Coordination of leaf hydraulic, anatomical, and economical traits in tomato seedlings acclimation to long-term drought

Background Leaf hydraulic and economics traits are critical for balancing plant water and CO2 exchange, and their relationship has been widely studied. Leaf anatomical traits determine the efficiency of CO2 diffusion within mesophyll structure. However, it remains unclear whether leaf anatomical traits are associated with leaf hydraulic and economics traits acclimation to long-term drought. Results To address this knowledge gap, eight hydraulic traits, including stomatal and venation structures, four economics traits, including leaf dry mass per area (LMA) and the ratio between palisade and spongy mesophyll thickness (PT/ST), and four anatomical traits related to CO2 diffusion were measured in tomato seedlings under the long-term drought conditions. Redundancy analysis indicated that the long-term drought decreased stomatal conductance (gs) mainly due to a synchronized reduction in hydraulic structure such as leaf hydraulic conductance (Kleaf) and major vein width. Simultaneously, stomatal aperture on the adaxial surface and minor vein density (VDminor) also contributed a lot to this reduction. The decreases in mesophyll thickness (Tmes) and chlorophyll surface area exposed to leaf intercellular air spaces (Sc/S) were primarily responsible for the decline of mesophyll conductance (gm) thereby affecting photosynthesis. Drought increased leaf density (LD) thus limited CO2 diffusion. In addition, LMA may not be important in regulating gm in tomato under drought. Principal component analysis revealed that main anatomical traits such as Tmes and Sc/S were positively correlated to Kleaf, VDminor and leaf thickness (LT), while negatively associated with PT/ST. Conclusions These findings indicated that leaf anatomy plays an important role in maintaining the balance between water supply and CO2 diffusion responses to drought. There was a strong coordination between leaf hydraulic, anatomical, and economical traits in tomato seedlings acclimation to long-term drought.

The implication of leaf anatomical structure for the selective breeding of lilacs

The cultivars of the common lilac (Syringa vulgaris) grown in the south of the Russian Far East are not always winter-hardy and are often damaged by fungal diseases due to a very humid climate. A promising trend in the selective breeding of lilacs in Russia is the creation of new breeding material based on the gene pool of the broadleaf lilac (S. oblata) and its hybrids in order to introduce valuable adaptive traits into cultivars. The present work aimed to identify the traits of leaf anatomy in species and cultivars of Syringa resistant and susceptible to Pseudocercospora lilacis, the causative agent of brown leaf spot disease. The study was carried out on the living collection of the Botanical Garden-Institute, Far Eastern Branch, Russian Academy of Sciences (Vladivostok). The leaf anatomical structure of two Syringa species showing different degrees of resistance to P. lilacis in the monsoon climate of the Far East (resistant S. oblata and weakly resistant S. vulgaris, and also their hybrid cultivars) has been analyzed. The differences between species, subspecies, and cultivars are quantitative: they differ in the number of spongy mesophyll layers, the cell height in the first layer of palisade mesophyll, the cell height in the upper and lower epidermises, and the thickness of both mesophylls. The interspecific hybrids resistant or weakly resistant to P. lilacis (brown leaf spot disease) mainly retain the leaf anatomy structure of the maternal plant. One of the traits determining the resistance of hybrid lilac cultivars is an increased number of spongy mesophyll layers in the leaf blade. The study of leaf anatomy has shown that the four-layered spongy mesophyll leaf parenchyma correlates with the resistance of lilacs from the subsection Euvulgaris to P. lilacis. In S. oblata, this trait is inherited down the maternal line. To establish lilac cultivars resistant to fungal diseases, it is advisable to cross the two species (S. oblata and S. vulgaris) or their cultivars using one of S. oblata subspecies as a maternal plant.

Comparative morphoanatomical studies of south eastern Nigerian representatives of Oldenlandia L. (Rubiaceae)

Leaf and stem anatomical structure of the four Oldenlandia L. (O. affinis (Roem. & Schult.) DC., O. corymbosa L., O. herbacea (Linn.) Roxb., and O. lancifolia (Schumach) DC.) from some parts viz. Ogbokor (Edo State), Obiga-Asa (Abia State), IITA staion Onne (Rivers State), and Agricultural farm Uniport (Rivers State) Nigeria were examined by light microscopy. The epidermal cells are pentagonal to polygonal with straight, curved or wavy anticlinal walls, and paracytic stomata. All the species have dorsiventral leaf with the leaf vein vascular bundles embedded in the spongy mesophyll. The midribs vascular bundles form an arc enclosed by parenchymatous endodermal cells. O. herabcea is amphistomatic while the other species are hypostomatic. Raphide bundles were seen only in the lamina of O. corymbosa. Tuft hair is absent in O. herbacea but occurred on the adaxial leaf surfaces of O. affinis, O. corymbosa, and O. diffusa. The stem of O. diffusa is terete while other species have quadrangular stem. Papillae occurred on the adaxial epidermis of O. affinis and O. corymbosa. The stem pith thickness (PT)/cortical thickness (ET) ratio varied among the species. Notable diagnostic features in these species include the PT/ET ratio, layers of cortex in the stem, occurrence of tuft hairs on the leaf veins and surface, presence or absence of raphides and papillose, layer of abaxial and adaxial cortex in the midrib, and amphistomatatic or hypostomatic leaf.

Transcription factor WRKY22 regulates canker susceptibility in sweet orange (Citrus sinensis Osbeck) by enhancing cell enlargement and CsLOB1 expression

Pathological hypertrophy (cell enlargement) plays an important role in the development of citrus canker, but its regulators are largely unknown. Although WRKY22 is known to be involved in pathogen-triggered immunity and positively regulates resistance to bacterial pathogens in Arabidopsis, rice and pepper, the CRISPR/Cas9-mediated partial knockout of CsWRKY22 improves resistance to Xanthomonas citri subsp. citri (Xcc) in Wanjincheng orange (Citrus sinensis Osbeck). Here, we demonstrate that CsWRKY22 is a nucleus-localized transcriptional activator. CsWRKY22-overexpressing plants exhibited dwarf phenotypes that had wrinkled and thickened leaves and were more sensitive to Xcc, whereas CsWRKY22-silenced plants showed no visible phenotype changes and were more resistant to Xcc. Microscopic observations revealed that the overexpression of CsWRKY22 increased cell size in the spongy mesophyll. Transcriptome analysis showed that cell growth-related pathways, such as the auxin and brassinosteroid hormonal signaling and cell wall organization and biogenesis pathways, were significantly upregulated upon CsWRKY22 overexpression. Interestingly, CsWRKY22 activated the expression of CsLOB1, which is a key gene regulating susceptibility to citrus canker. We further confirmed that CsWRKY22 bound directly to the W-boxes just upstream of the transcription start site of CsLOB1 in vivo and in vitro. We conclude that CsWRKY22 enhances susceptibility to citrus canker by promoting host hypertrophy and CsLOB1 expression. Thus, our study provides new insights into the mechanism regulating pathological hypertrophy and the function of WRKY22 in citrus.

Maximum CO 2 diffusion inside leaves is limited by the scaling of cell size and genome size

Maintaining high rates of photosynthesis in leaves requires efficient movement of CO 2 from the atmosphere to the mesophyll cells inside the leaf where CO 2 is converted into sugar. CO 2 diffusion inside the leaf depends directly on the structure of the mesophyll cells and their surrounding airspace, which have been difficult to characterize because of their inherently three-dimensional organization. Yet faster CO 2 diffusion inside the leaf was probably critical in elevating rates of photosynthesis that occurred among angiosperm lineages. Here we characterize the three-dimensional surface area of the leaf mesophyll across vascular plants. We show that genome size determines the sizes and packing densities of cells in all leaf tissues and that smaller cells enable more mesophyll surface area to be packed into the leaf volume, facilitating higher CO 2 diffusion. Measurements and modelling revealed that the spongy mesophyll layer better facilitates gaseous phase diffusion while the palisade mesophyll layer better facilitates liquid-phase diffusion. Our results demonstrate that genome downsizing among the angiosperms was critical to restructuring the entire pathway of CO 2 diffusion into and through the leaf, maintaining high rates of CO 2 supply to the leaf mesophyll despite declining atmospheric CO 2 levels during the Cretaceous.

PRELIMINARY STUDIES RELATED TO MICROSCOPY AND THE SEDEM EXPERT SYSTEM PROFILE ON FREEZED-DRIED EXTRACT OF LYTHRI HERBA

"The floral tips of the plant species Lythrum salicaria L. represent a rich source of total polyphenols, among which with the largest share we mention tannins, and this is why this plant material has a standardized monograph in the European Pharmacopoeia 10.0th edition. According to the literature accessed so far, the plant material has antioxidant, anti-inflammatory, hemostatic, antibacterial and antifungal properties, along with modulatory action on carbohydrate metabolism. Powder microscopic examination is an important step in establishing the identity of the plant species used, highlighting elements specific to the aerial part such as spiral vessels of the stem, fragments of the spongy mesophyll with calcium oxalate clusters cells and anomocytic stomata. The application of the SeDeM method on dried plant extracts represents an innovative trend in pharmaceutical technology and contributes to the collection of data in a structured and standardized form. In this paper, the functions and applications of the SeDeM expert system are illustrated upon the freeze-dried extract of Lythri herba for the purpose of easier identification and standardization. Future applications may include obtaining chewable gums or tablets by direct compression."

Leaf blade anatomy of the rare Siberian flora species Mertensia sibirica (L.) G. Don fil. (Boraginaceae)

The authors present the findings of a leaf blade anatomy study for the rare relict Siberian flora species Mertensia sibirica (L.) G. Don fil. (Boraginaceae). They collected samples for the study from natural habitats in Chita Region (Chikoy Range) and then planted them in the introduction area of the Siberian Botanic Garden (Tomsk) located in the southern taiga subzone of Western Siberia. The parameters of the photosynthetic and stomatal complex of M. sibirica were studied for the first time. It was found out that the rosette and cauline leaves of the species under study are hypostomatous, with an anomocytic stomatal complex. The epidermis is single-layer. On average, the adaxial epidermis has larger cells vs. abaxial epidermis. The leaf mesophyll is 242.90–369.90 µm thick, dorsiventral. The adaxial side of the leaf comprises glandular trichomes surrounded with pronounced rosettes of cells in the base part. The cauline leaf significantly differs from the rosette leaf in finer cells of its adaxial and abaxial epidermis (and, consequently, their larger number per 1 mm2), while the adaxial epidermal cells are thicker, and in a larger number of stomata in the abaxial epidermis. The palisade mesophyll in the cauline leaf is more developed vs. the rosette leaf, while the cells are longer and the palisade/spongy mesophyll ratio is higher. The rosette leaves have a more developed system of vascular tissues vs. cauline ones, as they play the main role in providing plants with water and nutrients. The contribution of the cauline leaf palisade mesophyll to the photosynthetic potential of M. sibirica is higher vs. that of the rosette leaf (the ratio between palisade and spongy mesophyll is 0.45 vs. 0.36, respectively), which characterizes the cauline leaf as more heliophytic. The stomatal complex and mesophyll parameters under study are primarily characterized by low variance. As for dermal tissue parameters, medium variance is typical of the thickness and size of the abaxial and adaxial epidermal cells. Coefficients of variation for the cells of the upper mesophyll layer (CV=31.2–41.6%) and the number of stomata on the lower epidermis of the rosette leaf (CV=21.5%) demonstrate medium and high variance. A very high coefficient of variation (116.2–174.0) is registered for the adaxial epidermis parameter characterizing the density of trichomes per 1 mm2. The study results were used to develop an optimal M. sibirica cultivation regime under conditions of introduction in the southern taiga subzone of Western Siberia.

Peculiarities of the genus Clematis L. plants water regime

Clematis is a medicinal plant and a promising culture for introduction into urbophytocenoses. In order to ensure optimal growing conditions, it is necessary to take into account the ecological needs of plants, a key place among which is water supply. The experiments were carried out with cultivars and species of the genus Clematis: Clematis alpina ‘Pamela Jackman’, C. macropetala ‘Maidwell Hall’, C. integrifolia ‘Aljonushka’, C. ispahanica ‘Zvezdograd’, C. fargesii ‘Paul Farges’, C. taxensis ‘Princess Diana’, C. tibetana, C. viticella and C. heracleifolia. Ecological peculiarities of studied plants cause differences in the anatomical tissues structure and dynamic of physiological processes. The lowest content of dry matter in the leaves was found in C. alpina ‘Pamela Jackman’ (16,3 %) and C. macropetala ‘Maidwell Hall’ (18,3), indicating their potentially lowest drought resistance. The highest value of this index was identified in C. heracleifolia (27.5 %) and C. integrifolia ‘Aljonushka’ (23.4 %), that characterizes them as the most drought resistant among studied plants. A function describing the process of cutted leaves wilting at the temperature +60 °C was defined: f(x) = y0 + ae–bx. A significant correlation was found between the parameter y0 and the dry mass (0.99), water content (0.86) in the leaves and their weight before drying (0.91); the parameter a and the mass index of leaves before wilting (0.99), the water content (1.00) and dry matter (0.83), as well as the density (0.86) and the area of stomatas (0.81) on the adaxial surface of leaves. Parameter b correlated with the values of dry mass (—0.75), its fraction in the total leaf mass (—0.84), the water fraction (0.83) and the width of spongy mesophyll cells (0.76). The peculiarities of anatomical structure and dynamic of leaves water loss process among investigated plants indicate the difference in their potential drought resistance. Obtained results allow to choose the optimal conditions for growing of investigated plants of the genus Clematis and planning additional care measures.

Comparative analysis of anatomical structure of wood plant leaf under exposure to volatile organic compounds

Industrial enterprises of thermal power engineering, fuel, chemical and petrochemical industry, mechanical engineering, non-ferrous metallurgy are sources of volatile organic compounds, the emissions of which can now reach a significant amount due to changes in technological processes. Studying the effect of volatile organic compounds on changes in anatomical parameters of a plant sheet is a little-studied aspect compared to exposure to oxides of nitrogen, carbon, sulfur, ammonia, heavy metals. The aim of the work was therefore to study the anatomical features of the tree leaf as adaptive features under the influence of emissions from industrial plants containing selected volatile organic compounds. Time preparations of the cross section of the leaf were used for anatomical studies. The thickness of the epidermis, the mesophyll, the number of upper and lower epideric cells, the number of wellheads and their width, the size of the conductive beam, the palisadity coefficient (the ratio of the thickness of the columnar mesophyll to the sum of the thickness of the columnar and spongy mesophyll) and the oral index (the ratio of the number of wellheads to the total number of epidermal cells). Impressions of the upper and lower epidermis were made with colorless varnish. As objects for studying the features of the anatomy of the leaf were chosen the leaves of a number of species of wood plants, which are among the most common near the industrial enterprises of the city of Gomel: drooping birch Betula pendula Roth., maple holly Acer platanoides L. Leaf samples were taken in the zone of influence of emissions of industrial enterprises containing xylenes and butylacetate (JSC «Gomel plant leaves and normals»), as well as benz(a)pyrene (heat and power plant). As a result of the studies, the cells of the columnar mesophyll in the birch leaves were found to have the greatest sensitivity to organic toxicants (xylenes and butylacetate) at the end of the vegetation compared to the maple holly leaves and the parameters of the spongy mesophyll. Drooping birch was characterized as the species in which sclerenchyma in the region of the conducting bundle under technogenic conditions was the thinnest, especially at the beginning of the growing period. Also in birch, when growing around industrial plants, there was a decrease in the number of cells of the upper and lower epidermis compared to control in most variants, especially the upper epidermis in samples exposed to xylenes and butylacetate at the beginning of the growing period. Maple holly showed a more intense decrease in the number of oysters and the value of the oral index compared to control than birch. When exposed to the benz(a)pyrene of heat and power plant emissions, both wood plant species studied showed an increase in mesophyll palisadity coefficient during the most intensive sheet plate formation processes. The conducting bundles of the studied wood plants were characterized by a decrease in the largest diameter when growing under technogenic conditions, most intensively in may at the maple holly. In general, the study of anatomical features of leaf plates of wood plants when growing in the area of exposure to volatile organic compounds of industrial emissions is great interest in terms of understanding the adaptive mechanisms of plants to stress conditions. The seasonal dynamics of changes in anatomical parameters in the birch leaf was characterized by a decrease in their values in most cases in september compared to may in the territory of the industrial enterprises under consideration. In maple holly approximately in equal amounts there was both a decrease and an increase in anatomical parameters between may and september.