Ring Of Cambium Research Articles

Comparative stem and wood anatomy of Ipomoea eriocarpa R.Br. (Convolvulaceae) growing in the arid zone and tropical deciduous forest

Family Convolvulaceae is dominated by climbing species and in most of the members, radial growth is achieved by forming vascular variants. The present study compares stem anatomy and structural modifications in the secondary xylem of Ipomoea eriocarpa R.Br. (Convolvulaceae) growing at Banni (Kachchh, arid zone) and at Toranmal (Tropical dry deciduous forest). Individuals growing at both biogeographic zones showed similar ontogeny for the development of successive cambia, inter-and intraxylary phloem, intraxylary cambium, and non-lignified axial (and radial) parenchyma wedges. However, as plants grew older, stems of individuals growing at Banni became lobbed in outline and showed the development of successive cambia and bidirectional intraxylary cambium. The thickest stems of samples from Banni possessed three successive cambial rings, vessels mostly solitary and relatively narrow in diameter with a greater number of non-lignified axial parenchyma wedges. In contrast, samples collected from Toranmal showed two successive cambial rings with relatively few numbers of non-lignified axial parenchyma wedges, intraxylary cambium was unifacial and exclusively produced intraxylary phloem. The secondary xylem was diffuse-porous, vessels usually in tangential multiples or clusters. Though, the time of seed germination and establishment of seedlings remained the same; in Banni samples, initiation of successive cambia, intraxylary cambium and its derivatives (i.e. xylem and phloem) began before the individuals growing at Toranmal. Samples from both locations showed the presence of inverse cambia on the inner margin of the xylem produced by the first successive cambium. These alterations in the behaviour may be correlated with the ephemeral lifecycle of Banni plants.

Stem anatomy and ontogeny of phloem wedges in some species of Gymnema (Apocynaceae)

The anatomy of climbing plants shows a fascinating arrangement of vascular tissues, which may vary from species to species. In the present study, stem anatomy of Gymnema cuspidatum, G. latifolium, G. montanum and G. sylvestre (Apocynaceae) and the occurrence of vascular variants are described here for the first time. They were compared histologically to understand the structural variations in the secondary xylem and ontogeny of vascular variants if any within the species. All four species increase their stem diameter by a single ring of vascular cambium like most of the eudicots. In thick stems, periderm forms distinct ridges and furrows in all the species except G. sylvestre, in which it was minimal. Differential activity of the cambium resulted in the formation of distinct and deep phloem wedges in G. latifolium and G. sylvestre while in other species they were either shallow or almost absent. The secondary xylem was diffuse-porous with distinct growth rings in G. cuspidatum and G. montanum while they were indistinct in G. latifolium and G. sylvestre. Besides regular xylem elements, the presence of perforated ray cells and radially oriented laticifers in the xylem rays was observed frequently in all the investigated samples. The formation of the intraxylary primary phloem was observed concomitant to the regular protoxylem and protophloem at the pith margin. Subsequently, an additional intraxylary phloem was developed from the adjacent pith cells and by the activity of intraxylary/medullary cambium at the pith margin. In thick stems, parenchymatous cells situated between the protoxylem and intraxylary protophloem led to the initiation of intraxylary cambium. In conclusion, three species showed distinct ridges and furrows due to the formation of periderm except G. sylvestre, phloem ray parenchyma showed the formation of sclerenchyma only in the thick stems of G. sylvestre. The formation of intraxylary phloem in all four species may serve as an additional way for the transport of organic nutrients.

EFFECT OF ORGANIC FERTILIZERS AND NUTRIENTS ON ANATOMICAL TRAITS OF RED BEETROOTS

A field experiment was conducted during fall season 2021-2022 In order to study the effect of soil as an agricultural medium, organic fertilizers (Vermecompost, cow manure) and foliar spraying of silicon and calcium on skin, bark and cambium ring thickness of three beetroot varieties (Red, Dark Red, and Cylindra). Seeds directly sown in the fields of Station A College of Agricultural Engineering Sciences - University of Baghdad - Al-Jadriya campus- Within RCBD a split-plot experiment, where the cultivars were the main unites, organic fertilizer, and foliar spray as the subunits, with three replicates, the number of treatments was 27. The results revealed that the triple interaction treatment of Dark Red, Vermicompost, and silicon spray V2S2F1 was superior in epidermis thickness, cortex thickness, and cambium ring thickness (55.00 μm, 78.90 μm, and 182.07μm) respectively, compared with Cylindra cultivar, soil medium, and spraying with distilled water V3S1F0, which produced the lowest averages (21.77 μm, 31.23 μm, 64.57 μm) respectively. The interaction treatment between Red cultivar, cow manure and spraying with distilled water V1S3F0 excelled in the thickness of the middle xylem ring ( 261.33 μm). Compared with the thinnest middle xylem (143.8 μm) in red cultivar roots treated with soil medium and distilled water.

Workflow for phenotyping sugar beet roots by automated evaluation of cell characteristics and tissue arrangement using digital image processing

BackgroundCell characteristics, including cell type, size, shape, packing, cell-to-cell-adhesion, intercellular space, and cell wall thickness, influence the physical characteristics of plant tissues. Genotypic differences were found concerning damage susceptibility related to beet texture for sugar beet (Beta vulgaris). Sugar beet storage roots are characterized by heterogeneous tissue with several cambium rings surrounded by small-celled vascular tissue and big-celled sugar-storing parenchyma between the rings. This study presents a procedure for phenotyping heterogeneous tissues like beetroots by imaging.ResultsTen Beta genotypes (nine sugar beet and one fodder beet) were included to establish a pipeline for the automated histologic evaluation of cell characteristics and tissue arrangement using digital image processing written in the programming language R. The identification of cells has been validated by comparison with manual cell identification. Cells are reliably discriminated from intercellular spaces, and cells with similar morphological features are assigned to biological tissue types.ConclusionsGenotypic differences in cell diameter and cell arrangement can straightforwardly be phenotyped by the presented workflow. The presented routine can further identify genotypic differences in cell diameter and cell arrangement during early growth stages and between sugar storage capabilities.

Brassinosteroids promote parenchyma cell and secondary xylem development in sugar beet (Beta vulgaris L.) root.

Increasing crop yield has always been an important goal in agriculture. Brassinosteroids (BRs) are growth‐promoting steroid hormones with vital roles in many root developmental processes. Sugar beet ( Beta vulgaris L.) is a root crop with a tertiary root structure. The differentiation of vascular bundles and the division of cambial cells increase root diameter. However, little is known about how BRs regulate the transverse growth of beetroot. Therefore, sugar beet with eight leaves was grown in medium containing epibrassinolide or brassinazole, an inhibitor of BR biosynthesis. BRs increased the spacing between the cambial rings by increasing the size of parenchyma cells between the rings and ultimately increasing root diameter. BRs also promoted secondary xylem differentiation. Moreover, the gene expression analysis of BvXTH33, BvSHV3, BvCESA6, BvPARVUS, and BvCEL1, which were related to the cell wall biosynthesis, indicated that BR could promote the growth of cell wall. These findings showed that BRs function in transverse development in beetroot.

Effect of polar auxin transport and gibberellins on xylem formation in pine cuttings under adventitious rooting conditions

Maturation-related decline of adventitious root formation is one of the major factors affecting adventitious rooting in forest tree species. We demonstrate that inhibition of polar auxin transport promoted cambium and xylem differentiation in rooting-competent hypocotyl cuttings from Pinus radiata under conditions of adventitious root formation. Treatments with bioactive gibberellins inhibited rooting while at the same time inducing both the differentiation of a continuous ring of cambium and xylem formation. Treatments with inhibitors of gibberellin biosynthesis did not affect the rooting response. The results demonstrate that xylem parenchyma and procambial cells at the xylem poles of rooting-competent hypocotyl cuttings after excision and under conditions of adventitious root induction become adventitious root meristems or xylem, depending on the directional auxin flow. Gibberellin may interact with this pathway, inducing xylem differentiation and inhibiting rooting. We conclude that modifications of auxin flow at the rooting sites, and the priming of cambial cells to differentiate into xylem during tree ageing, may be associated with the maturation-related decline of adventitious root formation.

Tissue composition and arrangement in sugar beet genotypes of different tissue strength with regard to damage and pathogen infestation

Drought stress affects yield formation and quality of sugar beet. The aim of this study was to identify the growing period, in which drought stress has the greatest impact on growth, and furthermore, to analyze the response of different sugar beet genotypes. Causes for a different response should be identified. In pot experiments in the greenhouse, drought stress was simulated by reducing irrigation to 60% of the water holding capacity (WHC) for four weeks at various growth stages followed by re-watering. Growth reduction was greatest when drought stress occurred early in the season: the content of the quality-determining non-sugars was highest, sugar yield and beet diameter were lowest. Responses of the genotypes in sugar yield, but primarily in the accumulation of osmotically active substances differed. Despite re-watering after drought stress the restrictions could not be compensated during growth. The transpiration coefficient of the drought-stressed treatments was only slightly different to the control, because water consumption in the control did not either increase at average air temperatures beyond 23 °C. The strong effect of early drought stress could be attributed to the high growth rates, so that a limited water supply affected yield formation more than at later growth stages. The storage losses of sugar beet genotypes are closely related to damage during harvest and subsequent infestation with mould and rots. Genetic variation for storability seems to be primarily linked to textural properties of the roots such as the resistance against mechanical damage. However, no information is available about the tissue strength, tissue composition and structural organization leading to an enhanced resistance against damage and pathogen attack. Therefore, the aims of the study were the identification of genotypic differences concerning tissue strength of the beet, the relation to damage and pathogen infestation and the underlying physiological basis of tissue strength. Field trials were carried out with 6 genotypes at 2 locations in 2018. The roots were harvested in August and November. After harvest in November, a storage trial was carried out. The root strength increased from August to November. Beets with a high puncture resistance of the periderm also had a firm inner tissue. Genotypic differences in puncture resistance were not affected by the harvest time, indicating that this trait is stable throughout the growing period. A higher puncture resistance of the beet was related to a lower mould growth during storage. Genotypes with varying tissue strength also differed in fiber content (AIR), but the composition of AIR was stable over genotypes. The number of cambium rings seems not to essentially influence the tissue strength of the beet. In the further course of the project, microscopic analyzes will clarify, whether genotypic differences in tissue strength can be attributed to cell size or cell wall thickness.

Development of successive cambia and formation of secondary xylem in Suaeda nudiflora and S. fruticosa (Amaranthaceae s.l.)

Amaranthaceae s.l. and its allied families like Amaranthaceae s.s., Chenopodiaceae s.s. and Phytolaccaceae s.s. are always debated in the literature about their pattern of secondary growth; when their stem diameter increases by forming successive cambia. In the present study, development of successive cambia and differentiation of its derivatives was investigated in Suaeda fruticosa and S. nudiflora (Amaranthaceae s.l.). After primary growth, the first complete ring of cambium was formed by the successive cambium due to failure in the development of interfascicular cambium between adjacent vascular bundles. The first ring of successive cambium initiated from the parenchymatous cells (pericyclic derivatives) external to the protophloem. This newly formed cambium was functionally bidirectional and produced secondary xylem centripetally and phloem centrifugally. Subsequent renewal of cambium was observed as small segments instead of complete ring. They interconnect with existing cambium and form anastomosing network. Due to the renewal of small sectors, the secondary phloem formed by earlier cambial segments became enclosed within the secondary xylem and conjunctive tissue. Formation of vessels and sieve elements were found confined only to few fusiform cells while rest of the cambial sector exclusively produced conjunctive tissue on either side. The secondary xylem formed in the beginning of successive rings of xylem remained rayless while thick stems showed presence of heterocellular rays with several cells in height and width. Accumulation of starch along with the presence of nuclei in the xylem fibres even after deposition of the secondary wall is consistent feature in both the species.

Importance of canopy closure and dry matter partitioning for yield formation of sugar beet varieties

Phenotyping of sugar beet canopy for yield estimate requires a close relationship between canopy characteristics and final sugar yield. The objective of the study was to identify the importance of early canopy closure and of dry matter partitioning for high sugar yields, or more general, to study whether sugar beet yield is limited more by the source or by the sink capacity. Randomized field trials were conducted with two varieties (sugar type, yield type) in three sowing dates and four harvest dates at two sites in three years (2012–2014). Results showed very stable variety characteristics for all parameters and a linear increase of sugar yield with thermal time from September to November. Although variety 2 had reached canopy closure 100 GDD later and had a lower LAI and leaf yield than variety 1 throughout the growing season, it reached a higher sugar yield. That could be attributed to a higher RUE and a higher fraction of dry matter partitioned to sugar storage, while total dry matter did not differ distinctly. In the storage root, more cambial rings were formed, indicating a higher sink strength. Hence, sugar yield is more determined by dry matter partitioning (sink) than by canopy formation (source), making phenotyping difficult.

Development of successive cambia and structure of the secondary xylem in some members of the family Amaranthaceae

Young stems of Aerva javanica (Burm.f.) Juss. ex Schult., A. lanata (L.) Juss. ex Schult, A. monsonia Mart., A. sanguinolenta (L.) Blume, Alternanthera bettzickiana (Regel) G. Nicholson, A. philoxeroides (Mart.) Griseb., Gomphrena celosioides Mart., G. globosa L. and Telanthera ficoidea (L.) Moq., showed the renewal of small sectors of cambium by replacing with new segments. Therefore, the secondary phloem formed by earlier cambial segments form isolated islands of phloem enclosed within conjunctive tissues became embedded in the secondary xylem. As the stem grows older, complete ring of cambium is renewed; sometimes an anastomosing network of successive cambia may be seen due to the renewal of larger segments of the cambium. Renewal of the cambium takes place by repeated periclinal division in the parenchyma cells positioned outside to the phloem formed by the previous cambium. Functionally the cambium is bidirectional and exclusively composed of fusiform cambial cells. Differentiation of conducting elements of the secondary xylem and phloem remains restricted to the certain cambial cells while rest of the segments exclusively produce conjunctive cells. Accumulation of starch along with the presence of nuclei in the xylem fibers even after deposition of the secondary wall is consistent in all the species and it seems to be associated with the absence of rays in the secondary xylem and phloem of nine species from four genera. The significance of successive cambia, rayless xylem and nucleated xylem fibers were correlated with plant habit.

Stem anatomy at various developmental stages of secondary growth in Turbina corymbosa (Convolvulaceae)

Background – Population growth of lianas in the tropical forest is credited to their ability of CO2 sequestration and efficiency of the narrow stems to supply water required for the amount of foliage it bears. Turbina corymbosa (L.) Raf. (Convolvulaceae Juss.) is one of the fast-growing invasive species of scrambling woody lianas. It covers trees entirely within a short period to compete with above-ground resources (particularly sunlight). However, no information is available on how it manages to cope up with an increasing demand of water supply and mineral nutrients. What are the structural and developmental patterns adapted by this species to expand the stem diameter for efficient supply of below-ground resources? Therefore, our aim was to investigate the secondary growth patterns and structure of secondary xylem and phloem in T. corymbosa.Methods – Several samples of the stem with various diameters were studied using a histological method. Morphological and anatomical analyses were carried out using light microscopy.Key results – With the initiation of secondary growth, stems lose their circular outline rapidly due to unequal deposition of secondary xylem and formation of successive cambia. New successive cambia initiate from parenchymatous cells as small crescent-shaped fragments on asymmetric/opposite sides and result in a different stem conformation. Though several segments of successive cambia are formed, very few stem samples form complete cambium rings. The secondary xylem formed by successive cambia is diffuse porous with indistinct growth rings and is composed of both wide and narrow (fibriform) vessels, tracheids, fibres, axial and ray parenchyma cells. The secondary phloem consists of sieve tube elements, companion cells, axial and ray parenchyma cells. In fully grown plants, cambial action (internal cambium) occurrs between the intraxylary phloem and protoxylem and produces secondary xylem and phloem near the pith region.Conclusion – Structural alterations and unequal deposition of conducting elements, occurrence of intraxylary phloem and flattening of the stem are suggested to facilitate rapid growth of the plants by providing required minerals and nutrients. Internal cambium formed at the periphery of the pith is bidirectional and produces secondary xylem externally and intraxylary phloem internally. Continued development of intraxylary phloem from the internal cambium provides an additional path for rapid and safe translocation of photosynthates.

Wound Stress, an Unheeded Factor for Echinacoside Accumulation in Cistanche deserticola Y. C. Ma.

Cistanche deserticola Y. C. Ma, a precious parasitic medicinal herb distributed in desert areas in the Northwest of China, also known as “desert ginseng”, has been used in China for thousands of years for its nourishing effects. The phenylethanoid glycosides (PeGs) have been proven as the main effective compounds due to their neuroprotective effects and were used for quality control. In this study, echinacoside content, a representative PeG, total phenolic content, DPPH scavenging activity, and PAL activity were determined in different tissues of C. deserticola. Our results showed that most indices had a similar pattern of scale > cambium ring > pith and bottom part > middle part > upper part. Besides, stereomicroscopic observation showed that the scale surface was densely covered with physical wounds formed during vertical and broadwise growth in sand. Thus, wound area was quantified and a linear regression analysis was conducted between wound area and PAL activity, total phenolics, and echinacoside content. Our results suggested that physical wounding caused by sand might play an important role in echinacoside biosynthesis which has never been noticed in C. deserticola development. Furthermore, the coexistence of the highest PAL activity and highest echinacoside accumulation in scale tissue might indicate that the biosynthetic site of echinacoside in C. deseticola Y. C. Ma is mainly in the scale tissue.

Investigation of morphological and anatomical underground parts structure of genus Primula L. Cultivated species

Investigation of morphological and anatomical underground parts structure of genus Primula L. Cultivated species

ДОСЛІДЖЕННЯ АНАТОМІЧНОЇ БУДОВИ ПІДЗЕМНИХ ОРГАНІВ РОДОВИКА ЛІКАРСЬКОГО (SANGUISORBA OFFICINALIS L. )

Мета роботи. Родовик лікарський (Sanguisorba о№ сіпаіів L.) - багаторічна трав’яниста рослина, підземні органи якої здавна використовують у медицині як в'яжучий і кровоспинний засіб. Офіційною медициною використовуються препарати родовика лікарського з кореневища з коренями. У наукових джерелах недостатньо інформації про фармакогностичне вивчення підземних органів родовика лікарського, тому метою нашої роботи було вивчити анатомічну будову, встановити і зіставити діагностичні ознаки кореневищ і коренів, зібраних восени на першому і другому роках вегетації даного виду.Матеріали і методи. Виготовлення мікропрепаратів проводили за загальноприйнятими методами. Використовували мікроскоп МС 10 (окуляри Х5, Х10, 15, об’єктиви Х10, Х40). Мікрофотографії зроблені фотокамерою Sаmsung PL50.Результати й обговорення. Кореневище. Підземна частина родовика лікарського представлена багаторічним епігеогенним кореневищем з придатковими коренями. Кореневище поступово дерев’яніє, стає пухким, порожнистим у центрі. Анатомічна будова кореневища безпучкова. Молоді однорічні кореневища вкриті темно-бурим, поздовжньо зморшкуватим корком. У особин другого року вегетації клітини корка ущільнюються, починають злущуватись. Первинна кора однорічних кореневищ представлена шарами крупноклітинної паренхіми. Ксилема і флоема паренхіматизовані, пронизані розширеними радіальними серцевинними променями. В клітинах накопичуються прості і складні крохмальні зерна, часто зустрічаються друзи. Помітно виділяється щільне кільце камбію. Провідна система представлена судинами. Механічні волокна розташовані відокремлено, невеликими ділянками поблизу судин або утворюють суцільне кільце поряд з камбієм. Серцевина з міжклітинниками, паренхімні клітини з крохмальними зернами і друзами кальцій оксалату. Корені мають вторинну будову. Корок шаруватий, кільця з коричневим або жовтуватим вмістом чергуються з кільцями світлішими або безбарвними. Зона камбію багатошарова, темніша, добре помітна. Ксилема промениста. Трахеїди пористі. Серцевинних променів багато. У клітинах наявні дрібні прості овальні та округлі крохмальні зерна, друзи та поодинокі призматичні або багатогранні кристали кальцію оксалату. У дворічних коренів зовнішній шар корка товстий, темно-коричневий, з тріщинами; чітко виділяються річні кільця ксилеми, серцевинних променів багато, волокна лубу чисельні, здерев’янілі.Висновки. Досліджено анатомічну будову підземних органів родовика лікарського, зібраних на першому і другому роках вегетації. Виявлено мікроскопічні діагностичні ознаки кореневищ і коренів.

Stem anatomy and development of inter- and intraxylary phloem in Leptadenia pyrotechnica (Forssk.) Decne. (Asclepiadaceae)

Modification of external morphology and internal structure of plants is a key feature of their successful survival in extreme habitats. They adapt to arid habitats not only by modifying their leaves, but also show several modifications in their conducting system. Therefore, the present study is aimed to investigate the pattern of secondary growth in Leptadenia pyrotechnica (Forssk.) Decne., (Asclepiadaceae), one such species growing in Kachchh district, an arid region of Gujarat State. A single ring of vascular cambium, responsible for radial growth, divided bidirectionally and formed the secondary xylem centripetally and the phloem centrifugally. After a short period of secondary xylem differentiation, small arcs of cambium began to form secondary phloem centripetally instead of secondary xylem. After a short duration of such secondary phloem formation, these segments of cambium resumed their normal function to produce secondary xylem internally. Thus, the phloem strands became embedded within the secondary xylem and formed interxylary phloem islands. Such a recurrent behavior of the vascular cambium resulted in the formation of several patches of interxylary phloem islands. In thick stems the earlier formed non-conducting interxylary phloem showed heavy accumulation of callose on the sieve plates followed by their crushing in response to the addition of new sieve elements. Development of intraxylary phloem is also observed from the cells situated on the pith margin. As secondary growth progresses further, small arcs of internal cambium get initiated between the protoxylem and intraxylary phloem. In the secondary xylem, some of the vessels are exceptionally thick-walled, which may be associated with dry habitats in order to protect the vessel from collapsing during the dryer part of the year. The inter- and intraxylary phloem may also be an adaptive feature to prevent the sieve elements to become non-conducting during summer when the temperature is much higher.

Development of successive cambia and wood structure in stem of Rivea hypocriteriformis (Convolvulaceae)

Abstract This study examined the formation of successive rings of cambia in Rivea hypocriteriformis Choisy (Convolvulaceae). The mature stem is composed of four to five rings of xylem alternating with phloem. Successive cambia originate as smaller and larger segments; union and anastomosing of small cambial segments often leads to the formation of discontinuous rings. In the initial stage of growth, several vascular bundles interconnect to form the first ring of vascular cambium. The cambium remains functional for one complete season and becomes dormant during summer; a new ring of cambium is completed prior to the subsequent monsoon season and sprouting of new leaves. Successive cambia are initiated from the pericyclic parenchyma situated three to four cell layers outside of the protophloem. Functionally, all the successive cambia are bidirectional and produce secondary xylem centripetally and phloem centrifugally. The secondary xylem is diffuse-porous, with indistinct growth rings and consisting of wide fibriform vessels, fibre tracheids, and axial and ray parenchyma cells. The xylem rays are uni- to multiseriate and heterocellular. The multiseriate rays contain lignified marginal ray cells and thin-walled, unlignified central cells. The central ray cells also show accumulations of starch and druses. Discrete strands of intraxylary phloem occur at the periphery of the pith, and additional intraxylary phloem develops from adjacent cells as secondary growth progresses. Earlier-formed phloem shows heavy accumulation of callose, followed by its compaction. The development of successive cambia is correlated with extension growth and with the phenology of the plant.

Evaluation of sugar beet genotypes for root traits by principal component analysis and cluster analysis

Sugar beet is the most important crop for sugar production in Europe. Wide genetic variability is essential in sugar beet breeding programs. The aim of this study is to evaluate variability for the main root traits and differences between monogerm and multigerm sugar beet genotypes from the breeding collection at the Institute of Field and Vegetable Crops. The following traits were analyzed: root weight (g), dry matter content (%), root head weight (g), root/head ratio (%), number of cambial rings, root length (cm) and root diameter (cm). Mean values for two years per genotype were standardized and used for analysis. Principal Component Analysis (PCA) and Cluster Analysis (CA) were used to examine the level of diversity for 20 genotypes and to rank the contributions of the variables. According to CA genotypes could be placed into five main groups, where a large number of multigerm genotypes were put in one group. On average multigerm genotypes were characterized by higher mean values for root weight, length, diameter and lower root head ratio. Multigerm genotypes had higher coefficients of variation for nearly all measured root traits.

Structure of Stem and Cambial Variant in <I>Spatholobus parviflorus</I> (DC.) Kuntze. (Fabaceae)

Spatholobus parvifloru (DC.) Kuntze. is a tropical woody climber which shows abnormal secondary growth in thickness, due to the formation and activity of successive cambia. By the dedifferentiation of groups of parenchyma cells outside the band of sclereid fibers, the cambial rings are formed. The sclereid band is formed between the primary bark fibers. Each successive cambium first produces a layer of sclereid fibers which separate the vascular tissue produced by cambial activity. The epidermis is replaced by the periderm. This periderm helps the vessel segments to remain undamaged when the woody stem twist around the support.

Comparative study on secondary xylem and formation of successive cambia in stems and roots of Antigonon leptopus Hook. & Arn. (Polygonaceae)

Antigonon leptopus Hook. & Arn. (Polygonaceae) being a climbing member increases their stem and root diameter by forming successive cambia. The first successive ring of cambium initiates as small segments from the parenchymatous cells located on the inner side of group of primary phloem fibres. These small arcs of cambia produced secondary xylem internally and phloem externally while portion between newly initiated cambial arcs exclusively produce thin walled parenchyma cells on either side. With the increase in age, vessel diameter and their frequency not only decreased in roots but also showed complete absence of wider vessels or observed occasionally in thick roots. In thick stems, strands of lignified derivatives once closely arranged became separated and appeared as embedded in parenchymatous ground mass. At this stage, these parenchyma cells underwent proliferation and formed small arcs of meristematic cells and produce vascular elements. Formation of xylem and phloem from these arcs appear like vascular bundles embedded in conjunctive tissue. Since, major portion of the stem is composed of parenchyma cells, presence of fibre with distinct bordered pits instead of wider vessels might be related with additional mechanical support and to provide additional path for the water conduction in absence of wider vessels in roots.

Effect of Extending the Growing Period on Yield Formation of Sugar Beet

AbstractAutumn sown sugar beets (winter beets) are expected to yield markedly higher than spring sown beets. This requires a continuous growth during an extended growing period. So far, bolting‐resistant sugar beet varieties are not available to test winter beets under field conditions in Central Europe. The objective of this study was therefore to analyse yield formation and sugar storage of sugar beet plants during an extended growing period to estimate whether sugar beet has the potential to generate the theoretically expected yield increase. From 2008 to 2012, pot experiments were carried out in the glasshouse with 11 sowing dates spread over the years with sequential harvests. The oldest plants were grown for 859 days (14 242 °Cd). Root fresh matter yield continuously increased till the latest harvest. In contrast, the sugar concentration reached an optimum value between 3400 and 5000 °Cd and then decreased with time. Despite longer growing periods, the number of cambium rings, which are regarded as essential for sugar storage, did not change. This points to an early and genetically fixed determination of the formation of cambium rings. Additionally, the rate of photosynthesis decreased concomitantly with the sugar concentration. In conclusion, there is some evidence that the sugar concentration of the storage root is limited by the sink capacity, which in turn controls the source activity by a feedback regulation of photosynthesis and leaf formation. The dry matter composition of the storage root changed towards lower sugar concentration and concurrent higher concentration of cell wall compounds (marc). The sugar yield still increased beyond a thermal time at which winter beets will probably be harvested in practice. Hence, the theoretical yield increase in autumn sown sugar beets can be realized, provided that the plants show sufficient winter hardiness and bolting resistance.