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1.
R. B. Pearce 《Forest Pathology》1990,20(5):275-289
Suberization responses to naturally-occurring fungal colonization of living xylem tissues were detected in 30 of 37 woody species examined. These responses comprised the suberization of traumatic parenchyma tissues in compartmentalization wall 4 barrier zones laid down in the vicinity of fungally infected wounds, or the suberization of parenchyma cells, tyloses and vessel linings in reaction zone decay margins in fully differentiated sapwood. Additionally, in a few species, suberization of xylem fibres and tracheids was observed where juvenile xylem tissues, apparently still incompletely differentiated, had been exposed by wounding. These xylem suberization responses are considered to increase the decay resistance of the altered cells, and may protect the hydraulic integrity of adjacent tissue, thus contributing to the antimicrobial defence of the living sapwood. 相似文献
2.
Colonization of Carya cordiformis sapwood by Ceratocystis smalleyi and subsequent host defence responses following artificial inoculation were investigated using anatomical and histological techniques. Hyphae of C. smalleyi were observed in all sapwood xylem features confirming the ability of the pathogen to invade and colonize the xylem tissues of the host species. The fungus was isolated from within and at the margins of discoloured sapwood areas at 2 and 12 months after inoculation. General host defence responses that included vessel occlusion with gels or tyloses, lipid accumulation, and production of phenolic compounds were observed in xylem tissues of inoculated C. cordiformis stems. Pectic substances, lipids, and to a rare extent, phenolic compounds were detected in vascular gels. The lipid‐rich barriers observed likely prevent lateral expansion of the fungus in the sapwood. Furthermore, lack of fungus sporulation within vessels may restrict axial spread of the fungus. C. smalleyi appears to be a limited vascular wilt pathogen of bitternut hickory based on these observations and previously reported sap flow reduction correlated with multiple infections in artificially inoculated trees. 相似文献
3.
Anatomical and cellular responses of Pinus monticola stem tissues to invasion by Cronartium ribicola
J. W. Hudgins G. I. McDonald P. J. Zambino N. B. Klopfenstein V. R. Franceschi 《Forest Pathology》2005,35(6):423-443
White pine blister rust (Cronartium ribicola) causes extensive damage to white pines and their associated ecosystems across North America. The anatomical and cellular characteristics of C. ribicola colonization in Pinus monticola branch and stem tissues were studied as a basis for understanding host tree reactions that may be related to resistance. Samples examined showed typical fusiform swelling and some had produced aecia. The reaction of phloem and xylem tissues was compared with non-infected tissue using light and electron microscopy. Cortical parenchyma and phloem polyphenolic parenchyma cells underwent mitotic division, cell swelling, and ca sixfold greater accumulation of phenolic compounds in colonized vs. control stems. In the cortex and secondary phloem, haustoria were common in parenchymatous cells, and hyphae were abundant in the intercellular spaces, but cell death was rare, unless aecia had ruptured the stem cortex. Hyphae were also common in xylem rays, tracheids and between tracheids. Disease-induced changes in the cambial zone included development of cambium-derived xylem traumatic resin ducts. Results demonstrate that diverse host defence responses were activated in the bark of apparently susceptible trees, but lack of mechanical damage by C. ribicola to the phenol-containing host cells and the resin duct system allowed extensive colonization and development of aecia despite elicitation of these stem defences. Interactions between P. monticola and C. ribicola are discussed and compared with other conifer–fungus pathosystems. 相似文献
4.
The seasonal progression of xylem dysfunction from tyloses and embolism induced both by cavitation and frost was studied in Quercus rubra L. and Quercus alba L. branches. Vessel lengths and diameters were measured in current-year rings of branches of various ages. Vessels in current-year shoots are about the same size as those in many diffuse porous trees, but vessels in older branches are two to six times larger in diameter and typically more than 10 times longer. Large Quercus vessels were more vulnerable to cavitation than small vessels. The small vessels in current-year shoots were more vulnerable to cavitation than vessels of comparable size in diffuse porous species. Earlywood vessels are completely blocked by tyloses within a year of their formation. Tylose growth starts in winter, but the vessels are not fully blocked until the next summer. Many latewood vessels, by contrast, remain free of complete blockage for several years. In Q. rubra, loss of hydraulic conductivity in current-year shoots due to cavitation reaches 20% by August and > 90% after the first hard frost. Both laboratory and field observations confirm that the role of frost in causing loss of hydraulic conduction by embolism is much more dramatic in Quercus than in conifers and diffuse porous hardwoods. 相似文献
5.
Roman Gebauer Roman Plichta Emilie Bednářová Jiří Foit Václav Čermák Josef Urban 《European Journal of Forest Research》2018,137(1):57-67
While needles represent a proportionally large fraction of whole-plant hydraulic resistance, no studies to date have investigated how source–sink disturbances affect needle xylem structure. In this study, we evaluated structural changes in xylem in current-year needles of Scots pine 227 and 411 days after stem girdling (hereafter referred to as DAG). Maximum and minimum tracheid lumen diameters and therefore also the size of tracheid lumen areas increased in needles 227 DAG compared to control needles. In contrast, tracheid dimensions were similar in needles 411 DAG as in the control needles, but smaller xylem area and lower number of tracheids resulted in the lower theoretical needle hydraulic conductivity of those needles. Several needle xylem parameters were intercorrelated in both control and girdled trees. These observed changes provide a new understanding of the processes that occur following a source–sink disturbance. Considering anatomical parameters such as the number of tracheids, tracheid dimension, or needle xylem area, which are rarely described in physiological studies, could be helpful, for example, in understanding to tree hydraulic systems or for modeling gas exchange. Finally, empirical equations were developed to calculate needle theoretical hydraulic conductivity and the number of tracheids in needles using an easily measurable parameter of needle xylem area. 相似文献
6.
Haustorial morphology of the cone-rust pathogen, C. conigenum, was investigated among naturally infected female strobili of three Guatemalan pines, P. maximinoi, P. pseudostrobus, and P. oocarpa. Among the three pine species, haustorial shapes and sizes were more variable in P. maximinoi and P. oocarpa than in P. pseudostrobus. The haustorial shapes and sizes were more variable in parenchyma cells of the cortex, xylem, and pith than in the cells in the phloem, xylem rays, and tracheids. The haustoria were also present in larger numbers in the parenchyma cells of the cortex, xylem, and pith than in phloem parenchyma cells and tracheids. In living cells, the tips of some haustoria were appressed to the host nuclei. 相似文献
7.
The “wood” of palms consists of primary vascular bundles imbedded in a parenchymatous ground tissue. The texture and hardness of a palm stem or petiole depend largely upon the distribution of vascular bundles and the amount of sclerenchyma present. The sieve elements are structurally similar to those in other angiosperms. However, in palms the sieve elements are long-lived, unlike those in most dicotyledons and gymnosperms. Metaxylem tracheary elements vary in their morphology depending on the organ and/or species in which they occur. Scanning electron microscopy observations indicate that the distinction between tracheids and vessels is not sharp but is a matter of degree. The fibers usually have a well developed secondary wall with a characteristically mulilayered appearance. There are indications that the protoplast of these cells continues to lay down secondary walls over a long period. Fibers are commonly associated with silica-containing cells, the stegmata. 相似文献
8.
The fine structure of differentiating and mature sieve elements, tracheary elements and fibers of palms has been studied. The fine structure of sieve elements in general resembles that of the sieve elements in angiosperms except that not all the species of palms have P-protein. Material examined after taking precautions to minimize sudden release of pressure in the phloem indicate that the sieve-plate pores may be free of occlusions in intact sieve elements. Sieve elements in the basal parts of the stem estimated to be several decades old maintain their structural integrity and apparently remain functional throughout the life of the palm. Differentiating xylem elements are characterized by the presence of amoeboid plastids with electron-dense granular stroma. All the organelles normally present in meristematic cells are also present in differentiating tracheary elements. Bundles of microfilaments are often present in such elements. Structural changes that occur as the tracheary element matures are comparable to those observed in tracheary elements of other angiosperms. Xylem parenchymatous cells do not have the so called protective wall layer. The most striking ultrastructural feature in differentiating fibers of the root is the deep invagination of plasmalemma that traverses almost the entire width of the cell. The secondary wall of the fibers is characteristically multilayered.This paper was presented at the Eighth Cellulose Conference, Syracuse, New York, U.S.A. 相似文献
9.
Summary Anatomical differences in xylem between the upper and lower sides formed in the inclined stems of Buxus microphylla with different angular displacement from the vertical were examined microscopically. B. microphylla exhibited a pronounced growth promotion on the lower side of the inclined stems. Formation of tension wood (gelatinous fibers) was not observed. Xylem formed on the lower side showed some interesting features resembling the compression wood formed in gymnosperms. The reaction wood tracheids and vessels showed an excessive lignification in their secondary walls but lacked both helical cavities and an S3 layer, features that were almost the same as those of primitive gymnosperms. These results indicate that B. microphylla has an ability to form compression wood, suggesting that in the genus Buxus a different mechanism in the conducting elements was developed in the phylogenetic evolution.The first author would like to express his sincere thanks to Dr. T. E. Timell, College of Environmental Science and Forestry, State University of New York, Syracuse, New York, for his invaluable suggestions in connection with this research 相似文献
10.
N. Yoshizawa A. Inami S. Miyake F. Ishiguri S. Yokota 《Wood Science and Technology》2000,34(3):183-196
Summary Anatomical features of reaction wood formed in two Magnolia species, M. obovata Thunb. and M. kobus DC. which are considered to be among the primitive angiosperms, were observed. In addition, the distribution of guaiacyl
and syringyl units of lignins in the cell walls of normal and reaction wood was examined using ultraviolet (UV)- and visible
light (VL)- microspectrophotometry coupled with the Wiesner and M?ule reactions. The two Magnolia species formed a tension-like reaction wood without possessing the typical gelatinous layer (G-layer) on the upper side of
the inclined stem or branch, in which a radial growth promotion occurred. Compared with the normal wood, the reaction wood
had the following anatomical features: (1) the secondary walls of fiber tracheids lacked the S3 layer, (2) the innermost layer of fiber-tracheid walls showed a small microfibril angle, a fact being similar to the orientation
of the microfibril angle of the G-layer in tension wood, and (3) the amounts of lignin decreased in the cell walls of fiber
tracheids, especially with great decrease in proportion of guaiacyl units in lignins. In addition, VL-microspectrophotometry
coupled with the Wiesner and M?ule reactions adopted in the present study showed potential to estimate the lignin contents
in the cell walls and the proportion of guaiacyl and syringyl units in lignins.
Received: 15 July 1998 相似文献
11.
Ethylene release from Pinus thunbergii Parl. seedlings was examined after inoculation with virulent and avirulent isolates of Bursaphelenchus xylophilus. Enhanced ethylene release was observed only in seedlings inoculated with the virulent isolate. The avirulent isolate induced necrosis of xylem ray cells and embolism in some tracheids, however, the cambium and outermost xylem was intact where water conduction was maintained. The ethylene increase coincided with cambial death in seedlings inoculated with the virulent isolate. 相似文献
12.
中国蒺藜科3种旱生植物的木材解剖适应性 总被引：2，自引：0，他引：2
从木材次生木质部特性和径向变异两方面,对中国西部区的蒺藜科的3种旱生植物(Zygophyllumxanthoxylon,Nitrariatangutorum,Tetraenamongolica)进行了对比研究。3树种具有的共同特点为:生长轮分界明显,但是霸王和四合木的年轮有时不连续,半环孔到环孔材,具单穿孔,穿孔板倾斜,导管壁间纹孔互列,木纤维无横隔膜,联合傍管轴向薄壁组织,导管壁上呈现螺纹加厚和异型射线。所选树种明显区别是导管排列方式和导管的数量化指标:四合木导管直径较小,长度较短,频率较大,水分传导安全性增加。其他2种树种之间导管指标没有多大差别,但均比沙冬青的值大。树种导管要素长和纤维要素长的水平变动不规律,树种间和同一树种个体间差异显著。并且对该树种的解剖学特征和沙漠环境的适应性进行了讨论。图19表2参24。 相似文献
13.
Cell behavior in the cambium and developing xylem of 3-year-old Japanese cedar (Cryptomeria japonica D. Don.) trees, during and after an 11-day suspension of irrigation, was analyzed. Leaf xylem pressure potential and tangential strain of the stem surface were monitored throughout the experiment. Anatomical features and numbers of developing tracheids and cambial cells were observed in four trees, sampled on Days 0, 4, 8 and 11 after irrigation was suspended. Daytime xylem pressure potential decreased to -1.9 MPa on Day 7 and remained the same until irrigation was resumed on Day 11. The transverse dimensions of the tracheids, which began to form secondary walls, began to decrease on Day 4. The number of cells in the cambial zone and cell expansion zone decreased abruptly on Day 8. Tangentially aligned developing tracheids with collapsed cell walls were observed in samples harvested on Days 8 and 11. Secondary wall formation was recognized in these tracheids. After the resumption of irrigation, xylem pressure potential recovered rapidly to the same value as before the suspension of irrigation. Tangential strain increased within 30 min after the resumption of irrigation, and continued to increase until the onset of light the next day. Eighteen days after the resumption of irrigation, anatomical features of cells in the cambium and cell-expansion zone were similar to those observed before suspension of irrigation. 相似文献
14.
Telewski FW 《Tree physiology》1989,5(1):113-121
Wood produced during flexure in one-year-old leaders of Abies fraseri (Pursh) Poir. (Fraser fir) was analyzed anatomically and radio-densitometrically. More xylem cells were produced in stems subjected to flexing than in stems that were not flexed. The lumens of tracheids produced in response to flexure were smaller than the lumens of tracheids in normal wood. This was manifest as an increase in the cell wall area/cell lumen area ratio. Microfibril orientation in flexure-induced wood approached the less extreme values found in compression wood. The growth ring composed of flexure-induced wood also had a greater density than normal wood. Compression wood, as defined by cellular characteristics observed in transverse section, was absent in flexed stems. Detailed analysis of the anatomical structure, wood density and biomechanical properties of flexure-induced wood indicated that it has more in common with compression wood than with normal wood. 相似文献
15.
《Scandinavian Journal of Forest Research》2012,27(1-4):45-58
Flooding of soil for 55 days altered the rate of growth and stem anatomy of 9‐month‐old Cryptomeria japonica seedlings. Although flooding did not affect height growth it reduced the rate of dry weight increment of seedlings while increasing stem diameter. The reduction in dry weight increment of seedlings resulted largely from decay of roots and, to a lesser extent, from inhibition of growth of roots and needles. The increased diameter growth of flooded seedlings resulted largely from an increase in bark thickness associated with increased phloem production and greater amount of intercellular space. Flooding reduced xylem increment in submerged stems but increased it above the water level because of larger tracheids rather than more tracheids per radial file. Flooding also increased lumen diameters of tracheids, decreased tracheid wall thickness (as a proportion of tracheid diameter), and stimulated formation of axial parenchyma cells in the xylem. Cryptomeria japonica seedlings adapted to flooding by forming adventitious roots, primarily on the original root system and submerged portion of the stem. Such new roots originated in the xylem ray parenchyma. Flooding stimulated ACC synthesis in roots and ethylene production in stems. The role of ethylene in alteration of stem anatomy is discussed. 相似文献
16.
YANG Shu-min FURUKAWA Ikuo 《林业研究》2006,17(3):247-251
Secondary xylem characteristics and horizontal variations were described in three xerophytic species, Zygophyllum xanthoxylon, Nitraria tangutorum, Tetraena mongolica of Zygophyllaceae native to western China. All the species have obvious growth ring boundaries except sometimes discontinuous in T. mongolica and Z xanthoxylum ring to semi-ring-porosity; simple perforation plate; alternate intervessel pitting; non-septate fibres; paratracheal confluent axial parenchyrna; helical thickenings and heterocellular rays. However the vessel arrangement and quantitative features of vessels were different. Vessel elements tend to be shorter and narrower and more frequent in T. mongolica than in other two species that are hardly different could lead to greater conductive safety. The variation of vessel element length and fibre length along radial direction showed irregular tendency. There was significant difference in both fibre length and vessel element length among-tree and within-tree. Furthermore, the relationships between anatomical features and adaptability to desert environments were also discussed. 相似文献
17.
蒸腾能使木质部产生不超过-0.1MPa的有限负压,这个负压在木质部内自上而下依次向下传递。水分在导管或管胞内所受的吸附力、毛管力、真空力等综合作用力要大于或等于所受的重力,这个综合作用力可以将水分托住而不受重力作用而下移,使水分在负压作用下以分段移动的方式从根部上升到植物顶端。空穴和栓塞是两个不同的概念,其形成过程、恢复机制都有其本质的不同。空穴的发生与负压和水分的分段移动有密切的关系。 相似文献
18.
Keiko Kuroda 《Journal of Forest Research》2012,17(1):58-64
Xylem dysfunction progresses rapidly in Pinus thunbergii infected with pine wilt disease. The present report deals with the timing and process of the extensive dehydration of tracheids
by embolism and the subsequent desiccation of the xylem with disease development. An ultrasonic acoustic emission (AE) technique
was used to detect embolisms in the xylem of pine trunks. In most of the P. thunbergii saplings inoculated with the pathogen Bursaphelenchus xylophilus, the AE frequency suddenly increased in the second week after inoculation. The high-frequency AE continued for about 3 days
and into the nights. Harvesting of specimens at this time revealed that white air-filled patches, representing the dehydrated
and dysfunctional areas, had just emerged in the sapwood. The AE events in the night must be due to something other than embolisms
in healthy trees. Frequent embolism of tracheids, which was suggested by the elevation of the AE frequency, might occur due
to the decrease in the tensile strength of xylem sap. This hypothesis is supported by previously reported data. Host cells
that had reacted to infection with B. xylophilus produce and release chemicals which can lower the surface tension of xylem sap. During the second increase of AEs, most of
which occurred in the third week, xylem desiccation and needle yellowing progressed. Needle fading then became distinct, and
the tree was close to death when the AE frequency dropped during the fourth week. By monitoring the AE, the first physiological
abnormality that took place very early after infection was detected. 相似文献
19.
Bond's "slow seedling" hypothesis proposes that, because of slow growth rates caused by an inefficient transport system and low leaf photosynthetic capacity, gymnosperm seedlings are weak competitors with angiosperms in productive habitats. We measured component (shoot, leaf, and root) and whole-plant hydraulic conductances of sapling-sized tropical plants growing on nitrogen-poor white sand in Borneo. After accounting for size effects, there were no significant differences in conductances between evergreen angiosperms (nine species) and conifers (three species). Plant successional status or transpiration rate seemed more important than soil fertility in determining hydraulic conductance-colonizers had significantly higher whole-plant conductance than late-succession species. Contrary to prediction, leaf hydraulic conductance (normalized by projected leaf area) was unrelated to complexity of venation in conifers and angiosperms, but was highly correlated with whole-plant conductance. Analyses of published data showed that leafless branches of temperate deciduous angiosperms had higher leaf-area normalized hydraulic conductivity than conifers, but there was no significant difference in adult, whole-plant conductance between these taxa. Thus, at the branch level, conifers with narrow tracheids have less efficient transport than angiosperms with wider vessels, but variations in other resistance components and hydraulic architecture (e.g., sapwood/leaf area ratio) ultimately equalize the sufficiency of water transport to leaves of conifers and angiosperms. Although failing to support one of the proposed mechanisms, our findings did not refute the "slow seedling" hypothesis per se. 相似文献
20.
中国裸子植物木材管胞瘤状层的电镜观察 总被引：4，自引：2，他引：4
本文对中国裸子植物11科、41属、99种木材管胞瘤状层进行了系统观察。瘤状层的有无及形态特征是区分裸子植物材的重要标志。此外并对5种针叶树材在一个年轮内,瘤状层从早材到晚材大小、分布密度的变化做了观察;12种针叶树材的切片,用0.5％次氯酸钠溶液处理后,瘤状物减小、以至消失;在另6个树种的管胞内,观察到瘤状层被白腐菌或软腐菌溶解。 相似文献