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Dive into the research topics where Shahanara Begum is active.

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Featured researches published by Shahanara Begum.


Physiologia Plantarum | 2013

Regulation of cambial activity in relation to environmental conditions: understanding the role of temperature in wood formation of trees.

Shahanara Begum; Satoshi Nakaba; Yusuke Yamagishi; Yuichiro Oribe; Ryo Funada

The timing of cambial reactivation plays an important role in determination of the amount and quality of wood and the environmental adaptivity of trees. Environmental factors, such as temperature, influence the growth and development of trees. Temperatures from late winter to early spring affect the physiological processes that are involved in the initiation of cambial cell division and xylem differentiation in trees. Cumulative elevated temperatures from late winter to early spring result in earlier initiation of cambial reactivation and xylem differentiation in tree stems and an extended growth period. However, earlier cambial reactivation increases the risk for frost damage because the cold tolerance of cambium decreases after cambial reactivation. The present review focuses on temperature regulation on the timing of cambial reactivation and xylem differentiation in trees, and also highlights recent advances in our understanding of seasonal changes in the cold stability of microtubules in trees. The review also summarizes the present understanding of the relationships between the timing of cambial reactivation, the start of xylem differentiation and changes in levels of storage materials in trees, as well as an attempt to identify the source of energy for cell division and differentiation. A better understanding of the mechanisms that regulate wood formation in trees and the influence of environmental conditions on such mechanisms should help in efforts to improve and enhance the exploitation of wood for commercial applications and to prepare for climatic change.


Annals of Botany | 2010

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.

Shahanara Begum; Satoshi Nakaba; Yuichiro Oribe; Takafumi Kubo; Ryo Funada

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.


Annals of Botany | 2012

A rapid decrease in temperature induces latewood formation in artificially reactivated cambium of conifer stems

Shahanara Begum; Satoshi Nakaba; Yusuke Yamagishi; Kenichi Yamane; Md. Azharul Islam; Yuichiro Oribe; Jae-Heung Ko; Hyun-O Jin; Ryo Funada

BACKGROUND AND AIMS Latewood formation in conifers occurs during the later part of the growing season, when the cell division activity of the cambium declines. Changes in temperature might be important for wood formation in trees. Therefore, the effects of a rapid decrease in temperature on cellular morphology of tracheids were investigated in localized heating-induced cambial reactivation in Cryptomeria japonica trees and in Abies firma seedlings. METHODS Electric heating tape and heating ribbon were wrapped on the stems of C. japonica trees and A. firma seedlings. Heating was discontinued when 11 or 12 and eight or nine radial files of differentiating and differentiated tracheids had been produced in C. japonica and A. firma stems, respectively. Tracheid diameter, cell wall thickness, percentage of cell wall area and percentage of lumen area were determined by image analysis of transverse sections and scanning electron microscopy. KEY RESULTS Localized heating induced earlier cambial reactivation and xylem differentiation in stems of C. japonica and A. firma as compared with non-heated stems. One week after cessation of heating, there were no obvious changes in the dimensions of the differentiating tracheids in the samples from adult C. japonica. In contrast, tracheids with a smaller diameter were observed in A. firma seedlings after 1 week of cessation of heating. Two or three weeks after cessation of heating, tracheids with reduced diameters and thickened cell walls were found. The results showed that the rapid decrease in temperature produced slender tracheids with obvious thickening of cell walls that resembled latewood cells. CONCLUSIONS The results suggest that a localized decrease in temperature of stems induces changes in the diameter and cell wall thickness of differentiating tracheids, indicating that cambium and its derivatives can respond directly to changes in temperature.


Annals of Botany | 2014

The effects of localized heating and disbudding on cambial reactivation and formation of earlywood vessels in seedlings of the deciduous ring-porous hardwood, Quercus serrata.

Kayo Kudo; Eri Nabeshima; Shahanara Begum; Yusuke Yamagishi; Satoshi Nakaba; Yuichiro Oribe; Koh Yasue; Ryo Funada

BACKGROUND AND AIMS The networks of vessel elements play a vital role in the transport of water from roots to leaves, and the continuous formation of earlywood vessels is crucial for the growth of ring-porous hardwoods. The differentiation of earlywood vessels is controlled by external and internal factors. The present study was designed to identify the limiting factors in the induction of cambial reactivation and the differentiation of earlywood vessels, using localized heating and disbudding of dormant stems of seedlings of a deciduous ring-porous hardwood, Quercus serrata. METHODS Localized heating was achieved by wrapping an electric heating ribbon around stems. Disbudding involved removal of all buds. Three treatments were initiated on 1 February 2012, namely heating, disbudding and a combination of heating and disbudding, with untreated dormant stems as controls. Cambial reactivation and differentiation of vessel elements were monitored by light and polarized-light microscopy, and the growth of buds was followed. KEY RESULTS Cambial reactivation and differentiation of vessel elements occurred sooner in heated seedlings than in non-heated seedlings before bud break. The combination of heating and disbudding of seedlings also resulted in earlier cambial reactivation and differentiation of first vessel elements than in non-heated seedlings. A few narrow vessel elements were formed during heating after disbudding, while many large earlywood vessel elements were formed in heated seedlings with buds. CONCLUSIONS The results suggested that, in seedlings of the deciduous ring-porous hardwood Quercus serrata, elevated temperature was a direct trigger for cambial reactivation and differentiation of first vessel elements. Bud growth was not essential for cambial reactivation and differentiation of first vessel elements, but might be important for the continuous formation of wide vessel elements.


Annals of Botany | 2012

Gibberellin is required for the formation of tension wood and stem gravitropism in Acacia mangium seedlings

Widyanto Dwi Nugroho; Yusuke Yamagishi; Satoshi Nakaba; Shiori Fukuhara; Shahanara Begum; Sri Nugroho Marsoem; Jae-Heung Ko; Hyun-O Jin; Ryo Funada

BACKGROUND AND AIMS Angiosperm trees generally form tension wood on the upper sides of leaning stems. The formation of tension wood is an important response to gravitational stimulus. Gibberellin appears to be involved in the differentiation of secondary xylem, but it remains unclear whether gibberellin plays a key role in the formation of tension wood and plant gravitropism. Therefore, a study was designed to investigate the effects of gibberellin and of inhibitors of the synthesis of gibberellin, namely paclobutrazole and uniconazole-P, on the formation of tension wood and negative stem gravitropism in Acacia mangium seedlings. METHODS Gibberellic acid (GA(3)), paclobutrazole and uniconazole-P were applied to seedlings via the soil in which they were growing. Distilled water was applied similarly as a control. Three days after such treatment, seedlings were tilted at an angle of 45° from the vertical, and samples of stems were collected for analysis 2 weeks, 2 months and 6 months after tilting. The effects of treatments on the stem recovery degree (Rº) were analysed as an index of the negative gravitropism of seedlings, together the width of the region of tension wood in the upper part of inclined stems. KEY RESULTS It was found that GA(3) stimulated the negative gravitropism of tilted seedling stems of A. mangium, while paclobutrazole and uniconazole-P inhibited recovery to vertical growth. Moreover, GA(3) stimulated the formation of tension wood in tilted A. mangium seedlings, while paclobutrazole and uniconazole-P strongly suppressed the formation of tension wood, as assessed 2 weeks after tilting. CONCLUSIONS The results suggest that gibberellin plays an important role at the initial stages of formation of tension wood and in stem gravitropism in A. mangium seedlings in response to a gravitational stimulus.


Planta | 2012

Cold stability of microtubules in wood-forming tissues of conifers during seasons of active and dormant cambium

Shahanara Begum; Masaki Shibagaki; Osamu Furusawa; Satoshi Nakaba; Yusuke Yamagishi; Joto Yoshimoto; Hyun-O Jin; Yuzou Sano; Ryo Funada

The cold stability of microtubules during seasons of active and dormant cambium was analyzed in the conifers Abies firma, Abies sachalinensis and Larix leptolepis by immunofluorescence microscopy. Samples were fixed at room temperature and at a low temperature of 2–3°C to examine the effects of low temperature on the stability of microtubules. Microtubules were visible in cambium, xylem cells and phloem cells after fixation at room temperature during seasons of active and dormant cambium. By contrast, fixation at low temperature depolymerized microtubules in cambial cells, differentiating tracheids, differentiating xylem ray parenchyma and phloem ray parenchyma cells during the active season. However, similar fixation did not depolymerize microtubules during cambial dormancy in winter. Our results indicate that the stability of microtubules in cambial cells and cambial derivatives at low temperature differs between seasons of active and dormant cambium. Moreover, the change in the stability of microtubules that we observed at low temperature might be closely related to seasonal changes in the cold tolerance of conifers. In addition, low-temperature fixation depolymerized microtubules in cambial cells and differentiating cells that had thin primary cell walls, while such low-temperature fixation did not depolymerize microtubules in differentiating secondary xylem ray parenchyma cells and tracheids that had thick secondary cell walls. The stability of microtubules at low temperature appears to depend on the structure of the cell wall, namely, primary or secondary. Therefore, we propose that the secondary cell wall might be responsible for the cold stability of microtubules in differentiating secondary xylem cells of conifers.


Annals of Botany | 2016

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

Shahanara Begum; Kayo Kudo; Yugo Matsuoka; Satoshi Nakaba; Yusuke Yamagishi; Eri Nabeshima; Hasnat Rahman; Widyanto Dwi Nugroho; Yuichiro Oribe; Hyun-O Jin; Ryo Funada

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.


Trees-structure and Function | 2018

Climate change and the regulation of wood formation in trees by temperature

Shahanara Begum; Kayo Kudo; Hasnat Rahman; Satoshi Nakaba; Yusuke Yamagishi; Eri Nabeshima; Widyanto Dwi Nugroho; Yuichiro Oribe; Peter Kitin; Hyun-O Jin; Ryo Funada

Key messageA better understanding of the influence of environmental conditions on wood formation should help to improve the radial growth of trees and to prepare for climate change.AbstractThe cambial activity of trees is associated with seasonal cycles of activity and dormancy in temperate zones. The timing of cambial reactivation in early spring and dormancy in autumn plays an important role in determination of the cambial growth and the environmental adaptivity of temperate trees. This review focuses on the temperature regulation of the timing of cambial reactivation and xylem differentiation and highlights recent advances of bud growth in relation to cambial activity of temperate trees. In addition, we discuss relationships between the timing of cambial reactivation, start of xylem differentiation and changes in levels of storage materials to identify the source of the energy required for cell division and differentiation. We also present a summary of current understanding of the effects of rapid increases and decreases in temperature on cambial activity, by localized heating and cooling, respectively. Increases in temperature from late winter to early spring influence the physiological processes that are involved in the initiation of cambial reactivation and xylem differentiation both in localized heated stems and under natural conditions. Localized cooling has a direct effect on cell expansion, the thickening of walls of differentiating tracheids, and the rate of division of cambial cells. A rapid decrease in temperature of the stem might be the critical factor in the control of latewood formation and the cessation of cambial activity. Therefore, temperature is the main driver of cambial activity in temperate trees and trees are able to feel changes in temperature through the stem. The climate change might affect wood formation in trees.


Secondary Xylem Biology#R##N#Origins, Functions, and Applications | 2016

Xylogenesis in Trees: From Cambial Cell Division to Cell Death

Ryo Funada; Yusuke Yamagishi; Shahanara Begum; Kayo Kudo; Eri Nabeshima; Widyanto Dwi Nugroho; Rahman Hasnat; Yuichiro Oribe; Satoshi Nakaba

Abstract Wood is produced by the cambium of stems of trees. The cambial activity of trees exhibits seasonal cycles of activity and dormancy in temperate and cool zones. The timing of cambial reactivation in the early spring plays an important role in the determination of the quantity of wood and the environmental adaptivity of trees. Numerous studies have demonstrated that the cambial reactivation is controlled by the temperature of stems. As soon as cambial cells lose the ability to divide, they start to differentiate into secondary xylem cells. Finally, cell death occurs in secondary xylem cells, but its timing is different among the types and positions of cells. During formation of the secondary wall in tracheids or wood fibers, the cellulose microfibrils change their orientation progressively to form thick cell walls with a highly organized structure. In addition, secondary xylem cells form modifications of the cell wall, such as helical thickening and pits, by the localized deposition of cellulose microfibrils. There are considerable evidences that the dynamics of cortical microtubules are closely related to the orientation and localization of newly deposited cellulose microfibrils in the differentiating secondary xylem cells, indicating that microtubules control the structure of cell wall, thereby wood quality.


Annals of Botany | 2013

Gibberellin mediates the development of gelatinous fibres in the tension wood of inclined Acacia mangium seedlings.

Widyanto Dwi Nugroho; Satoshi Nakaba; Yusuke Yamagishi; Shahanara Begum; Sri Nugroho Marsoem; Jae-Heung Ko; Hyun-O Jin; Ryo Funada

BACKGROUND AND AIMS Gibberellin stimulates negative gravitropism and the formation of tension wood in tilted Acacia mangium seedlings, while inhibitors of gibberellin synthesis strongly inhibit the return to vertical growth and suppress the formation of tension wood. To characterize the role of gibberellin in tension wood formation and gravitropism, this study investigated the role of gibberellin in the development of gelatinous fibres and in the changes in anatomical characteristics of woody elements in Acacia mangium seedlings exposed to a gravitational stimulus. METHODS Gibberellin, paclobutrazol and uniconazole-P were applied to the soil in which seedlings were growing, using distilled water as the control. Three days after the start of treatment, seedlings were inclined at 45 ° to the vertical and samples were harvested 2 months later. The effects of the treatments on wood fibres, vessel elements and ray parenchyma cells were analysed in tension wood in the upper part of inclined stems and in the opposite wood on the lower side of inclined stems. KEY RESULTS Application of paclobutrazol or uniconazole-P inhibited the increase in the thickness of gelatinous layers and prevented the elongation of gelatinous fibres in the tension wood of inclined stems. By contrast, gibberellin stimulated the elongation of these fibres. Application of gibberellin and inhibitors of gibberellin biosynthesis had only minor effects on the anatomical characteristics of vessel and ray parenchyma cells. CONCLUSIONS The results suggest that gibberellin is important for the development of gelatinous fibres in the tension wood of A. mangium seedlings and therefore in gravitropism.

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Ryo Funada

Tokyo University of Agriculture

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Satoshi Nakaba

Tokyo University of Agriculture and Technology

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Yusuke Yamagishi

Tokyo University of Agriculture and Technology

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Kayo Kudo

Tokyo University of Agriculture and Technology

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Widyanto Dwi Nugroho

Tokyo University of Agriculture and Technology

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Hasnat Rahman

Tokyo University of Agriculture and Technology

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Md. Azharul Islam

Tokyo University of Agriculture and Technology

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Takafumi Kubo

Tokyo University of Agriculture and Technology

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