DNA Barcoding and Fertilization Strategies in Sideritis syriaca subsp. syriaca, a Local Endemic Plant of Crete with High Medicinal Value

Herein, we applied DNA barcoding for the genetic characterization of Sideritis syriaca subsp. syriaca (Lamiaceae; threatened local Cretan endemic plant) using seven molecular markers of cpDNA. Five fertilization schemes were evaluated comparatively in a pilot cultivation in Crete. Conventional inorganic fertilizers (ChFs), integrated nutrient management (INM) fertilizers, and two biostimulants were utilized (foliar and soil application). Plant growth, leaf chlorophyll fluorescence, and color were assessed and leaf content of chlorophyll, key antioxidants (carotenoids, flavonoids, phenols), and nutrients were evaluated. Fertilization schemes induced distinct differences in leaf shape, altering quality characteristics. INM-foliar and ChF-soil application promoted yield, without affecting tissue water content or biomass partitioning to inflorescences. ChF-foliar application was the most stimulatory treatment when the primary target was enhanced antioxidant contents while INM-biostimulant was the least effective one. However, when the primary target is yield, INM, especially by foliar application, and ChF, by soil application, ought to be employed. New DNA sequence datasets for the plastid regions of petB/petD, rpoC1, psbK-psbI, and atpF/atpH were deposited in the GenBank for S. syriaca subsp. syriaca while the molecular markers rbcL, trnL/trnF, and psbA/trnH were compared to those of another 15 Sideritis species retrieved from the GenBank, constructing a phylogenetic tree to show their genetic relatedness.

Plants exposed to titanium dioxide nanoparticles acquired contrasting photosynthetic and morphological strategies depending on the growing light intensity: a case study in radish

Due to the photocatalytic property of titanium dioxide (TiO₂), its application may be dependent on the growing light environment. In this study, radish plants were cultivated under four light intensities (75, 150, 300, and 600 μmol m^-2 s^-1 photosynthetic photon flux density, PPFD), and were weekly sprayed (three times in total) with TiO₂ nanoparticles at different concentrations (0, 50, and 100 μmol L^-1). Based on the obtained results, plants used two contrasting strategies depending on the growing PPFD. In the first strategy, as a result of exposure to high PPFD, plants limited their leaf area and send the biomass towards the underground parts to limit light-absorbing surface area, which was confirmed by thicker leaves (lower specific leaf area). TiO₂ further improved the allocation of biomass to the underground parts when plants were exposed to higher PPFDs. In the second strategy, plants dissipated the absorbed light energy into the heat (NPQ) to protect the photosynthetic apparatus from high energy input due to carbohydrate and carotenoid accumulation as a result of exposure to higher PPFDs or TiO₂ concentrations. TiO₂ nanoparticle application up-regulated photosynthetic functionality under low, while down-regulated it under high PPFD. The best light use efficiency was noted at 300 m^-2 s^-1 PPFD, while TiO₂ nanoparticle spray stimulated light use efficiency at 75 m^-2 s^-1 PPFD. In conclusion, TiO₂ nanoparticle spray promotes plant growth and productivity, and this response is magnified as cultivation light intensity becomes limited.

Metal nanoparticles: Phytotoxicity on tomato and effect on symbiosis with the Fusarium solani FsK strain

The effect of copper (Cu-NPs, CuO-NPs), silver (Ag-NPs) and zinc oxide (ZnO-NPs) nanoparticles (NPs) on plant growth, physiological properties of tomato plants and their symbiotic relationships with the endophytic Fusarium solani FsK strain was investigated. Fungitoxicity tests revealed that the FsK strain was significantly more sensitive to Cu-NPs and ZnO-NPs than CuO-NPs and Ag-NPs both in terms of mycelial growth and spore germination. All NPs were more toxic to FsK compared to their bulk counterparts except for AgNO₃, which was 8 to 9-fold more toxic than Ag-NPs. Apart from AgNO₃, NPs and bulk counterparts did not affect the number of germinated tomato seeds even in higher concentrations, while root length was significantly reduced in a dose dependent way in most cases. Dry weight of tomato plants was also significantly reduced upon treatment with NPs and counterparts with most pronounced effects in the cases of AgNO₃, Cu-NPs, ZnO-NPs, and ZnSO₄. Root and shoot length of grown tomato plants was also affected by treatments while differences between NPs and bulk counterparts varied. A marked oxidative stress response was recorded in all cases of NPs/bulk counterparts as indicated by increased MDA and H₂O₂ levels of treated plants. Treated plants had significantly reduced chlorophyl-a and carotenoid levels compared to the untreated control. NPs and counterparts did not affect FsK colonization of roots indicating a possible shielding effect of tomato plants once the endophyte was established inside the roots. Vice versa, a possible alleviation of CuO-NPs, ZnO-NPs, and ZnSO₄ toxicity was observed in the presence of FsK inside tomato roots in terms of plant dry weight. The results suggest that phytotoxicity of NPs in tomato treated plants should be considered before application and while both FsK and tomato are sensitive to NPs, their reciprocal benefits may extent to resistance towards these toxic agents.

Morphological Diversity, Genetic Characterization, and Phytochemical Assessment of the Cypriot Tomato Germplasm

Tomato (Solanum lycopersicum L.) is considered one of the most valuable and versatile vegetable crops globally and also serves as a significant model species for fruit developmental biology. Despite its significance, a severe genetic bottleneck and intense selection of genotypes with specific qualitative traits have resulted in the prevalence of a restricted number of (geno)types, also causing a lack of diversity across widespread cultivated types. As a result, the re-emergence of landraces as well as traditional and heirloom varieties is largely acknowledged as a countermeasure to restore phenotypic, phytochemical and genetic diversity while enriching the aroma/taste tomato palette. On those grounds, the Cypriot tomato germplasm was assessed and characterized. Ten landrace accessions were evaluated under greenhouse conditions and data were collected for 24 IPGRI discrete phenotypic traits. Grouping of accessions largely reflected the fruit shape and size; four different fruit types were recorded across accessions (flattened, heart-shaped, rounded and highly rounded). Moreover, a single run panel consisting of ten SSRs was developed and applied in order to genetically characterize 190 Cypriot genotypes and foreign heirloom varieties. Based on genetic indexes it was established that tomato landraces have a rather low level of heterogeneity and genetic variation. Finally, mineral and phytochemical analyses were conducted in order to estimate biochemical attributes (total phenolics, ascorbic acid, lycopene, β-carotene, total soluble content, titratable acidity) across genotypes; thus, ascertaining that the Cypriot panel has a high nutritional value. Due to the thermo-drought adaptation and tolerance of these genotypes, the current study serves as a roadmap for future breeding efforts in order to incorporate desirable traits or develop novel tomato lines combining resilience and alimentary value.

Blue Light Improves Photosynthetic Performance during Healing and Acclimatization of Grafted Watermelon Seedlings

To investigate the importance of light on healing and acclimatization, in the present study, grafted watermelon seedlings were exposed to darkness (D) or light, provided by blue (B), red (R), a mixture of R (68%) and B (RB), or white (W; 35% B, 49% intermediate spectra, 16% R) LEDs for 12 days. Survival ratio, root and shoot growth, soluble carbohydrate content, photosynthetic pigments content, and photosynthetic performance were evaluated. Seedling survival was not only strongly limited in D but the survived seedlings had an inferior shoot and root development, reduced chlorophyll content, and attenuated photosynthetic efficiency. RB-exposed seedlings had a less-developed root system. R-exposed seedlings showed leaf epinasty, and had the smallest leaf area, reduced chlorophyll content, and suppressed photosynthetic apparatus performance. The R-exposed seedlings contained the highest amount of soluble carbohydrate and together with D-exposed seedlings the lowest amount of chlorophyll in their scions. B-exposed seedlings showed the highest chlorophyll content and improved overall PSII photosynthetic functioning. W-exposed seedling had the largest leaf area, and closely resembled the photosynthetic properties of RB-exposed seedlings. We assume that, during healing of grafted seedlings monochromatic R light should be avoided. Instead, W and monochromatic B light may be willingly adopted due to their promoting effect on shoot, pigments content, and photosynthetic efficiency.

Structural Diversity and Highly Specific Host-Pathogen Transcriptional Regulation of Defensin Genes Is Revealed in Tomato

Defensins are small and rather ubiquitous cysteine-rich anti-microbial peptides. These proteins may act against pathogenic microorganisms either directly (by binding and disrupting membranes) or indirectly (as signaling molecules that participate in the organization of the cellular defense). Even though defensins are widespread across eukaryotes, still, extensive nucleotide and amino acid dissimilarities hamper the elucidation of their response to stimuli and mode of function. In the current study, we screened the Solanum lycopersicum genome for the identification of defensin genes, predicted the relating protein structures, and further studied their transcriptional responses to biotic (Verticillium dahliae, Meloidogyne javanica, Cucumber Mosaic Virus, and Potato Virus Y infections) and abiotic (cold stress) stimuli. Tomato defensin sequences were classified into two groups (C8 and C12). Our data indicate that the transcription of defensin coding genes primarily depends on the specific pathogen recognition patterns of V. dahliae and M. javanica. The immunodetection of plant defensin 1 protein was achieved only in the roots of plants inoculated with V. dahliae. In contrast, the almost null effects of viral infections and cold stress, and the failure to substantially induce the gene transcription suggest that these factors are probably not primarily targeted by the tomato defensin network.

The Cypriot Indigenous Grapevine Germplasm Is a Multi-Clonal Varietal Mixture

Cypriot vineyards are considered as one among the earliest niches of viticulture and a pivotal hub for the domestication and dissemination of grapevine. The millennial presence of Vitis spp. in this Eastern Mediterranean island has given rise to a plethora of biotypes that have not been adequately characterized, despite their unique attributes and stress tolerance. This ancient germplasm also has an additional value since it survived the phylloxera outbreak; hence, it possesses a large amount of genetic diversity that has been unnoticed. In order to provide useful insights to the lineage of Cypriot vineyards, a two-year-spanning collection of centennial grapevine cultivars mostly regarded to belong to four indigenous variety clusters ("Mavro", "Xynisteri", "Maratheftiko", and "Veriko") was initiated. There were 164 accessions across the broader Commandaria wine zone sampled and characterized using a universal microsatellite primer set. Genetic analysis indicated that considered indigenous Cypriot germplasm has a polyclonal structure with a high level of heterozygosity. Moreover, several lineages or unexplored varieties may exist, since a larger than considered number of discrete genotypes was discovered. Furthermore, it was established that grapevine lineages in Cyprus were shaped across eras via clonal, as well as, sexual propagation. The special attributes of the Cypriot landscape are discussed.

Stomatal behavior following mid- or long-term exposure to high relative air humidity: A review

High relative air humidity (RH ≥ 85%) is frequent in controlled environments, and not uncommon in nature. In this review, we examine the high RH effects on plants with a special focus on stomatal characters. All aspects of stomatal physiology are attenuated by elevated RH during leaf expansion (long-term) in C₃ species. These include impaired opening and closing response, as well as weak diel oscillations. Consequently, the high RH-grown plants are not only vulnerable to biotic and abiotic stress, but also undergo a deregulation between CO₂ uptake and water loss. Stomatal behavior of a single leaf is determined by the local microclimate during expansion, and may be different than the remaining leaves of the same plant. No effect of high RH is apparent in C₄ and CAM species, while the same is expected for species with hydropassive stomatal closure. Formation of bigger stomata with larger pores is a universal response to high RH during leaf expansion, whereas the effect on stomatal density appears to be species- and leaf side-specific. Compelling evidence suggests that ABA mediates the high RH-induced stomatal malfunction, as well as the stomatal size increase. Although high RH stimulates leaf ethylene evolution, it remains elusive whether or not this contributes to stomatal malfunction. Most species lose stomatal function following mid-term (4-7 d) exposure to high RH following leaf expansion. Consequently, the regulatory role of ambient humidity on stomatal functionality is not limited to the period of leaf expansion, but holds throughout the leaf life span.

The Role of Proteases in Determining Stomatal Development and Tuning Pore Aperture: A Review

Plant proteases, the proteolytic enzymes that catalyze protein breakdown and recycling, play an essential role in a variety of biological processes including stomatal development and distribution, as well as, systemic stress responses. In this review, we summarize what is known about the participation of proteases in both stomatal organogenesis and on the stomatal pore aperture tuning, with particular emphasis on their involvement in numerous signaling pathways triggered by abiotic and biotic stressors. There is a compelling body of evidence demonstrating that several proteases are directly or indirectly implicated in the process of stomatal development, affecting stomatal index, density, spacing, as well as, size. In addition, proteases are reported to be involved in a transient adjustment of stomatal aperture, thus orchestrating gas exchange. Consequently, the proteases-mediated regulation of stomatal movements considerably affects plants' ability to cope not only with abiotic stressors, but also to perceive and respond to biotic stimuli. Even though the determining role of proteases on stomatal development and functioning is just beginning to unfold, our understanding of the underlying processes and cellular mechanisms still remains far from being completed.

Polyamine homeostasis in tomato biotic/abiotic stress cross-tolerance

Adverse conditions and biotic strain can lead to significant losses and impose limitations on plant yield. Polyamines (PAs) serve as regulatory molecules for both abiotic/biotic stress responses and cell protection in unfavourable environments. In this work, the transcription pattern of 24 genes orchestrating PA metabolism was investigated in Cucumber Mosaic Virus or Potato Virus Y infected and cold stressed tomato plants. Expression analysis revealed a differential/pleiotropic pattern of gene regulation in PA homeostasis upon biotic, abiotic or combined stress stimuli, thus revealing a discrete response specific to diverse stimuli: (i) biotic stress-influenced genes, (ii) abiotic stress-influenced genes, and (iii) concurrent biotic/abiotic stress-regulated genes. The results support different roles for PAs against abiotic and biotic stress. The expression of several genes, significantly induced under cold stress conditions, is mitigated by a previous viral infection, indicating a possible priming-like mechanism in tomato plants pointing to crosstalk among stress signalling. Several genes and resulting enzymes of PA catabolism were stimulated upon viral infection. Hence, we suggest that PA catabolism resulting in elevated H₂O₂ levels could mediate defence against viral infection. However, after chilling, the activities of enzymes implicated in PA catabolism remained relatively stable or slightly reduced. This correlates to an increase in free PA content, designating a per se protective role of these compounds against abiotic stress.

Changes in sugar metabolism associated to stem bark thickening partially assist young tissues of Eriobotrya japonica seedlings under boron stress

Boron (B) toxicity frequently affects plant performances and productivity, especially in arid and semi-arid environments. In this experiment, loquat seedlings were subjected to 25 μM (control) or 400 μM B (B excess) to test the hypothesis that (i) B alters sugar/polyol metabolism in polyol-producing tree species as loquat and (ii) changes of leaf and stem anatomy assist young tissues against toxic effect of B. Gas exchange was monitored from the beginning of the experiment (FBE) till one week after the first visible symptoms of B toxicity appeared in the upper part of the stems (147 d FBE). At 147 FBE, plant biometric parameters and pattern of B accumulation, leaf and stem anatomy, chlorophyll a fluorescence kinetics as well as biochemical measurements were assessed in top (asymptomatic) leaves and upper stem bark. Boron accumulated principally (in the row) in top leaves > top bark > top wood in B-stressed plants, but no changes in allocation pattern were found between controls and B-stressed plants. Excess B promoted the increase in the spongy layer of top leaves and caused the development of cork and numerous collenchyma cells with increased cell wall thickness. This mechanism, which has never been described before, can be considered an attempt to store excessive B in tissues where B ions are less harmful. The accumulation of sorbitol (B-complexing polyol) in top leaves and stem bark can be considered as a further attempt to detoxify B excess. However, B toxicity drastically affects the photosynthetic rate of top leaves, mainly due to non-stomatal limitations, i.e., reduction of ambient CO₂ use efficiency and of photosystem II (PSII) efficiency, modification of the partitioning excess energy dissipation in PSII, thus leading to an increased level of lipid peroxidation. Our results suggest that changes in sugar metabolism associated with leaf and stem bark thickening partially assist (but not totally preserve) young tissues of loquat plants under B stress.

Spatial and temporal distribution of genes involved in polyamine metabolism during tomato fruit development

Polyamines are organic compounds involved in various biological roles in plants, including cell growth and organ development. In the present study, the expression profile, the accumulation of free polyamines and the transcript localisation of the genes involved in Put metabolism, such as Ornithine decarboxylase (ODC), Arginine decarboxylase (ADC) and copper containing Amine oxidase (CuAO), were examined during Solanum lycopersicum cv. Chiou fruit development and maturation. Moreover, the expression of genes coding for enzymes involved in higher polyamine metabolism, including Spermidine synthase (SPDS), Spermine synthase (SPMS), S-adenosylmethionine decarboxylase (SAMDC) and Polyamine oxidase (PAO), were studied. Most genes participating in PAs biosynthesis and metabolism exhibited an increased accumulation of transcripts at the early stages of fruit development. In contrast, CuAO and SPMS were mostly expressed later, during the development stages of the fruits where a massive increase in fruit volume occurs, while the SPDS1 gene exhibited a rather constant expression with a peak at the red ripe stage. Although Put, Spd and Spm were all exhibited decreasing levels in developing immature fruits, Put levels maxed late during fruit ripening. In contrast to Put both Spd and Spm levels continue to decrease gradually until full ripening. It is worth noticing that in situ RNA-RNA hybridisation is reported for the first time in tomato fruits. The localisation of ADC2, ODC1 and CuAO gene transcripts at tissues such as the locular parenchyma and the vascular bundles fruits, supports the theory that all genes involved in Put biosynthesis and catabolism are mostly expressed in fast growing tissues. The relatively high expression levels of CuAO at the ImG4 stage of fruit development (fruits with a diameter of 3 cm), mature green and breaker stages could possibly be attributed to the implication of polyamines in physiological processes taking place during fruit ripening.

Gene transcript accumulation and in situ mRNA hybridization of two putative glutamate dehydrogenase genes in etiolated Glycine max seedlings

Glutamate dehydrogenase (EC 1.4.1.2) is a multimeric enzyme that catalyzes the reversible amination of α-ketoglutarate to form glutamate. We characterized cDNA clones of two Glycine max sequences, GmGDH1 and GmGDH2, that code for putative α- and β-subunits, respectively, of the NADH dependent enzyme. Temporal and spatial gene transcript accumulation studies using semiquantitative RT-PCR and in situ hybridization have shown an overlapping gene transcript accumulation pattern with differences in relative gene transcript accumulation in the organs examined. Detection of NADH-dependent glutamate dehydrogenase activity in situ using a histochemical method showed concordance with the spatial gene transcript accumulation patterns. Our findings suggest that although the two gene transcripts are co-localized in roots of etiolated soybean seedlings, the ratio of the two subunits of the active holoenzyme may vary among tissues.

Low temperature storage affects the ascorbic acid metabolism of cherry tomato fruits

Tomato fruits are an important source of l-Ascorbic acid, which is an essential compound of human diet. The effect of the widespread practice of cold storing (5-10 °C) tomato fruits was monitored to determine its impact on the concentration and redox status of l-Ascorbic acid. Total l-Ascorbic acid levels were well maintained in both attached fruits and cold treated fruits, while in other treatments its levels were considerably reduced. However, low temperature storage conditions enhanced the expression of most genes coding for enzymes involved in l-Ascorbic acid biosynthesis and redox reactions. The findings suggest that the transcriptional up-regulation under chilling stress conditions of most genes coding for l-Ascorbic acid biosynthetic genes galactono-1,4-lactone dehydrogenase, GDP-d-mannose 3,5-epimerase but also for the isoenzymes of ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase enzyme, glutathione reductase that are strongly correlated to the l-Ascorbic redox status. Moreover, fruits stored at 10 °C exhibited higher levels of transcript accumulation of MDHAR2, DHAR1, DHAR2, GR1 and GR2 genes, pointing to a better ability to manage chilling stress in comparison to fruits stored at 5 °C.