Structural Changes in the Vascular Cambium of Pinus strobus L. during an Annual Cycle

The changes in the ultrastructure of cambial cells of easternwhite pine (Pinus strobus L.) during an annual cycle are observedand recorded as are relationships of cambial cells during dormancyand at resumption of cambial activity. Cambial activity wasresumed late in March or early in April, when a few cells dividedpericlinally. Cambial activity reached a maximum during thelatter part of May with 15 to 20 undifferentiated cells present.In July it declined markedly, and the number of undifferentiatedcells equalled that of the dormant period. The xylem and phloemtissue cells produced late in the annual cycle overwinteredat varying developmental stages. In October cambial cells structurallyresembled dormant cells. The number of dormant cells in easternwhite pine cambium varied from 6 to 10. Active cells were characterizedby a large central vacuole, by an abundance of all cell organelles,and by thin cell walls. Dormant cells were characterized bynumerous small vacuoles, by structurally and quantitativelymodified cell organelles, and by relatively thick cell walls.     

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 Activity in Acacia raddiana Savi

Cambial activity and extension growth of Acacia raddiana Saviwere investigated. Both types of growth are strongly dependenton relatively high temperatures. In contrast with the behaviourof the cambium of trees with a clear interrupted growth period,the cambium of A. raddiana saplings did not respond to the twodifferent photoperiods tried. A correlation between extension growth and cambial activitycould not always be observed. The cambium was always activeonly in young green twigs, and in their close proximity, underconditions where intensive extension growth took place. In oldertwigs the cambial activity was found to occur independentlyof the extension growth, even in the very same branches in whichextension growth occurs.     

Seasonal Production of Secondary Phloem in the Twigs of Certain Tropical Timber Trees

Secondary phloem production in four deciduous (Albizzia lebbeck,Dalbergia sissoo, Tectona grandis and Terminalia crenulata)and three evergreen plants (Calophyllum inophyllum, Mangiferaindica and Morinda tinctoria) is briefly described. The totalduration of phloem production for each year was worked out forall these plants. In three of the four deciduous trees therewere two instalments of phloem production in correspondencewith the presence of two flushes of cambial activity while inTectona grandis and in all the three evergreen trees there wasonly one instalment. The time of initiation and cessation ofphloem tissue production was found to be variable in the differentplants studied. Periodicity in the production of different componentsof phloem tissue as well as the difference in the dimensionsof the different phloic elements produced during each flushof cambial activity resulted in detectable growth increments(or ‘rings’) within the phloem. There was a distinctshortening of the different phloem elements during the approachof dormancy/least activity. Conspicuous changes were found inthe ergastic contents of phloem parenchyma and ray cells adjacentto the cambial zone during the initiation of cambial activityand during the approach of dormancy/least activity. Seasonal growth, secondary phloem, deciduous and evergreen trees, cambial activity     

Periodicity of Wood Formation in Some Trees of Lowland Rainforest in Nigeria

Freshly prepared chlor-zinc-iodide was used to determine theperiodicity of wood formation at breast height (144 cm fromthe ground) in the trunks of some trees growing in the LowlandRainforest around Ibadan, Nigeria. Wood formation shows seasonal periodicity in the plants studied.The cambial derivates on the xylem side differentiate into woodcells, which at a certain stage of differentiation have abundantcellulose in their secondary walls. The cellulose stains deepblue in chlor-zinc-iodide. This has been used as a criterionfor deciding that wood formation has started. When no cellswith deep blue staining secondary walls are found the cambiumis known to be dormant or quiscent. The resumption of cambial activity is correlated positivelywith bud break and unfolding of new leaves. In Bombax buonopozenseP. Beauv. the relationship may be obscured by local cambialactivity induced by injury. Wood formation stops in the trunks either towards the end ofthe rainy season or at the early part of the dry season. Itstarts either during the dry season or at the beginning of therainy season; but the bulk of the wood is formed during therainy season. Cambial activity stops in most cases before leaffall. At the cessation of wood formation the fully lignifiedxylem elements abut on the xylem mother cells or on xylem cellswith incompletely thickened cell walls. Presence or absence of a starch-free-zone and the noding ofthe vascular rays also give indications of seasonal periodicityin wood formation. Growth rings are periodic and one growthring is generally formed each year.     

The regulation of cambial division and secondary xylem differentiation in xanthium by auxins and gibberellin

Cambial division continued in decapitated Xanthium plants without concomitant xylem fiber differentiation. The application of indoleacetic acid to these plants did not affect the production of cambial derivatives or induce xylem fiber differentiation. When naphthaleneacetic acid was applied either to the second internode or to the stump of a lateral shoot, xylem fiber differentiation was induced in the newly formed cambial derivatives on the xylem side of the cambium in the stem. When naphthaleneacetic acid was applied unilaterally, xylem fiber differentiation was restricted to that side of the stem in the first internode and hypocotyl. Naphthaleneacetic acid also enhanced the production of cambial derivatives. Gibberellic acid enhanced cambial derivative production but did not affect the differentiation of xylem fibers. Similar numbers of cambial derivatives were produced in some naphthaleneacetic acid-treated plants in which xylem fiber differentiation was induced and in gibberellic acid-treated plants which did not differentiate xylem. When naphthaleneacetic acid was applied 72 hours after decapitation, the oldest of the cambial derivatives on the xylem side failed to develop into fibers although younger cells did. These results suggest that auxin has its direct effect on the induction of xylem differentiation rather than the induction of divisions prerequisite to differentiation.     

The Period of Time Taken by Cambial Derivatives to Grow and Differentiate into Tracheids in Pinus radiata: D. Don

Cambial activity and tracheid development were studied in astand of Pinus radiata D. Don growing in Victoria, Australia.Samples were taken at weekly intervals from 16 August 1966 to19 September 1967. Cell counts were made from these samplesand the results used to estimate the time periods required tocomplete various phases of tracheid development. The average time required for cells of the cambial zone to completea division cycle was about 4 weeks, with little evidence ofany variation during the growing season. The time required forradial growth was about 3 weeks early in the season, graduallyreducing to about 1.5 weeks before the period of dormancy setin. The time required for the deposition of the secondary cellwall was 3 to 4 weeks early in the season, increasing to 8 to10 weeks, later. This increased period was accompanied by areduced rate of deposition of cell-wall material.     

Polarity of Xylem Formation in Isolated Stem Segments of Pinus silvestris

The culture of isolated stem sogments was used as a technique to study polarity of xylem formation in Pinus silvestris L. Cambial activity was greatest at the apical or the basal end, whichever received the complete fresh medium, but decreased more abruptly with increasing distance when the basal end was so supplied. Whether gradients of activity increased basipetally or acropetally also depended upon the end to which the auxin and the sugar components were supplied. Ring-barking of segments, then cultur-ing them with apical supply of medium to the xylem, resulted in inhibition of xylem production below, and above, the ring. Cambial activity at the apical ends of such segments was expressible as a logarithmic function of the uninterrupted length of contiguous extraxylary tissues. The involvement of polarity phenomena in control of cambial activity in isolated stem segments is confirmed.     

Effect of shade treatment on biosynthesis of catechins in tea plants

When tea plants were shaded with black lawn cloth for severaldays in the field, the accumulations of (—)-epicatechin,(—)-epicatechin-3-gallate, (—)-epigallocatechinand (—)-epigallocatechin-3-gallate decreased in newlydeveloping tea shoots. Radioactive tracer studies showed thatthe conversions of glucose-U-¹⁴C, shikimic acid-G-¹⁴C and phenylalanine-U-¹⁴Cinto (—)-epicatechin and (—)-epigallocatechin moietieswere depressed by the shade treatment for tea plants but theincorporation of trans-cinnamic acid-3-¹⁴C was not affected.The treatment was found to have no significant effect on theactivities of phospho-2-keto-3-deoxy-heptonate. aldolase (EC.4.1.2.15 [EC] ), 3-dehydroquinate synthase (EC. 4.6.1.3 [EC] ), 3-dehydroquinatedehydratase (EC. 4.2.1.10 [EC] ), shikimate dehydrogenase (EC. 1.1.1.25 [EC] )and trans-cinnamate 4-monooxygenase (EC. 1.14.13.11 [EC] ) in theshoots, whereas the activity of phenylalanine ammonia-lyase(EC. 4.3.1.5 [EC] ) clearly decreased. (Received March 17, 1980; )     

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.     

Growth and Dry-weight Distribution in Callistephus chinensis as Influenced by Lighting Treatment

Plants of two cultivars of Callistephus chinensis (Queen ofthe Market and Johannistag) were grown in 8 h of daylight perday with one of the following treatments given during the 16h dark period: (a) darkness—‘uninterrupted night’,(b) I h of light in the middle of the dark period—a ‘nightbreak’, (c) I min of light in every hour of the dark period—‘cycliclighting’, (d) light throughout—‘continuouslight’. The plants receiving uninterrupted dark periods remained compactand rosetted in habit with small leaves, while leaf expansion,stem extension, and flower initiation were promoted in all threeillumination treatments (b, c, d). Although these three treatmentsproduced similar increases in leaf area, continuous light wasthe most effective for the promotion of both stem growth andflower initiation while cyclic lighting was generally more effectivethan a I-h night break. Continuous light also caused more dry matter to be divertedto stems at any given vegetative dry weight and it was shownthat the stem weight ratio of both varieties was correlatedwith stem length.     

The response of tomato roots (Lycopersicon esculentum Mill.) to iron deficiency stress: alterations in the pattern of protein synthesis

Dicotyledon plants adapt to iron (Fe) deficiency through a seriesof reactions that increase the ability of the plant to assimilateFe and to increase the efficiency of Fe utilization. In an attemptto gain an insight into these adaptive processes, the specificchanges in protein synthesis associated with the onset of theFe deficiency response in tomato roots (Lycopersicon esculentumMill cv. Rutgers) have been investigated. Roots were grown underFe—sufficient and —deficient conditions, and thepattern of protein synthesis was analysed by in vitro translationof root mRNA and by in vivo labelling of root proteins. Polypeptideswere resolved by two—dimensional polyacrylamide gel elec—trophoresis.Seven polypeptides were identified by in vitro translation,whose synthesis was significantly increased during Fe deficiency.The increase was probably specific to Fe deficiency in thatthe polypep—tide synthesis was not increased during phosphatedeficiency stress, was less prominent following prolonged Fedeficiency and was decreased following re—supply of Feto the hydroponic medium. The pattern of in vitro translation of mRNA isolated from Fe—deficientroots was compared to the results obtainedin vivo followingradiolabelling of proteins. In these analyses, eight polypeptideswere identified, tentatively including the seven polypeptidespreviously identified by in vitro translation. All polypeptideswere characterized with regard to molecular mass and pl andtheir localization in the cell, whether being membrane boundor soluble. It is suggested that members of this group of polypeptidesare involved in the response of the root to Fe deficiency: althoughtheir functions remain to be identified. Key words: In vitro protein synthesis, iron, iron deficiency, root, 2-dimensional PAGE     

Flower-Inducing Activity of Exogenous Lysine in Lemna paucicostata 151 Cultured on Nitrogen-Rich Medium

Flower-inducing activity of lysine was examined in Lemna paucicostata151, a weakly responsive short-day plant, cultured on nitrogen-richmedium under long-day conditions (continuous light). Lemna paucicostata151 was homogenized in a solution of lysine and the homogenatewas centrifuged. The supernatant (lysine-containing extract)was added to nitrogen-rich medium after passage through a membranefilter to give various concentrations of lysine in the medium.Flowering was induced in plants grown for six days on mediumthat contained lysine at concentrations above 0.25 µM.In plants grown on medium that contained 1 µM lysine,a significant flowering response was observed on the fourthday of culture. However, the flower-inducing activity of lysinedisappeared when the lysine-containing extract was added tothe medium and the medium was then autoclaved, suggesting thatthe active principle is unstable to autoclaving. Among derivativesof lysine tested, lysine hydroxamate had the highest flower-inducingactivity and lysyl lysine had almost same activity as that oflysine. When added to the medium without homogenization withplant material, lysine and lysyl lysine had flower-inducingactivity but lysine hydroxamate did not induce flowering. (Received April 26, 1993; Accepted November 8, 1993)     

Reproductive Development and Nitrogen Fixation in Soybean (Glycine max [L.] Merril)

Gomes, M. A. F. and Sodek, L. 1987. Reproductive developmentand nitrogen fixation in soybean (Glycine max (L.) Merril).—J.exp. Bot. 38: 1982–1987. Nitrogenase activity (acetylene reduction) was measured duringthe growth cycle of soybean plants induced to flower at twodifferent ages. The decline in nitrogenase activity towardsthe end of the cycle was clearly associated with pod-fillingfor both flowering dates when plants were cultivated under lowerlight and temperature conditions (out of season). Under higherlight and temperature conditions (normal growing season) thedecline was independent of the flowering date. Furthermore,the timing of the decline was not altered when plants were maintainedunder long-day (vegetative) conditions nor when flowers wereremoved. It is suggested that under more favourable growth conditionsthe diversion of assimilates by the fruits is not the primarycause of the decline in nodule activity, but competition bythe fruits may be important when the production of photo-assimilatesis more limited. Key words: Glycine max, nitrogenase, source-sink     

Storage Organ Development in Radish (Raphanus sativus L.). 2. Effects of Growth Promoters on Cambial Activity in Cultured Roots, Decapitated Seedlings and Intact Plants

The radish varieties Cherry Belle and Long White Icicle wereused to investigate the role of the shoot and the effects ofsynthetic growth promoters in controlling cambial activity inthe seedling axis. Development was compared in excised roots, roots with hypocotylsattached and intact seedlings cultured aseptically on a nutrientmedium. No cambial divisions were seen in isolated radicleswhich had been cultured for ten days following excision butretention of hypocotyl tissue or the entire shoot resulted incambial activity and the production of secondary vascular tissues.Enriching the culture medium by raising the sucrose conantrationto 8% and including 10^–5 M indol-3yl acetic acid (IAA)5 x 10^–6 M 6-benzylaminopurine (BA) and 5 x 10^–4Minositol enhanced root thickening, increasing stele and xylemdiameters in roots cultured both with and without attached shoottissues. The effects of shoot tissues and enrichment of themedium were additive. The effects of auxin, cytokinin and gibberellin (gibberellicacid, GA²) were also studied on daxpitated seedlings. BA wasmuch more effective in inducing cell divisions in the hypocotylthan either IAA or GA supplied separately but a mixture of IAA+GAalso produced clearly defined arcs of cambial tissue. Littlesecondary tissue had been produced after seven days' treatment,and stelar enlargement was due to the development of a cambialzone and cell expansion in the primary tissues. Only minor differencesin response were observed between the two varieties. No stimulation of storage organ development occurred when auxin,cytokinin or inositol was inwrporated into the inorganic culturesolution in which plants of Cherry Belle were grown. Rnphanus sarivus, radish, storage organ, cambial activity, growth promoters, indol-3-ylacetic acid, 6-benzylaminopurine, gibberellic acid     

Periodicity of Wood Formation in Twigs of some Tropical Trees in Nigeria

The periodicity of wood formation was studied in twigs of treesgrowing in three ecological areas in Nigeria, namely lowlandrainforest, Southern Guinea savanna and mangrove swamp. Initiationof cambial activity was correlated with bud break, and wheremultiple vegetative bud formation occurred in the lowland rainforestand the Southern Guinea savanna, the number of growth ringscorresponded with the number of times the vegetative buds opened.In the mangrove swamp, although there may be a clear correlationbetween vegetative bud growth and wood formation in 1 to 2 year-oldtwigs of Drepanocarpus lunatus and Ormacarpum verrucosum therewas no such correlation in Dalbergia ecastaphyllum. Short axillarybranches and inflorescences which developed irregularly in plantsof the mangrove swamp induced multiple growth ring formation.In D. ecastaphyllum, the pattern of unfolding of young leavesseems to play a major role in the formation of multiple growthrings. In each of the areas multiple growth ring formation couldbe induced by injury. In Daniellia oliveri there was periodicdeposition of prismatic crystals. The crystals were depositedeach time wood formation stopped. In plants in which flowersopened before the opening of the vegetative buds, there wasinitiation of cambial activity by the opened flowers in thetwigs on which the flowers were borne.     

Behavioral responses of leaves and vascular cambium of Prosopis cineraria (L.) Druce to different regimes of coal-smoke pollution

Abstract

The foliar and cambial responses of Prosopis cineraria to five different coal-smoke regimes in Delhi, India, were studied using the monthly collections of leaves and cambial blocks as well as the data on SO₂, NO₂ and particulate concentrations from each of the five study sites. Coal-smoke inhibited pigment concentration, NR activity and sugar content and promoted stomatal index and the nitrate and sulfur contents. Stomatal conductance was low, leading to a drop in the net photosynthetic rate. Cambial activity started quite late and the annual increment of wood was reduced despite a prolonged active phase, possibly due to a distinctly retarded rate of cambial cell division. Vessel proportion in the wood increased but the size of vessel elements and fibers decreased. Such studies may help in identifying trees suitable for cultivation in the pollution-affected areas.     

Hormonal control of cambial activity and vessel differentiation in Quercus robur

Cambial activity and vessel differentiation of the Quercus robur stem were investigated in relation to concentration of growth regulators and sucrose, seasonal changes in the sensitivity of cambial cells, and axial polarity of the stem. Basipetal efflux of natural auxin was measured in the oak stem cambial region. IAA, GA₃, kinetin and sucrose affected cambial activity and/or initiation of vessel differentiation differently, depending upon concentration. Depending upon the season, kinetin increased or reduced the stimulation of cambial activity caused by IAA and GA₃, but it did not affect the differentiation of vessels. Supply of sucrose in higher concentrations reduced the number of differentiated vessels but did not decrease the stimulation of cambial divisions.Unlike stimulation of cambial activity by GA₃, auxin stimulation of cambial divisions and differentiation of vessels were highly dependent upon stem polarity, 2,3,5-triiodobenzoic acid (TIBA) inhibited formation of vessels, but not cambial activity. The oscillations in basipetal efflux of natural auxin from the cambial stem region of successive 6 mm long sections substantiate the hypothesis that the histogenesis of xylem tissue in ring-porous species is under control of the vectoriat field that is associated with oscillatory phenomena in polar auxin transport.     

Isolation and Identification of Nicotinic Acid as a Flower-Inducing Factor in Lemna

Extracts of flowering plants of the long-day plant Lemna gibbaG3 and the short-day plants Lemna paucicostata 151 and 381 weretested on L. paucicostata 151 for flower-inducing activity.Crude extracts failed to show any activity but after severalpurification steps three fractions with flower-inducing activitywere obtained. One fraction obtained from all three plants wasshown to contain nicotinic acid by mass spectroscopic and NMRspectroscopic analyses. These results raise the possibilitythat nicotinic acid may act to influence the flowering processin Lemna. (Received August 28, 1985; Accepted October 29, 1985)