Periodicity of cambial activity in Abies balsamea. I. Effects of temperature and photoperiod on cambial dormancy and frost hardiness

The relationship between from hardiness and growth potential, and their dependence on temperature and photoperiod, was investigated in the one-year-old cambium of balsam fir [Abies balsamea (L.) Mill.]. Six-year-old trees were exposed for 9 weeks to either the natural environment or one of 4 controlled environments in the fall (18 September-18 November), spring (12 April–14 June) and summer (19 July – 19 September). The 4 controlled environments were (1) WS, warm temperature (24/20°C in day/night) + short day (8 h). (2) WL. warm temperature (24/20°C) + long day (8 h + 1 h night break), (3) CS. cold temperature (9/5°C) + short day (8 h) and (4) CL, cold temperature (9/5°C) + long day (8 h + 1 h night break). At the beginning and end of each exposure, cambial activity was measured by recording the number of xylem, cambium and phloem cells, frost hardiness was estimated from the cambium's ability to survive freezing to –40°C, and cambial growth potential was deduced from the duration of the cell cycle and the production of xylem, cambium and phloem cells in cuttings cultured for 4 weeks with exogenous indole-3-acetic acid (IAA) under environmental conditions favourable for cambial activity. In the natural environment, frost hardening began in September and was completed in November, while dehardening occurred when the cambium reactivated. CL, CS, and to a lesser extent WS, promoted hardening in the summer and fall, but did not prevent dehardening in the spring. The cambial growth potential in the natural environment declined from a maximum in April to a low level in June, reached a minimum in September, then increased to a high level in November. This potential was promoted by CL and CS on all dates by WL in the summer and fall. The ratio of xylem to phloem induced by IAA treatment was greatest in June and least in September in cuttings from trees exposed to the natural environment, and was increased by CL and CS in the fall. The cambium in intact branches of trees protected from chilling during the fall and winter resumed cell cycling after less than 9 weeks of dormancy, but produced mostly or only phloem in the subsequent growing period. It is concluded that the frost hardiness of the cambium, the IAA-induced cycling of cambial cells, and IAA-induced xylem to phloem ratio vary independently with season, temperature and photoperiod, and that the periodicity of these processes is regulated endogenously.     

Concentrations of oxygen and indole-3-acetic acid in cambial region during latewood formation and dormancy development in Picea abies stems

To manipulate the occurrence of latewood formation and cambial dormancy in Picea abies (L.) Karst. stems, potted seedlings were transferred from the natural environment on 9 July, when tracheids early in the transition between earlywood and latewood were being produced, and cultured for up to 5 weeks in a controlled environment chamber having: (1) Warm LD, (25/15C during day/night) and long (16 h) photoperiod, (2) Warm SD, (25/15C) and short (8 h) photoperiod, or (3) Cold SD, (18/8°C) and short (8 h) photoperiod. In Warm LD trees, the radial enlargement of primary-walled derivatives on the xylem side of the cambium, as well as xylem production, continued at the same magnitude throughout the experiment. In Warm SD and Cold SD trees, the radial enlargement of primary-walled derivatives declined and the cambium entered dormancy, both developments occurring faster in the Warm SD trees. The concentrations of indole-3-acetic acid (IAA) was higher in developing xylem tissue than in cambium+phloem tissues, but did not vary with environmental treatment or decrease during the experimental period. The O2 concentration in the cambial region followed the order of Cold SD>Warm SD>Warm LD trees and was <5%, the threshold for the inhibition of IAA-induced proton secretion, for the first 3 weeks in Warm SD and Warm LD trees. Thus, neither latewood formation nor cambial dormancy can be attributed to decreased IAA in the cambial region. Nor does lower O2 concentration in the cambial region appear to be inhibiting the IAA action that is associated with cambial growth.     

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.     

Effect of local heating and cooling on cambial activity and cell differentiation in the stem of Norway spruce (Picea abies)

BACKGROUND AND AIMS The effect of heating and cooling on cambial activity and cell differentiation in part of the stem of Norway spruce (Picea abies) was investigated. METHODS: A heating experiment (23-25 degrees C) was carried out in spring, before normal reactivation of the cambium, and cooling (9-11 degrees C) at the height of cambial activity in summer. The cambium, xylem and phloem were investigated by means of light- and transmission electron microscopy and UV-microspectrophotometry in tissues sampled from living trees. KEY RESULTS: Localized heating for 10 d initiated cambial divisions on the phloem side and after 20 d also on the xylem side. In a control tree, regular cambial activity started after 30 d. In the heat-treated sample, up to 15 earlywood cells undergoing differentiation were found to be present. The response of the cambium to stem cooling was less pronounced, and no anatomical differences were detected between the control and cool-treated samples after 10 or 20 d. After 30 d, latewood started to form in the sample exposed to cooling. In addition, almost no radially expanding tracheids were observed and the cambium consisted of only five layers of cells. Low temperatures reduced cambial activity, as indicated by the decreased proportion of latewood. On the phloem side, no alterations were observed among cool-treated and non-treated samples. CONCLUSIONS: Heating and cooling can influence cambial activity and cell differentiation in Norway spruce. However, at the ultrastructural and topochemical levels, no changes were observed in the pattern of secondary cell-wall formation and lignification or in lignin structure, respectively.     

Light-modulation of nitrate reductase activity in leaves and roots of maize

The nuclear DNA content in ray cells from the 1-year-old vascular cambium of white ash ( Fraxinus americana L.) trees was determined at intervals during the annual cycle of cambial activity and dormancy by using Feulgen microspectrophotometry. By 10 September, these cells had entered dormancy in G₁ with a normal DNA distribution and a minimal average DNA content of 2.65 pg. The average amount of DNA increased to 3.51 pg by 30 November, remained at this elevated value until at least 30 March, when the cambium was still dormant, then declined to the minimum level on 1 May and 10 June, when the cells were mitotically active. The springtime decline appeared to occur both before and during cell division. Between 1 May and 10 June, the prophase (4C) and telophase (2C) DNA contents decreased significantly. The amount of nuclear DNA measured by microspectrophotometry was verified by using flow cytometry and image analysis. The results support the view that there is an annual oscillation in the nuclear genome size of shoot meristematic cells in tree species native to the northern temperate zone.     

Cambial sensitivity to rising temperatures by natural condition and artificial heating from late winter to early spring in the evergreen conifer Cryptomeria japonica

Differences in the timing of cambial reactivation and the initiation of xylem differentiation in response to the sum of daily maximum temperatures were studied in two Cryptomeria japonica trees with cambium of different ages under natural and locally heated conditions. In addition, we observed the effects of low temperature on cambial activity. The timing of cambial reactivation and of the initiation of xylem differentiation differed between 55- and 80-year-old cambium under natural conditions. In the 55-year-old cambium, cambial reactivation occurred when the cambial reactivation index (CRI), calculated on the basis of daily maximum temperatures in excess of 10°C, was 94 and 97°C in 2007 and 2008, respectively. In 80-year-old cambium, cambial reactivation occurred when the CRI, calculated on the basis of daily maximum temperatures in excess of 11°C, was 69 and 71°C in 2007 and 2008, respectively. After cambial reactivation in 2007, normal cell division was evident in the cambium even though the minimum temperature had fallen between −2 and −3°C. Under natural conditions, xylem differentiation started 38–44 days after cambial reactivation. In heated stems, the time between cambial reactivation and the initiation of xylem differentiation ranged from 14 to 16 days, a much shorter time than under natural conditions, indicating that continuous exposure to an elevated temperature had induced earlier xylem differentiation. Our observations indicate that the sensitivity to reactivation inducing stimuli of the cambium depends on both the stage of dormancy and tree age of the cambium.     

The role of auxin stored in scots pine trunk during spring activation of cambial activity

In a 9-year-old pine girdled during the winter cambial activity was observed below the girdle in the next spring. This indicates that cambial activity was initiated without auxin produced in the spring by buds. The auxin produced in apical shoots successively flows down the stem, where as a result of periodic restriction in transport it remains over the winter till the next year. This auxin of apical origin but locally stored over the winter in the stem is responsible for the activation of cambium before the new flow of auxin produced in the apical meristems arrives. Calculations based on seasonal changes in auxin levels can explain both, earlier spring activation of cambium in the crown and the temporary cambial divisions below the girdle, without assumption of direct auxin synthesis in the lateral meristems.     

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.     

Seasonal dynamics of wood formation in Oriental beech (Fagus orientalis Lipsky) along an altitudinal gradient in the Hyrcanian forest, Iran

The cambium dynamics and wood formation of Oriental beech (Fagus orientalis Lipsky) was investigated during the 2008 growing season in the Nowshahr Hyrcanian forest, Iran (36°N, 51°E). Three study sites were selected along an altitudinal gradient (650, 1,100 and 1,600 m a.s.l.), and cambial activity rates of cell formation and cell maturation were studied on micro-cores collected in intervals of 10–20 days. The cambium reactivation of the low-altitude (L) and mid-altitude (M) trees occurred contemporaneously in late March, and also the consecutive phases of cell differentiation took place almost at the same time; however, the entry into cambial dormancy varied considerably from late August to mid-November. Due to lower temperature, the upper-altitude (U) trees showed a 10-day delay in their cambium reactivation, an earlier entry into cambium dormancy (mid-September) and a slower growth rate resulting in narrower tree rings. Despite these differences, the daily increment rates of the trees at all sites reached maximum values coincidently in the early June. Since the photoperiod is the only common external factor among different sites, it is concluded that the timing of the highest growth rate is controlled by the photoperiod.     

Relationships between cambial activity,cell differentiation and the localization of starch in storage tissues around the cambium in locally heated stems of<Emphasis Type="Italic"> Abies sachalinensis</Emphasis> (Schmidt) Masters

A study was made, in a cool-temperate zone, of the extent of cell division in the cambium, the extent of differentiation of cambial derivatives, and the localization of storage starch around the cambium in locally heated (22–26°C) stems of the evergreen conifer Abies sachalinensis (Schmidt) Masters during cambial dormancy and immediately after natural reactivation of the cambium. In locally heated regions of stems during cambial dormancy, heating induced localized reactivation of the cambium. However, the cells in the heated and reactivated cambium stopped dividing soon after only a few cells had been generated. In addition, no differentiation of the xylem and the disappearance of starch from storage tissues around the cambium were observed. In regions of stem that had been locally heated after natural reactivation of the cambium, cell division continued in the cambium and earlywood tracheids with a large radial diameter and secondary walls were formed, with abundant starch in the storage tissues around the cambium. Our results suggest that the extent of both cell division in the cambium and cell differentiation depends on the amount of starch in storage tissues around the cambium in the locally heated stems of an evergreen conifer growing in a cool-temperate zone.     

Effect of constant and fluctuating temperature on daily melatonin production by eyecups from Rana perezi

We analysed the effect of daily temperature cycles in relation to constant temperature on day/night melatonin synthesis in frog eyecups in culture. Eyecups were cultured for 24 h under 12L:12D photoperiod and two thermal regimes, constant temperature (25, 15 and 5 °C) and thermoperiod (WL/CD, thermophase coinciding with photophase and cryophase coinciding with scotophase; and CL/WD, cryophase coinciding with photophase and thermophase coinciding with scotophase). A negative correlation between ocular serotonin N-acetyltransferase activity and culture temperature for both diurnal and nocturnal activities has been observed. This effect of increased ocular activity at low temperature is more pronounced than the well-known stimulatory effect of darkness, and it does not depend on the photoperiod phase. The lack of interactions between the phase of photoperiod and culture temperature indicates that the effects of both factors are independent. Nighttime temperature is the key factor in determining the amplitude of the melatonin rhythm in the Rana perezi retina. However, daytime temperature can not counteract the inhibitory effect of light on ocular melatonin synthesis. Accepted: 22 June 1995     

Photoperiodic and thermal regulation of antifreeze protein levels in the beetle Dendroides canadensis

The importance of photoperiod, temperature and their interaction in controlling the seasonal pattern of haemolymph antifreeze protein levels in larvae of the beetle Dendroides canadensis was investigated. A complete photoperiodic response curve for antifreeze protein production was generated at 20°C with larvae collected in early fall. Individuals exposed to a 10-h photoperiod or less, including constant darkness, had significantly elevated antifreeze levels over those maintained in an 11-h photoperiod or more, including constant light. The critical daylength resulting in 50% population response lies between LD 11:13 and LD 10:14. This photoperiodic response was masked at sufficiently low (threshold between 15 and 10°C) and high (threshold between 25 and 30°C) temperatures. Partial photoperiodic response curves (at 17 and 25°C) obtained within this specified temperature range indicate that the position of the critical photoperiod (between 10 and 11 h) is stable while the amplitude of the response curve is temperature dependent.Experiments investigating the mechanisms controlling the spring depletion of protein antifreeze levels suggest that both photoperiod and temperature are important.The dominant response of photoperiod in the fall along with the modifying effects of temperature are considered to provide the necessary precision to assure adequate cold tolerance early in the fall and the flexibility to protect the species from yearly variation in weather conditions.     

Patterns of protein synthesis in the cambial region of Scots pine shoots during reactivation

Changes in protein synthesis in cambial region cells were monitored in 1-year-old cuttings of Scots pine ( Pinus sylvestris L.) collected in November, when the cambium was dormant, and subjected to environmental conditions that promoted or inhibited cambial growth. The proteins were labelled in vivo with L-[³⁵S]-methionine and separated using 2-dimensional polyacrylamide gel electrophoresis. In budded cuttings cultured under environmental conditions favoring cambial reactivation, there was a reproducible quantitative change in 55 proteins (33 induced and 22 repressed), a less certain increase or decrease in 40 proteins, and no apparent change in about 150 proteins. Under the same conditions, 8 proteins were induced and 6 others were repressed in debudded cuttings treated apically with 1 mg indole-3-acetic acid (IAA) in 1 g lanolin, in which cambial reactivation occurred, compared with debudded cuttings treated with plain lanolin in which the cambium did not reactivate. Three of the proteins induced in the IAA-reated cuttings only appeared after cambial cell division and derivative differentiation actually began, and the same proteins were found in budded cuttings after their cambium had become reactivated. In contrast, protein expression in cuttings exposed to environmental conditions that prevented cambial reactivation was similar at the beginning and end of the experimental period. These results indicate that the cambium was in the quiescence stage of dormancy at the start of the experiment, that quiescent cambial region cells can synthesize proteins as soon as exposed to environmental conditions favoring reactivation, and that only 3 of the approximately 250 proteins detected were specifically involved in cambial growth     

Localized cooling of stems induces latewood formation and cambial dormancy during seasons of active cambium in conifers

Background and Aims In temperate regions, trees undergo annual cycles of cambial growth, with periods of cambial activity and dormancy. Environmental factors might regulate the cambial growth, as well as the development of cambial derivatives. We investigated the effects of low temperature by localized cooling on cambial activity and latewood formation in two conifers, Chamaecyparis obtusa and Cryptomeria japonica.Methods A plastic rubber tube that contained cooled water was wrapped around a 30-cm-wide portion of the main stem of Chamaecyparis obtusa and Cryptomeria japonica trees during seasons of active cambium. Small blocks were collected from both cooled and non-cooled control portions of the stems for sequential observations of cambial activity and for anatomical measurements of cell morphology by light microscopy and image analysis.Key Results The effect of localized cooling was first observed on differentiating tracheids. Tracheids narrow in diameter and with significantly decreased cambial activity were evident 5 weeks after the start of cooling in these stems. Eight weeks after the start of cooling, tracheids with clearly diminished diameters and thickened cell walls were observed in these stems. Thus, localized low temperature induced narrow diameters and obvious thickening of secondary cell walls of tracheids, which were identified as latewood tracheids. Two months after the cessation of cooling, a false annual ring was observed and cambium became active again and produced new tracheids. In Cryptomeria japonica, cambial activity ceased earlier in locally cooled portions of stems than in non-cooled stems, indicating that the cambium had entered dormancy sooner in the cooled stems.Conclusions Artificial cooling of stems induced latewood formation and cessation of cambial activity, indicating that cambium and its derivatives can respond directly to changes in temperature. A decrease in the temperature of the stem is a critical factor in the control of cambial activity and xylem differentiation in trees.     

Modification of cambial cell wall architecture during cambium periodicity in Populus tomentosa Carr.

Cambium periodicity is correlated with changes in the cambial cell wall, but the heterogeneity of cell wall structure and composition makes it difficult to give an accurate interpretation, especially for complex secondary vascular tissues. A combination of different methods is necessary to reveal the structure of this complex cell wall. In this study, the cell wall architecture and composition of active and dormant cambial cells in Populus tomentosa were investigated by a combination of light microscopy, rapid-freezing and deep-etching electron microscopy, Fourier-transform infrared microspectroscopy and immuno-histochemistry. The results showed that the architecture of dormant cambial cell walls displayed a multi-layered structure, denser fibril network, smaller pore size, and fewer crosslinks between microfibrils than active cambial cell walls. The FTIR spectra of cell walls from active and dormant cambium showed differences in the intensity of bands near 1,740, 1,629, 1,537, 1,240, and 830 cm⁻¹, which reflected differences in cell wall composition. Immuno-labeling indicated that high methyl-esterified homogalacturonan and (1 → 4)-β-d-galactan epitopes were abundant and distributed in active cambial cell walls, and relatively de-esterified homogalacturonan and (1 → 5)-α-l-arabinan epitopes had weak labeling in the active cambium, while almost no labeling or very weak labeling for high methyl-esterified homogalacturonan, (1 → 4)-β-d-galactan and (1 → 5)-α-l-arabinan epitopes occurred in dormant cambial cells, except for the de-esterified homogalacturonan epitope, which was abundant in dormant cambial cells. These results demonstrate that there are great differences, both in structure and composition, between active and dormant cambial cell walls, which reflect their dynamic changes during cambium activity.     

Proteolytic activity in relation to seasonal cambial growth and xylogenesis in Pinus banksiana.

Proteolytic activity in the cambial zone and developing xylem of Pinus banksiana Lamb. was investigated over an annual cycle of growth and dormancy. Highest proteolytic activity was associated with the most active period of primary-wall radial expansion of cambial derivatives, in early spring, before protoplasmic autolysis was initiated in developing earlywood. Three pH maxima of proteolytic activity, near pH 3.0, 6.5 and 9.5, were observed at that time. In general, activities measured at pH values below 7.0 were greater than those determined above pH 7.0 at all stages in the annual cycle, in both cambial zone and developing xylem, although elevated activity at alkaline pH was also observed during springtime growth. Polyvinylpolypyrollidone (PVP) treatment markedly enhanced pH 7.5 but not pH 4.0 proteolytic activity in the cambial zone, but not in developing xylem, indicating the presence of PVP-binding proteinase regulators in the cambium. By fractionation and effector studies total proteolysis was determined to comprise interactions between serine, cystine, aspartate and metallo-proteases having MWs, by gel chromatography, between 10 and 100 kDa. The observations point to a complex regulatory mechanism controlling the presence and catalytic rates of the distinct types of proteases in the cambial region throughout an annual cycle of growth and dormancy.     

Day and Night Temperature Control of Floral Induction in Stylosanthes guianensis var. guianensis cv. Schofield

Floral initiation in seedlings of Stylosanthes guianensis var.guianensis cv. Schofield grown at a photoperiod marginal forflowering (12–11.75 h) was promoted by a combination oflow day (25 °C) and low night (16 or 21 °C) temperatures,and completely inhibited by a 35 °C day temperature. Additionally,earliness of floral initiation under naturally decreasing daylengthwas negatively related to temperature regime over the range35/30 to 20/15 °C (day/night). Stylosanthes guianensis var, guianensis, flowering, temperature, photoperiod, short-day plant     

Growth and Dormancy in Norway Spruce Ecotypes (Picea abies) I. Interaction of Photoperiod and Temperature

Growth and dormancy as affected by photoperiod and temperature have been studied in Norway spruce ecotypes of different latitudinal and altitudinal origin. First-year seedlings were used. In all ecotypes apical growth cessation and terminal bud formation occurred within 2 weeks after exposure to SD at temperatures of 18 to 24°C. At lower temperatures or at near-critical photoperiods the response was delayed. The critical photoperiod for apical growth cessation varied from 21 hours in ecotype Steinkjer, Norway (64°N) to about 15 hours in ecotype Lankowitz, Austria (47°04′N). High-elevation ecotypes also had longer critical pholoperiods than low-elevation ecotypes from the same latitude. A detectable growth depression resulted from as little as 1 or 2 SDs of 10 hours, and with 4 or more SDs apical growth cessation took place. In contrast to the situation in the shoot, root growth was not affected by photoperiod. Accordingly, the top:root ratio is drastically affected by photoperiod. The critical photoperiod for cambial growth was shorter than that for apical growth in all ecotypes and cambial growth cessation was delayed for several weeks compared with cessation of apical growth. A transition to formation of late-wood tracheids with thick walls and narrow lumens took place upon exposure to SD. The photoperiodic effects were significantly modified by temperature, but the critical photoperiods were only slightly changed by temperature in the range of 12 to 24°C. However, a 10-hour “night” at 4°C caused growth cessation in continuous light in four ecotypes tested. Temperature optimum for apical growth under non-limiting photoperiods (24 hours) was 21°C in all ecotypes, but with little difference among 18,21 and 24°C. The Q₁₀ for apical growth was 3.5 in the temperature range 12 to 18°C. The growth potential as determined in 24-hour photoperiods was not significantly different among the various ecotypes except for one northern eco-type which was clearly inferior to the others. However, the growth of ecotype Steinkjer (64°N) was greatly suppressed even by the long midsummer days at 59°40′N, thus demonstrating the misleading impression one gets of the growth potential of northern ecotypes when they are moved southwards.     

Concomitant analysis of cambial abscisic acid and cambial growth activity in poplar

Endogenous levels of cambial region abscisic acid (ABA) were quantified by immunoassay and assessed together with cambial growth activity in poplar (Populus nigra L. × P. maximowiczii Henry, clone Kamabuchi) over the course of a growing season. The level of cambial region ABA increased from spring to late-summer but decreased sharply in autumn. Cambial growth activity, measured as the radial number of undifferentiated cambial cells and enlarging xylem cells, also increased from spring to summer and decreased sharply in autumn, indicating the onset of cambial dormancy. Exogenous ABA, applied laterally to poplar stems at two times within the growing season, enhanced cambial growth activity, as the radial number of undifferentiated cambial cells increased in ABA-treated trees subsequent to the two application times. Xylem cell development was also affected by exogenous ABA as fibre length increased significantly in ABA-treated trees at both application times. The positive correlation of cambial region ABA and cambial growth activity as well as the positive effects of exogenous ABA application thereon sheds new light on the role of this hormonal growth regulator.     

Effects of Temperature and Photoperiod on Winged Beans [Psophocarpus tetragonolobus (L.) D.C.]

The effects of temperature and photoperiod on winged beans werestudied using 15 University of New Guinea (UPS) selections andfive Sri Lanka (SL) selections. They were grown at 25/20 or30/25 °C day/ night temperature at 11 or 14 h photoperiodwith 12 h thermoperiod. Differences in stomatal density wereobserved among selections and between photoperiods. Higher densitiesoccurred at 14 h photoperiod than at 11 h photoperiod. Whenstomatal density was high due to a photoperiod or temperatureeffect, there was a corresponding increase in leaf area andd. wt of plants. Total chlorophyll content at 25/20 °C was higher at 11 hphotoperiod than at 14 h photoperiod in all selections whilethe total chlorophyll content at 30/25 °C varied with thephotoperiod and selection. Leaf area of SL selections was greater than that of UPS selections.Also greater leaf area was observed at 14 h photoperiod thanat 11 h photoperiod, irrespective of the growing temperature. Temperature was as important as photoperiod in controlling floweringof winged beans. All the UPS selections and two SL selectionsflowered at 11 h photoperiod at 25/20 °C but failed to flowerat the same photoperiod at 30/25 °C indicating an interactionbetween temperature and photoperiod. It is likely that wingedbeans have a narrow photoperiodic range, particularly the SLselections. Psophocarpus tetragonolobus (L.) D.C., winged bean, stomatal density, leaf area, flowering, temperature, photoperiod