CAMBIAL DIVISIONS IN PSEUDOTSUGA MENZIESH

Mitotic activity in the vascular cambium was determined from nine samples from a single internode in each of four Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) trees. Counts of mitotic nuclei and populations of potentially dividing cells in each sample were used to determine the average mitotic index per core. The sampling error was determined for the average mitotic index per core and the internode as a whole. Significant differences were found between the mitotic indexes of samples within the internodes of three of the trees; however, no differences were observed in the rate of division among trees. A significant correlation was established between the number of cells in the cambial zone and the average mitoses per core per sample.     

CAMBIAL ACTIVITY IN ALASKAN WHITE SPRUCE

Cambial activity in white spruce stems in Alaska was observed during a 2-year period in 50–60-year-old natural stands. Mitotic index was used as a measure of the rate of periclinal division of fusiform cells in the cambial zone. Anticlinal divisions were relatively rare, averaging only one per 27S periclinal divisions in most stems. Mitotic index, at any given time, appeared uniform throughout the cambial zone of an internode, among internodes of the same tree, and even among trees growing at markedly different rates. Diurnal variation in mitotic index was observed. There were three distinct growing season periods: early, grand, and late. Early period activity was characterized by reactivation of periclinal division, erratic mitotic indices, and an approximate doubling of the number of cambial zone cells per radial file (NCZ). Production of the first new xylem and phloem elements marked the beginning of the grand period. Rate of cell production in the cambial zone remained about equal to derivative production for the next 45–50 days, when about 80 % of annual xylem and phloem increment occurred. There was a drop in NCZ at the beginning of the late period coincident with a decline in mitotic index, and NCZ soon dropped to the dormant level. Complete termination of cambial activity was gradual, extending through late August and perhaps into September.     

Changes in total nitrogen, soluble protein, and peroxidases in the expanding leaf zone of eastern cottonwood

Nitrogen content and soluble protein and anodal peroxidase banding in acrylamide gel changed with leaf and internode development in the expanding leaf zone of eastern cottonwood (Populus deltoides Bartr.). Nitrogen per unit leaf area was high near the apex and decreased to a constant value at the sixth node below it. Soluble protein banding was qualitatively similar for leaves and internodes in this zone, but anodal peroxidases differed between leaves and internodes. The major leaf peroxidase band was absent from the second leaf below the apex but present in the fourth and sixth leaves; its appearance and intensification seemed to parallel the development of photosynthetic activity. The major internode peroxidase band was present in the apex, second, fourth, and sixth internodes, and intensified during internodal development. It is suggested that these two “isoenzymes” may have different functions in vivo.     

Methyl jasmonate-induced ethylene production is responsible for conifer phloem defense responses and reprogramming of stem cambial zone for traumatic resin duct formation

Conifer stem pest resistance includes constitutive defenses that discourage invasion and inducible defenses, including phenolic and terpenoid resin synthesis. Recently, methyl jasmonate (MJ) was shown to induce conifer resin and phenolic defenses; however, it is not known if MJ is the direct effector or if there is a downstream signal. Exogenous applications of MJ, methyl salicylate, and ethylene were used to assess inducible defense signaling mechanisms in conifer stems. MJ and ethylene but not methyl salicylate caused enhanced phenolic synthesis in polyphenolic parenchyma cells, early sclereid lignification, and reprogramming of the cambial zone to form traumatic resin ducts in Pseudotsuga menziesii and Sequoiadendron giganteum. Similar responses in internodes above and below treated internodes indicate transport of a signal giving a systemic response. Studies focusing on P. menziesii showed MJ induced ethylene production earlier and 77-fold higher than wounding. Ethylene production was also induced in internodes above the MJ-treated internode. Pretreatment of P. menziesii stems with the ethylene response inhibitor 1-methylcyclopropene inhibited MJ and wound responses. Wounding increased 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase protein, but MJ treatment produced a higher and more rapid ACC oxidase increase. ACC oxidase was most abundant in ray parenchyma cells, followed by cambial zone cells and resin duct epithelia. The data show these MJ-induced defense responses are mediated by ethylene. The cambial zone xylem mother cells are reprogrammed to differentiate into resin-secreting epithelial cells by an MJ-induced ethylene burst, whereas polyphenolic parenchyma cells are activated to increase polyphenol production. The results also indicate a central role of ray parenchyma in ethylene-induced defense.     

POLARITY OF INDUCTION AND PATTERN OF PRIMARY PHLOEM FIBER DIFFERENTIATION IN COLEUS

The differentiation of primary phloem fibers was studied in Coleus blumei on a quantitative basis. The pattern of fiber differentiation in intact, untreated plants was found to be in the acropetal direction (from a mature internode to a young one). The youngest internodes to differentiate primary phloem fibers were those with cambial activity. In plants grown in the winter, fibers started to differentiate in internodes closer to leaf #2 than in spring-grown plants. A wound changes the pattern of fiber differentiation surrounding it. A wound in which the tissues above and below it were separated with parafilm, prevented fiber differentiation in the tissues directly below the wound, and caused more fiber differentiation in the tissues above and lateral to it. Under wounds with no parafilm separation, few or many fibers differentiated depending on the angle of the wound. The number of fibers under diagonal wounds was five to nine times more than under a horizontal wound. By excision experiments it was found that mature leaves were the source of induction of fiber differentiation. Leaves that produced induction caused fiber differentiation in the internode below them but did not cause fiber differentiation in the internode above. The induction, which can flow through a wound and cause fiber differentiation in at least two internodes below the source, is a polar induction in the basipetal direction (i.e., in the direction from the leaves to the root). Phloem fibers differentiated only in the vascular strands and not from the parenchyma cells between the strands. Therefore, they follow the new regenerative sieve and vessel elements in the pre-existing vascular strands, but do not follow them in their regeneration between the longitudinal strands.     

Tracheid production in response to indole-3-acetic acid varies with internode age in Pinus sylvestris stems

Summary Different concentrations of indole-3-acetic acid (IAA) in lanolin were applied to the cambial region of approximately 10- and 34-year-old internodes in the main stem of Pinus sylvestris (L.) trees during the tracheid production period. After 5 weeks of treatment, the radial width of xylem produced in both ages of internode was positively related to exogenous IAA concentration measured at 0, 1 and 3 cm directly below the application site. Tracheid production in response to exogenous IAA in the 34-year-old internode was approximately one-half of that in the 10-year-old internode. The endogenous IAA level in the 7-, 17- and approximately 34-year-old internodes of similar trees was measured by radioimmunoassay, using gas chromatography-selected ion monitoring-mass spectrometry for validation. No consistent relationship was found between xylem radial width and IAA concentration. The data indicate that the cambium's ability to respond to exogenous IAA is qualitatively the same in 1-year-old shoots and older internodes. However, as the internode ages, there is a decrease in the extent of the response and in the optimal IAA level for inducing tracheid production.     

Spatial Pattern of Phomopsis Cane and Leaf Spot Symptoms in Commercial Vineyards in Ohio

Spatial patterns of incidence of Phomopsis cane and leaf spot were examined using 57 data sets obtained from a statewide survey of grape vineyards in Ohio from 2002–2004. To characterize small‐scale patterns at the vine scale or below, discrete‐distributional analyses were used to quantify the heterogeneity of disease incidence within vineyards. The number of diseased leaves and internodes (out of 15) per sampling unit was better fitted by the beta‐binomial than the binomial distribution in 67% and 91% of the cases, respectively. The index of aggregation was significantly >1 for 78% and 98% of the cases for diseased leaves and internodes, respectively. These results indicated aggregation of this disease at an individual vine scale (or lower). Conversely, there was little evidence of aggregation at scales larger than a vine (e.g. disease foci extending beyond individual vines) for most vineyards based on Spatial Analysis by Distance IndicEs (SADIE). SADIE analysis suggested a random pattern of the count of diseased leaves and internodes in the majority (>86%) of the cases. Based on SADIE, there was significant (P ≤ 0.05) evidence of association between leaf and internode disease counts per vineyard in 75% of cases, indicating that the dispersal of inoculum from the previously infected wood tissues (canes) affected both leaf and internode in the same manner. In contrast, association of disease counts from one year to the next was only significant in approximately 15% of the cases, indicating the difficulty in predicting the level of disease in a section of a vineyard based on the previous year’s observations alone.     

The role of the leaves in the regulation of internode elongation in Phaseolus vulgaris

Time-course patterns of leaf and internode elongation were studied in bean plants. Each leaf started its main elongation period when the leaf below reached half of its final length. The onset of leaf unfolding was nearly synchronous with the initiation of the elongation of the subjacent internode. Excision of young leaves increased the rate of stem elongation as a result of an earlier unfolding of the next upper leaves and the concomitant advancement in the elongation of their subjacent internodes. IAA or NAA (1% in lanolin) suppressed the enhancement effects of leaf excision on leaf and internode elongation. The excision of a young leaf increased the final length of internodes located below it, and at the same time decreased the final length of the internodes located above the excised leaf. The reduction was greater the younger the internode. Differences in internode elongation after leaf excision were related to changes during internode ontogenesis in their relative response to the availability of assimilates on the one hand, and on the other hand to hormonal factors transported acropetally from the young leaves to the growing internodes.     

Internodal elongation and orientation of cellulose microfibrils and microtubules in deepwater rice

Excised stem sections of deepwater rice (Oryza sativa L.) containing the highest internode were used to study the induction of rapid internodal elongation by gibberellin (GA). It has been shown before that this growth response is based on enhanced cell division in the intercalary meristem and on increased cell elongation. In both GA-treated and control stem sections, the basal 5-mm region of the highest internode grows at the fastest rate. During 24 h of GA treatment, the internodal elongation zone expands from 15 to 35 mm. Gibberellin does not promote elongation of internodes from which the intercalary meristem has been excised. The orientation of cellulose microfibrils (CMFs) is a determining factor in cell growth. Elongation is favored when CMFs are oriented transversely to the direction of growth while elongation is limited when CMFs are oriented in the oblique or longitudinal direction. The orientation of CMFs in parenchymal cells of GA-treated and control internodes is transverse throughout the internode, indicating that CMFs do not restrict elongation of these cells. Changes in CMF orientation were observed in epidermal cells, however. In the basal 5-mm zone of the internode, which includes the intercalary meristem, CMFs of the epidermal cell walls are transversely oriented in both GA-treated and control stem sections. In slowly growing control internodes, CMF orientation changes to the oblique as cells are displaced from this basal 5-mm zone to the region above it. In GA-treated rapidly growing internodes, the reorientation of CMFs from the transverse to the oblique is more gradual and extends over the 35-mm length of the elongation zone. The CMFs of older epidermal cells are obliquely oriented in control and GA-treated internodes. The orientation of the CMFs parallels that of the cortical microtubules. This is consistent with the hypothesis that cortical microtubules determine the direction of CMF deposition. We conclude that GA acts on cells that have transversely oriented CMFs but does not promote growth of cells whose CMFs are already obliquely oriented at the start of GA treatment.     

Evaluating Mitotic Activity in Canine and Feline Solid Tumors: Standardizing the Parameter

Three different methods for evaluating mitotic activity (mitotic count, mitoses/area, mitotic index) were applied to different types of canine and feline solid tumors to determine the method that is most objective and correlates best with other parameters of cell proliferation. Mitotic activity was evaluated on toluidine blue stained his-tological sections. Slides stained with histochemical (AgNOR proteins) and im-munohistochemical (MEB1, PCNA) markers of cell proliferation were available for each case. Quantitation of mitotic activity and cell proliferation parameters was performed with an image analyzer. Mitotic activity assessment was compared with cell proliferation indices and its ability to discriminate tumors grouped on histologically based criteria including the histological type, malignant or benign characteristics, and grade. A significant correlation by linear regression analysis with other parameters assessing cell proliferation revealed that mitotic index correlated 100% and mitoses/area and mitotic count correlated 40% of the time. In discriminating the proliferative activity of tumors grouped by histological criteria, mitotic index and mitotic count revealed 100% concordance with the other parameters of cell proliferation, while mitoses/areas showed 80% concordance.     

SHOOT GROWTH AND HISTOGENESIS OF TREES POSSESSING DIVERSE PATTERNS OF SHOOT DEVELOPMENT

Shoot growth and histogenesis were followed in five unrelated tree taxa possessing inherently diverse patterns of shoot development. Following the resumption of growth in spring, each species differs quantitatively in the number of internodes elongating contemporaneously, in rates and duration of internodal elongation and seasonal periodicity of shoot growth. The basic pattern of internode elongation and histogenesis is qualitatively similar in each of the dicotyledonous species observed irrespective of growth habit or final form of the shoot produced. During the intial phase of internode development, growth is essentially uniform throughout young internodes, corresponding to an active period of cell division during which time pith cells increase in size to about one-third their final length. Subsequently, the pattern of cell division shifts progressively upward concomitant with increased elongation and maturation of pith cells in the basal portion of developing internodes. Thereafter, a wave of cell division accompanied by cell elongation continues to proceed acropetally until growth finally ceases in the distal portion of each internode. As long as internode elongation continues, frequently at distances 15–20 cm below the shoot apex, cell divisions still occur in the distal growing portion. As successive portions of each internode mature acropetally, final length of pith cells becomes relatively uniform throughout the internode. During the process of internode growth and development, cell lengths increase only two- to threefold, whereas cell numbers increase ten- to 30-fold, indicating the dominant role of cell division and increases in cell number to final internode length. Morphological patterns of shoot expression associated with differences in internode lengths along the axis of either preformed or neoformed shoots, as well as sylleptic branches, are due to differences in cell number rather than final cell length. Significant variations in final internode lengths along the axis of episodic shoots, caused by either endogenous or exogenous factors, are also attributed to differences in cell number.     

Maize stem tissues: ferulate deposition in developing internode cell walls

It has been hypothesized that ferulates are only deposited in the primary cell wall of grasses. To test this hypothesis, the fourth elongating, above-ground internode of maize (Zea mays l.) was sampled from three maize hybrids throughout development. Cell wall composition was determined by the Uppsala Dietary Fibre method. Ester- and ether-linked ferulates were determined by HPLC analysis of ferulic acid released from the internodes by low and high temperature alkaline treatments. Internode length increased from 9 to 152 mm over 96 days of growth, with elongation being complete in the first 12 days. More than half of the cell wall material in the maize internodes accumulated after elongation had ended. Deposition of cell wall material appeared to reach its maximum extent 40 days after sampling began, well before physiological maturity of the maize plants. Galactose and arabinose began to accumulate early in cell wall development which was presumed to be associated with primary wall growth during internode elongation. The major secondary wall constituents (analyzed as glucose, xylose, and Klason lignin) did not begin to accumulate rapidly until shortly before internode elongation ended. Ferulate ester deposition began before ferulate ethers were observed in the cell wall, but both forms of ferulate continued to accumulate in secondary cell walls, long after internode elongation had ceased. These data clearly show that contrary to the hypothesis, ferulate deposition was not restricted to the primary wall and that active lignin/polysaccharide cross-linking mediated by ferulates occurs in the secondary wall.     

浙江天童常绿阔叶林藤本植物的适应生态学研究 II.攀援能力和单株攀援效率

选用节间长、节数和支持木大小作为攀援能力的指标,单株攀援的支持木种类、数量及水平扩展面积作为单株攀援效率的指标,对浙江天童常绿阔叶林中5类12种大中型木质藤本的攀援能力及生态适应性和其中2种藤本单株攀援效率进行了分析,结果发现:1)不同攀援类型的节间长和节数存在显著差异,对支持木大小要求不同,反映出攀援能力在类型间的差异;没有一类藤本兼具所有优势,攀援能力是节间长、节数和支持木大小不同组合的结果;卷须类的广东蛇葡萄(Ampelopsiscantoniensis)和暗色菝葜(Smilaxlanceifoliavar.opaca)节间最长、节数居中、要求较小支持木;枝卷类的香港黄檀(Dalbergiamillettii)节数和支持木大小与卷须类接近,但节间较短;不定根类的中华常春藤(Hederanepalensisvar.sinensis)、扶芳藤(Euonymusfortunei)、薜荔(Ficuspumila)和络石(Trachlospermumjasmi noides)以及吸盘类的异叶爬山虎(Parthnocissusheterophylla)节间最短、但节数最多,要求较大支持木;茎缠绕类的白花野木瓜(Stauntonialeucantha)、羊角藤(Morindaumbellata)、忍冬(Lonicerajaponica)和薯莨(Dioscoreacirrhosa)节间长居中,节数最少,要求中等但幅度较宽的支持木。2 )同类型不同藤本的节间长、节数和支持木大小的差异反映出由非亲缘关系植     

Xyloglucan endotransglycosylase activity in pea internodes. Effects of applied gibberellic acid.

Xyloglucan endotransglycosylase (XET) activity extractable from internodes of tall and dwarf varieties of pea (Pisum sativum L.) was assayed radiochemically using tamarind seed xyloglucan as donor substrate and an oligosaccharidyl-[3H]alditol as acceptor substrate. Internodes I and II showed little elongation during the period 15 to 21 d after sowing; XET activity remained relatively constant and was unaffected by exogenous gibberellic acid (GA3). A single application of GA3 to the dwarf genotype resulted in a small enhancement of elongation in internode III between d 17 and 21 and caused a small increase in XET activity in internode III. Repeated applications of GA3 caused internode V to elongate between d 20 and 26, to the same extent as in the tall variety, and concomitantly led to greatly elevated XET activity (expressed per unit fresh weight, per unit of extractable protein, and per internode). Thus, XET activity correlated with GA3-enhanced length in pea internodes; the possibility that this represents a causal relationship is discussed.     

Transition from absolute to quantitative short-day control in Nicotiana tabacum cv. Maryland Mammoth

The response in vitro of thin cell layers, excised from different stem regions of Nicotiana tabacum cv. Maryland Mammoth plants at various developmental stages, was studied under different photoperiodic treatments. The aim was to determine at which stage of plant development, and in which region of the stem, the absolute short-day requirement, indispensable for the induction of the flowering process in this genotype, becomes quantitative and whether it remains short-day. The explants were cultured on a medium suitable for flower neoformation, and were exposed for 30 days to the following treatments: continuous darkness, 8 h light/16 h dark per day, 16 h light/8 h dark per day, and continuous light. The first flowers on explants were observed from plants that were still in the vegetative state, but whose apex showed an accelerated production of axillary vegetative buds, as observed histologically. These explants were excised from the first 10 internodes below the first node with a leaf ≥ 5 cm in length (apical site), and produced flowers only under short-day treatment. When the apical dome initiated the organization of the terminal flower, the apical site explants developed flowers under both short-day and long-day treatments. At the same stage, explants from the 15th to the 20th internode below the first leaf ≥ 5 cm in length also formed flowers, but only under short-day. When the plant showed a complete inflorescence, flowers were also present on explants from the most basal stem internodes and from the inflorescence branches. At this stage, flower neoformation occurred under all treatments; however, under short-day the number of explants showing flowers not associated with vegetative buds on the same sample greatly exceeded that observed under other treatments, as did the mean number of flowers per explant (except the basal regions). In conclusion, in the post-inductive phases of the flowering process, the photoperiodic requirement of this genotype is always short-day. The superficial tissues of the stem require either absolute or quantitative short-day treatment, depending on their position on the stem and the stage of evolution of the flowering process in the terminal apex.     

Vertical and radial profiles in tracheid characteristics along the trunk of Douglas-fir trees with implications for water transport

The main stems of three young Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirbel) Franco) trees were dissected to obtain samples of secondary xylem from internodes axially along the trunk and radially within each internode. From these samples, measurements were obtained of tracheid diameter, length, the number of inter-tracheid pits per tracheid, and the diameter of the pit membranes. In addition, samples were obtained along the trunks of three old growth trees and also a small sample of roots for measurement of tracheid diameter. A gradient was apparent in all measured anatomical characters vertically along a sequence among the outer growth rings. These gradients arose not because of a gradient vertically along the internodes, but because of the strong gradients present at each internode among growth rings out from the pith. Tracheid characteristics were correlated: wider and longer tracheids had more numerous pits and wider pits, such that total pit area was about 6% of tracheid wall area independent of tracheid size. A stem model combining growth rings in parallel and internodes in series allowed for estimates of whole trunk conductance as a function of tree age. Conductance of the stem (xylem area specific conductivity) declined during the early growth of the trees, but appeared to approach a stable value as the trees aged.     

Correlative Growth in Young Terminalia superba in a Controlled Environment: Effect of the Leaves on Internode Elongation

Young Terminalia superba plants were cultivated in a controlledenvironment at the Phytotron. Effects of the excision of a youngleaf at definite elongation stages and at two given levels ofthe main axis were studied on the elongation of internodes inthese plants. Effects of the leaf did not seem to depend onits nodal position on the main axis but predominantly occurredon the immediate surrounding internodes. The excision of a youngleaf enhanced the growth rate of the internode located belowit and markedly decreased the elongation of the internode aboveit but slightly affected internode growth duration. This excisionenhanced the final length of the internode located below theleaf and decreased the final length of the internode locatedabove the removed leaf. Significant linear regressions werefound between the length of the excised leaf and the internodefinal lengths. Microscopic examination of epidermal cells ofcontrol and disrupted internodes revealed that the decreasedelongation after leaf excision could be attributed to reductionof cell divisions. The increased elongation after leaf excisioncould be attributed both to slight increase in the length ofcells (significant negative correlation was found with the lengthof the removed leaf) and to increase of cell divisions. Terminalia superba, leaf excision, cell division, internode elongation, correlative growth     

Nycthemeral variations of mitotic activity in the adrenal cortex of the rat]

Working on histologic sections 7 microns thick in the equatorial part of male rat adrenal cortex, we found two high mitotic activity periods. The first one stays at midnight and shows an average number of 42 mitoses per section; the second one occurs at 5 a.m. with an average number of mitoses of 70,1 per section. If we except these particular points, the mitotic activity is low, the average number of mitoses being 13,2 per section.     

Morphological and histological differences in the development of dwarf mutants of sexual and somatic origin in diverse woody taxa

Morphological and histological observations were made on eight dwarf mutants arising either as seedlings from sexual reproduction or from somatic bud mutations (witches'-brooms in the crowns of normal trees). The most predominate morphological trait contributing to the expression of dwarfism in all taxa was the reduction of final internode lengths along the shoot axis. In taxa of sexual origin, with the exception of Prunus, there was a consistent reduction in the number of preformed leaves contained in the winter buds. In addition, in two taxa (Liquidambar and Tsuga) there was an almost complete absence of neoformed leaves and sylleptic branches on current year shoots. Conversely, in mutants of somatic origin there was no apparent reduction in the number of preformed leaves. Genetic dwarfness in this group resulted solely from decreases in final internode length. Significant differences in the cellular basis of dwarfism between mutants of different genetic origins are clearly evident. In dwarf trees arising from sexual reproduction, reduction in final internode length is attributed predominately to inhibition of mitotic activity in developing internodes resulting in highly significant decreases in final cell number, and not cell length. In mutants of somatic origin, the reduction in length of mature internodes results from a decrease in final cell length, rather than a decrease in cell number. Physiological mechanisms associated with the genetic expression of these morphogenetic differences are suggested.     

Precision and accuracy of tree-ring-based death dates of mountain pines in the Swiss National Park

Key message

Mountain pines in the Swiss National Park show evidence of partial cambial mortality, which affects the precision of tree-ring-based death dates, followed by lagged crown mortality.

Abstract

The time of tree death is commonly reconstructed by dating the outermost ring of tree-ring series. However, due to the occurrence of partial cambial mortality, the date of the outermost tree ring may vary between different locations on the tree stem. Furthermore, a tree may continue to live following the formation of the most recent tree ring. In this study, we quantified precision and accuracy of tree-ring-based death dates from 229 dead mountain pines (Pinus montana) from a 28 km² study area in the Swiss National Park. For almost two-thirds of the trees, a maximum difference of just 0–4 years between the dates of cambial mortality from three increment cores was observed, however, for a few trees the difference reached 30–65 years. Higher maximum differences between the dates of cambial mortality are expected for trees on steep slopes, for old trees or for trees that died a long time ago. For 84 % of dead mountain pines, which were sampled in a permanent sample plot with 2-year remeasurement intervals, the difference between the date of observed crown mortality and the death date determined from three cores was 0–5 years. Sampling two or just one core per tree decreases the accuracy of tree-ring-based death dates. Based on the findings of our study, we recommend a prior assessment of the precision and accuracy of tree-ring-based death dates for any dendroecological study dealing with the reconstruction of tree mortality.