Development and Structure of the Root Cortex in Caltha palustris L. and Nymphaea odorata Ait.

Structural features of the mature root cortex and its apoplasticpermeability to dyes have been determined for two dicotyledonouswetland plants of differing habitats: Nymphaea odorata, growingrooted in water and mud, and Caltha palustris, growing in temporalwetlands among cattails. In mature roots, movement of the apoplasticdyes, berberine and safranin, into the roots was blocked atthe hypodermis, indicating the presence of an exodermis. A hypodermiswith an exodermis, i.e. Casparian bands in the outermost uniseriatelayer plus suberin lamellae, is present in both species. InN. odorata, hypodermal walls are further modified with cellulosicsecondary walls. Roots of N. odorata and C. palustris have anendodermis with Casparian bands only. A honeycomb aerenchymais produced by differential expansion in N. odorata and includesastrosclereids and diaphragms, while roots of C. palustris haveno aerenchyma, but some irregular lacunae are found in old roots.These aspects of cortex structure are related to an open meristemorganization, with unusual patterns of cell divisions in certainground meristem cells (called semi-regular hexagon cells) ofN. odorata. The correlation between aerenchyma pattern and hypodermalstructure appears to be related to habitat differences.Copyright2000 Annals of Botany Company Caltha palustris, Nymphaea odorata, root development, cortex, endodermis, aerenchyma, exodermis, hypodermis, permeability, wetland plants     

Similarity and diversity in adventitious root anatomy as related to root aeration among a range of wetland and dryland grass species

Assessments of the anatomy, porosity and profiles of radial O₂ loss from adventitious roots of 10 species in the Poaceae (from four subfamilies) and two species in the Cyperaceae identified a combination of features characteristic of species that inhabit wetland environments. These include a strong barrier to radial O₂ loss in the basal regions of the adventitious roots and extensive aerenchyma formation when grown not only in stagnant but also in aerated nutrient solution. Adventitious root porosity was greater for plants grown in stagnant compared with aerated solution, for all 10 species in the Poaceae. The ‘wetland root’ archetype was best developed in Oryza sativa and the two species of the Cyperaceae, in which the stele contributed less than 5% of the root cross‐sectional area, the cells of the inner cortex were packed in a cuboidal arrangement, and aerenchyma was up to 35–52%. Variations of this root structure, in which the proportional and absolute area of stele was greater, with hexagonal arrangements of cells in the inner cortex and varying in the extent of aerenchyma formation, were present in the other wetland species from the subfamilies Pooideae, Panicoideae and Arundinoideae. Of particular interest were Vetiveria zizanoides and V. filipes, wetland grass species from the tribe Andropogoneae (the same tribe as sorghum, maize and sugarcane), that had a variant of the root anatomy found in rice. The results are promising with regard to enhancing these traits in waterlogging intolerant crops.     

Anatomical patterns of aerenchyma in aquatic and wetland plants

A well-developed aerenchyma is a major characteristic of aquatic plants. However, because such tissues are also found in wetland and terrestrial plants, it is not always possible to use their presence or absence to distinguish aquatic species. Whereas patterns of aerenchyma in roots have been studied in detail, those of the shoots have not. We collected and tested 110 species of various aquatic and wetland plants, including ferns (5), basal angiosperms (5), monocots (65), and eudicots (35). Three common and two rare types of aerenchyma were observed in their roots (three schizogeny and two lysigeny), plus five types of schizogeny in their shoots. We re-confirmed that, although a well-developed aerenchyma is more common in most organs of aquatic plants than in wetland plants, this presence cannot be used as strict evidence for the aquatic quality of vascular plants. Here, aerenchyma patterns were stable at the genus level, and the consistency of pattern was stronger in the roots than in the shoots. Furthermore, significant trends were verified in several higher taxa, and those consistencies of patterns partially coincided with their phylogeny.     

Changes in cell structure during the formation of root aerenchyma inSAGITTARIA LANCIFOLIA (Alismataceae)

In many wetland species, root aerenchyma is produced by the predictable collapse of root cortex cells, indicating a programmed cell death (PCD). The objective of this study was to characterize the cellular changes that accompany this PCD in the marsh species Sagittaria lancifolia. Structural changes in membranes and organelles were examined during development of root cortex cells to compare with previous examples of PCD. The organization of cortical microtubule (CMT) arrays in root cells from S. lancifolia was also evaluated as a possible predictor of cell lysis. Nuclear fragmentation and condensation were the earliest changes observed in cells undergoing lysis. Breakdown of the tonoplast and other organelles and disruption of the plasma membrane followed. After loss of cytoplasm, cells collapsed to form gas spaces. These results were compared to collapse of root cortical cells of Zea mays and Oryza sativa during aerenchyma development. Changes in the appearance of the cytoplasm of all three species were similar at later stages of aerenchyma development. The relative timing of disintegration of the tonoplast and middle lamella appeared to differ among the three species. Changes in the organization of CMT arrays did not appear to be a predictor of PCD in S. lancifolia. Aerenchyma production in plants involves a type of PCD that is morphologically distinct from PCD described from many animals.     

Specific features of root aerenchyma formation in <Emphasis Type="Italic">Sium latifoliun</Emphasis> L. (Apiaceae)

Types of aerenchyma formation in adventive roots of wild plant S. latifolium L. have been described for the first time. Specific cell divisions and patterns of cell growth in the inner and outer root cortex at the initial stages of aerenchyma formation were highlighted in detail. Destructive processes in cells that occurred under aerenchyma formation were considered in the view of known stages of programmed cell death in plants.     

Constraints of root response to waterlogging in Alisma triviale

To understand the economics of root aerenchyma formation in wetland plants, we investigated in detail the response of Alisma triviale to waterlogging. We hypothesized costs being associated with development of a large root air space. In three out-door pot experiments, seedlings (1 experiment) and mature plants (2 experiments) were grown under waterlogged and drained conditions for up to 2?months. Waterlogging promoted growth, and was associated with increased root porosity and decreased root density (fresh mass per volume). The increased formation of aerenchyma was associated with a higher root dry matter content for a given root density. Despite improved growth and earlier flowering, the waterlogged plants also showed signs of being constrained by the anoxic substrate, such as shallower roots, and a higher leaf dry matter content. The formation of aerenchyma was associated with costs, such as increased root dry matter content and reduced metaxylem vessel diameter. The faster growth of the seedlings under the waterlogged conditions, despite some signs of being stressed, was possibly a result of decreased requirements to allocate biomass below ground. In mature plants the increased aerenchyma allowed deeper root penetration, and ameliorated the effects of anoxia, reducing the differences in plant traits between the treatments.     

Cortical Aerenchyma formation in hypocotyl and adventitious roots of Luffa cylindrica subjected to soil flooding

BACKGROUND AND AIMS: Aerenchyma formation is thought to be one of the important morphological adaptations to hypoxic stress. Although sponge gourd is an annual vegetable upland crop, in response to flooding the hypocotyl and newly formed adventitious roots create aerenchyma that is neither schizogenous nor lysigenous, but is produced by radial elongation of cortical cells. The aim of this study is to characterize the morphological changes in flooded tissues and the pattern of cortical aerenchyma formation, and to analyse the relative amount of aerenchyma formed. METHODS: Plants were harvested at 16 d after the flooding treatment was initiated. The root system was observed, and sections of fresh materials (hypocotyl, tap root and adventitious root) were viewed with a light or fluorescence microscope. Distributions of porosity along adventitious roots were estimated by a pycnometer method. KEY RESULTS: Under flooded conditions, a considerable part of the root system consisted of new adventitious roots which soon emerged and grew quickly over the soil surface. The outer cortical cells of these roots and those of the hypocotyl elongated radially and contributed to the development of large intercellular spaces. The elongated cortical cells of adventitious roots were clearly T-shaped, and occurred regularly in mesh-like lacunate structures. In these positions, slits were formed in the epidermis. In the roots, the enlargement of the gas space system began close to the apex in the cortical cell layers immediately beneath the epidermis. The porosity along these roots was 11-45 %. In non-flooded plants, adventitious roots were not formed and no aerenchyma developed in the hypocotyl or tap root. CONCLUSIONS: Sponge gourd aerenchyma is produced by the unique radial elongation of cells that make the expansigeny. These morphological changes seem to enhance flooding tolerance by promoting tissue gas exchange, and sponge gourd might thereby adapt to flooding stress.     

穿叶眼子菜茎叶结构及其通气组织发育解剖学研究

通气组织(aerenchyma)是植物薄壁组织内一些气室或腔隙的集合,对于水生及湿地植物体内的气体运输至关重要。该实验以沉水植物穿叶眼子菜为材料,利用石蜡切片技术,通过对茎的纵切面及横切面结构进行观察,从时间和空间上分析其茎、叶通气组织的发生过程。结果表明:(1)穿叶眼子菜的茎结构包括表皮、皮层及维管柱,通气组织发达,存在于内皮层与表皮之间;茎通气组织由距茎尖约0.6mm处开始形成,并成熟于约2.4mm处。(2)穿叶眼子菜的叶由表皮、皮层薄壁细胞及维管柱组成,其通气组织形成于靠近茎尖的第2~3片新生叶且仅形成于主叶脉。(3)穿叶眼子菜的茎和叶通气组织的发育过程相似,起初为排列致密的细胞团,然后由皮层细胞的分裂产生小的细胞间隙,随后的腔隙膨大过程涉及细胞的生长分裂及细胞降解,最终形成发达的通气组织。(4)穿叶眼子菜的通气组织发育过程可划分为实心期、形成期、膨大期、成熟期四个时期;不同时期茎通气组织的发达程度差异很大,实心期、形成期、膨大期和成熟期的孔隙度分别为0.54%、10.90%、27.61%和57.58%;但节处通气组织不发达,成熟期的节处孔隙度仅为3.62%。     

Trade-off between root porosity and mechanical strength in species with different types of aerenchyma

The objective of this work was to study the existence of a trade-off between aerenchyma formation and root mechanical strength. To this end, relationships among root anatomical traits and mechanical properties were analysed in plant species with contrasting root structural types: Paspalidium geminatum (graminaceous type), Cyperus eragrostis (cyperaceous type), Rumex crispus (Rumex type) and Plantago lanceolata (Apium type). Variations in anatomical traits and mechanical strength were assessed as a function of root diameter by exposing plants to 0, 7, 15 and 30 d of control and flooded conditions. For each species, the proportion of root cortex was positively associated with the increment of root diameter, contributing to the increase in root porosity under both control and flooded conditions. Moreover, cell lysis produced an additional increase in root porosity in most species under flooded conditions (except R. crispus). Both structural types that presented a uniseriate layer (epidermis) to cope with compression (Rumex and Apium types) were progressively weakened as root porosity increased. This effect was significant even when the increment of root porosity was solely because of increased root diameter (R. crispus), as when both processes (root diameter and cell lysis) added porosity to the roots (P. lanceolata). Conversely, structural types that presented a multiseriate ring of cells in the outer cortex (graminaceous and cyperaceous types) maintained mechanical strength over the whole range of porosity, in spite of lysogenic processes registered in the inner cortex. In conclusion, our study demonstrates a strong trade-off between aerenchyma formation and mechanical strength in root structural types that lacked a multiseriate ring of tissue for mechanical protection in the outer cortex. The results suggest that this ring of tissue plays a significant role in maintaining the mechanical strength of roots when flooding induces the generation of additional aerenchyma tissue in the root cortex.     

Dynamics of Aerenchyma distribution in the cortex of sulfate-deprived adventitious roots of maize

BACKGROUND AND AIMS: Aerenchyma formation in maize adventitious roots is induced in nutrient solution by the deprivation of sulfate (S) under well-oxygenated conditions. The aim of this research was to examine the extent of aerenchyma formation in the cortex of sulfate-deprived adventitious roots along the root axis, in correlation with the presence of reactive oxygen species (ROS), calcium levels and pH of cortex cells and root lignification. METHODS: The morphometry of the second whorl of adventitious (W2) roots, subject to S-deprivation conditions throughout development, was recorded in terms of root length and lateral root length and distribution. W2 roots divided into sectors according to the mean length of lateral roots, and cross-sections of each were examined for aerenchyma. In-situ detection of alterations in ROS presence, calcium levels and pH were performed by means of fluorescence microscopy using H(2)DCF-DA, fluo-3AM and BCECF, respectively. Lignification was detected using the Wiesner test. KEY RESULTS: S-deprivation reduced shoot growth and enhanced root proliferation. Aerenchyma was found in the cortex of 77 % of the root length, particularly in the region of emerging or developing lateral roots. The basal and apical sectors had no aerenchyma and no aerenchyma connection was found with the shoot. S-deprivation resulted in alterations of ROS, calcium levels and pH in aerenchymatous sectors compared with the basal non-aerenchymatous region. Lignified epidermal layers were located at the basal and the proximal sectors. S-deprivation resulted in shorter lateral roots in the upper sectors and in a limited extension of the lignified layers towards the next lateral root carrying sector. CONCLUSIONS: Lateral root proliferation is accompanied by spatially localized induced cell death in the cortex of developing young maize adventitious roots during S-deprivation.     

Physiological adaptation of waxapple to waterlogging

Waxapple (Syzygium samarangense Men. et. Perry) plants receiving up to 40d of continuous flooding treatment showed no symptoms of physiological disorder, but the treatment resulted in early flowering. In this report, several physiological parameters of flooded plants are compared with those of nonflooded plants. Both control plants and 9-d-flooding-treated plants exhibited aerenchyma formation in the cortex tissue beginning 5 cm from the root tip. After 7d flooding treatment, the oxygen consumption rate of the root section was only 20% of that of the controls. Following flooding treatment, the roots showed an increase in alcohol dehydrogenase activity as well as an increase in three isozymes. However, malate dehydrogenase activity was decreased, and no significant change of NADP-malic enzyme activity was observed. There were no significant differences in levels of ethylene, 1-aminocyclopropane-1-carboxylic acid and 1-(malonylamino) cyclopropane-1-carboxylic acid in petiole and roots of flooded and non-flooded plants during the stage examined. It is inferred that the presence of aerenchyma in the root cortex allows a higher level of internal gas exchange, and thus, makes waxapple surprisingly flood tolerant. However, reduced root oxygen consumption rate may have limited root respiration rate and vegetative growth.     

Variation in the Structure and Response to Flooding of Root Aerenchyma in some Wetland Plants

The structure and response to flooding of root cortical aerenchyma(air space tissue) in a variety of wetland (flood-tolerant)species was investigated and compared with some flood-intolerantspecies. In some species aerenchyma consisted of enlarged schizogenousintercellular spaces and in others aerenchyma formation involvedlysigeny. Two types of lysigenous aerenchyma were distinguished.In the first the diaphragms between lacunae were arranged radiallyand consisted of both collapsed and intact cells. In the secondtype, which was confined to the Cyperaceae, the radial diaphragmscontained intact cells, and stretched between them were tangentially-arrangeddiaphragms of collapsed cells. Flooding in sand culture generally increased root porosity (airspace content) although there were exceptions. The flood-intolerantspecies Senecio jacobaea produced aerenchyma but did not survivelong-term flooding. Among the flood-tolerant species, Filipendulaulmaria did not produce extensive aerenchyma even when flooded.Eriophorum angustifolium and E. vaginatum produced extensiveaerenchyma under drained conditions which was not increasedby flooding. In Nardus stricta root porosity was increased bylow nutrient levels as well as by flooding. Aerenchyma, root cortex, wetland plants, waterlogging, flooding-tolerance, Ammophila arenaria, Brachypodium sylvalicum, Caltha palustris, Carex curia, Eriophorum vaginatum, Filipendula ulmaria, Glyceria maxima, Hieracium pilosella, Juncus effusus, Myosotis scorpioides, Nardus stricta, Narthecium ossifragum, Phalaris arundinacea, Senecio jacobaea, Trichophorum cespitosum     

Aerenchyma formation in maize roots

Maize (Zea mays L.) is generally considered to be a plant with aerenchyma formation inducible by environmental conditions. In our study, young maize plants, cultivated in various ways in order to minimise the stressing effect of hypoxia, flooding, mechanical impedance or nutrient starvation, were examined for the presence of aerenchyma in their primary roots. The area of aerenchyma in the root cortex was correlated with the root length. Although 12 different maize accessions were used, no plants without aerenchyma were acquired until an ethylene synthesis inhibitor was employed. Using an ACC-synthase inhibitor, it was confirmed that the aerenchyma formation is ethylene-regulated and dependent on irradiance. The presence of TUNEL-positive nuclei and ultrastructural changes in cortical cells suggest a connection between ethylene-dependent aerenchyma formation and programmed cell death. Position of cells with TUNEL-positive nuclei in relation to aerenchyma-channels was described.     

Aerenchyma develops by cell lysis in roots AND CELL SEPARATION IN LEAF PETIOLES IN Sagittaria lancifolia (Alismataceae)

Aerenchyma gas spaces are important for plants that survive flooding because these spaces provide an internal pathway for oxygen transport to the root zone. The objective of this study was to characterize the development of aerenchyma gas spaces in Sagittaria lancifolia L., a dominant species in freshwater wetlands adjacent to the Gulf of Mexico. Tissue at different developmental stages was collected from hydroponically grown plants, embedded in plastic, and sections were observed with a light microscope. In S. lancifolia roots, lysigeny (cell lysis) produced gas spaces that increased in volume from the root meristem to the most mature root tissue. Shoot aerenchyma occurred in the large petioles of S. lancifolia and through the blade midrib, but not in the laminar portion of the blade. In contrast to the roots, gas spaces in the petiole were formed by schizogeny (cell separation during development). Shoot initials produced cells that formed interlocking cylinders in the cortex and diaphragm cells that bridged the central portion of the cylinders. Division and expansion of both these cell types increased the diameter of the cylinders and created schizogenous gaps between diaphragm layers that produced large gas spaces in mature tissue. Therefore, aerenchyma development occurs by two different processes in S. lancifolia.     

Pattern and Amount of Aerenchyma Relate to Variable Methane Transport Capacity of Different Rice Cultivars

Abstract: Aerenchyma, developed in both root and aboveground parts of rice plants, is predominantly responsible for plant‐mediated transfer of methane (CH₄) from the soil to the atmosphere. To clarify the pathways of CH₄ transport through the rice plant and find differences that may determine the large¡variation in the patterns of methane transport capacity (MTC) of rice cultivars, we examined the appearance, the distribution pattern, and the density of aerenchyma in different parts of rice¡plants of three widely varying rice cultivars during panicle initiation, flowering, and maturity stages. The data on the amount and density of small (> 1 ¡Á 10³? 5 ¡Á 10³Ìm²), medium (> 5 ¡Á 10³? 20 ¡Á 10³Ìm²) and large aerenchyma lacunae (> 20 ¡Á 10³Ìm²) were collected using a computer assisted image‐analyzing system. The brightfield optical microscopy of roots of all tested rice plants demonstrated the continuity of aerenchyma channels in the roots that function as conduits for bi‐directional transport of gases. The aerenchyma channels of primary roots showed direct connection with those of culms. Intercalary meristems were found at the transition zone of rootaCculm aerenchyma connections. Well‐developed aerenchyma lacunae present in the internodal region of the culm base were uniformly distributed in the peripheral cortical zone. The nodal region had relatively fewer and smaller aerenchyma lacunae that showed a non‐uniform distribution pattern. As a result, few aerenchyma channels continued from the internodal region through to the nodal region. The aerenchyma in the cortex zone of the culm expanded along with the growing secondary tiller, developing continuity between the culm and the secondary tiller. The micrographs of longitudinal sections of different specimens of culmaCleaf sheath intersection showed the continuity of aerenchyma channels from the culm to the leaf. The amount of medium and large aerenchyma lacunae in the leaf sheath was respectively 2 and 33 times greater as compared to those of the tiller. The proportion of the large lacunae in the total amount of aerenchyma in leaf sheath was 75 % as compared to only 8 % in the tiller, revealing higher number and larger size of aerenchyma in the former. There were significant differences in amount and density of aerenchyma between individual cultivars at a given growth stage, as well as in the development patterns. While the amount and density of medium and small aerenchyma lacunae in the internodal region of the culm base did not show any relationship with MTC of rice cultivars, large aerenchyma lacunae exhibited highly significant correlations with MTC of different cultivars, suggesting that the wide variation in MTC of rice plants during different growth stages are related to these structural features.     

洞庭湖四种优势湿地植物茎、叶通气组织的比较研究

对通气组织的解剖观察有助于了解湿地植物的生长、分布及对不同生境的适应。采用石蜡切片技术,在光学显微镜下对洞庭湖湿地沿水位高程梯度分布的4种优势植物——荻Miscanthus sacchariflorus、水蓼Polygonum hydropiper、红穗苔草Carex argyi、虉草Phalaris arundinacea的茎和叶解剖结构进行了比较研究。结果表明：茎通气组织的形成部位主要在皮层、维管束和髓腔,其中髓腔所占比例最大（〉77%）。茎通气组织大小为：水蓼（57.8%）〉红穗苔草（45.5%）≥虉草（41.7%）≥荻（37.8%）。4种湿地植物的叶均在叶肉组织和（或）维管束内形成通气组织,如荻、虉草的形成部位是维管束,水蓼的是叶肉组织,而红穗苔草在叶肉组织和维管束内均可以形成,但以叶肉组织中为主,占99%。红穗苔草叶通气组织最发达,为33.8%,其它3种植物相对不发达,仅为0.13%～1.68%。除虉草外,其它3种植物通气组织大小与其分布位置具有很好的一致性。可见,湿地植物通气组织与其分布有较好的相关性。     

Cellular Dimorphism in the Maize Root Cortex: Involvement of Microtubules,Ethylene and Gibberellin in the Differentiation of Cellular Behaviour in Postmitotic Growth Zones

Detailed morphometric analysis of cell shapes and an immunofluorescent study of microtubules were carried out on primary roots of Zea mays L. Two types of cells were found to be formed within the postmitotic isodiametric growth (PIG) region of the root cortex that were differentially responsive to low level of exogenous ethylene. The innermost and central cell rows of the cortex were sensitive to ethylene treatment and showed a disturbed distribution of cortical microtubules (CMTs) as well as changed polarity of cell growth, whereas the 2–3 outermost cell rows were less sensitive in this respect. This suggests that post-mitotic cells of the inner cortex are specific targets for ethylene action. These properties of the inner cortex are compatible with its cells being involved in the formation of aerenchyma; they may also favour root growth in compacted soil. By contrast, the specific properties of the outer cortex indicate that this tissue domain is necessary for the gaseous impermeability and the mechanical strengthening of subjacent aerenchymatous cortex, especially in the mature region of the root. Ethylene affected neither the pattern of cortical cell expansion in the meristem nor the position of the PIG region with respect to the root tip. This contrasts with gibberellin-deficiency which affected these parameters in both parts of the cortex. These observations indicate a fundamental difference between the role of these two phytohormones in the morphogenesis and development of maize roots.     

Lysigenous aerenchyma formation in maize root is confined to cortical cells by regulation of genes related to generation and scavenging of reactive oxygen species

To adapt to waterlogging, maize (Zea mays) forms lysigenous aerenchyma in root cortex as a result of ethylene-promoted programmed cell death (PCD). Respiratory burst oxidase homolog (RBOH) gene encodes a homolog of gp91^phox in NADPH oxidase, and has a role in the generation of reactive oxygen species (ROS). Recently, we found that during aerenchyma formation, RBOH was upregulated in all maize root tissues examined, whereas an ROS scavengingrelated metallothionein (MT) gene was downregulated specifically in cortical cells. Together these changes should lead to high accumulations of ROS in root cortex, thereby inducing PCD for aerenchyma formation. As further evidence of the involvement of ROS in root aerenchyma formation, the PCD was inhibited by diphenyleneiodonium (DPI), an NADPH oxidase inhibitor. Based on these results, we propose a model of cortical cell-specific PCD for root aerenchyma formation.Key words: aerenchyma, ethylene, laser microdissection, maize (Zea mays), metallothionein, programmed cell death, reactive oxygen species, respiratory burst oxidase homologIn both wetland and non-wetland plants, lysigenous aerenchyma is formed in roots by creating gas spaces as a result of death and subsequent lysis of some cortical cells, and allows internal transport of oxygen from shoots to roots under waterlogged soil conditions.^1–3 In rice (Oryza sativa) and some other wetland plant species, lysigenous aerenchyma is constitutively formed under aerobic conditions, and is further enhanced under waterlogged conditions.⁴ On the other hand, in non-wetland plants, including maize (Zea mays), lysigenous aerenchyma does not normally form under well-drained soil conditions, but is induced by waterlogging.⁵ Ethylene is involved in lysigenous aerenchyma formation,^1–3,6,7 but the molecular mechanisms are unclear.We recently identified two reactive oxygen species (ROS)-related genes that were specifically regulated in maize root cortex by waterlogged conditions, but not in the presence of an ethylene perception inhibitor 1-methylcyclopropene (1-MCP).⁵ One was respiratory burst oxidase homolog (RBOH), which has a role in ROS generation and the other was metallothionein (MT), which has a role in ROS scavenging. These results suggest that ROS has a role in ethylene signaling in the PCD that occurs during lysigenous aerenchyma formation.     

湿地植物根形态结构和泌氧与盐和重金属吸收、积累、耐性关系的研究进展

目前大面积湿地面临着重金属污染和盐渍化问题。利用湿地植物修复这些受损生态系统和提高海水稻的产量、减少毒性金属元素在稻米中的积累是当前面临的重要任务。湿地植物(包括水稻)已发展出各种策略和机制来耐受不同的环境胁迫,它们的根系发育具有可塑性,如根形态和解剖结构会随外界条件的变化而变化,这些变化直接影响其对环境胁迫的适应性能。近年来,对湿地植物根形态和结构、泌氧与其对盐、重金属的吸收、积累和耐性之间的关系方面进行了一些重要研究。本文分别对湿地植物根系形态、质外体屏障、通气组织和泌氧与其对盐和重金属吸收、积累和耐性的关系等方面的研究进展进行了综述,并对该领域未来的发展方向作了展望。     

Progressive Cortical Senescence and Formation of Lysigenous Gas Space (Aerenchyma) Distinguished by Nuclear Staining in Adventitious Roots of Zea mays

The pattern of loss of nuclear integrity in the epidermis andcortex of maize adventitious roots was examined during (1) non-pathogeniccortical senescence associated with root ageing, and (2) lysigenousaerenchyma formation, to determine whether these phenomena arerelated. Nuclear integrity was estimated by counting the percentageof cells with nuclei detectable by acridine orange fluorescence. In roots of both soil-grown (90 d) and solution-grown (19 d)plants, nuclei were lost progressively, from the epidermis andfrom successively deeper cortical cell layers, with increasingdistance behind the root tips; this occurred irrespective ofthe degree of aeration in solution culture, and independentlyof aerenchyma formation. Aerenchyma developed in soil-grownplants and in sub-ambient oxygen concentrations (<5 kPa partialpressure) in solution culture. It started to form in the middlecortex and coincided with a marked loss of nuclear stainingin the inner cortex, especially in the innermost cortical celllayer next to the endodermis, but not in the remaining cellsof the middle cortex. Two distinct patterns of nuclear deletionfrom the cortex were thus demonstrated; they occurred independentlybut simultaneously in some conditions. These findings are discussed in relation to mechanisms of celldeath, and the metabolic status of root cortical cells participatingin ion transport to the xylem. Zea mays L., maize, roots, aerenchyma, cell death, nuclei