Amount Of Starch Grains Research Articles

Total Flavonoid Content, Microscopic and Microbial Evaluation of Syrian Ginkgo Biloba Products

Ginkgo Biloba (GB) is a widely used finished herbal product. Due to its natural source there is no demand to evaluate its quality before marketing. Although GB products have shown promising potential with the efficacy, many of these products remain untested. The Current work aims to evaluate some quality parameter of GB finished products like total flavonoid content (TFC), microscopic, Loss On Drying (LOD) and microbial tests in comparison with GB crude plant. The TFC ranged from (22.86 to78.74 mg/g). Microscopic findings revealed the presence of large amounts of starch grains in product A. Furthermore, most of the products were heavily contaminated with bacteria and fungi. As bacterial colony counts ranged from (103 to 7.5 × 105 CFU/g) and from (1.7 × 103 to 0.75 × 107 CFU/g) for fungal colony counts. Most of the products exceeded the reference limits for LOD. thus may pose a threat to consumer's health.

Anatomical features, fatty acid profile and tocopherol content of the Tunisian Cakile maritima subsp. maritima Scop. Fruit

This study reported for the first time anatomical features, fatty acid composition and tocopherol content for the fruits of Cakile maritima subsp. maritima Scop. collected from two sites located at the coastal part of North Tunisia (Bizerte and Soliman). Anatomical investigations characterized the indehiscent siliqua of Soliman population. Transverse sections through fresh fruit show a large number of prismatic crystals located at the three first layers of the mesocarp, which parenchyma was characterized by the presence of large amounts of starch grains and solitary oil drops. A particular anatomical structure is identified at the valves junction. The endocarp is a thin tissue composed of 2-3 layers of small lignified wall cells and one layer of tangentially elongated and thin cells surrounding the seed. Moreover, the fruit oil from both populations are characterized by their richness in unsaturated fatty acids, particularly monounsaturated ones. The major identified fatty acids with GC/MS analysis of fatty acid methyl esters for Bizerte and Soliman populations are oleic (20.20 ± 1.42 and 23.9 ± 2.87%, respectively), erucic (20.82 ± 1.60 and 22.04 ± 2.65%, respectively) and linoleic (24.09 ± 2.47 and 21.34 ± 2.76%, respectively) acids. Besides, analysis of tocopherols allowed the identification of two isoforms (α- and γ-tocopherols). The α-tocopherol was found as the prominent one in the two fruit oils and was most important in Soliman population than in Bizerte one (31.13 ± 2.45 mg/kg against 28.88 ± 2.21 mg/kg).

Changes in the structural indices of annual shoots of Quercus rubra under anthropogenic impact

Changes in the structural indices of annual shoots of Quercus rubra under anthropogenic impact

Physiological, morphological and ultrastructural responses to exposure to ultraviolet radiation in the red alga Aglaothamnion uruguayense (W.R. Taylor)

In this study, we examined the effect of ultraviolet radiation (UV) at the thalli of Aglaothamnion uruguayense (W.R. Taylor) N.E. Aponte, D.L. Ballantine & J.N. Norris exposed to two different conditions of radiation: PAR (control) and PAR + UVA + UVB for 3 h per day during 7 days. The effects of radiation on growth rates, photosynthetic pigments, cell viability, phenolic compounds and total soluble sugar and starch were analyzed. The morphology and the ultrastructure were also assessed. Algae were cultivated and then exposed to photosynthetically active radiation (PAR) at 14 W m−2 and PAR + UVA (0.70 W m−2) + UVB (0.35 W m−2) 3 h per day for 7 days. After exposure to PAR + UVA + UVB, A. uruguayense exhibited a 75% reduction in growth. Photosynthetic pigments, in particular, phycobiliproteins (allophycocyanin, phycocyanin and phycoerythrin), increased after exposure to PAR + UVA + UVB. UVR exposure changed the synthesis of carotenoids, including decreased of lutein by 67.1% and increased of β-carotene by 64.3% and of zeaxanthin by 23%. Phenolic compounds were reduced while flavonoids decreased by approximately 12.9% compared with samples exposed to PAR (control). Moreover, as determined by PAS, TEM and total starch extraction, the amount of starch grains decreased in algae exposed to UV. When observed under confocal microscopy, treated samples showed a significant reduction in the number and shape alteration of chloroplasts. TEM revealed changes in ultrastructure, including increased cell wall thickening and disorganization of cellulose microfibrils. Chloroplasts showed disrupted thylakoid membranes, damage to envelope membranes, and increased number of plastoglobuli. From these results, it can be concluded that UVB is a factor that negatively affects the growth and development of the macroalga A. uruguayense.

Compatibilidad anatómica de Jatropha curcas (L.) injertada en portainjerto de Jatropha cinerea (Ortega) Muell.Arg

Graft compatibility of Jatropha curcas on Jatropha cinerea was confirmed by obtaining a high survival (95%) of the total grafted plants. Their regeneration and development was accomplished by histological assays observing compatibility of the vessel tissues. At anatomical level, both species had the same cell types (parenchyma in the external cortex, specific cells forming phloem tissues, vascular and xylem cambium) completely differentiated at the moment of grafting. When comparing different tissues, the parenchyma cells of J. curcas had fewer amounts of starch grains than those of J. cinerea. Another anatomical difference was vascular cambium amplitude, which was greater in J. cinerea than in J. curcas. The results of the histological cuts in the grafted stems showed integration of J. curcas tissue with J. cinerea stock when they developed as one plant only.

Low Night Temperature Affects the Phloem Ultrastructure of Lateral Branches and Raffinose Family Oligosaccharide (RFO) Accumulation in RFO-Transporting Plant Melon (Cucumismelo L.) during Fruit Expansion.

Due to the importance and complexity of photo assimilate transport in raffinose family oligosaccharide (RFO)-transporting plants such as melon, it is important to study the features of the transport structure (phloem) particularly of the lateral branches connecting the source leaves and the sink fruits, and its responses to environmental challenges. Currently, it is unclear to what extents the cold environmental temperature stress would alter the phloem ultrastructure and RFO accumulation in RFO-transporting plants. In this study, we firstly utilized electron microscopy to investigate the changes in the phloem ultrastructure of lateral branches and RFO accumulation in melons after being subjected to low night temperatures (12°C and 9°C). The results demonstrated that exposure to 9°C and 12°C altered the ultrastructure of the phloem, with the effect of 9°C being more obvious. The most obvious change was the appearance of plasma membrane invaginations in 99% companion cells and intermediary cells. In addition, phloem parenchyma cells contained chloroplasts with increased amounts of starch grains, sparse cytoplasm and reduced numbers of mitochondria. In the intermediary cells, the volume of cytoplasm was reduced by 50%, and the central vacuole was present. Moreover, the treatment at 9°C during the night led to RFO accumulation in the vascular bundles of the lateral branches and fruit carpopodiums. These ultrastructural changes of the transport structure (phloem) following the treatment at 9°C represented adaptive responses of melons to low temperature stresses. Future studies are required to examine whether these responses may affect phloem transport.

Agatharesinol biosynthesis-related changes of ray parenchyma in sapwood sticks of Cryptomeria japonica during cell death.

The work demonstrates a relationship between the biosynthesis of the secondary metabolite, agatharesinol, and cytological changes that occur in ray parenchyma during cell death in sapwood sticks of Cryptomeria japonica under humidity-regulated conditions. To characterize the death of ray parenchyma cells that accompanies the biosynthesis of secondary metabolites, we examined cell death in sapwood sticks of Cryptomeria japonica under humidity-regulated conditions. We monitored features of ray parenchyma cells, such as viability, the morphology of nuclei and vacuoles, and the amount of starch grains. In addition, we analyzed levels of agatharesinol, a heartwood norlignan, by gas chromatography-mass spectrometry in the same sapwood sticks. Dramatic changes in the amount of starch grains and in the level of agatharesinol occurred simultaneously. Therefore, the biosynthesis of agatharesinol appeared to originate from the breakdown of starch. Furthermore, we observed the expansion of vacuoles in ray parenchyma cells prior to other cytological changes at the final stage of cell death. In our experimental system, we were able to follow the process of cell death and to demonstrate relationships between cytological changes and the biosynthesis of a secondary metabolite during the death of ray parenchyma cells.

Pharmacognostic study and establishment of quality parameter for medicinal plant of Dipterocarpaceae in Northeastern state Tripura

Background: Dipterocarpus turbinatus and Shorea robosta are widely distributed in the Northeastern state of Tripura. Tribals of Tripura used both the plant and plant derived product for various purposes in their daily life. Aim: The present investigation deals with the macroscopic, microscopic, and preliminary phytochemical screening to establish quality parameters for evaluation of the bark and bark powder of D. turbinatus and S. robosta. Materials and Methods: The microscopic study was done by Magnus lab photomicroscope and physicochemical properties were studied by standard procedure. Barks for these studies were procured from Tripura. Results: Chief characters of the transverse section and powder of the drugs include cork, cortex, parenchymatous cells, stone cell, lignified fiber, and calcium oxalate crystals along with the abundant amount of starch grains. In quantitative, microscopy length and width of lignified fiber and diameter of starch grains had been measured, which shows a significant difference between the two plants of the same family. Physiochemical and preliminary phytochemical evaluation of both the plants show the difference in alkaloid and sponin content. The chief chemical entity present in both the plants includes steroids, flavonoids, terpenoids, and tannins. Conclusion: The established parameter can be used as a biological standard to identify both the plants.

Alterations in the sugar metabolism and in the vacuolar system of mesophyll cells contribute to the desiccation tolerance of Haberlea rhodopensis ecotypes.

Haberlea rhodopensis belongs to the small group of resurrection plants having the unique ability to survive desiccation to air dry state retaining most of its chlorophyll content and then resume normal function upon rehydration. It prefers the shady valleys and northward facing slopes of limestone ridges in mountain zones with high average humidity. Nevertheless, it can be found rarely on rocks directly exposed to the sunlight, without the coverage of the canopy. In the present study, we follow the alterations in the subcellular organization of mesophyll cells and sugar metabolism upon desiccation of shade and sun H. rhodopensis plants. Composition and content of soluble carbohydrates during desiccation and rehydration were different in plants grown below the trees or on the sunny rocks. Sucrose, however, was dominating in both ecotypes. The amount of starch grains in chloroplasts was inversely related to that of sugars. Concomitantly with these changes, the number of vacuoles was multiplied in the cells. This can be explained by the development of small (secondary) vacuoles peripherally in the cytoplasm, rather than by the fragmentation of the single vacuole, proposed earlier in the literature. Accordingly, the centripetal movement of chloroplasts and other organelles may be a result of the dynamic changes in the vacuolar system. Upon rehydration, the inner vacuoles enlarged and the organelles returned to their normal position.

Molecular, Biochemical and Ultrastructural Changes Induced by Pb Toxicity in Seedlings of Theobroma cacao L.

Pb is a metal which is highly toxic to plants and animals, including humans. High concentrations of Pb have been observed in beans of T. cacao, as well as in its products. In this work, we evaluated the molecular, biochemical, and ultrastructural alterations in mature leaves and primary roots of seedlings of two progenies of T. cacao, obtained from seed germination in different concentrations of Pb (0, 0.05, 0.1, 0.2, 0.4, 0.8 g L-1), in the form of Pb(NO3)2. The progenies resulted from self-fertilization of Catongo and a cross of CCN-10 x SCA-6. The Pb, supplied via seminal, caused alterations in the ultrastructures of the mesophyll cells and in the amount of starch grains in the chloroplasts. The dosage of substances reactive to thiobarbituric acid showed that Pb induced lipid peroxidation. The activity of guaiacol peroxidases and the expression of genes associated to synthetase of phytochelatin, SODcyt and PER increased in response to Pb. In addition, there was alteration in the expression of stress-related proteins. The progeny of CCN-10 x SCA-6 was more tolerant to Pb stress when compared to Catongo, since: (i) it accumulated more Pb in the roots, preventing its translocation to the shoot; (ii) it presented higher activity of peroxidases in the roots, which are enzymes involved in the elimination of excess of reactive oxygen species; and (iii) increased expression of the gene in the phytochelatin biosynthesis route. The results of the proteomic analysis were of paramount importance to differentiate the defense mechanisms used by both progenies of T. cacao.

Callus ontogeny of the Kappaphycus alvarezii (Rhodophyta, Gigartinales) brown tetrasporophyte strain

This study analyzes the callus ontogeny of the Kappaphycus alvarezii brown strain tetrasporophyte using micropropagation and tissue culture. Calli were induced from axenic explants and grown for 2 months. Ontogenic analysis was made in explants collected from days7 to 60 of culture and observed under light and transmission electron microscopy (TEM). At the end of the experimental period, 60-day samples were also analyzed by confocal microscopy. Formation of calli was initiated in the first week from medullary and cortical cells of the explant region in air contact. Alterations in the apical region of the cells were observed in TEM as cell wall thickening, proliferation of convoluted membranes, increased number of mitochondria and chloroplast alterations, indicating the dedifferentiation of these cells. Throughout the experiment, the thick cell wall of the cells which compose callus filaments showed the presence of acidic polysaccharides, suggesting a large amount of carrageenan and neutral polysaccharides. The cytoplasm showed the following main characteristics: large amount of starch grains, presence of chloroplasts with al- tered plastoglobules, as well as disorganized thylakoids, presence of several convoluted membranes, and vacuoles. These filaments maintained their uniseriate organization and irregular branching with many intercellular connections be- tween them. Despite the initial stress caused by explant isolation and the beginning of callus formation, results showed that filaments were capable of reorganization and development, retaining their dedifferentiated cells, which, in turn, strongly suggested the potential of callus-based micropropagation.

Anther structure and pollen ontogeny of Hosta Tratt. and its systematic significance

Anther structure and pollen ontogeny of six species of Hosta Tratt. was studied to provide additional data for its classification. Microscopic observation found that their male gametogenesis has the following structural characteristics: (1) the four microsporangia are linearly arranged on introrse side of anther connective tissue; (2) mature anther wall is composed of an epidermis, endothecium, middle layer(s), and tapetum; (3) microsporogenesis is successive; (4) mature pollen grains are three-celled at anthesis, with a vegetative cell filled with large amounts of starch grains; (5) pollen ontogeny is obviously asynchronous; (6) each tepal has about 9–13 vascular traces in cross-section view. The above observations suggest that genus H. Tratt. should be classified as family Hostaceae, in agreement with Dahlgren and Clifford (1982), Takhtajan (1997), and Wu et al. (2003).

Stoloniferous shoot protoplast, an efficient cell system in potato for somatic cell genetic manipulations

The present study reports that protoplasts isolated from stoloniferous shoots (SS) of potato represent an efficient system for somatic cell genetic manipulations. SS were established from single-node cuttings on MS medium supplemented with either 0.1 or 0.2 M sucrose (Suc), and protoplasts were isolated and cultured within the alginate strip, following an improved method. SS induced by 0.1 M Suc yielded 8–22 × 10 5 protoplasts g −1 fresh mass, with a high morphogenic competence. However, 0.2 M Suc-induced SS yielded protoplasts that contained large amounts of starch grains, resulting in their high degree of fragility, delayed cell division and poor morphogenic competence. For symmetric somatic hybridization (electrofusion) between Solanum tuberosum Gp. Tuberosum androgenic (di)haploid (2 n = 2 x = 24) ‘C-13’ and diploid (2 n = 2 x = 24) wild species S. pinnatisectum, protoplasts isolated from 0.1 M Suc-induced SS were also found to be most responsive. Out of several putative somatic hybrids, there were two tetraploids and five diploids, with 48 and 24 chromosomes, respectively at all the three shoot layers (L 1–L 3). This precluded the occurrence of mixoploidy vis-à-vis chimaerism in regenerants, as common in somatic fusion involving mesophyll protoplasts of S. pinnatisectum. Nuclear microsatellite analyses based on the two single-locus nSSR loci ( STM0037 and STM2030) confirmed that one of the tetraploids was a true nuclear hybrid (heterokaryon), while the other a homokaryon of the Tuberosum parent ‘C-13’. The use of 0.2 M Suc-induced SS protoplasts for fundamental studies on tissue- and/or cell type-specific transient gene expression underlying tuberization has been discussed.

Pollen tube reuses intracellular components of nucellar cells undergoing programmed cell death in Pinus densiflora

Through the process known as programmed cell death (PCD), nucelli of Pinus densiflora serve as the transmitting tissue for growth of the pollen tube. We sought to clarify the processes of degradation of nucellar cell components and their transport to the pollen tube during PCD in response to pollen tube penetration of such nucelli. Stimulated by pollination, synthesis of large amounts of starch grains occurred in cells in a wide region of the nucellus, but as the pollen tube penetrated the nucellus, starch grains were degraded in amyloplasts of nucellar cells. In cells undergoing PCD, electron-dense vacuoles with high membrane contrast appeared, assumed a variety of autophagic structures, expanded, and ultimately collapsed and disappeared. Vesicles and electron-dense amorphous materials were released inside the thickened walls of cells undergoing PCD, and those vesicles and materials reaching the pollen tube after passing through the extracellular matrix were taken into the tube by endocytosis. These results show that in PCD of nucellar cells, intracellular materials are degraded in amyloplasts and vacuoles, and some of the degraded material is supplied to the pollen tube by vesicular transport to support tube growth.

Changes in ultrastructure and responses of antioxidant systems of algae ( Dunaliella salina) during acclimation to enhanced ultraviolet-B radiation

Because of depletion of the stratospheric ozone layer, levels of solar ultraviolet-B (UV-B) radiation (280–315 nm), which penetrates the water column to an ecologically-significant depth, are increasing. In order to assess changes in ultrastructure and responses of antioxidant systems of algae during acclimation to enhanced ultraviolet-B radiation, Dunaliella salina was treated with higher dose of UV-B radiation (13.2 kJ m −2 d −1 dose) in this study. As compared to the control panel (8.8 kJ m −2 d −1), the treatment D. salina had many changes in ultrastructures: (1) thylakoids became swelled, and some of them penetrated into the pyrenoid; (2) lipid globules accumulated; (3) the amounts of starch grains increased; (4) cristae of mitochondria disintegrated; (5) inclusions in vacuoles reduced; and (6) cisternae of Golgi dictyosomes became loose and swollen. Enhanced UV-B irradiation also induced different responses of the antioxidant systems in D. salina: (1) contents of TBARS (thiobarbituric acid reacting substance) and H 2O 2 increased significantly ( p < 0.05); (2) levels of MAAs (mycosporine-like amino acids) increased at the beginning and subsequently decreased, and finally they leveled off at lower values; (3) there were not apparent variations for carotenoid contents, and contents of chlorophyll a presented a trend of initial increase and ultimate decrease; (4) both ascorbate and glutathione contents increased significantly ( p < 0.05); and (5) for the enzyme activities, POD activities increased remarkably ( p < 0.05), and SOD activities declined apparently ( p < 0.05), and CAT activity in D. salina had slight variations ( p > 0.05). In addition, growth curve displayed that enhanced UV-B radiation prominently inhibited increase of cell concentration when compared with control panel ( p < 0.05). Our results indicated that enhanced UV-B radiation caused ultrastructural changes of D. salina and induced different responses of antioxidant systems in D. salina.

Effect of Water Deficit Stress on the Physiology, Growth and Leaf Cell Ultrastructure of Sorghum (&lt;i&gt;Sorghum bicolor&lt;/i&gt;r (L.) Moench)

An experiment was conducted in growth chambers to study the response of sorghum cultivars to water deficit stress. Seven sorghum cultivars were evaluated under three water deficit levels [control (-0.05 MPa), mild stress (-0.27 MPa), and severe stress (-0.96 MPa)] in a hydroponic culture in a completely randomised block design replicated three times. The three water deficit levels were created by adding 0, 10 and 20% (w/v) polyethylene glycol 6000 (PEG 6000) to the nutrient solution. The results indicated that water deficit, especially severe water deficit (-0.96 MPa), severely affected the growth and physiology of sorghum. Water deficit stress reduced plant height, leaf area, dry matter accumulation, water use efficiency, root length, and stomatal density. Water deficit stress increased stomatal closure and thus leaf diffusive resistance. Stressed plants deposited larger amounts of epicuticular wax on leaf surfaces and stomatal openings. Water stress significantly reduced the amount of starch grains in the chloroplasts. Sorghum cultivars displayed distinctive response to water deficit stress for many of the parameters. Jigurti, Gambella 1107 and Meko grew better than P9403 and SA1486 under water deficit conditions. Jigurti showed no significant reduction in any of the growth parameters even under severe water deficit (-0.96 MPa) conditions. Keywords: Epicuticular wax; Leaf diffusive resistance; Leaf relative water content; Starch; Stomata; Water use efficiency.Ethiopian Journal of Biological Sciences Vol. 5 (2) 2006: pp. 161-176

Refshøjgård – Et bemærkelsesværdigt gravfund fra enkeltgravskulturen

Refshøjgård – Et bemærkelsesværdigt gravfund fra enkeltgravskulturen

Rapid degradation of starch in chloroplasts and concomitant accumulation of soluble sugars associated with ABA-induced freezing tolerance in the moss Physcomitrella patens

Abscisic acid (ABA) has been postulated to play a role in the development of freezing tolerance during the cold acclimation process in higher plants, but its role in cold tolerance in lower land plants has not been elucidated. The moss Physcomitrella patens rapidly developed freezing tolerance when its protonemata were grown in a medium containing ABA, with dramatic changes in the LT 50 value from –2 °C to over –10 °C. We examined physiological and morphological alterations in protonema cells caused by ABA treatment to elucidate early cellular events responsible for rapid enhancement of freezing tolerance. Microscopic observations revealed that ABA treatment for 1 day resulted in a dramatic alteration in the appearance of intracellular organelles. ABA-treated cells had slender chloroplasts, with a reduced amount of starch grains, in comparison with those of non-treated cells. The ABA-treated cells also had several segmented vacuoles while many of non-treated cells had one central vacuole. When frozen to –4 °C, freezing injury-associated ultrastructural changes such as formation of aparticulate domains and fracture-jump lesions were frequently observed in the plasma membrane of non-treated protonema cells but not in that of ABA-treated cells. The ABA treatment increased the osmotic concentration of the protonema cells, in correlation with accumulation of free soluble sugars. These results suggest that ABA-induced accumulation of soluble sugars, associated with morphological changes in organelles, mitigated freezing-induced structural damage in the plasma membrane, eventually leading to enhancement of freezing tolerance in the protonema cells.

ニホンナシの花芽分化に伴う茎頂細胞の微細構造の変化

To elucidate the mechanism of flower differentiation, ultrastructural changes, particularly the changes in amount and shape of organelles were investigated in the apical meristem of the buds of Japanese pear (Pyrus pyrifolia Nakai cv. Shinsui) during flower bud differentiation.1. The most important stages in the flower bud differentiation were from the beginning of activation of corpus cells on June 26 to the differentiation of sepal primordia on July 17. During these periods all the organelles in the cell underwent remarkable changes.2. During flower differentiation the number of dictiosomes markedly increased with concomitant cytomorphological changes such as many larger vesicles and the reduction in length of dictiosome itself. Distribution of endoplasmic reticulum (ER) also increased with the increase in ribosome. ER evolved into a kind of network from a discontinuous linear shape. There also existed active dictiosomes associated with ER.3. The number and size of mitochondria increased during flower differentiation. As the size increased the shape became spherical or oval. The number and size of plastids in the cells of active tissues did not differ between flower buds and vegetative buds. The size of plastids in the cells of quiescent zone changed markedly, increasing initially and then decreasing, because the size was closely related to the amount of starch grains the plastids contained.4. While flower differentiation progressed, chromatin in the nucleus increased and became densely stained in the cells of apical meristem of the flower buds. Nucleoli also increased in size, and occasionally two nucleoli were observed in a nucleus. Actively dividing cells in the apical meristem of flower buds were also characterized by many small vacuoles.5. These ultrastructural changes of the organelles in the cell of flower buds were discussed in relation to their physiological roles.

Ultrastructural Changes in Chloroplast and Phloem of Rice Leaves during Senescense under Different Nitrogen Supply.

Rice seedlings of 7.2 in leaf age were transplanted into pots containing culture solution. The control plants received the complete solution and the N-deficient plants received the -N solution. Samples for electron microscopy were cut from the central part of the 7th leaf blades 0, 15 and 34 days after expansion (DAE) . In the control plants, a large amount of starch grains in the chloroplasts from leaves 0 DAE was disappeared and the inner membrane system of chloroplast was more developed at 15 DAE. The decrease in inner membranes and the contraction of chloroplasts were observed at 34 DAE. In the N-deficient plants, however, the decrease in inner membranes and the contraction of chloroplast were occurred at 15 DAE, without disappearance of the starch grains. The protophloem sieve element-companion cell complexes of small bundles showed an apparent degeneration at 0 DAE, but the degeneration was not observed in the metaphloem, in which the P-plastids appeared in the thick-walled sieve elements. In the control plants, a part of the metaphloem had begun to degenerate at 15DAE and the greater part of the metaphloem was degenerating at 34 DAE. In the N-deficient plants, however, an extensive degeneration was observed at 15 DAE. The degeneration of phloem was characterized by the plasmolysis of sieve elements and companion cells, the swelling and breakdown of mitochondria, and the accumulation of osmiophilic globules in the companion cells. It can be considered that the degeneration of metaphloem is closely related to the decline of transport activity in the senescent leaf.