Per Cycle Research Articles

Identification, expression, and functional analysis of CLE genes in radish (Raphanus sativus L.) storage root.

BackgroundRadish (Raphanus sativus L.) is a widespread agricultural plant forming storage root due to extensive secondary growth which involves cambium proliferation and differentiation of secondary conductive tissues. Closely related to the model object Arabidopsis thaliana, radish is a suitable model for studying processes of secondary growth and storage root development. CLE peptides are a group of peptide phytohormones which play important role in the regulation of primary meristems such as SAM, RAM, and procambium, as well as secondary meristems. However, the role of CLE peptides in lateral growth of root during storage root formation has not been studied to date.ResultsIn present work we studied the role of CLE peptides in the development of storage root in radish. We have identified 18 CLE genes of radish (RsCLEs) and measured their expression in various plant organs and also at different stages of root development in R. sativus and Raphanus raphanistrum—its close relative which does not form storage root. We observed significant decline of expression levels for genes RsCLE1, 2, 11, 13, and 16, and also multifold increase of expression levels for genes RsCLE19, and 41 during secondary root growth in R. sativus but not in R. raphanistrum. Expression of RsCLE 2, 19, and 41 in R. sativus root was confined to certain types of tissues while RsCLE1, 11, 13, and 16 expressed throughout the root. Experiments on overexpression of RsCLE2, 19 and 41 or treatment of radish plants with synthetic CLE peptides revealed that CLE19 and CLE2 increase the number of xylem elements, and CLE41 induces the formation of extra cambium foci in secondary xylem. Expression levels of RsCLE2 and 19 strongly decrease in response to exogenous cytokinin, while auxin causes dramatic increase of RsCLE19 expression level and decrease of RsCLE41 expression.ConclusionsOur data allow us to hypothesize about the role of RsCLE2, 19 and 41 genes in the development of storage root of Raphanus sativus, e.g. RsCLE19 may play a role in auxin-dependent processes of xylem differentiation and RsCLE41 stimulates cambium activity.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0687-y) contains supplementary material, which is available to authorized users.

Ferns: the missing link in shoot evolution and development.

Shoot development in land plants is a remarkably complex process that gives rise to an extreme diversity of forms. Our current understanding of shoot developmental mechanisms comes almost entirely from studies of angiosperms (flowering plants), the most recently diverged plant lineage. Shoot development in angiosperms is based around a layered multicellular apical meristem that produces lateral organs and/or secondary meristems from populations of founder cells at its periphery. In contrast, non-seed plant shoots develop from either single apical initials or from a small population of morphologically distinct apical cells. Although developmental and molecular information is becoming available for non-flowering plants, such as the model moss Physcomitrella patens, making valid comparisons between highly divergent lineages is extremely challenging. As sister group to the seed plants, the monilophytes (ferns and relatives) represent an excellent phylogenetic midpoint of comparison for unlocking the evolution of shoot developmental mechanisms, and recent technical advances have finally made transgenic analysis possible in the emerging model fern Ceratopteris richardii. This review compares and contrasts our current understanding of shoot development in different land plant lineages with the aim of highlighting the potential role that the fern C. richardii could play in shedding light on the evolution of underlying genetic regulatory mechanisms.

Clinical efficacy of vitamin support in lung adenocarcinoma patients treated with pemetrexed second-line chemotherapy

To analyze the clinical efficacy and toxicity of vitamin support in lung adenocarcinoma patients treated with pemetrexed second-line chemotherapy. Two hundred and eighty-three patients with stage 3/4 lung adenocarcinoma treated at our hospital from August 2010 to August 2013 were included in this study. The lung adenocarcinomas in all the 283 patients were confirmed by pathology or cytology, all were EGFR-negative, and all patients received pemetrexed second line chemotherapy. The 283 patients were randomly divided into two groups: the improved treatment group (142 cases) and the conventional treatment group (141 cases). The patients of conventional treatment group received 400 µg folic acid per os daily for 7 days before the first dose of pemetrexed, and continued until 21 days after the last dose of pemetrexed. Besides, they received 1000 µg vitamin B12 injection at 7 days before the first dose of pemetrexed, and once per cycle of pemetrexed for 3 cycles after the last dose of pemetrexed. The patients of the improved treatment group took 400 µg folic acid daily per os from the day before the first dose to 21 days after the last dose of pemetrexed. They also received 500 µg vitamin B12 by injection one day before the first dose, and one day before each therapy cycle of pemetrexed therapy. The mean number of cycles of pemetrexed chemotherapy was 4 in both groups. In the 142 patients of improved treatment group, complete response (CR) was observed in two cases, partial remission (PR) in 28, stable disease (SD) in 21, and progressive disease (PD) in 91 cases, with a total effective rate of 21.1%. While in the conventional treatment group, CR was observed in one case, PR in 27 cases, SD in 23 cases, and PD in 90 cases, with a total effective rate of 19.9%. The median progression-free survival (PFS) was 3.8 months in the improved treatment group and 4.2 months in the conventional treatment group (P=0.143). The toxicity of chemotherapy was mild in both groups, with no significant difference between the two groups (P>0.05). The most common side effects of hematological system were leukopenia and neutropenia, and the most common side effects of non-blood system were nausea and vomiting. The most common grade 3-4 toxic reaction in both groups was leukopenia and neutropenia, with no significant difference between the two groups (P>0.05). Multivariate analysis showed that the age of patients was an independent factor of grade 3-4 chemotherapy toxic reaction (P<0.05), while gender, the baseline level of PS score or blood system had no significant effect on the grade 3-4 chemotherapy toxic reaction (P>0.05). Compared with the conventional treatment scheme, the improved treatment scheme has similar therapeutic effects and could be used more conveniently, while the toxic effects of chemotherapy are not increased at the same time. Our results indicate that pemetrexed-based chemotherapy does not need to delay the chemotherapy because of vitamin support treatment.

Sunlight-induced bark formation in long-lived South American columnar cacti

Previous research has shown that sunlight-induced bark formation (epidermal browning) on vertical surfaces of tall, long-lived columnar cactus species leads to premature death of entire plants. The bark cambium that produces bark for cactus species has been shown to involve proliferation of epidermal cells only. The purpose of this research was to understand (1) the characteristics of cuticles, epidermal and hypodermal cells, (2) the process of sunlight-induced bark formation, and (3) changes in hypodermal cells during the bark formation process for many species of long-lived, columnar cacti from South America. A wide diversity of epidermal and hypodermal cells occurred among the species studied. Epidermal depths ranged from 8.7 to 49.7μm and involved one to several epidermal cells while the thickness of hypodermal cell layers ranged from 42.7 to 661μm among the species studied. During bark cambium formation, each epidermal cell underwent at least one anticlinal cell division prior to numerous periclinal cell divisions since lengths of initially produced bark cambium cells were half the lengths of uninjured epidermal cells. Some cactus species exhibited hypodermal cell injuries during bark formation. This study reports: (1) quantitative measurements of cuticles, epidermal and hypodermal layers, (2) the presence of anticlinal cell divisions of epidermal cells to produce the bark cambium, and (3) the destruction of hypodermal cells during bark formation for columnar cactus species of South America. Possibly these results are specific for sunlight-induced bark formation for cactus species while other types of injuries may result in bark production by other means.

UPAYA MENINGKATAN HASIL BELAJAR LEMPAR TANGKAP BOLA MELALUI PERMAINAN LETABOTAI

The purpose of this study was to determine the increase of learning outcomes through the game throwing the ball catching letabotai the first grade students of SDN 03 Pagojengan District of Paguyangan Brebes. This study uses the results of the analysis of action research kelas.Berdasarkan percentage per cycle, learning through games throwing a ball catching letabotai have a positive impact on improving student learning outcomes characterized by increased mastery learning students in each cycle of the first cycle fulfilled Affective Value 62.50% , the second cycle are met 95.00%. Value cognitive cycle I fulfilled 55.00%, 90.00% second cycle. Psychomotor value of the first cycle are met 10.00%, 92.50% second cycle.

A Note on the Observable Bark Coloration of Quaking Aspen (Populus tremuloides)

The bark of quaking aspen (Populus tremuloides), a clonal hardwood that is dominant in many Rocky Mountain forests, varies from white to orange to green among both ramets and populations. The proximate causes of this color variation remain controversial. We collected 72 samples of aspen bark from 11 locations in Boulder County, Colorado, and used microscopy, dissection, and thin layer chromatography to assess the structural and biochemical basis for the color gradient. Our study shows that the cork cells closest to the cork cambium of the aspen were consistently orange and conglutinated. Outward from this layer, the cork cells transitioned from orange to white; they aged and simultaneously lost cohesion. Green bark was visible due to thinnest cork layers, which revealed subcortical chlorenchyma tissue, the only bark tissue in which photosynthetic pigments were detected. Tests for photosynthetic pigmentation in the cork were negative. Comparison to standards indicated that b-carotene is not the pigment responsible for the orange hue of the cambium. We conclude that the powdery substance found on the tree surface is composed of bark cells, and their color variation seen on the aspen bark is attributed to the cell's pigment content and thickness, although the molecule responsible for cork cell coloration remains unidentified.

Anti-diabetic Effect of FriedelanTriterpenoids in Streptozotocin Induced Diabetic Rat

We herein report the anti-diabetic effect of the natural friedelan tritepenoid, 4-oxa-3, 4-secofriedelan (cerin), isolated from cork tissue of Quercus suber L. and its oxygenated derivative, 4-oxa-3, 4-secofriedelan-3-oic acid (cerinox) in streptozotocin (STZ)-induced diabetic rat. Male Sprague Dawley rats were randomized into four groups: non-diabetic control (Group I), STZ-induced diabetic rats (Group II), STZ-induced diabetic rats treated with cerin (Group III), and STZ-induced diabetic rats treated with cerinox (Group IV). Administration of cerin (3mg/kg) and cerinox (3mg/kg) orally to STZ-diabetic rats for three weeks improved the body weight, reduced serum glucose level and activities of alkaline phosphatase, acid phosphatase, glutamate-oxaloacetate transaminase and glutamate-pyruvate transaminase, and restored liver antioxidant status.

Pharmacognostical Standardisation and HPTLC Quantification of Gallic acid in Homonoia riparia Lour

Background: Homonoia riparia Lour. (Family: Euphorbiaceae) is an important medicinal plant in Indian and Chinese systems of medicine used in the treatment of various medical conditions like urolithiasis, renal problems, and inflammation. This is the first report on the pharmacognostical standardisation and phytochemical evaluation of whole plant of Homonoia riparia Lour. Objective: To establish the pharmacognostical and physicochemical standardisation parameters of whole plant of Homonoia riparia Lour. Materials and Methods: The plant was studied for the morpho-anatomical characters, standardisation parameters such as ash value, extractive value, fluorescence analysis, loss on drying, swelling index, foaming index according to Indian Pharmacopoeia and WHO guidelines. Phytochemical analysis was also performed by standard methods. Quantification of gallic acid in Homonoia riparia was carried out using HPTLC technique. Results: The detailed microscopy of root revealed the presence of cork, cork cambium, pericyclic fibres, thick walled parenchyma and starch granules. The distinguishing characters of stem are presence of sclereids, xylem, phloem, fibres. Leaf microscopy showed the presence of anomocytic stomata, bicollateral vascular bundles ensheathed by fibres. Rosette crystals are present in all the parts of the plant. Starch grains are abundantly present in root and stem but absent in leaves. Various physicochemical parameters were also determined. Phytochemical screening of the extract and HPTLC quantification of gallic acid was also performed. Conclusion: The present study provides pharmacognostical, physicochemical and phytochemical details of the whole plant of Homonoia riparia which are useful in laying down standardization and pharmacopoeia parameters.

Antioxidant and α-glucosidase inhibitory activities of constituents from Euonymus alatus twigs

Euonymus alatus (Thunb.) Sieb. (Celastraceae) well-known as winged euonymus, is a deciduous and popular ornamental tree. The cork cambium on E. alatus twigs is called ‘gui-jun woo’ and is known to have anticancer activity. The chemical constituents of E. alatus twigs were investigated and their antioxidant and α-glucosidase inhibitory activities thoroughly studied. The chopped plant material was extracted with 80% aqueous MeOH under reflux. Phytochemical investigation of CHCl3-soluble and n-BuOH-soluble fractions from the crude MeOH extract resulted in the isolation and identification of 12 constituents (1–12) using the repeated column chromatography, followed by semi-preparative HPLC purification. The structures were identified as lupeol (1), betulin (2), betulinic acid (3), hederagenin (4), quercetin (5), kaempferol (6), naringenin (7), hyperoside (8), rutin (9), (+)-catechin (10), ferulic acid (11), and vanillic acid (12) by spectroscopic methods including 1H NMR and 13C NMR, and MS analysis. The isolated compounds (1–12) were examined for antioxidant and α-glucosidase inhibitory activities. The isolated compounds 5, 8, 9 and 10 showed antioxidant activities with IC50 values in the range of 39.6–59.4μM. In addition, the compounds 3, 4, 6 and 7 showed α-glucosidase inhibition activities with IC50 values in the range of 83.6–107.8μM. These findings strongly suggest that E. alatus twigs can be a potential source of natural antioxidants and/or anti-diabetic agents in pharmaceutical and health functional foods. The isolated compounds are the likely contributors to the antioxidant and anti-diabetic effects.

Determining the Composition of Lignins in Different Tissues of Silver Birch.

Quantitative and qualitative lignin analyses were carried out on material from the trunks of silver birch (Betula pendula Roth) trees. Two types of material were analyzed. First, whole birch trunk pieces were cryosectioned into cork cambium, non-conductive phloem, the cambial zone (conductive phloem, cambium and differentiating xylem), lignified xylem and the previous year’s xylem; material that would show differences in lignin amount and quality. Second, clonal material from one natural birch population was analyzed to show variations between individuals and between the lignin analysis methods. The different tissues showed marked differences in lignin amount and the syringyl:guaiacyl (S/G) ratio. In the non-conductive phloem tissue containing sclereids, the S/G ratio was very low, and typical for phloem fibers and in the newly-formed xylem, as well as in the previous year’s xylem, the ratio lay between five and seven, typical for broadleaf tree xylem. Clonal material consisting of 88 stems was used to calculate the S/G ratios from the thioacidolysis and CuO methods, which correlated positively with an R2 value of 0.43. Comparisons of the methods indicate clearly that the CuO method is a good alternative to study the monomeric composition and S/G ratio of wood lignins.

Lateral Meristems Responsible for Secondary Growth of the Monocotyledons: A Survey of the State of the Art.

This review highlights key historical works and the recent research on the monocot lateral meristems. It discusses the terminological issues (elucidating the terminological inconsistency found in the literature concerned), origination of secondary meristems, their morphology and characteristic features of the derivative tissues. Also the monocot cambium response to hormonal and gravitational stimuli is discussed. The summarized inputs in the present note are believed to renew interest in this field, which is important for a more comprehensive understanding of the abnormal secondary growth in the monocotyledons.

Cork structural discontinuities studied with X-ray microtomography

Abstract Cork is a natural cellular material with a rather unique set of properties, and its best known application is as stopper for wine bottles. The cork tissue contains structural discontinuities, for example, lenticular channels (LCh), that influence the in-use performance of cork products. X-ray microtomography, in combination with image analysis, has been used for cork characterisation and provided new insights into the three-dimensional location of discontinuities, which are hidden for a visual inspection. It was demonstrated that the presence of LCh is positively correlated with cork density, and the void fraction of LCh in the lower part of a cork stopper is strongly related to the oxygen ingress in the bottle during the first month after bottling. The results contribute to better understanding the natural variation of cork properties.

Periderm in Ophioglossaceae

This paper describes the occurrence of periderm in three genera, &lt;i&gt;Botrychium&lt;/i&gt; Swartz., &lt;i&gt;Helminthostachys&lt;/i&gt; Kaulfuss, and &lt;i&gt;Ophioglossum&lt;/i&gt; Linn. under field conditions. Not all plants of an area belonging to the same or different species possess it. Based on population survey it is suggested that production of functional cork cambium (phellogen), a feature unlike &lt;i&gt;Fillicenae&lt;/i&gt; may be an inherited trait.

Vascular Cambium Development.

Secondary phloem and xylem tissues are produced through the activity of vascular cambium, the cylindrical secondary meristem which arises among the primary plant tissues. Most dicotyledonous species undergo secondary development, among them Arabidopsis. Despite its small size and herbaceous nature, Arabidopsis displays prominent secondary growth in several organs, including the root, hypocotyl and shoot. Together with the vast genetic resources and molecular research methods available for it, this has made Arabidopsis a versatile and accessible model organism for studying cambial development and wood formation. In this review, we discuss and compare the development and function of the vascular cambium in the Arabidopsis root, hypocotyl, and shoot. We describe the current understanding of the molecular regulation of vascular cambium and compare it to the function of primary meristems. We conclude with a look at the future prospects of cambium research, including opportunities provided by phenotyping and modelling approaches, complemented by studies of natural variation and comparative genetic studies in perennial and woody plant species.

Antiproliferative effect of the hydroalcoholic extract of Hymenaea stigonocarpa Mart. ex Hayne (Fabaceae, Caesalpinioideae) on the meristematic cells of Allium cepa L. roots

This study evaluates the hydroalcoholic extract obtained from the cork cambium of Hymenaea stigonocarpa (jatoba-do-cerrado) on the meristematic cells of Allium cepa roots, at 3 concentrations, 0.5, 1.0, and 1.5 mg/mL, and 2 exposure times, 24 h and 48 h. The slides were made through the crushing technique. Cells were analyzed throughout the cell cycle, totaling 5,000 for each control and concentration group. We found that the 3 concentrations significantly decreased the cell division rate at the exposure time of 48 h when compared to their respective controls. The mitotic index of the exposure time of 48 h was statistically different when compared to the cell division rate of the exposure time of 24 h for all concentrations. The number of cell abnormalities observed was not statistically significant by means of the chi-square test used. Therefore, under the conditions analyzed, the 3 concentrations tested for the cork cambium of jatoba-do-cerrado significantly decreased, in statistical terms, the cell division rate in the meristematic cells of A. cepa roots.

Pharmacognostic Evaluation of the Bark of &lt;i&gt;Acacia suma&lt;/i&gt; Roxb (Fabaceae)

Purpose: To undertake the pharmacognostic evaluation of Acacia suma Roxb bark for the purpose of identification and differentiation from related species. Methods: The macroscopic and microscopic features of the bark were studied, including the use of powder microscopy with the aid of suitable tools and reagents. Physicochemical parameters such as ash values, extractive values and loss on drying were also determined. The bark powder was successively extracted with different solvents followed by preliminary phytochemical screening of the extracts. Results: Macro- and microscopic studies revealed an outer hard and woody exfoliating old bark consisting of dead elements of secondary bast alternating with tangential strips of compressed cork tissue. The outer layer consists of cork cell with lenticels, followed by phellum, phellogen and pheloderm layers. Concentric rings of secondary phloem tissue alternating with regularly arranged polygonal stone cells and radially traversed medullary rays were present. Preliminary phytochemical screening showed the presence of alkaloids, carbohydrates, proteins, tannins and phenolic compounds, gums and mucilages, steroids and triterpenoids, saponins and flavonoids in the bark. Conclusion: The findings of this study will facilitate pharmacognostic standardization of the plant material and aid in the preparation of a herbal monograph for the species.

MiRNA profiling in leaf and cork tissues of Quercus suber reveals novel miRNAs and tissue-specific expression patterns

The differentiation of cork (phellem) cells from the phellogen (cork cambium) is a secondary growth process observed in the cork oak tree conferring a unique ability to produce a thick layer of cork. At present, the molecular regulators of phellem differentiation are unknown. The previously documented involvement of microRNAs (miRNAs) in the regulation of developmental processes, including secondary growth, motivated the search for these regulators in cork oak tissues. We performed deep sequencing of the small RNA fraction obtained from cork oak leaves and differentiating phellem. RNA sequences with lengths of 19–25 nt derived from the two libraries were analysed, leading to the identification of 41 families of conserved miRNAs, of which the most abundant were miR167, miR165/166, miR396 and miR159. Thirty novel miRNA candidates were also unveiled, 11 of which were unique to leaves and 13 to phellem. Northern blot detection of a set of conserved and novel miRNAs confirmed their differential expression profile. Prediction and analysis of putative miRNA target genes provided clues regarding processes taking place in leaf and phellem tissues, but further experimental work will be needed for functional characterization. In conclusion, we here provide a first characterization of the miRNA population in a Fagacea species, and the comparative analysis of miRNA expression in leaf and phellem libraries represents an important step to uncovering specific regulatory networks controlling phellem differentiation.

Extraction-less, rapid assay for the direct detection of 2,4,6-trichloroanisole (TCA) in cork samples

2,4,6-trichloroanisole (TCA), the cork taint molecule, has been the target of several analytical approaches over the few past years. In spite of the development of highly efficient and sensitive tools for its detection, ranging from advanced chromatography to biosensor-based techniques, a practical breakthrough for routine cork screening purposes has not yet been realized, in part due to the requirement of a lengthy extraction of TCA in organic solvents, mostly 12% ethanol and the high detectability required. In the present report, we present a modification of a previously reported biosensor system based on the measurement of the electric response of cultured fibroblast cells membrane-engineered with the pAb78 TCA-specific antibody. Samples were prepared by macerating cork tissue and mixing it directly with the cellular biorecognition elements, without any intervening extraction process. By using this novel approach, we were able to detect TCA in just five minutes at extremely low concentrations (down to 0.2ppt). The novel biosensor offers a number of practical benefits, including a very considerable reduction in the total assay time by one day, and a full portability, enabling its direct employment for on-site, high throughput screening of cork in the field and production facilities, without requiring any type of supporting infrastructure.

Introducing wood anatomical and dendrochronological aspects of herbaceous plants: applications of the Xylem Database to vegetation science

AbstractObjectivesAlthough more than half of the Earth's landmass is covered by non‐forest vegetation and forests only account for ca. 20%, the majority of wood anatomical and dendrochronological studies still centre on trees and their timber products of secondary meristem growth. Comprehensive assessments of the anatomy, taxonomy, physiology and dendrochronology of herbs are, however, still missing. We therefore aim to evaluate the importance of stem anatomical and dendrochronological aspects of herbaceous plants for vegetation science, and further intend to explore if species‐specific differences in xylem anatomy can be linked with patterns of life form, plant size and site ecology.LocationsNumerous extra‐tropical sites within six biogeographic regions on six continents, spanning an elevational gradient of 4400 m from sea level to the alpine zone.MethodsWe employ the Xylem Database to investigate well‐established and newly defined wood anatomical and dendrochronological traits in 3347 dicotyledonous tree, shrub and herb species from 140 families and 952 genera. The obtained site information is placed in a global context of vegetation cover.ResultsWe demonstrate that plants included in the Xylem Database broadly represent the diversity of growth forms, habitats and life histories of extra‐tropical dicots, thus validating its potential for a range of uses within vegetation science. An unexpectedly rich catalogue of xylem anatomical and dendrochronological features is found in the stems of almost all dwarf shrub and herb species, with the quantity and diversity of their characteristics being comparable to larger plants, including most tree species. Annual rings are formed independently of life form, plant size and site ecology. Secondary growth, which is an expression of plant age, defines the main principle of terrestrial angiosperm development.ConclusionsBased on a first assessment of the Xylem Database, we suggest merging the traditionally separated research communities of wood anatomy and dendrochronology (including dendroclimatology and ‐ecology), as well as expanding their joint application to all non‐forest, extra‐tropical vegetation types. Moreover, we recommend overcoming the theoretical life form separation of trees, shrubs and herbs. This conceptual advancement will likely provide annually resolved insight on the past dynamics of dry matter production and carbon allocation for many marginal vegetation zones beyond the geographic limits of forest growth, which are particularly vulnerable to environmental change. Our study may further stimulate timely efforts in comparing plant morphological and wood anatomical characteristics with phylogenetic reconstructions.

Role of Abscisic Acid in Flood-Induced Secondary Aerenchyma Formation in Soybean (Glycine max) Hypocotyls

Phellogen (cork cambium) usually produces cork tissue, but when flooded it produces secondary aerenchyma, comprising living cells with non-suberized walls in the stems, roots, and root nodules of some Fabaceae. In the cell walls of cork tissues, the plant hormone abscisic acid (ABA), promotes suberin deposition. Thus, ABA may decrease in flooded tissues, where secondary aerenchyma cells are developing. Here, we investigated whether ABA is involved in the formation of aerenchyma in soybean (Glycine max) hypocotyls when flooded. Hypocotyls flooded with water produced a large amount of secondary aerenchyma, and were highly porous. On the other hand, application of 1.0 μM ABA suppressed the enlargement of phellogen-derived cells, thereby suppressing subsequent gas space formation, and then almost completely inhibited aerenchyma development. Berberine-aniline blue staining indicated that not only elongated cells in the secondary aerenchyma but also packed cells, which were formed under flooding with ABA, contained no suberized cell walls. Compared to non-flooded plants, the endogenous ABA concentration in the flooded hypocotyls was decreased to 50% within 24 hr, and the low level was maintained for at least 72 hr. In addition, phellogen developed at 48 hr after flooding and secondary aerenchyma was observed at 72 hr. These results indicate that secondary aerenchyma formation requires a decrease in negative regulator ABA in soybean plants, that is, ABA inhibits elongation of cells derived from phellogen in secondary aerenchyma formation such as internodal cell elongation of floating rice stems.