Seasonal variations in the cambial anatomy of Tectona grandis (Verbenaceae)

A study of seasonal activity of the cambium in Tectona grandis L. f. has shown that the activity initiates in the first week of June, reaches a peak in July and then slowly declines. The length of fusiform cambial initials undergo considerable variations during the activity and dormancy of the cambium. The initiation of cambial activity is closely associated with the opening of the dormant foliar buds in the first week of May. Cambium is more active with high numbers of immature xylem and phloem elements from July to September when the trees are with mature foliage and flowers and dormant from January to April when leaves dry and defoliation takes place. The differentiation of xylem and phloem starts simultaneously and the number of their immature elements reach the maximum in July.     

The Annual Rhythm of Activity of the Lateral Meristems (Cambium and Phellogen) in Cupressus sempervirens L

The annual rhythm of cambial activity in Cupressus sempervirensseems to be endogenous and fits well the Mediterranean climaticrhythm. Under outdoor conditions the cambium begins its activitytowards the autumn when temperatures drop and water is lesslimiting. The cambium continues to be active during the mildMediterranean winter and enters dormancy towards the beginningof the dry summer. A constant supply of water is not enoughto avoid cambial dormancy but may result in earlier onset anda prolonged period of activity. Relationships between xylemand phloem production, between shoot and root, and between cambialand phellogen activity are discussed. Cupressus sempervirens L., cypress, cambium, phellogen, annual rhythm, wood production     

Seasonal histochemical changes in the cambium ofTectona grandis L. f. andgmelina arborea roxb

Starch, lipids and proteins are localized histochemically in fusiform and ray initials ofTectona grandis andGmelina arborea during the periodicity of cambium in the year 1978. The histochemical variations are correlated with the seasonal activity and dormancy of the cambium and phenology. Starch grains appear in the cambial cells with the development of young leaves after defoliation. Lipid and protein bodies are significantly high in dormant cambial cells and scarce in active ones.     

EFFECT OF ISOLATION OF BARK ON CAMBIAL ACTIVITY AND DEVELOPMENT OF XYLEM AND PHLOEM IN TREMBLING ASPEN

Circular patches of bark were surgically isolated on the sides of trembling aspen (Populus tremuloides Michx.) trees at breast height at various times during the dormant and growing seasons. Subsequently, samples of wood and attached bark were taken from isolated and control sites to determine the effects of isolation of the bark on cambial activity and xylem and phloem development. In control trees cambial activity and xylem and phloem development occurred normally. Isolation of bark during the dormant season (in November, February, or March) did not prevent initiation of cambial activity and of phloem differentiation in spring but continued normal cambial activity and phloem developmented were prevent. Xylem differentiation was essentially prevented by isolation of tissues during the dormant season. The ultimate effect of isolation of the bark on the cambium, either during the dormant season or during the growing season, was subdivision of all fusiform cambial cells into strands of parenchymatous elements; the ultimate effect on the newly formed phloem was early death of the sieve elements. The most conspicuous effect of isolation of the bark after xylem differentiation had begun was the curtailment of secondary wall formation. Shortening of cells of the cambial region was reflected in the length of the vessel members which differentiated from such cells. These results indicate that normal cambial activity and xylem and phloem development require a supply of currently translocated regulatory substances from the shoots.     

INFLUENCE OF PHLOEM BLOCKAGE ON CAMBIAL GROWTH OF SUGAR MAPLE

Circular patches of bark were surgically isolated on the sides of sugar maple (Acer saccharum Marsh.) trees at breast height at various times during the dormant and growing seasons. Subsequently, samples of wood and attached bark were taken from isolated and control sites to determine the effects of isolation of the bark on cambial activity and xylem and phloem development. In control sites cambial activity and xylem and phloem development occurred normally. Isolation of bark during the dormant season (in November, February, or March) prevented initiation of cambial activity and xylem and phloem development in isolated areas of half of the trees. Varying degrees of cambial activity (periclinal divisions) occurred in the remaining isolated areas, but normal cambial activity and xylem and phloem development were prevented. Isolation of bark after initiation of cambial activity and phloem differentiation, but prior to initiation of xylem differentiation, resulted in the formation of very narrow xylem and phloem increments with atypically short vessel members and sieve-tube members, respectively. The xylem increments consisted primarily of parenchyma cells. Isolation of bark after initiation of xylem differentiation resulted in curtailment of secondary wall formation in the last-formed part of many increments. The last-formed vessel members of all these xylem increments were atypically short. Similarly, the last formed sieve-tube members of corresponding phloem increments were atypically short. The atypically short cells in the xylem and phloem of isolated areas reflected the effect of isolation on the cambial region, viz., the subdivision of all fusiform cells into strands of cells. Ultimately, the strands of short fusiform cells lapsed into maturity, leaving only strands of parenchymatous elements between xylem and phloem.     

Cambial reactivation in locally heated stems of the evergreen conifer Abies sachalinensis (Schmidt) Masters

A study was made of cambial activity, the localization of storage starch around the cambium, and the localization and occurrence of microtubules in cambial cells from dormancy to reactivation in locally heated (22–26 °C) stems of the evergreen conifer Abies sachalinensis. Heating induced localized reactivation of the cambium in the heated portions of the stem. Erect ray cambial cells resumed cell division 1 d prior to the reactivation of fusiform cambial cells and procumbent ray cambial cells. The re-initiation of the division of fusiform cambial cells occurred first on the phloem side. During the heat treatment, the amount of storage starch decreased in procumbent ray cambial cells and in the phloem parenchyma adjacent to the cambium but increased in fusiform cambial cells. Preprophase bands of microtubules, spindle microtubules and phragmoplast microtubules were observed both in erect ray cambial cells and in procumbent ray cambial cells. By contrast, no evidence of the presence of such preprophase bands of microtubules was detected in fusiform cambial cells. The results suggest that the localized heating of stems of evergreen conifers might provide a useful experimental model system for studies of the dynamics of cambial reactivation in intact trees. Received: 25 May 2000 / Accepted: 12 July 2000     

SEASONAL DEVELOPMENT OF THE SECONDARY PHLOEM IN ACER NEGUNDO

Functional sieve elements are present year-round in the secondary phloem of the trunk of Acer negundo L., the box elder tree. Judging from numerous collections made between May, 1962, and May, 1964, the seasonal cycle of phloem development is as follows: cambial activity and new phloem differentiation begin in late March or early April; xylem differentiation begins about a month later and is completed in most trees in late August. At the time of cessation of cambial activity most of the relatively wide sieve elements of the current season's increment are mature. However, numerous groups of narrow, immature sieve elements and companion cells located on the outer margin of the cambial zone do not reach maturity until fall and winter. By the time of cambial reactivation in spring, most, if not all, of these narrow elements are mature. Some of the sieve elements which reach maturity either shortly after cessation of cambial activity or during dormancy become non-functional within 6 weeks after resumption of cambial activity in spring, while others remain functional until mid-August. For the phloem increment of a given year, cessation of function begins in September with the accumulation of definitive callose on the sieve plates of the first-formed sieve elements and spreads to all but the last-formed ones by the end of December.     

Seasonal Rhythms of Structure and Behaviour of Vascular Cambium in Ficus rumphii

Cambial structure and activity of Ficus rumphii Blume vary withthe changes in local climate. The cambial cells start swellingearly in April prior to the onset of periclinal divisions whichare most frequent in August. Cell division stops in October.During the growth season, initiation as well as cessation ofthe phloem production precedes that of xylem. A moderately hightemperature is correlated with the cambial reactivation. Onceinitiated, the activity continues at relatively low temperatures.Hot and dry environment favours the phloem production, whereashot and moderately humid conditions induce xylogenesis. Thesize and relative proportion of cambial initials also changewith season. Fusiform initials are shorter and broader duringthe rainy season (July–September) than for the rest ofthe year. Multiseriate and triseriate rays, as also the tallrays, outnumber the other types of rays throughout the year. Ficus rumphii, vascular cambium, phenology, climatic variation     

Cambial growth dynamics and climatic control of different tree life forms in tropical mountain forest in Ethiopia

Munessa Forest is a mountain forest in south-eastern Ethiopia experiencing seasonal rainfall variation. We investigated seasonal cambial activity and dormancy from increment rates of four different tree species belonging to varying life forms, namely, evergreen native conifer (Podocarpus falcatus), evergreen introduced conifer (Pinus patula), evergreen broadleaved tree (Prunus africana) and deciduous broadleaved tree (Celtis africana). Measurements of stem radius fluctuations were registered with the help of high-resolution electronic dendrometers. Daily amplitudes of stem diameter variations and daily and monthly net growth rates were determined and related to climatic variables measured at local climate stations. Thin sections of wood collected with a microcorer every 3–6 weeks allowed a visual control of newly formed wood cells during consecutive time intervals. Lack of water availability during the long dry season induced cambial dormancy of 5–7 months depending on life forms. After the onset of the short rainy season, stem swelling started quite synchronously with a variation of only single days in all studied species. Evergreen tree species were able to initiate wood formation during the short rainy season, whereas growth in the deciduous broadleaved species started in the long rainy season. The acquired data provide a basis for delineating the species-specific growth boundaries and the duration of the cambial growing season.     

Seasonal Variation in Radial Growth and Phloem Activity of Terminalia ivorensis A. Chev

Radial growth in five Terminalia ivorensis trees has been recordedfrom dendrometer reading for a period of 12 months. The durationof the growing season was 7–9 months. Variation in annualradial increment between individual trees was observed to bedue both to differences in the length of the growing seasonand the rate of growth during that period. Seasonal changesin the diameter of sieve elements, and the extent of callosedeposition on the sieve plates have also been investigated.Sieve element diameters were smallest in the dry season, possiblybecause of shrinkage. The width of phloem tissue showing definitivecallose was fairly constant throughout the year, but the zonewith open pores on the sieve plates changed, being widest inSeptember, and narrowest in March when the trees were almostbare. There were two peaks of cambial activity, indicated byan increase in width of the ‘open pore zone’, onein April at the time of bud break, and a second in September. The sugar concentration of the phloem exudate obtained fromsmall cuts into the bark of the trees varied throughout theyear. Concentrations were highest in March, during the dry season,and lowest in May, when the young leaves were expanding. Terminalia ivorensis A. Chev., tropical timber tree, radial growth, callose, phloem exudate, phloem activity     

Reactivation of the Cambium in Aesculus hippocastanum L.: A Transmission Electron Microscope Study

Changes taking place during cambial reactivation in Aesculushippocastanum have been studied using transmission electronmicroscopy. Cytoplasmic activity in the form of vesicle productionby dictyosomes and endoplasmic reticulum, and coated vesicleformation at the plasmalemma, was observed in samples collectedin mid-Feb. The first cell divisions occurred 1 month later,in cells to the phloem side of the cambium, and were of twotypes: penclinal divisions producing new phloem precursors,and oblique anticlinal divisions in phloem mother cells formedat the end of the previous growing season producing putativecompanion cell/sieve element pairs. The fusiform initial wasidentified as the cell adjacent to the boundary-layer of parenchymacells and was the last cell to divide, 2 weeks after the firstdivisions in phloem precursors. For the next 4 weeks phloemcells only were produced The first new differentiating xylemelements were formed in the middle of Apr., following a surgein the rate of cell division by the initial aRd its derivativexylem mother cells. These were a mixture of developing fibresand vessel elements. Some of the boundary-layer cells were converteddirectly to vessel elements without any division taking place,while others were derived from daughter cells of the fusiforminitial produced following its reactivation. Aesculus hippocastanum L., cambium, dormancy, reactivation     

Cambial Activity in Zygophyllum dumosum Boiss

Cambial activity in Zygophyllum dumosum Boiss.—a dominantdesert shrub in Israel—was investigated. Cambial activityin young plants seems to be greatly affected by water supply,while cambial activity in old specimens was found to be moreendogenously controlled. A late-summer cambial dormancy wasobserved under field conditions even in plants that were irrigated.     

Induction of cambial reactivation by localized heating in a deciduous hardwood hybrid poplar (Populus sieboldii x P. grandidentata)

BACKGROUND AND AIMS: The timing of cambial reactivation plays an important role in the control of both the quantity and the quality of wood. The effect of localized heating on cambial reactivation in the main stem of a deciduous hardwood hybrid poplar (Populus sieboldii x P. grandidentata) was investigated. METHODS: Electric heating tape (20-22 degrees C) was wrapped at one side of the main stem of cloned hybrid poplar trees at breast height in winter. Small blocks were collected from both heated and non-heated control portions of the stem for sequential observations of cambial activity and for studies of the localization of storage starch around the cambium from dormancy to reactivation by light microscopy. KEY RESULTS: Cell division in phloem began earlier than cambial reactivation in locally heated portions of stems. Moreover, the cambial reactivation induced by localized heating occurred earlier than natural cambial reactivation. In heated stems, well-developed secondary xylem was produced that had almost the same structure as the natural xylem. When cambial reactivation was induced by heating, the buds of trees had not yet burst, indicating that there was no close temporal relationship between bud burst and cambial reactivation. In heated stems, the amount of storage starch decreased near the cambium upon reactivation of the cambium. After cambial reactivation, storage starch disappeared completely. Storage starch appeared again, near the cambium, during xylem differentiation in heated stems. CONCLUSIONS: The results suggest that, in deciduous diffuse-porous hardwood poplar growing in a temperate zone, the temperature in the stem is a limiting factor for reactivation of phloem and cambium. An increase in temperature might induce the conversion of storage starch to sucrose for the activation of cambial cell division and secondary xylem. Localized heating in poplar stems provides a useful experimental system for studies of cambial biology.     

Changes in the localization and levels of starch and lipids in cambium and phloem during cambial reactivation by artificial heating of main stems of Cryptomeria japonica trees

Background and Aims

Cambial reactivation in trees occurs from late winter to early spring when photosynthesis is minimal or almost non-existent. Reserve materials might be important for wood formation in trees. The localization and approximate levels of starch and lipids (as droplets) and number of starch granules in cambium and phloem were examined from cambial dormancy to the start of xylem differentiation in locally heated stems of Cryptomeria japonica trees in winter.

Methods

Electric heating tape was wrapped on one side of the stem of Cryptomeria japonica trees at breast height in winter. The localization and approximate levels of starch and lipids (as droplets) and number of starch granules were determined by image analysis of optical digital images obtained by confocal laser scanning microscopy.

Key Results

Localized heating induced earlier cambial reactivation and xylem differentiation in stems of Cryptomeria japonica, as compared with non-heated stems. There were clear changes in the respective localizations and levels of starch and lipids (as droplets) determined in terms of relative areas on images, from cambial dormancy to the start of xylem differentiation in heated stems. In heated stems, the levels and number of starch granules fell from cambial reactivation to the start of xylem differentiation. There was a significant decrease in the relative area occupied by lipid droplets in the cambium from cambial reactivation to the start of xylem differentiation in heated stems.

Conclusions

The results showed clearly that the levels and number of storage starch granules in cambium and phloem cells and levels of lipids (as droplets) in the cambium decreased from cambial reactivation to the start of xylem differentiation in heated stems during the winter. The observations suggest that starch and lipid droplets might be needed as sources of energy for the initiation of cambial cell division and the differentiation of xylem in Cryptomeria japonica.     

毛白杨维管形成层带细胞超微结构的季节性变化

木材(次生木质部)是树木形成层细胞分化的产物,形成层的活动方式不仅影响木材的产量,而且影响木材的结构和性质.利用透射电子显微镜观察了生长在北京地区的毛白杨(Populus tomentosa Carr.)枝条形成层带细胞一个完整活动周期的超微结构变化.在木质部母细胞完全恢复活动之前,形成层纺锤状原始细胞的分裂和韧皮部细胞的分化已经开始.枝条上芽的展开和幼叶的生长可能决定了形成层带细胞的这种活动方式.透射电镜观察更清楚地揭示了树木形成层细胞在活动初期的分化特点.活动期形成层细胞中的大液泡在进入休眠期后逐渐分成许多小液泡分散在细胞质中.随着液泡融合逐渐消失的深色蛋白类物质又重新充满了大部分液泡.油滴和淀粉颗粒的年变化情况同液泡中的蛋白类物质基本相似.无论在活动期还是休眠期,形成层纺锤形细胞的质膜上都发现有许多可能与物质运输有关的小泡状内折.由核膜、内质网和高尔基体及其分泌小泡组成的细胞内膜系统,在形成层活动周期的不同阶段,其形态和分布明显不同,尤其在形成层细胞的恢复活动及其衍生木质部细胞次生壁的沉积过程中发挥着重要作用.整个活动周期中,形成层纺锤形细胞的径向壁都比弦向壁厚,处在休眠期的形成层带细胞,其径向壁与弦向壁的差别则更明显.形成层恢复活动时,径向壁上特别是与弦向壁相连的角隅处出现部分自溶现象.细胞壁特别是径向壁的变薄是形成层细胞恢复活动的重要特征.     

SUCCESSIVE CAMBIA IN THE STEM OF PHYTOLACCA DIOICA

Phytolacca dioica L., an evergreen tree of the Phytolaccaceae, is one of the species of Phytolacca which shows anomalous secondary thickening in its stem. This mode of thickening has been regarded as successive cambial activity or alternatively, in some more recent interpretations, as thickening by unidirectional activity of a cambial zone. The stem thickening of P. dioica is of the former type. The cambium produces fascicular strands, showing centrifugal differentiation of xylem and centripetal differentiation of phloem on opposite sides of the cambial layer, and rays are produced between the fascicular areas. In both xylem and phloem the younger elements are closer to the cambium than the older elements. Succeeding cambia arise periodically by periclinal divisions in a layer of parenchyma cells two or three cells beyond the outermost intact phloem derived from the current cambium. Each cambium forms a few parenchyma cells on both sides before it forms derivatives which mature into lignified xylem elements or conductive elements of the phloem. The parenchyma thus formed toward the outside later becomes the site of the origin of the succeeding cambium. Only one or two layers of this phloem parenchyma go on to form the new cambium; the remaining cells accumulate between the outermost phloem and the cortex. P. weberbaueri shows stem structure similar to P. dioica. P. meziana, a shrub, shows normal stem structure.     

The Relationship between Endogenous Hormone Levels in the Plant and Seasonal Aspects of Cambial Activity

The auxin levels at different heights in a ring-porous (Ulmusglabra) and a diffuse-porous (Populus trichocarpa) tree werefollowed in spring. There was shown to be a correlation betweenthe pattern of spread of cambial activity and auxin gradients.The observed continuation of cambial activity after cessationof extension growth in ring-porous species is apparently dueto the fact that the mature leaves produce auxin, whereas littleauxin is produced by the leaves of diffuse-porous species underthese conditions. The spring/summerwood transition in ring-porousspecies can be related to a fall in auxin level at the timethat shoot extension-growth ceases. There is evidence of phloemproduction after the cessation of xylem production in Ailanthusaltissima and Robinia pseudacacia, but not in Betula pubescentand Acer pseudoplatanus. It is suggested that, in Ailan-thus,phloem production continues because high endogenous gibberellinlevels are present after the auxin level has been reduced byshort-day treatment.     

THE CAMBIUM AND SEASONAL DEVELOPMENT OF THE PHLOEM IN ROBINIA PSEUDOACACIA

The cambium in black locust consists of several layers of cells at all times. Cambial reactivation (division) is preceded by a decrease in density of cambial cell protoplasts and cell wall thickening but not by cell enlargement. During the resumption of cambial activity, periclinal divisions occur throughout the cambial zone. Early divisions contribute largely to the phloem side. The period of greatest cambial activity coincides with early wood formation. Judged by numerous collections made during two seasons (October, 1960-October, 1962) the seasonal cycle of phloem development is as follows. Phloem differentiation begins in early April, ends in late September. The amount of phloem produced is quite variable (range: 1-10 bands of sieve elements per year). Cessation of function begins with the accumulation of definitive callose in the first-formed sieve elements and spreads to those more recently formed. By late November all but the last-formed sieve elements are collapsed. All sieve elements are collapsed by mid-winter and before the resumption of new phloem production in spring. Phloem differentiation precedes xylem differentiation by at least 1 week, and apparently functional sieve elements are present 3 weeks before new functional vessel elements. Xylem and phloem production ends simultaneously in most trees.