Search

Key message: The proteomic analysis of PMeV-complex-infected C. papaya unveiled proteins undergoing modulation during the plant's development. The infection notably impacted processes related to photosynthesis and cell wall dynamics. The development of Papaya Sticky Disease (PSD), caused by the papaya meleira virus complex (PMeV-complex), occurs only after the juvenile/adult transition of Carica papaya plants, indicating the presence of tolerance mechanisms during the juvenile development phase. In this study, we quantified 1609 leaf proteins of C. papaya using a label-free strategy. A total of 345 differentially accumulated proteins were identified—38 at 3 months (juvenile), 130 at 4 months (juvenile/adult transition), 160 at 7 months (fruit development), and 17 at 9 months (fruit harvesting)—indicating modulation of biological processes at each developmental phase, primarily related to photosynthesis and cell wall remodeling. Infected 3- and 4-mpg C. papaya exhibited an accumulation of photosynthetic proteins, and chlorophyll fluorescence results suggested enhanced energy flux efficiency in photosystems II and I in these plants. Additionally, 3 and 4-mpg plants showed a reduction in cell wall-degrading enzymes, followed by an accumulation of proteins involved in the synthesis of wall precursors during the 7 and 9-mpg phases. These findings, along with ultrastructural data on laticifers, indicate that C. papaya struggles to maintain the integrity of laticifer walls, ultimately failing to do so after the 4-mpg phase, leading to latex exudation. This supports initiatives for the genetic improvement of C. papaya to enhance resistance against the PMeV-complex. [ABSTRACT FROM AUTHOR]

Fibraurea tinctoria Lour. (Menispermaceae) is a medicinal plant used by many local tribes in Indonesia and other countries. This species has pharmacological potential, such as antimalaria, antibacterial, antitumor, antioxidant, anticancer, antidiabetic, anti‐inflammatory, and hepato‐protector. However, the secretory structures and sites of secondary metabolite accumulation still need to be studied. This study aimed to explore the secretory structures and reveal the accumulation sites of the main classes of secondary metabolites in the root, stem, and leaves of F. tinctoria. Histochemical analysis using various specific reagents was performed on freehand sections of the fresh organs to detect alkaloids, phenolics, terpenoids, and lipophilic compounds. Observations of secretory structures were carried out using light microscopy. The result showed that idioblast was the predominant secretory structure in the plant organs and contained all the chemical groups investigated, while laticifer accumulated alkaloids were found only in the stem. Some secondary metabolites were localized in the xylem, intercellular space, and cuticle layer. Crystals were observed in the root, stem, and leaf of this species. These results might be helpful as guide information for extracting the particular plant parts to obtain the desired secondary metabolites. It suggested that leaves are a potential alternative source of medicinal raw material of this species, in addition to the stem. Research Highlights: The first study on secretory structures of Fibraurea tinctoria.Secondary metabolites in F. tinctoria organs accumulate in specialized and unspecialized structures.The idioblast is the primary secretory structure in the organs of F. tinctoria spreading over the root, stem, and leaves. [ABSTRACT FROM AUTHOR]

Summary: In Catharanthus roseus, monoterpenoid indole alkaloids (MIAs) are produced through the cooperation of four cell types, with final products accumulating in specialized cells known as idioblasts and laticifers. To explore the relationship between cellular differentiation and cell type‐specific MIA metabolism, we analyzed the expression of MIA biosynthesis in germinating seeds.Embryos from immature and mature seeds were observed via stereomicroscopy, fluorescence microscopy, and electron microscopy. Time‐series MIA and iridoid quantification, along with transcriptome analysis, were conducted to determine the initiation of MIA biosynthesis. In addition, the localization of MIAs was examined using alkaloid staining and imaging mass spectrometry (IMS).Laticifers were present in embryos before seed maturation. MIA biosynthesis commenced 12 h after germination. MIAs accumulated in laticifers of embryos following seed germination, and MIA metabolism is induced after germination in a tissue‐specific manner.These findings suggest that cellular morphological differentiation precedes metabolic differentiation. Considering the well‐known toxicity and defense role of MIAs in matured plants, MIAs may be an important defense strategy already in the delicate developmental phase of seed germination, and biosynthesis and accumulation of MIAs may require the tissue and cellular differentiation. [ABSTRACT FROM AUTHOR]

Gall formation impacts the development of plant species by altering the structure and mobilization of reserves, and the functional and physiological patterns of the host organ. The current study aimed to evaluate the impact generated by the Neolithus fasciatus galling insect (Hemiptera: Triozidae) in Sapium glandulosum leaves (Euphorbiaceae) at the cytological, histological, histochemical, and biochemical levels. Non-galled leaves and galls in the young, mature, and senescent stages were evaluated. The non-galled leaf has a uniseriate epidermis, stomata only on the abaxial side, a dorsiventral mesophyll, and parenchyma cells with thin primary walls containing chloroplasts with plastoglobules. The gall has a parenchymatous compartmentalized cortex. The young and mature galls already have a dense cytoplasm, especially in the inner cells of the cortex, with chloroplasts, mitochondria, Golgi complex, and large and evident nuclei. In senescent galls, there are signs of organelle degradation and cell digestion. Carbohydrates occur in greater amounts in the mature gall, mainly in the starch grain form, while proteins and lipids predominate in non-galled leaves. Secondary metabolites occur mainly in the young gall and may be related to its protection and to the signaling of its development. Sapium glandulosum galls have histological and cytological compartmentalization of the cortex with a large amount of carbohydrates, which supply energy to maintain the development of the structure. [ABSTRACT FROM AUTHOR]

Cannabaceae species garner attention in plant research due to their diverse secretory structures and pharmacological potential associated with the production of secondary metabolites. This study aims to update our understanding of the secretory system in Hops (Humulus lupulus L.), an economically important species especially known for its usage in beer production. For that, stems, leaves, roots, and inflorescences were collected and processed for external morphology, anatomical, histochemical, ultrastructural and cytochemical analyses of the secretory sites. Our findings reveal three types of secretory structures comprising the secretory machinery of Hops: laticifer, phenolic idioblasts and glandular trichomes. The laticifer system is articulated, anastomosing and unbranched, traversing all plant organs, except the roots. Phenolic idioblasts are widely dispersed throughout the leaves, roots and floral parts of the species. Glandular trichomes appear as two distinct morphological types: capitate (spherical head) and peltate (radial head) and are found mainly in foliar and floral parts. The often-mixed chemical composition in the secretory sites serves to shield the plant from excessive UVB radiation, elevated temperatures, and damage inflicted by herbivorous animals or pathogenic microorganisms. Besides the exudate from peltate glandular trichomes (lupulin glands), latex and idioblast content are also likely contributors to the pharmacological properties of different Hop varieties, given their extensive presence in the plant body. [ABSTRACT FROM AUTHOR]

Herbivorous insects frequently exhibit sexual dimorphism in body size and a variety of other traits. Such differences often lead to distinct behaviors, which may present themselves in insect responses to conspecifics, plant defenses, and feeding. Based on a previous study of a congeneric species, we hypothesized that sexual dimorphism may yield differences in how the host-specific red milkweed beetle Tetraopes tetrophthalmus (Coleoptera: Cerambycidae) deactivates milkweed defenses, a behavior in which beetles cut latex-delivering veins prior to feeding. We also predicted that beetles would display differences in their subsequent feeding patterns and attraction of conspecifics. Although beetles were size dimorphic (females were larger than males), we did not find consistent differences in the rates of vein cutting or initiation of feeding between males and females. Females did, however, cut more milkweed veins per leaf, and attracted more conspecifics than males. Sex differences in size and other traits were thus associated with differential attraction, but not strongly associated with the overall deactivation of plant defense. [ABSTRACT FROM AUTHOR]

At least 20,000 plant species produce latex, a capacity that appears to have evolved independently on numerous occasions. With a few exceptions, latex is stored under pressure in specialized cells known as laticifers and is exuded upon injury, leading to the assumption that it has a role in securing the plant after mechanical injury. In addition, a defensive effect against insect herbivores and fungal infections has been well established. Latex also appears to have effects on viruses, and laticifers are a hostile environment for virus colonization. Only one example of successful colonization has been reported: papaya meleira virus (PMeV) and papaya meleira virus 2 (PMeV2) in Carica papaya. In this review, a summary of studies that support both the pro- and anti-viral effects of plant latex compounds is provided. The latex components represent a promising natural source for the discovery of new pro- and anti-viral molecules in the fields of agriculture and medicine. [ABSTRACT FROM AUTHOR]

A novel combination of widely used commercial histochemical reagents, Mayer’s mucicarmine and Lugol’s reagent, was applied to survey anatomical analysis of various plant organs: Euphorbia splendens stem, Hibiscus rosa - sinensis petiole, Homalocladium platycladum stem base, Phalaenopsis sp. aerial root, Rhipsalis sp. stem, Schoenoplectus lacustris stem base, and Urtica dioica stem primary structure. The staining resulted in red coloration of non-lignified cell walls and mucilage, yellow coloration of lignified cell walls and protein-rich components of the protoplasts, and dark staining of starch. The method was found to be cheap, easy, fast, and informative, and thus widely applicable in both teaching and research.

Cannabaceae species garner attention in plant research due to their diverse secretory structures and pharmacological potential associated with the production of secondary metabolites. This study aims to update our understanding of the secretory system in Hops (Humulus lupulus L.), an economically important species especially known for its usage in beer production. For that, stems, leaves, roots, and inflorescences were collected and processed for external morphology, anatomical, histochemical, ultrastructural and cytochemical analyses of the secretory sites. Our findings reveal three types of secretory structures comprising the secretory machinery of Hops: laticifer, phenolic idioblasts and glandular trichomes. The laticifer system is articulated, anastomosing and unbranched, traversing all plant organs, except the roots. Phenolic idioblasts are widely dispersed throughout the leaves, roots and floral parts of the species. Glandular trichomes appear as two distinct morphological types: capitate (spherical head) and peltate (radial head) and are found mainly in foliar and floral parts. The often-mixed chemical composition in the secretory sites serves to shield the plant from excessive UVB radiation, elevated temperatures, and damage inflicted by herbivorous animals or pathogenic microorganisms. Besides the exudate from peltate glandular trichomes (lupulin glands), latex and idioblast content are also likely contributors to the pharmacological properties of different Hop varieties, given their extensive presence in the plant body.

At least 20,000 plant species produce latex, a capacity that appears to have evolved independently on numerous occasions. With a few exceptions, latex is stored under pressure in specialized cells known as laticifers and is exuded upon injury, leading to the assumption that it has a role in securing the plant after mechanical injury. In addition, a defensive effect against insect herbivores and fungal infections has been well established. Latex also appears to have effects on viruses, and laticifers are a hostile environment for virus colonization. Only one example of successful colonization has been reported: papaya meleira virus (PMeV) and papaya meleira virus 2 (PMeV2) in Carica papaya. In this review, a summary of studies that support both the pro- and anti-viral effects of plant latex compounds is provided. The latex components represent a promising natural source for the discovery of new pro- and anti-viral molecules in the fields of agriculture and medicine.

Calotropis procera cysteine peptidases (CpCPs) have been used for reducing cow's milk allergenicity or as rennet in cheesemaking. Due to their residual presence in food products, the present study evaluated, for the first time, different protocols for their immobilization on different supports. Although the yield of immobilization on sulfopropyl-agarose (99%, at pH 7.0) was better than when using DEAE- and MANAE-agarose (40% and 15%, respectively), the derivatives had low recovered activity (4%). On the other hand, MANAE-agarose at pH 10.0 (200 mM buffer) exhibited the highest recovered enzymatic activity (~23%). Regarding the covalent immobilization, the peptidases immobilized on glyoxyl-agarose (glyoxyl-CpCPs) showed broader pH stability (pH 3.0–10.0), 60-fold more stable at 60 °C, and retained 70% of their initial activities after five reaction cycles, even though the immobilization has induced some structural changes analyzed by Fourier-Transform Infrared (FTIR) spectroscopy as well as altered some of enzyme kinetic parameters (V max , K m , K cat , and catalytic efficiency). In addition, this biocatalyst (glyoxyl-CpCPs) hydrolyzed the major cow's milk allergens (whey proteins) to a greater extent (65%) than the soluble enzymes (8%) and a commercial hypoallergenic formula (50%). [Display omitted] • Calotropis procera cysteine peptidases (CpCPs) were immobilized on different supports. • Glyoxyl-agarose was the best among all ionic and covalent supports. • The immobilization induced structural changes and altered the enzyme kinetics. • But the biocatalyst had better pH stability and was 60-fold more stable at 60 °C. • It reduced the milk protein antigenicity to a level lower than of a commercial formula. [ABSTRACT FROM AUTHOR]

Latex diagnosis (LD) is applied to optimize the natural rubber production and prevent tapping panel dryness (TPD), a physiological syndrome affecting latex production in Hevea brasiliensis. The reduced thiol content (RSH) is one of the biochemical parameters associated with the risk of TPD. However, RSH is difficult to interpret because of the influence of the environment. In order to better understand the regulation of antioxidants and to better interpret RSH, a key parameter of LD, this study analysed in latex both oxidised and reduced forms of ascorbic acid (AsA) and glutathione, and their cofactors as well as other latex diagnosis parameters in response to harvesting stress (tapping and ethephon stimulation) and TPD occurrence. The content of antioxidants in latex had a high variability among five rubber clones. The concentration in AsA was about ten times higher than GSH in laticifer, GSH accounting for about 50% of RSH. For short-term harvesting stress, RSH increased with tapping frequency and ethephon stimulation. TPD is associated with high latex viscosity and bursting of lysosomal particles called lutoids, as well as for several rubber clones with lower RSH and GSH contents. These results suggest that a high level of RSH shows the capacity of laticifer metabolism to cope with harvesting stress, while a drop in RSH is the sign of long stress related to lower metabolic activity and TPD occurrence. RSH remains an essential physiological parameter to prevent TPD when associated with reference data under low and high harvesting stress. This study paves the way to understand the role of AsA and GSH, and carry out genetic studies of antioxidants.

Abstract Background Sucrose (Suc), as the precursor molecule for rubber biosynthesis in Hevea brasiliensis, is transported via phloem-mediated long-distance transport from leaves to laticifers in trunk bark, where latex (cytoplasm of laticifers) is tapped for rubber. In our previous report, six Suc transporter (SUT) genes have been cloned in Hevea tree, among which HbSUT3 is verified to play an active role in Suc loading to the laticifers. In this study, another latex-abundant SUT isoform, HbSUT5, with expressions only inferior to HbSUT3 was characterized especially for its roles in latex production. Results Both phylogenetic analysis and subcellular localization identify HbSUT5 as a tonoplast-localized SUT protein under the SUT4-clade (=type III). Suc uptake assay in baker’s yeast reveals HbSUT5 to be a typical Suc-H+ symporter, but its high affinity for Suc (Km = 2.03 mM at pH 5.5) and the similar efficiency in transporting both Suc and maltose making it a peculiar SUT under the SUT4-clade. At the transcript level, HbSUT5 is abundantly and preferentially expressed in Hevea barks. The transcripts of HbSUT5 are conspicuously decreased both in Hevea latex and bark by two yield-stimulating treatments of tapping and ethephon, the patterns of which are contrary to HbSUT3. Under the ethephon treatment, the Suc level in latex cytosol decreases significantly, but that in latex lutoids (polydispersed vacuoles) changes little, suggesting a role of the decreased HbSUT5 expression in Suc compartmentalization in the lutoids and thus enhancing the Suc sink strength in laticifers. Conclusions Our findings provide insights into the roles of a vacuolar sucrose transporter, HbSUT5, in Suc exchange between lutoids and cytosol in rubber-producing laticifers.

Main conclusion: A chitin-binding domain could contribute to the antifungal ability of chitinase through its affinity to the fungal lateral wall by hydrophobic interactions. Complementary DNA encoding the antifungal chitinase of gazyumaru (Ficus microcarpa), designated GlxChiB, was cloned and expressed in Escherichia coli cells. The results of cDNA cloning showed that the precursor of GlxChiB has an N-terminal endoplasmic reticulum targeting signal and C-terminal vacuolar targeting signal, whereas mature GlxChiB is composed of an N-terminal carbohydrate-binding module family-18 domain (CBM18) and a C-terminal glycoside hydrolase family-19 domain (GH19) with a short linker. To clarify the role of the CBM18 domain in the antifungal activity of chitinase, the recombinant GlxChiB (wild type) and its catalytic domain (CatD) were used in quantitative antifungal assays under different ionic strengths and microscopic observations against the fungus Trichoderma viride. The antifungal activity of the wild type was stronger than that of CatD under all ionic strength conditions used in this assay; however, the antifungal activity of CatD became weaker with increasing ionic strength, whereas that of the wild type was maintained. The results at high ionic strength further verified the contribution of the CBM18 domain to the antifungal ability of GlxChiB. The microscopic observations clearly showed that the wild type acted on both the tips and the lateral wall of fungal hyphae, while CatD acted only on the tips. These results suggest that the CBM18 domain could contribute to the antifungal ability of chitinase through its affinity to the fungal lateral wall by hydrophobic interactions. [ABSTRACT FROM AUTHOR]

Latex is an endogenous fluid exuded by some plants after injury. It is rich in different molecules and has shown many biological activities against different fungi and insects. This work aimed to isolate a peptide fraction from Calotropis procera (PepCp) latex and to evaluate its activity against two fungi and an insect. The chromatographic profile showed that PepCp is constituted mainly by 7 kDa peptides. PepCp showed a low effect against the spore germination of both fungi Colletotrichum gloeosporioides and Fusarium solani. However, PepCp (1.25 mg mL−1) inhibited the mycelial growth of C. gloeosporioides by 80%. On the other hand, PepCp, 0.05% (w/w), reduced the larval weight of Callosobruchus maculatus by 90%, and at 0.2%, no larva was found. At 0.05%, there was a delay of 2 days in the emergence of adult insects, while at 0.1%, no emergence of adult insects was noticed. Our results corroborate the hypothesis of the defense role played by latex and that PepCp can be an interesting biological source of new fungicidal or insecticidal peptides. [ABSTRACT FROM AUTHOR]

Insect folivores on plants protected by secretory canals commonly sever leaf veins or cut trenches before feeding beyond the cuts. Previous studies reported that vein cutting occurs when canals have an arborescent arrangement, whereas trenching is found when canals have a net-like arrangement. However, some danaine species, such as the monarch caterpillar, Danaus plexippus, show both behaviors on the same milkweed plant; early instars cut circular trenches and later instars chew furrows in the leaf midrib. This study tests the hypothesis that milkweed canals differ in arrangement at different scales, thus requiring different behaviors from early and late instars. I compared common milkweed, Asclepias syriaca (Apocynaceae) with prickly lettuce, Lactuca serriola (Asteraceae). Leaves were damaged with standard wounds and the response of the laticifers was compared by measuring latex exudate. With L. serriola, severing either the primary or secondary veins failed to reduce latex emission beyond the cuts. The veins and associated laticifers form an interconnected network; plusiine caterpillars on L. serriola disarm the network with a trench. With A. syriaca, transecting the midrib virtually eliminated distal exudation. However, severing a secondary vein caused only a partial reduction. To decrease exudation beyond secondary veins, milkweed insects need either to sever multiple adjacent veins (as shown by Labidomera clivicollis beetles) or to cut a trench (as in early instar danaine larvae). Thus, in both A. syriaca and L. serriola, herbivore behaviors match the laticifer systems as predicted by the hypothesis that canal architecture has a central role in determining behavior. [ABSTRACT FROM AUTHOR]

Key message: The proteomic analysis of vascular tissues in rubber tree reveals differentially expressed proteins related to laticifer differentiation in mature phloem and secondary cell wall formation in mature xylem for latex/wood-yield improvement. Rubber tree (Hevea brasiliensis) is a latex-producing plant that has worldwide economic importance for the rubber and wood industries. Natural rubber latex is produced from laticiferous vessels (laticifers) located in the secondary phloem tissue of rubber trees. Improving latex production from rubber tree clones by studying the molecular genetics of vascular development has received much attention, but less information has been obtained from proteomic approaches. This study performed a comparative proteomic analysis of the vascular tissues in high latex-yield and high wood-yield rubber tree clones. One primary vascular tissue (newly developed stem) and two secondary vascular tissues (mature phloem/laticifers and mature xylem/wood) were investigated by qualitative/quantitative proteomic analysis using GeLC-MS/MS. The differentially expressed proteins (DEPs) in the specific vascular tissues were analyzed, and the protein functions in the biological processes related to vascular development and to the specific characteristics of each clone were clarified. The predicted protein–protein interaction network and GO annotation revealed DEPs related to photosynthesis, carbohydrate metabolism, energy production and jasmonic acid-responsive proteins involved in positive regulation of laticifer differentiation in mature phloem of the high latex-yield clone, while DEPs related to cell cytoskeleton maintenance, secondary cell wall components and auxin-, brassinosteroid-, abscisic acid-responsive proteins involved in xylem differentiation were abundant in mature xylem of the high wood-yield clone. This is the first report to demonstrate the correlation and functions of DEPs in phloem/laticifers and xylem/wood differentiation in rubber trees. The regulation of vascular development could be useful in improvement of latex and wood yields from rubber trees. [ABSTRACT FROM AUTHOR]

Abstract Background Acyl-CoA-binding proteins (ACBPs) are mainly involved in acyl-CoA ester binding and trafficking in eukaryotic cells, and their various functions have been characterized in model plants, such as Arabidopsis thaliana (A. thaliana), Oryza sativa (rice), and other plant species. In the present study, genome-wide mining and expression analysis of ACBP genes was performed on Hevea brasiliensis (the para rubber tree), the most important latex-producing crop in the world. Results Six members of the H. brasiliensis ACBP family genes, designated HbACBP1-HbACBP6, were identified from the H. brasiliensis genome. They can be categorized into four classes with different amino acid sequences and domain structures based on the categorization of their A. thaliana counterparts. Phylogenetic analysis shows that the HbACBPs were clustered with those of other closely related species, such as Manihot esculenta, Ricinus communis, and Jatropha carcas, but were further from those of A. thaliana, a distantly related species. Expression analysis demonstrated that the HbACBP1 and HbACBP2 genes are more prominently expressed in H. brasiliensis latex, and their expression can be significantly enhanced by bark tapping (a mechanical wound) and jasmonic acid stimulation, whereas HbACBP3-HbACBP6 had almost the same expression patterns with relatively high levels in mature leaves and male flowers, but a markedly low abundance in the latex. HbACBP1 and HbACBP2 may have crucial roles in lipid and latex metabolism in laticifers, so their subcellular location was further investigated and the results indicated that HbACBP1 is a cytosol protein, whereas HbACBP2 is an endoplasmic reticulum-associated ACBP. Conclusions In this study, the H. brasiliensis ACBP family genes were identified. Phylogenetic analyses of the HbABCPs indicate that there is a high conservation and evolutionary relationship between ACBPs in land plants. The HbACBPs are organ/tissue-specifically expressed and have different expression patterns in response to stimulation by bark tapping or ethrel/jasmonic acid. HbACBP1 and HbACBP2 are two important latex ACBPs that might be involved in the lipid and latex metabolism. The results may provide valuable information for further investigations into the biological functions of HbACBPs during latex metabolism and stress responses in H. brasiliensis.

We described the ectomycorrhizae (ECM) of the Japanese Lactarius section Deliciosi species L. akahatsu , L. hatsudake , L. laeticolor , and L. subindigo with the aim of promoting the use of mycorrhizae for taxonomy and expansion of available cultures. Lactarius tottoriensis (sect. Lactarius) was also included as a comparator. The ECM of the four species of sect. Deliciosi showed orange laticifers and plectenchymatous mantles, whereas those of L. tottoriensis showed white laticifers and pseudoparenchymatous mantles. The ECM of L. hatsudake and L. subindigo showed complex rhizomorphs with thicker walls and more developed vessel-like hyphae compared to the other three species. Cystidium-like cells were rarely found on the mantles of L. laeticolor and L. subindigo. Fungal cultures of the five Lactarius species from their ECM were morphologically characterized. Cultures produced laticifers on agar medium, but the five species showed different growth rates. Rhizomorphs of L. hatsudake and L. subindigo in cultures showed a similar morphology to their ECM. Molecular phylogenetic analyses of cultures from the ECM demonstrated that they were of the targeted Lactarius species and suggested the need for taxonomic studies of L. hatsudake , L. subindigo , and L. tottoriensis at the species and section levels. • Ectomycorrhizae of five Lactarius species were described. • Cultures of five Lactarius species were isolated from mycorrhizae. • Isolated cultures were morphologically described. • Species of mycorrhizae and cultures were phylogenetically identified. [ABSTRACT FROM AUTHOR]

Background: Sucrose (Suc), as the precursor molecule for rubber biosynthesis in Hevea brasiliensis, is transported via phloem-mediated long-distance transport from leaves to laticifers in trunk bark, where latex (cytoplasm of laticifers) is tapped for rubber. In our previous report, six Suc transporter (SUT) genes have been cloned in Hevea tree, among which HbSUT3 is verified to play an active role in Suc loading to the laticifers. In this study, another latex-abundant SUT isoform, HbSUT5, with expressions only inferior to HbSUT3 was characterized especially for its roles in latex production. Results: Both phylogenetic analysis and subcellular localization identify HbSUT5 as a tonoplast-localized SUT protein under the SUT4-clade (=type III). Suc uptake assay in baker's yeast reveals HbSUT5 to be a typical Suc-H+ symporter, but its high affinity for Suc (Km = 2.03 mM at pH 5.5) and the similar efficiency in transporting both Suc and maltose making it a peculiar SUT under the SUT4-clade. At the transcript level, HbSUT5 is abundantly and preferentially expressed in Hevea barks. The transcripts of HbSUT5 are conspicuously decreased both in Hevea latex and bark by two yield-stimulating treatments of tapping and ethephon, the patterns of which are contrary to HbSUT3. Under the ethephon treatment, the Suc level in latex cytosol decreases significantly, but that in latex lutoids (polydispersed vacuoles) changes little, suggesting a role of the decreased HbSUT5 expression in Suc compartmentalization in the lutoids and thus enhancing the Suc sink strength in laticifers. Conclusions: Our findings provide insights into the roles of a vacuolar sucrose transporter, HbSUT5, in Suc exchange between lutoids and cytosol in rubber-producing laticifers. [ABSTRACT FROM AUTHOR]

This study aimed to analyze the leaf anatomy of Manihot caerulescens, with emphasis on the ontogeny and secretion composition of the laticifers. Leaf samples were submitted the usual techniques in plant anatomy and histochemical tests to identify the main classes of secondary metabolites. The analyzes were performed using light and scanning electron microscopy. The leaves have a single layered epidermis coated by a uniform cuticle. The epidermal cells are elongated and papillose on the leaf abaxial surface of leaves. The mesophyll is isobilateral and the vascular bundle of the midrib is collateral. The laticifers are originated from ground meristem and procambium, and are of articulated anastomosing type. Besides the laticifers, two types of idioblasts were found: the secretory idioblasts, with a dense content, and the calcium oxalate druses idioblasts. Histochemical tests revealed different classes of chemicals for both secretory idioblasts and laticifers. In idioblasts, a positive reaction was detected for the general phenolic compounds, proteins, total polysaccharides and tannins. The laticifers reacted positively to total lipids and acids, essences, total polysaccharides and rubber. The individuals analyzed here are from caatinga and their leaf anatomical structure showed to be different from that described for the same species growing in the cerrado. [ABSTRACT FROM AUTHOR]

Although latex fluids are found in >20,000 plant species, the biochemical composition and biological function of their proteins are still poorly explored. Thus, this work aimed to conduct a proteomic analysis of Cryptostegia grandiflora latex (CgLP) for subsequent purification and characterization of an antifungal protein. After 2D-SDS-PAGE and mass spectrometry, 27 proteins were identified in CgLP, including a polygalacturonase inhibitor, cysteine peptidases, pathogenesis-related proteins (PR-4), and osmotins. Then, two osmotin isoforms (CgOsm) were purified, and a unique N-terminal sequence was determined (1 ATFDIRSNCPYTVWAAAVPGGGRRLDRGQTWTINVAPGTA 40). The PCR products revealed a cDNA sequence of 609 nucleotides for CgOsm, which encoded a polypeptide with 203 amino acid residues. The structure of CgOsm has features of typical osmotin or thaumatin-like proteins (TLPs), such as 16 conserved Cys residues, REDDD and FF motifs, an acidic cleft, and three main domains. Atomic force microscopy (AFM) and bioinformatics suggested that CgOsm is associated with three chain units. This result was interesting since the literature describes osmotins and TLPs as monomers. AFM also showed that Fusarium falciforme spores treated with CgOsm were drastically damaged. Therefore, it is speculated that CgOsm forms pores in the membrane of these cells, causing the leakage of cytoplasmic content. [ABSTRACT FROM AUTHOR]

Pada Artocarpus heterophyllus, pemula latisifer dibentuk dalam embrio pada awal perkembangan kotiledon. Pemula latisifier tersebut terdapat di tepi luar prokambium di daerah nodus kotiledon. Vesikula dalam berbagai ukuran merupakan komponen yang paling jelas dalam pemula latisifier tersebut. Selanjutnya pemula latisifier memanjang dan tumbuh secara intrusive sejajar dengan sumbu embrio kea rah radikula dan kotiledon. Dalam latisifier terjadi pembelahan inti tanpa diikuti sitokinesis, menghasilkan protoplas embrio kea rah radikula dan kotiledon. Dalam latisifer terjadi pembelahan inti tanpa diikutin sitokinesis, menghasilkan protoplas berinti banyak. Latisifer bercabang ke arah korteks dan empulur. Lateks dibentuk di dalam sitoplasma dan disimpan di dalam vakuola. Struktur latisifer adalah tak beruas dan bercabang. Tidak terjadi anastomosis di antara sel-sel latisifer yang letaknya berdekatan. Plasmodesmata jarang ditemukan pada dinding sel latisifer. Structure and Development of Laticifers in Embryos and Seedlings of Artocarpus heterophyllus Lam. In Artocarpus heterophyllus, laticifer initials are formed in the embryo at the beginning of the development of the cotyledons. The laticifer initials are located at the outer periphery of the procambium at the cotvledonary node. Vesicles of various sizes are the most conspicuous components in the laticifer initial. At subsequent growth, laticifer initials elongate parallel to the axis of the embryo and then grow intrusively towards the radicula and cotyledons. Nuclear division is not followed by cytokinesis and therefore a multinucleate protoplast is produced. The laticifers branch towards the cortex and the pith. Latex was built in the cytoplasm and stored in the vacuole. The structure of the laticifer are non-articulated and branched. No anastomosis occurs between adjacent laticifer cells. Plasmodesmata are rarely seen in the laticifer walls.

At least 20,000 plant species produce latex, a capacity that appears to have evolved independently on numerous occasions. With a few exceptions, latex is stored under pressure in specialized cells known as laticifers and is exuded upon injury, leading to the assumption that it has a role in securing the plant after mechanical injury. In addition, a defensive effect against insect herbivores and fungal infections has been well established. Latex also appears to have effects on viruses, and laticifers are a hostile environment for virus colonization. Only one example of successful colonization has been reported: papaya meleira virus (PMeV) and papaya meleira virus 2 (PMeV2) in Carica papaya . In this review, a summary of studies that support both the pro- and anti-viral effects of plant latex compounds is provided. The latex components represent a promising natural source for the discovery of new pro- and anti-viral molecules in the fields of agriculture and medicine.

During growth of woody plant-trunk, the secondary meristem functions in giving rise the xylem and phloem. Rubber tree (Hevea brasiliensis Muell. Arg.), in addition, contains laticifers (latex producing vessels) in the vicinity of phloem. Insights into regulatory mechanisms of gene networks underlying laticifer proliferation in rubber tree has remained very limited. The candidate vascular development-related genes were selected to investigate for expression profile in phloem and xylem tissues of high latex yield- and high wood yield-clones of rubber tree. The differential gene expression between the mature branch-xylem and -phloem tissues was clearly observed. The cis-regulatory motif analysis revealed the existent of putative jasmonic acid (JA)- and brassinosteroid (BR)-responsive regulatory motifs in promoter regions of these genes, and consequently the effect of exogenous application of JA, BR or their respective signaling inhibitors, on the formation of laticifers in rubber tree was demonstrated. Interestingly, the laticifer numbers were significantly increased in JA-treatment, correlated with up-regulation of phloem development-related genes in both rubber tree clones. On the contrary, the laticifers were decreased in BR-treatment accompanying by up-regulation of xylem development-related genes, especially in high wood yield-rubber tree clone. BR-inhibitor treatment also enhanced laticifer numbers, while JA-inhibitor suppressed laticifer differentiation. Taken together, this study unveils the molecular interplay between JA/BR on vascular development in rubber tree and how this impacts the appearance of laticifers in this plant. This process is vital for a better understanding on laticifer differentiation and its impact in the manipulation of wood and latex yield in rubber tree improvement program. [ABSTRACT FROM AUTHOR]

Highlights • Latex peptidases were able to perform total hydrolysis of caseins. • On the other hand, whey proteins were more resistant to proteolysis. • Heat pretreatment of the whey proteins enhanced the degree of hydrolysis. • In vivo tests showed that latex peptidases reduced antigenicity and allergenicity. • Results were similar to a commercial partially hydrolyzed formula. Abstract The present study evaluated four laticifer fluids as a novel source of peptidases capable of hydrolyzing proteins in cow's milk. The latex peptidases from Calotropis procera (CpLP), Cryptostegia grandiflora (CgLP), and Carica papaya (CapLP) were able to perform total hydrolysis of caseins after 30 min at pH 6.5, as confirmed by a significant reduction in the residual antigenicity. Casein hydrolysis by Plumeria rubra latex peptidases (PrLP) was negligible. Moreover, whey proteins were more resistant to proteolysis by latex peptidases; however, heat pretreatment of the whey proteins enhanced the degree of hydrolysis and reduced the residual antigenicity of the hydrolysates. The in vivo assays show that the cow's milk proteins hydrolysed by CgLP and CapLP exhibited no immune reactions in mice allergic to cow's milk, similar to a commercial partially hydrolysed formula. Thus, these peptidases are promising enzymes for the development of novel hypoallergenic formulas for children with a milk allergy. [ABSTRACT FROM AUTHOR]

Abstract The germin-like protein (GLP) purified from Thevetia peruviana , Peruvianin-I, is the only one described as having proteolytic activity. Therefore, the goal of this study was to investigate the structural features responsible for its enzymatic activity. Although the amino acid sequence of Peruvianin-I showed high identity with other GLPs, it exhibited punctual mutations, which were responsible for the absence of oxalate oxidase activity. The phylogenetic analysis showed that Peruvianin-I does not belong to any classification of GLP subfamilies. Moreover, Peruvianin-I contains a catalytic triad found in all plant cysteine peptidases. Molecular docking simulations confirmed the role of the catalytic triad in its proteolytic activity. Synchrotron radiation circular dichroism assays confirmed that Peruvianin-I was stable at pH ranging from 5.0 to 8.0 and that it presented significant structural changes only above 60 °C. The addition of iodoacetamide caused changes in its native conformation, but only a slight effect was observed after adding a reducing agent. This study reports an unusual protein with germin-like structure, lacking typical oxalate oxidase activity. Instead, the proteolytic activity observed suggests that the protein is a cysteine peptidase. These structural peculiarities make Peruvianin‑I an interesting model for further understanding of the action of laticifer fluids in plant defense. [ABSTRACT FROM AUTHOR]

Key message: The laticifer density in callus of young tissue is positively correlated with the rubber yields of adult trees and can serve as an early selection marker to accelerate rubber tree breeding.Abstract: The rubber tree (Hevea brasiliensis Muell. Arg.) is a perennial crop with a breeding cycle of approximately 30 years in the conventional breeding practices. The lack of suitable parameters linking the juvenile and adult trees has made the early selection attempts inefficient. We performed comparative morphology of laticifer cells in callus induced from young shoots and the primary and secondary laticifers in the trunk of adult trees, and investigated their relationships to rubber yields. Results indicate that the secondary laticifers have smooth lateral walls and perforated end walls and belong to articulated anastomosing laticifers. The primary laticifers are unbranched, non-articulated, and anastomosing, and have bumpy lateral walls when matured. The callus-derived laticifers are morphologically similar to the secondary laticifers with smooth lateral walls and the existence of end walls, and similar relative cell wall thickness. The laticifer density in callus and the laticifer ring number in bark are both genotype-dependent, and they are both highly correlated with the rubber yields with correlation coefficients R = 0.846 (P < 0.002) and R = 0.899 (P < 0.002) for the callus and bark, respectively. Since callus can be induced from tissues of young seedlings in cross-pollinated populations, the laticifer density in callus can serve as an early selection marker of seedlings for high rubber yields and may be used to shorten the rubber tree breeding cycle. [ABSTRACT FROM AUTHOR]

Allium is taxonomically a difficult genus with blurred taxonomic borders at all taxonomic ranks. In this research, anatomy and morphology of bulb tunics in 42 species of the genus representing its 16 currently recognized sections and 6 subgenera (Allium, Cepa, Reticulatobulbosa, Amerallium, Polyprason and Melanocrommyum) were investigated. Our results indicated the following characters to be most informative at sectional and subgeneric levels: features of calcium oxalate crystals and subepidermal cell layer of the outermost bulb tunic, type of tracheids, and bulbils presence. Three main types of crystals, i.e. prismatic, sand and druses, were fairly common among the investigated species except for the members of A. sect. Acanthoprason (A. subg. Melanocrommyum) that often lack crystals. The subepidermal layers of outer tunics were mostly composed of hexagonal, rectangular, or elongated cells but A. paradoxum (A. subg. Amerallium, sect. Briseis) showed the pentagonal type and A. longisepalum (A. subg. Amerallium, sect. Molium) the elliptic type of subepidermal cells. The members of A. sub. Melanocrommyum showed various types of tunic cells and crystals. [ABSTRACT FROM AUTHOR]

Main conclusion: Latexes in immature fruit, young petioles and lignified trunks of fig trees protect the plant using toxic proteins and metabolites in various organ-dependent ways.Latexes from plants contain high amounts of toxic proteins and metabolites, which attack microbes and herbivores after exudation at pest-induced wound sites. The protein and metabolite constituents of latexes are highly variable, depending on the plant species and organ. To determine the diversity of latex-based defense strategies in fig tree (Ficus carica) organs, we conducted comparative proteomic, transcriptomic and metabolomic analyses on latexes isolated from immature fruit, young petioles and lignified trunks of F. carica after constructing a unigene sequence library using RNA-seq data. Trypsin inhibitors were the most abundant proteins in petiole latex, while cysteine proteases (“ficins”) were the most abundant in immature fruit and trunk latexes. Galloylglycerol, a possible defense-related metabolite, appeared to be highly accumulated in all three latexes. The expression levels of pathogenesis-related proteins were highest in the latex of trunk, suggesting that this latex had adapted a defensive role against microbe attacks. Although young petioles and immature fruit are both unlignified soft organs, and potential food for herbivorous insects, unigenes for the sesquiterpenoid pathway, which likely produces defense-associated volatiles, and the phenylpropanoid pathway, which produces toxic furanocoumarins, were expressed less in immature fruit latex. This difference may indicate that while petioles and fruit protect the plant from attack by herbivores, the fruit must also attract insect pollinators at younger stages and animals after ripening. We also suggest possible candidate transcription factors and signal transduction proteins that are involved in the differential expression of the unigenes. [ABSTRACT FROM AUTHOR]

Background: Acyl-CoA-binding proteins (ACBPs) are mainly involved in acyl-CoA ester binding and trafficking in eukaryotic cells, and their various functions have been characterized in model plants, such as Arabidopsis thaliana (A. thaliana), Oryza sativa (rice), and other plant species. In the present study, genome-wide mining and expression analysis of ACBP genes was performed on Hevea brasiliensis (the para rubber tree), the most important latex-producing crop in the world. Results: Six members of the H. brasiliensis ACBP family genes, designated HbACBP1-HbACBP6, were identified from the H. brasiliensis genome. They can be categorized into four classes with different amino acid sequences and domain structures based on the categorization of their A. thaliana counterparts. Phylogenetic analysis shows that the HbACBPs were clustered with those of other closely related species, such as Manihot esculenta, Ricinus communis, and Jatropha carcas, but were further from those of A. thaliana, a distantly related species. Expression analysis demonstrated that the HbACBP1 and HbACBP2 genes are more prominently expressed in H. brasiliensis latex, and their expression can be significantly enhanced by bark tapping (a mechanical wound) and jasmonic acid stimulation, whereas HbACBP3- HbACBP6 had almost the same expression patterns with relatively high levels in mature leaves and male flowers, but a markedly low abundance in the latex. HbACBP1 and HbACBP2 may have crucial roles in lipid and latex metabolism in laticifers, so their subcellular location was further investigated and the results indicated that HbACBP1 is a cytosol protein, whereas HbACBP2 is an endoplasmic reticulum-associated ACBP. Conclusions: In this study, the H. brasiliensis ACBP family genes were identified. Phylogenetic analyses of the HbABCPs indicate that there is a high conservation and evolutionary relationship between ACBPs in land plants. The HbACBPs are organ/tissue-specifically expressed and have different expression patterns in response to stimulation by bark tapping or ethrel/jasmonic acid. HbACBP1 and HbACBP2 are two important latex ACBPs that might be involved in the lipid and latex metabolism. The results may provide valuable information for further investigations into the biological functions of HbACBPs during latex metabolism and stress responses in H. brasiliensis. [ABSTRACT FROM AUTHOR]

MYB transcription factors hold vital roles in the regulation of plant secondary metabolic pathways. Laticifers in rubber trees (Hevea brasiliensis) are of primary importance in natural rubber production because natural rubber is formed and stored within these structures. To understand the role of MYB transcription factors in the specialized cells, we identified 44 MYB genes (named HblMYB1 to HblMYB44) by using our previously obtained transcriptome database of rubber tree laticifer cells and the public rubber tree genome database. Expression profiles showed that five MYB genes were highly expressed in the laticifers. HblMYB19 and HblMYB44 were selected for further study. HblMYB19 and HblMYB44 bound the promoters of HbFDPS1, HbSRPP, and HRT1 in yeast. Furthermore, the transient overexpression of HblMYB19 and HblMYB44 in tobacco plants significantly increased the activity of the promoters of HbFDPS1, HbSRPP, and HRT1. Basing on this information, we proposed that HblMYB19 and HblMYB44 are the regulators of HbFDPS1, HbSRPP, and HRT1, which are involved in the biosynthesis pathway of natural rubber.

Environmental stress can lead to oxidative stress resulting from an increase in reactive oxygen species (ROS) and involves redox adjustments. Natural rubber is synthesized in laticifers, which is a non-photosynthetic tissue particularly prone to oxidative stress. This paper reviews the current state of knowledge on the ROS production and ROS-scavenging systems in laticifers. These regulations have been the subject of intense research into a physiological syndrome, called Tapping Panel Dryness (TPD), affecting latex production in Hevea brasiliensis. In order to prevent TPD occurrence, monitoring thiol content appeared to be a crucial factor of latex diagnosis. Thiols, ascorbate and γ-tocotrienol are the major antioxidants in latex. They are involved in membrane protection from ROS and likely have an effect on the quality of raw rubber. Some transcription factors might play a role in the redox regulatory network in Hevea, in particular ethylene response factors, which have been the most intensively studied given the role of ethylene on rubber production. Current challenges for rubber research and development with regard to redox systems will involve improving antioxidant capacity using natural genetic variability. [ABSTRACT FROM AUTHOR]

A família Apocynaceae é caracterizada por possuir grande diversidade de estruturas secretoras como idioblastos, coléteres, laticíferos e nectários florais. Este estudo teve por objetivo caracterizar anatomicamente as estruturas secretoras nos órgãos vegetativos e reprodutivos de Secondatia densiflora e identificar as principais classes de compostos químicos nos idioblastos e na secreção dos coléteres vegetativos. Os idioblastos estão distribuídos por todos os órgãos aéreos da planta possuindo conteúdo na maioria das vezes denso e fortemente corado pela safranina. Alguns idioblastos apresentam secreção de aspecto granulado. Os testes histoquímicos evidenciaram apenas compostos fenólicos. Os laticíferos são do tipo anastomosado podendo ser observados em todos os órgãos estudados e identificados pelo conteúdo diferenciado e, em alguns casos, pela presença de paredes celulares mais espessas que as paredes das células parenquimáticas. O látex tem cor branca e aspecto leitoso, sendo extravasado logo que a planta é lesionada. Os coléteres vegetativos são do tipo padrão, formados por uma porção alongada que se afina em direção à extremidade. A epiderme secretora em paliçada delimita uma região parenquimática e o curto pedúnculo é coberto por epiderme não secretora de formato retangular. Todo coléter é recoberto por cutícula fina. A mucilagem é constatada tanto no interior das células secretoras quanto no meio extracelular pelo vermelho de rutênio e pela reação PAS. Os nectários florais têm origem receptacular, possuem uma epiderme que reveste toda estrutura, parênquima nectarífero, e feixes vasculares; são fundidos na base e livres na região apical constituindo cinco unidades distintas.The family Apocynaceae is characterized for showing a wide variety of secretory structures such as idioblasts, colleters, laticiferous glands and floral nectaries. The present study aimed to anatomically characterize the secretory structures in vegetative and reproductive organs of Secondatia densiflora and to identify the major classes of chemical compounds in idioblasts and in the secretion of vegetative colleters. Idioblasts are distributed all over the aerial organs of the plant and their content is usually dense and strongly stained with safranin. Some idioblasts have secretion of granulated aspect. Histochemical tests evidenced phenolic compounds only. Laticiferous glands are of the anastomosed type and can be seen in all the studied organs and identified by their distinct content and, in some cases, by the presence of cell walls that are thicker than those of parenchyma cells. Latex is white, milky and leaks as the plant is injured. Vegetative colleters are of the standard type and formed of an elongated portion that becomes thinner towards the end. The secretory palisade epidermis delimits a parenchymatic region, while the short peduncle is covered by rectangular non-secretory epidermis. A thin cuticle covers the entire colleter. Mucilage is detected both inside the secretory cells and in the extracellular medium by ruthenium red staining and PAS reaction. Floral nectaries have receptacular origin and epidermis covering their entire structure, nectariferous parenchyma, and vascular bundles; they are fused at their bases but have free apical region, forming five distinct units.

Plants are unrivaled in the natural world in both the number and complexity of secondary metabolites they produce, and the ubiquitous phenylpropanoids and the lineage-specific glucosinolates represent two such large and chemically diverse groups. Advances in genome-enabled biochemistry and metabolomic technologies have greatly increased the understanding of their metabolic networks in diverse plant species. There also has been some progress in elucidating the gene regulatory networks that are key to their synthesis, accumulation and function. This review highlights what is currently known about the gene regulatory networks and the stable sub-networks of transcription factors at their cores that regulate the production of these plant secondary metabolites and the differentiation of specialized cell types that are equally important to their defensive function. Remarkably, some of these core components are evolutionarily conserved between secondary metabolism and specialized cell development and across distantly related plant species. These findings suggest that the more ancient gene regulatory networks for the differentiation of fundamental cell types may have been recruited and remodeled for the generation of the vast majority of plant secondary metabolites and their specialized tissues. [ABSTRACT FROM AUTHOR]

Sticky disease, which is caused by Papaya meleira virus (PMeV), is a significant papaya disease in Brazil and Mexico, where it has caused severe economic losses, and it seems to have spread to Central and South America. Studies assessing the pathogen-host interaction at the nano-histological level are needed to better understand the mechanisms that underlie natural resistance. In this study, the topography and mechanical properties of the leaf midribs and latex of healthy and PMeV-infected papaya plants were observed by atomic force microscopy and scanning electron microscopy. Healthy plants displayed a smooth surface with practically no roughness of the leaf midribs and the latex and a higher adhesion force than infected plants. PMeV promotes changes in the leaf midribs and latex, making them more fragile and susceptible to breakage. These changes, which are associated with increased water uptake and internal pressure in laticifers, causes cell disruption that leads to spontaneous exudation of the latex and facilitates the spread of PMeV to other laticifers. These results provide new insights into the papaya-PMeV interaction that could be helpful for controlling papaya sticky disease. [ABSTRACT FROM AUTHOR]

A ocorrência do distúrbio fisiológico conhecido como "Mancha Fisiológica do Mamão" (MFM) tem comprometido a qualidade do mamão (Carica papaya L.) produzido no Brasil. A obtenção de material genético tolerante à MFM faz parte das estratégias de ação de médio a longo prazo para minimizar os prejuízos decorrentes da ocorrência desse distúrbio. No presente trabalho, buscou-se avaliar a tolerância de vinte e dois híbridos de mamão à ocorrência da MFM, na região norte do Estado do Rio de Janeiro. Os frutos foram colhidos de um ensaio de competição instalado na Estação Experimental da PESAGRO-Rio, no município de Macaé-RJ. O ensaio consistiu de quatro repetições, num delineamento em blocos ao acaso, sendo que cada parcela foi constituída de oito plantas. Os dados foram submetidos a uma análise de variância e teste de média. Efetuou-se, inicialmente, uma análise conjunta, envolvendo os dois estádios de maturação avaliados - verde-maduro e ¾ maduro; considerando a significância da interação Estádio x Genótipo, procedeu-se a uma análise específica, por estádio de desenvolvimento do fruto. Em função da análise de variância, também, foi calculado o coeficiente de determinação genotípica (H²) para o caráter em estudo, o qual demonstrou que a avaliação do nível de severidade da MFM, no estádio ¾ maduro, caracteriza melhor as diferenças genotípicas. Com base nesses resultados, inferimos que há uma expressiva variabilidade genética, para o caráter MFM, dentre os genótipos avaliados. Isto sugere um bom potencial em se obter, através do melhoramento genético, material vegetal (híbridos e variedades) com maior tolerância à MFM. O melhoramento genético associado ao manejo do ambiente poderá permitir o cultivo do mamoeiro sem as limitações advindas da ocorrência da MFM.The occurrence of the physiological disturbance known as "Skin Freckle on Papaya" (MFM) has reduced the quality of papaya (C. papaya L.) cultivated in Brazil. The acquisition of genetic material tolerant to MFM is a very good strategy to overcome or at least to decrease the negative effects of such disturbance. In this present work, 22 papaya genotypes were evaluated in relation to the MFM, in the Northern region of Rio de Janeiro State. The fruits were collected from a field testing installed in an Experimental Station of PESAGRO-Rio, in the municipality of Macaé. The experiment consisted of a randomized complete block design with four replications, with eight individual plants per plot. The data were submitted to the analysis of variance and to the mean comparison test. Firstly it was conducted a combined analysis involving the two ripening stages - green-mature and ¾ mature. As the genotype by ripening stage was significant, each individual ripening stage was analyzed. Based on the ANOVA, the genotypic determination index (H²) for the trait MFM was estimated, which demonstrated that the evaluation on the second stage (¾ mature) shows higher value (67.85%) than in the green-mature stage (28.95%). Thus, in such stage there is a better differentiation among genotypes. Based on such results, it may be stated that there is expressive genetic variability among the evaluated genotypes, for this trait. So, there is a positive perspective of obtaining better genotypes - hybrids and varieties - in terms of tolerance to MFM via breeding programs. Considering the strategy of breeding procedures, associated to adjustment of cultural practices, it represents new possibilities of growing papaya without the limitations caused by the MFM.