study, multifunctional avermectin/polysuccinimide with glycine methyl ester nanoparticles (AVM-PGA) were prepared by the self-assembly process. The AVM loading capacity was up to 23.7%. After 24 h of UV irradiation, there was still about 70% of AVM remaining in PGA₄₂ nanocarriers, as opposed to less than 5% of the free-form AVM. The rising ambient pH promoted the release of AVM using an in vitro releasing test, revealing a favorable pH-responsively controlled-release property. The mortality rate of Plutella xylostella with 2.5 μg/mL of AVM content of AVM-PGA₄₂ was 96.3% after 48 h, while that of free AVM was only 51.5%. In addition, the AVM could be detected in stems and all leaves treated with AVM-PGA₄₂ nanoparticles, whereas rare AVM was detected only in treated leaves for the free-form AVM, which achieved the transportation of nanocarriers carrying AVM in rice for the first time. Furthermore, the PGA nanoparticles performed a good growth promoting effect on rice. These results show that the AVM-PGA₄₂ nanopesticides have a great potential application prospect to control the pest and improve the drug utilization efficiency on agriculture.

Chemical modification of L-glutamine to alpha-amino glutarimide on autoclaving facilitates Agrobacterium infection of host and non-host plants: A new use of a known compound

BACKGROUND

Accidental autoclaving of L-glutamine was found to facilitate the Agrobacterium infection of a non host plant like tea in an earlier study. In the present communication, we elucidate the structural changes in L-glutamine due to autoclaving and also confirm the role of heat transformed L-glutamine in Agrobacterium mediated genetic transformation of host/non host plants.

RESULTS

When autoclaved at 121°C and 15 psi for 20 or 40 min, L-glutamine was structurally modified into 5-oxo proline and 3-amino glutarimide (α-amino glutarimide), respectively. Of the two autoclaved products, only α-amino glutarimide facilitated Agrobacterium infection of a number of resistant to susceptible plants. However, the compound did not have any vir gene inducing property.

CONCLUSIONS

We report a one pot autoclave process for the synthesis of 5-oxo proline and α-amino glutarimide from L-glutamine. Xenobiotic detoxifying property of α-amino glutarimide is also proposed.

Agrobacterium-mediated genetic transformation of tea leaf explants: effects of counteracting bactericidity of leaf polyphenols without loss of bacterial virulence

Tea is one of the major crops in Asia and Africa, and its improvement by genetic modification is important for economy of many tea-producing regions. Although somatic embryos derived from cotyledon explants have been transformed with Agrobacterium, the leaves of several commercially important tea cultivars have remained recalcitrant to transformation, largely due to bactericidal effect of polyphenols that are exuded by tea leaves in vitro. Moreover, the commonly used polyphenol adsorbents and antioxidants cannot overcome this problem. Leaf explants, however, are more desirable than cotyledon-derived somatic embryos, especially when it is necessary to further improve a selected elite and also retain its superior traits. Thus, we developed a procedure for Agrobacterium-mediated genetic transformation of tea leaf explants which is based on the presence of L-glutamine in the co-cultivation medium. We then showed that the transformation process is facilitated via a protective action of L-glutamine against bactericidal effects of leaf polyphenols without affecting the bacterial virulence (vir) gene expression.