Abstract: Lodging in rice production often limits grain yield and quality by breaking or bending stems. Excessive nitrogen (N) fertilizer rates are the cause of poor lodging resistance in rice, but little is known about the effect of top-dressing N application rates on the mechanical strength of japonica rice plants, especially how the anatomical structure in culms is affected by N. In this study, field experiments on two japonica rice varieties with three top-dressing N application rates, 0 kg N ha−1 (LN), 135 kg N ha−1 (MN), and 270 kg N ha−1 (HN) as urea, were conducted. Wuyunjing23, a lodging-resistant japonica rice cultivar and W3668, a lodging-susceptible japonica rice cultivar were used. The lodging index, breaking strength, morphological and anatomical traits in culms were measured in this study. The visual lodging rate in japonica rice differed remarkably between genotypes and top-dressing N treatments. The higher lodging index of rice plants was primarily attributed to the weak breaking strength of the lower internodes. The longer elongated basal internodes were responsible for higher plant height and a higher lodging index. Correlation analysis showed that breaking strength was significantly and positively correlated with the thickness of the mechanical tissue but was significantly and negatively correlated with the inner diameter of the major axis (b2). With increasing top-dressing N rates, the sclerenchyma cells of the mechanical tissues and the vascular bundles of the Wuyunjing23 cultivar varied little. The plant height, inner diameter of the minor axis (a2) and b2 increased significantly, but the area of the large vascular bundle (ALVB) and the area of the small vascular bundle (ASVB) decreased significantly and resulted in lower stem strength and a higher lodging index under higher top-dressing N conditions. The culm diameter of the W3668 cultivar increased slightly with no significant difference, and the sclerenchyma cells in the mechanical tissues and vascular bundles showed deficient lignifications under high top-dressing N conditions. Moreover, the ALVB and the ASVB decreased significantly, while the area of air chambers (AAC) increased rapidly. An improvement in the lodging resistance of japonica rice plants could be achieved by reducing the length of the lower internodes, decreasing the inner culm diameter and developing a thicker mechanical tissue. Top-dressing N application increased the plant height and inner culm diameter and decreased the ALVB and the ASVB of the Wuyunjing23 cultivar and caused deficient lignified sclerenchyma cells, lowered the ALVB and the ASVB, and increased the AAC of the W3668 cultivar resulting in weaker stem strength and a higher lodging index.

Abstract: In this study, the toxicity of water-soluble carbon nanodots (C-dots) to maize (Zea mays L.) and their uptake and transport in plants were investigated. After exposed in sand matrix amended with 0–2000 mg/L C-dots for 4 weeks, we found that the phytotoxicity of C-dots was concentration-dependent. C-dots at 250 and 500 mg/L showed no toxicity to maize. However, 1000 and 2000 mg/L C-dots significantly reduced the fresh weight of root by 57% and 68%, and decreased the shoot fresh weight by 38% and 72%, respectively. Moreover, in maize roots, the exposure of C-dots at 2000 mg/L significantly increased the H2O2 content and lipid peroxidation (6.5 and 1.65 times higher, respectively), as well as, the antioxidant enzymes activities, up to 2, 1.5, 1.9 and 1.9 times higher for catalase, ascorbate peroxidase, guaiacol peroxidase and superoxide dismutase, respectively. On the other hand, C-dots were observed in detached root-cap cells, cortex and vascular bundle of roots and mesophyll cells of leaves through...

Abstract: Understanding cadmium (Cd) accumulation in plants is critical for the development of plant-based strategies for soil remediation and crop safety Sedum alfredii is a nonbrassica plant species known to hyperaccumulate Cd The characteristics of Cd uptake, distribution, and retranslocation affected by the Ca status were investigated at cellular levels in S alfredii Low Ca supply significantly increased Cd contents in shoots of S alfredii, particularly in the young leaves Micro x-ray fluorescence images confirmed that sequestration of Cd was greatly enhanced in the young leaves under Ca deficiency stress, with a significant amount of Cd localized in mesophyll cells, compared to the young leaves supplied with high Ca levels Cd influx into protoplasts isolated from young leaves was significantly inhibited by the addition of Ca channel inhibitors, but not by pre-exposure to Ca deficiency In stems, the Cd signal in vascular systems under low Ca levels was 10-fold higher than in those treated with higher Ca levels A detailed investigation of vascular bundles revealed that an extremely high Cd signal induced by low Ca supply occurred in the phloem tissues, but not in the xylem tissues Transfer of Cd pretreated plants to nutrient solutions at different Ca levels confirmed that a much higher amount of Cd was reallocated to the new growth tissues under low Ca stress compared to plants supplied with sufficient Ca These results suggest that Ca deficiency triggered a highly efficient phloem remobilization of Cd in S alfredii and subsequently enhanced Cd accumulation in its young leaves

Abstract: The membranes of Zea mays (maize) mesophyll cell (MC) chloroplasts are more vulnerable to salinity stress than are those of bundle sheath cell (BSC) chloroplasts. To clarify the mechanism underlying this difference in salt sensitivity, we monitored changes in the glycerolipid and fatty acid compositions of both types of chloroplast upon exposure to salinity stress. The monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG) contents were higher in MC chloroplasts than in BSC chloroplasts, in both the presence and absence of salt treatment. Under salt conditions, the MGDG level in MC chloroplasts was significantly lower than under normal conditions, while it was unchanged in BSC chloroplasts. In both types of chloroplast, the contents of DGDG, phosphatidylglycerol and phosphatidylinositol remained at the same levels in control and salt-treated plants, whereas sulfoquinovosyldiacylglycerol and phosphatidylcholine were significantly lower and higher, respectively, upon salt treatment. In addition, the fatty acid composition and double bond index of individual lipid classes were changed by salt treatment in both BSC and MC chloroplasts, although these factors had no effect on glycerolipid content. These findings suggest that the difference in salt sensitivity of MC and BSC chloroplast membranes is related to differences in MGDG responses to salinity. Thus, we propose that the low MGDG content and the low sensitivity of MGDG to salinity in BSC chloroplasts render them more tolerant than MC chloroplasts to salinity stress.

Abstract: C4 photosynthesis represents an excellent example of convergent evolution that results in the optimization of both carbon and water usage by plants. In C4 plants, a carbon-concentrating mechanism divided between bundle sheath and mesophyll cells increases photosynthetic efficiency. Compared with C3 leaves, the carbon-concentrating mechanism of C4 plants allows photosynthetic operation at lower stomatal conductance, and as a consequence, transpiration is reduced. Here, we characterize transcriptomes from guard cells in C3 Tareneya hassleriana and C4 Gynandropsis gynandra belonging to the Cleomaceae. While approximately 60% of Gene Ontology terms previously associated with guard cells from the C3 model Arabidopsis (Arabidopsis thaliana) are conserved, there is much less overlap between patterns of individual gene expression. Most ion and CO2 signaling modules appear unchanged at the transcript level in guard cells from C3 and C4 species, but major variations in transcripts associated with carbon-related pathways known to influence stomatal behavior were detected. Genes associated with C4 photosynthesis were more highly expressed in guard cells of C4 compared with C3 leaves. Furthermore, we detected two major patterns of cell-specific C4 gene expression within the C4 leaf. In the first, genes previously associated with preferential expression in the bundle sheath showed continually decreasing expression from bundle sheath to mesophyll to guard cells. In the second, expression was maximal in the mesophyll compared with both guard cells and bundle sheath. These data imply that at least two gene regulatory networks act to coordinate gene expression across the bundle sheath, mesophyll, and guard cells in the C4 leaf.

Abstract: Regulation of water flow in an interconnected xylem vessel network enables plants to survive despite challenging environment changes that can cause xylem embolism. In this study, vulnerability to embolisms of xylem vessels and their water-refilling patterns in vascular bundles of maize leaves were experimentally investigated by employing synchrotron X-ray micro-imaging technique. A vascular bundle in maize consisted of a protoxylem vessel with helical thickenings between two metaxylem vessels with single perforation plates and nonuniformly distributed pits. When embolism was artificially induced in excised maize leaves by exposing them to air, protoxylem vessels became less vulnerable to dehydration compared to metaxylem vessels. After supplying water into the embolized vascular bundles, when water-refilling process stopped at the perforation plates in metaxylem vessels, discontinuous radial water influx occurred surprisingly in the adjacent protoxylem vessels. Alternating water refilling pattern in protoxylem and metaxylem vessels exhibited probable correlation between the incidence location and time of water refilling and the structural properties of xylem vessels. These results imply that the maintenance of water transport and modulation of water refilling are affected by hydrodynamic roles of perforation plates and radial connectivity in a xylem vascular bundle network.

Abstract: The adaptation mechanism of Melilotus officinalis was studied to understand this species’ mechanisms. Seedlings of Melilotus officinalis were treated with different NaHCO3 levels, with the control plants being grown without NaHCO3. Anatomical structure of three organs and ultrastruture of two organelles widespread were observed by making paraffin and ultrathin sections. The results showed that NaHCO3 treatments significantly affected vascular system of Melilotus officinalis. Vascular tissue throughout the roots, stems and leaflets underwent changes. Particularly, the diameter of xylem vessels declined significantly, which greatly limited the transportation and transverse diffusion of water; the cross section of stems was changed from near quadrangle to irregular shape, which increased the surface area of the stems and furthered the ability of photosynthesis; epidermis cell walls cutinization occurred and the diameter of xylem vessel decreased greatly, which reduced water loss through stomata and non-stomata cells. In spite of these dramatic morphological changes, organelles in cells, both chloroplast in stems and leaflets and mitochondria in roots, had minor changes. Particularly, thylakoid in chloroplast and cristae in mitochondria still had intact membrane system and sharp-edged laminated structure. Vascular tissue, the cross section of stems, cell walls of epidermis and mesophyll cell all underwent changes in Melilotus officinalis under NaHCO3 stress. While organelles in cells had minor changes. Maybe structural integrity of organelle was protected by active morphological change of tissues and cells in Melilotus officinalis.

Abstract: Laterally connected vascular bundles in the nodes of sugarcane (Saccharum species cv. Pindar) stalks allow a rapid redistribution of water across the stalk should the vascular continuity be partly disrupted. Tritiated water supplied to the roots exchanged rapidly between the xylem and storage tissue so that net movement up the stalk was slow. The half-time for exchange in a labeled stalk was about 4 hours so that the entire water content of a sugarcane stalk can turn over at least once in a single day. No rapid flux of sugar between xylem and phloem or xylem and storage tissue was detected. Functional xylem contained only low sugar concentrations: less than 0.3 % w/v in the stalk and less than 0.02% w/v in the leaf. Previous reports of high sugar levels (9 % w/v) in sugarcane stalk xylem reflect some degree of xylem blockage followed by a slow equilibration with free space sugars in the storage tissue.

Abstract: A comprehensive survey and descriptions on the petiole anatomy was undertaken on 16 species belonging to four selected genera (Anisoptera, Cotylelobium, Vatica and Upuna) in the tribe Dipterocarpeae to investigate variations in vascular bundle structure. Methods used in this study were petiole sectioning using a sliding microtome, staining, mounting and observation under light microscope. Findings had shown that all species studied have complex vascular bundle structures, consisting of outer and medullary vascular bundles. Four different types of vascular bundle arrangements were found and described as Types 1, 2, 3 and 4. The vascular bundle types were determined based on the arrangement and system of vascular bundle strands present in the petiole transverse sections. These vascular bundle types were determined and suggested for easy reference. The results showed that vascular bundles can be used for identification of certain species and can definitely be used for classification of different genera. The presence of sclerenchyma cells is useful in differentiating genera. As a conclusion, the petiole vascular bundle anatomical characteristics have taxonomic value, especially in the identification of some species and possibly applicable in the classification of the tribe Dipterocarpeae.

Abstract: Ratoon stunting disease (RSD), caused by the bacterium Leifsonia xyli subsp. xyli (Lxx), is one of the most economically important diseases of sugarcane worldwide. Because knowledge on the interaction of Lxx with its host at the microscopic level is limited, the development of tools to monitor Lxx during the colonization process could shed new light on the processes that control disease development. In this investigation, a transformation protocol was optimized and a mutant Lxx strain engineered that stably expressed the gfp gene in sugarcane tissues. In vitro, the growth of the mutant did not differ from that of the wild type. Also, plants inoculated with both strains showed comparable growth and development when analysed 180 days after inoculation (dai). Fluorescence microscopy of roots, stalks, meristems and leaf tissues of Lxx-GFP-inoculated plants was performed at 180 dai. In the leaves, Lxx-tagged cells were observed within the xylem vessels as has been described before but, in addition, they were found in a new niche within the host tissues, in the mesophyll and in the bundle sheath cells surrounding the vascular system. This finding indicates that Lxx is able to move from the xylem to the parenchyma of the leaf cells. This first report of an Lxx mutant expressing a heterologous gene revealed that colonization of sugarcane by this pathogen is not limited to the xylem vessels as commonly reported.

Abstract: Background Recent studies have shown that C4-like photosynthetic pathways partly reside in photosynthetic cells surrounding the vascular system of C3 dicots. However, it is still unclear whether this is the case in C3 monocots, especially at the molecular level.

Abstract: In C3 plants, photosynthetic efficiency is reduced by photorespiration. A part of CO2 fixed during photosynthesis in chloroplasts is lost from mitochondria during photorespiration by decarboxylation of glycine by glycine decarboxylase (GDC). Thus, the intracellular position of mitochondria in photosynthetic cells is critical to the rate of photorespiratory CO2 loss. We investigated the intracellular position of mitochondria in parenchyma sheath (PS) and mesophyll cells of 10 C3 grasses from 3 subfamilies (Ehrhartoideae, Panicoideae, and Pooideae) by immunostaining for GDC and light and electron microscopic observation. Immunostaining suggested that many mitochondria were located in the inner half of PS cells and on the vacuole side of chloroplasts in mesophyll cells. Organelle quantification showed that 62–75% of PS mitochondria were located in the inner half of cells, and 62–78% of PS chloroplasts were in the outer half. In mesophyll cells, 61–92% of mitochondria were positioned on the vacuole si...

Abstract: Burkholderia glumae is a well-known pathogen for causing bacterial panicle blight of rice. In this study, the infection process of B. glumae in rice plants at different growing stages was tracked by means of real-time fluorescence quantitative PCR. Burkholderia glumae tended to colonize at the growing point of rice plants, and the biomass of population was 104 to 108 CFU/g. The most intensive colonization was detected in the upmost leaf in the two-leaf period. However, after the two-leaf period, the population of pathogens decreased significantly, and they successfully recovered in the booting stage and broke out in panicles. We also illustrated the incubation location of B. glumae by presenting the infection pattern in the seedling and tillering stage of rice. Under fluorescent microscopy, the gfp-labelled pathogens were first found in the vascular bundle of lateral roots, taproots and injured cells, then they were observed in the root hairs, epidermal cells and main root cap. The pathogens in the vascular bundle laterally dispersed towards the epidermal cells. By spray application of a bacterial suspension, the pathogens landed on the leaf sheaths and leaves, colonized in the epidermal hairs and leaf hairs, or invaded into the cells through the stomas. At the same time, the pathogens from the vascular bundle of the roots spread into the vascular bundle of leaf sheaths and leaves, which caused the leaves to curl and wilt, beginning from the tip.

Abstract: Cucumber mosaic virus (CMV) has the broadest host range among plant viruses, causing enormous losses in agriculture. In melon, strains of subgroup II are unable to establish a systemic infection in the near-isogenic line SC12-1-99, which carries the recessive resistance gene cmv1 from the accession PI 161375, cultivar 'Songwhan Charmi'. Strains of subgroup I overcome cmv1 resistance in a manner dependent on the movement protein. We characterized the resistance conferred by cmv1 and established that CMV-LS (subgroup II) can move from cell to cell up to the veins in the inoculated leaf, but cannot enter the phloem. Immunogold labelling at transmission electron microscopy level showed that CMV-LS remains restricted to the bundle sheath (BS) cells in the resistant line, and does not invade vascular parenchyma or intermediary cells, whereas, in the susceptible line 'Piel de Sapo' (PS), the virus invades all vein cell types. These observations indicate that the resistant allele of cmv1 restricts systemic infection in a virus strain- and cell type-specific manner by acting as an important gatekeeper for virus progression from BS cells to phloem cells. Graft inoculation experiments showed that CMV-LS cannot move from the infected PS stock into the resistant cmv1 scion, thus suggesting an additional role for cmv1 related to CMV transport within or exit from the phloem. The characterization of this new form of recessive resistance, based on a restriction of virus systemic movement, opens up the possibility to design alternative approaches for breeding strategies in melon.

Abstract: Leaf anatomical changes were appraised in exogenously applied trehalose of radish (Raphanus sativus L.) plants grown under nonstress (well-watered) and water stress (60% field capacity) conditions. Two cultivars of radish namely, Manu and 40-Day, were grown in a pot experiment at the Botanical Garden, GCUF, Pakistan. Plants were subjected to 60% field capacity conditions after three weeks of germination. Trehalose (25 mM) was applied to the radish plants through two different modes (foliar and presowing). After 2 weeks of foliar-applied trehalose, the leaves were excised from the plants for studying different anatomical features. Water stress caused a significant reduction in the leaf vascular bundle area, leaf midrib thickness (only in cv. Manu), leaf parenchyma cell area, and the number of vascular bundles in both radish cultivars, while water stress increased leaf epidermis thickness of both radish cultivars. Exogenously applied trehalose through both (presoaking and foliar spray) modes was eff...

Abstract: As of today, the functions of fusoid cell, and the transport and loading pathways of photoassimilate in bamboo leaves are still not clear. In this paper, the leaves of Fargesia yunnanensis from a greenhouse and the wild were respectively used as samples to analyze the anatomical characteristics of fusoid cells and vascular bundles. The results showed that the bamboo leaves from greenhouse got shorter and thinner with fewer layers of palisade parenchyma cells than those from the wild. The volumes of fusoid cells were also increased. Fusoid cells originated from a huge parenchyma cell as testified by the observed nuclei. Several fusoid cells usually formed one cell complex close to the midrib. Crystals were detected in fusoid cells but no pits or plasmodesmata on their walls, suggesting that fusoid cells had the function of regulating water. The presence of fusoid cells determined the major difference between a leaf blade and sheath. There were prominent chloroplasts with simple stroma lamellae in the parenchymatous bundle sheath cells and starch grains were also observed in these chloroplast. Photoassimilates could be transported across vascular bundle sheath via symplasmic pathways for an abundant of plasmodesmata in sheath cell walls, and transported into phloem tube by apoplastic pathway as there were no pits in the walls of companion cells and phloem tubes.

Abstract: T'he photo-oxidation of cytochrome f (cytochrome C554) in bundle sheath cells isolated from leaves of maize (Zea mays var. DS 606A) has been compared with that in intact maize leaf and in isolated pea leaf cells (Pisum sativum L.). In all cases, illumination with red light caused a negative absorbance change at 554 nm which was attributed to the oxidation of cytochrome f. The extent of this change was greater using monochromatic red light at wavelengths above 700 nm compared with wavelengths below 700 nm. 3-(3,4-Dichlorophenyl)-1,1-dimethylurea abolished this difference in bundle sheath cells. After illumination for 1 minute or longer in bundle sheath cells, reduction of cytochrome f in the dark was rapid only if the wavelength of the illuminating light was below 700 nm. In the presence of 3-(3,4-dichlorophenyl)-1,1-dimethlyurea, reduction was slow after illumination at all wavelengths. Cytochrome f photo-oxidation was also followed in cells of a mutant of Chlamydomonas reinhardi, ac-21, which has isolated chloroplasts that exhibit photochemical reactions similar to those shown by isolated bundle sheath chloroplasts. No evidence was obtained for photoreduction of cytochrome f in the mutant. It was concluded that in the chloroplast of the intact bundle sheath cell of maize there is electron flow between photosystem 1I and cytochrome f resulting in photoreduction of the cytochrome.

Abstract: We studied assimilation of 14СО2 and distribution of 14С among the products of 3-min-long photosynthesis of maize (Zea mays L.) leaves. The day before the experiment, half of the plants were fertilized with Ca(NO3)2 (1 g/L of water) at a rate of 6 L/m2. Five days before the experiment, some plants were shaded for adaptation (illuminance was reduced by 50%). On the day of the experiment (before the application of 14СО2), several shaded plants were exposed to direct sunlight for 3 min, and some plants grown at full light (light plants) were shaded for 3 min (illuminance of 50%). Unfertilized plants adapted for 5 days to shading showed photosynthesis of 75.9% of control level (full light). If light plants were transferred to shading for 3 min, their photosynthesis decreased to 42.1%. In plants shaded for 5 days and then transferred to full light, photosynthesis in 3 min was 96.3% of control level. At full light, fertilization with nitrate boosted photosynthesis to 132.6% as compared with control material, but photosynthesis decreased to 43.5 and 65.4% of control level in plants shaded for 5 days and those shaded for 3 min, respectively. At the same time, the plants shaded for 5 days and then exposed for 3 min to full light restored photosynthesis to almost control level (95.5%). Analysis of 14С distribution among the products of 3-min-long photosynthesis showed that, the same as in C3 plants, a decrease in illuminance (especially a sudden one) in maize reduced the ratio between labeled sucrose and hexoses and elevates incorporation of 14С into malate, which indicated that its consumption in bundle sheath cells was suppressed. A decrease in the ratio between labeled sucrose and hexoses became more pronounced under the influence of nitrates with this effect also occurring in transport products of photosynthesis (20 cm below 14С-providing leaf area). In plants fertilized with nitrates, radioactivity of sucrose (% of radioactivity of soluble compounds) decreased in all the types of illumination. When illuminance was suddenly reduced for 3 min, incorporation of 14С into sucrose was 21.5 against 51.2% in light plants, and radioactivity of aspartate and malate sharply rose to 13.7 and 26.1% (against 2.1 and 8.9% in control material). Incorporation of 14С into compounds of glycolate pathway was low (less than 2.5%), but it was somewhat greater in nitrate plants. We concluded that the same mechanism of interaction between stomatal apparatus of leaf epidermis, invertase of mesophyll apoplast, and photosynthetic metabolism of carbon with electron flux via electron transport chain in chloroplasts of bundle sheath cells, which governs the rate of photosynthesis and assimilate export from the leaf but is triggered by the extent of consumption in the bundle sheath cells of C4 acids produced in the mesophyll operates in C4 plants (the same as in C3 plants).

Abstract: The high morphological diversity among species of the genus Ficus causes problems in the delimitation of the species. Therefore, there is a difficulty in offering a natural and well organized classification for the species of the genus. This research was based on the leaf characters of 3 species from Ficus growing in Iraq which is ( F. carica , F. elasticaa and F. religiosa ). All species of Ficus have crystals appeared very clear in the epidermis also recorded the stomatal type and found all the species under study have Actinocytic type and characterized by Hypostomatic (stomata on abaxial only). The shape of the guard cell are reniform in all species under study, and the ordinary cells straight walls and ribbed also the cell shapes are rectangular to polygonal as well as the study showed that the unglandular trichomes are normally founded on the Ficus carica and Ficus religiosa and the species Ficus elasticaa was glabrous. The vertical sections of leaves showing difference characteristics in epidermis and mesophyll in the species under study, the epidermis differ between the species and on this basis can be divided into three groups, the epidermis in all species is composed of oval cells with undulating walls, also the type of mesophyll in the species F. elasticaa and F. carica are Bifacil and isobilateral mesophyll in the species F. religiosa . The spongy layer were consisted from (3-5) rows of ordinary parenchyma cells in all species except the species F. elasticaa the spongy layer form was consisted from Aerenchyma cells. The shape of midrib cross section in the species under study were different between them, where the cross sectional shape of the species F. carica was quadrilateral shaped and the vascular bundle was crescent shaped also the shape of cross section in the F. elasticaa and F. religiosa were look like elongated jar or eye drawn and the vascular bundle were taken the same shape, likewise the vascular bundle were consisted from xylem and phloem and of several layers of sclerenchyma around the vascular bundles. Key words : Ficus , Iraq, leaf anatomy, Moraceae.

Abstract: Transverse sections of the leaf blade and petiole of three species of the genus Chrysophyllum namely C. albidum, C. subnudum and C. cainito were investigated to establish taxonomic relationship among them. The result obtained revealed that the shape of vascular bundle of the leaf in C. albidum and C. subnudum are semi-circular while in C. cainito, it is V-shaped. The vascular bundle is bicollateral in the three taxa investigated. The shape of petiole is semicircular in C. albidum and C. cainito but rounded in C. subundum. C. cainito and C. subundum have well developed Vascular bundle, about 6-7 arranged to form an arc with distinct xylem and phloem cells while in C. albidum, they are 3-7, arranged to form an arc with in the cortex. The result further strengthened the inter-specific relationship existing among them

Abstract: In the present study, histopathology of three varieties of sesame TS 3, TS 5 and SG 27 infected with Alternaria alternata was carried out to understand the mechanism of fungal infection and penetration in sesame plant as well as to determine the histological manifestation in sesame cells by light microscopy. Fungus was identified in infected tissues as a dark bluish black with toluidine blue O staining. Light microscopic examination of sesame stem showed that the fungus was present in epidermis, hypodermis and cortical parenchyma tissue as the symptoms became visible by naked eye ten days after inoculation (DAI). As the disease progress, the fungus moved from cortical parenchyma to vascular bundle, xylem and phloem. Later on, it completely overlapped the vascular bundle and entered in pith. When necrotic lesion appeared, fungus was present abundantly in epidermis, hypodermis, cortical parenchyma, vascular bundles and in pith. Due to its excessive growth and complete overlapping of cells, disorganization or destruction of cells of sesame took place. It was concluded that the Alternaria alternata was not a tissue limited pathogen instead of this it spread in to all tissues of stem from epidermis to pith.