Azolla, a small water fern, abscises its roots and branches within 30 min upon treatment with various stresses. This study was conducted to test whether, in the rapid abscission that occurs in ...Azolla, breakdown of wall components of abscission zone cells by ●OH is involved. Experimentally generated ●OH caused the rapid separation of abscission zone cells from detached roots and the rapid shedding of roots from whole plants. Electron microscopic observations revealed that ●OH rapidly and selectively dissolved a well‐developed middle lamella between abscission zone cells and resultantly caused rapid cell separation and shedding. Treatment of abscission zones of Impatiens leaf petiole with ●OH also accelerated the separation of abscission zone cells. However, compared with that of Azolla roots, accelerative effects in Impatiens were weak. A large amount of ●OH was cytochemically detected in abscission zone cells both of Azolla roots and of Impatiens leaf petioles. These results suggest that ●OH is involved in the cell separation process not only in the rapid abscission in Azolla but also in the abscission of Impatiens. However, for rapid abscission to occur, a well‐developed middle lamella, a unique structure, which is sensitive to the attack of ●OH, might be needed.
Azolla, a small water fern, abscises its roots and branches within 30 min upon treatment with various stresses. This study was conducted to test whether, in the rapid abscission that occurs in Azolla, the breakdown of wall components of abscission zone cells by ●OH is involved. Furthermore, the effects of ●OH on the cell separation of abscission zone cells of Impatiens leaf petioles were also examined and compared with those of Azolla. The results suggest that ●OH is involved in the cell separation process not only in the rapid abscission in Azolla but also in the abscission of Impatiens.
Changes in cell wall polysaccharides in oat (Avena sativa L.) leaf segments during senescence promoted by methyl jasmonate (JA-Me) were studied. During the incubation with water at 25 °C in the dark, ...the loss of chlorophyll of the segments excised from the primary leaves of 8-day-old green seedlings was found dramatically just after leaf excision, and leaf color completely turned to yellow after the 3- to 4-day incubation in the dark. Application of 10 µM JA-Me substantially promoted the loss of chlorophyll corresponding with the chloroplast degradation. Cell wall polysaccharides in oat leaf segments mainly consisted of hemicellulosic and cellulosic ones. During the process of leaf senescence, the amount of hemicellulosic I and II, and cellulosic polysaccharides decreased, but little in pectic polysaccharides. JA-Me significantly enhanced the decrease in cellulosic polysaccharides, but little in hemicellulosic ones. Arabinose, xylose and glucose were identified as main constituents of neutral sugars of hemicellulosic polysaccharides. The neutral sugar compositions of hemicellulosic polysaccharides changed little during leaf senescence both in the presence or absence of JA-Me. These facts suggest that JA-Me affects sugar metabolism relating to cellulosic polysaccharides during leaf senescence.
In studies on the mechanism of cell separation during abscission, little attention has been paid to the apoplastic environment. We found that the apoplastic pH surrounding abscission zone cells in ...detached roots of the water fern Azolla plays a major role in cell separation. Abscission zone cells of detached Azolla roots were separated rapidly in a buffer at neutral pH and slowly in a buffer at pH below 4.0. However, cell separation rarely occurred at pH 5.0–5.5. Light and electron microscopy revealed that cell separation was caused by a degradation of the middle lamella between abscission zone cells at both pH values, neutral and below 4.0. Low temperature and papain treatment inhibited cell separation. Enzyme(s) in the cell wall of the abscission zone cells might be involved in the degradation of the pectin of the middle lamella and the resultant, pH-dependent cell separation. By contrast, in Phaseolus leaf petioles, unlike Azolla roots, cell separation was slow and increased only at acidic pH. The rapid cell separation, as observed in Azolla roots at neutral pH, did not occur. Indirect immunofluorescence microscopy, using anti-pectin monoclonal antibodies, revealed that the cell wall pectins of the abscission zone cells of Azolla roots and Phaseolus leaf petioles looked similar and changed similarly during cell separation. Thus, the pH-related differences in cell separation mechanisms of Azolla and Phaseolus might not be due to differences in cell wall pectin, but to differences in cell wall-located enzymatic activities responsible for the degradation of pectic substances. A possible enzyme system is discussed.
We conducted “Auxin Transport” space experiments in 2016 and 2017 in the Japanese Experiment Module (JEM) on the International Space Station (ISS), with the principal objective being integrated ...analyses of the growth and development of etiolated pea (Pisum sativum L. cv Alaska) and maize (Zea mays L. cv Golden Cross Bantam) seedlings under true microgravity conditions in space relative to auxin dynamics. Etiolated pea seedlings grown under microgravity conditions in space for 3 days showed automorphogenesis. Epicotyls and roots bent ca. 45° and 20° toward the direction away from the cotyledons, respectively, whereas those grown under artificial 1 g conditions produced by a centrifuge in the Cell Biology Experimental Facility (CBEF) in space showed negative and positive gravitropic response in epicotyls and in roots, respectively. On the other hand, the coleoptiles of 4-day-old etiolated maize seedlings grew almost straight, but the mesocotyls curved and grew toward a random direction under microgravity conditions in space. In contrast, the coleoptiles and mesocotyls of etiolated maize seedlings grown under 1 g conditions on Earth were almost straight and grew upward or toward the direction against the gravity vector. The polar auxin transport activity in etiolated pea epicotyls and in maize shoots was significantly inhibited and enhanced, respectively, under microgravity conditions in space as compared with artificial 1 g conditions in space or 1 g conditions on Earth. An inhibitor of polar auxin transport, 2,3,5-triiodobenzoic acid (TIBA) substantially affected the growth direction and polar auxin transport activity in etiolated pea seedlings grown under both artificial 1 g and microgravity conditions in space. These results strongly suggest that adequate polar auxin transport is essential for gravitropic response in plants. Possible mechanisms enhancing polar auxin transport in etiolated maize seedlings grown under microgravity conditions in space are also proposed.
To clarify the mechanism of gravity-controlled polar auxin transport, we conducted the International Space Station (ISS) experiment “Auxin Transport” (identified by NASA's operation nomenclature) in ...2016 and 2017, focusing on the expression of genes related to auxin efflux carrier protein PsPIN1 and its localization in the hook and epicotyl cells of etiolated Alaska pea seedlings grown for three days in the dark under microgravity (μg) and artificial 1 g conditions on a centrifuge in the Cell Biology Experiment Facility (CBEF) in the ISS, and under 1 g conditions on Earth. Regardless of gravity conditions, the accumulation of PsPIN1 mRNA in the proximal side of epicotyls of the seedlings was not different, but tended to be slightly higher as compared with that in the distal side. 2,3,5-Triiodobenzoic acid (TIBA) also did not affect the accumulation of PsPIN1 mRNA in the proximal and distal sides of epicotyls. However, in the apical hook region, TIBA increased the accumulation of PsPIN1 mRNA under μg conditions as compared with that under artificial 1 g conditions in the ISS. The accumulation of PsPIN1 proteins in epicotyls determined by western blotting was almost parallel to that of mRNA of PsPIN1. Immunohistochemical analysis with a specific polyclonal antibody of PsPIN1 revealed that a majority of PsPIN1 in the apical hook and subapical regions of the seedlings grown under artificial 1 g conditions in the ISS localized in the basal side (rootward) of the plasma membrane of the endodermal tissues. Conversely, in the seedlings grown under μg conditions, localization of PsPIN1 was greatly disarrayed. TIBA substantially altered the cellular localization pattern of PsPIN1, especially under μg conditions. These results strongly suggest that the mechanisms by which gravity controls polar auxin transport are more likely to be due to the membrane localization of PsPIN1. This physiologically valuable report describes a close relationship between gravity-controlled polar auxin transport and the localization of auxin efflux carrier PsPIN1 in etiolated pea seedlings based on the μg experiment conducted in space.
The important role of auxin polar transport in the early growth stage of etiolated maize (Zea mays L. cv. Honey Bantam) seedlings was intensively studied. Rapid growth in the basal region of ...coleoptile and the apical region of mesocotyl was observed in etiolated maize seedlings in the dark. Indole-3-acetic acid (IAA) applied to the top of coleoptile substantially promoted the growth of coleoptile and mesocotyl dose-dependently, suggesting that endogenous IAA is responsible for the growth of coleoptile and mesocotyl in etiolated maize seedlings. Polar transport of radiolabeled IAA (
14
CIAA) in the coleoptile segment was significantly higher than that in the mesocotyl segment from etiolated maize seedlings. Auxin polar transport in the coleoptile and mesocotyl segments from etiolated maize seedlings increased with the growth of the seedlings from which the segments were excised. Maximum expression of the gene (ZmPIN1a) closely related to auxin polar transport was observed just prior to maximum levels of auxin polar transport in the coleoptile and mesocotyl segments. In addition, the growth rate was well correlated with the auxin polar transport and the expression of ZmPIN1a gene in coleoptile and mesocotyl of etiolated maize seedlings. These results strongly suggest that auxin polar transport regulated by ZmPIN1a protein is essentially required for the growth of coleoptile and mesocotyl in the early growth stage of etiolated maize seedlings.
This paper introduces the use of microarray data technology with Medicago (Medicago truncatula) microarrays to characterize global changes in the transcript abundance of etiolated Alaska pea (Pisum ...sativum L.) seedlings grown under microgravity (µg) conditions in comparison with those under artificial 1 g conditions on the International Space Station. Of the 44,000 genes of the Medicago microarray platform, more than 25,000 transcripts of pea seedlings were hybridized, suggesting that the microarray platform for Medicago could be useful in the study of gene expression of etiolated pea seedlings grown under µg conditions in space. Gene array data were analyzed according to stringent criteria that restricted the scored genes for specific hybridization values at least twofold. Expression of 1362 and 1558 genes in proximal side (the proximal side) and distal side of the epicotyl to the cotyledons (the distal side), respectively, were highly affected by µg conditions in space. Of the genes analyzed, 407 of 1362 transcripts in the proximal side and 740 of 1558 transcripts in the distal side were expressed at ratios at least twofold. However, in the presence of the auxin transport inhibitor TIBA, 212 of 399 transcripts and 255 of 477 transcripts were expressed at ratios at least twofold as high in the proximal and the distal sides of epicotyls in the seedlings grown under µg conditions, respectively. Based on Venn diagram analysis, 31 transcripts and 24 transcripts were found to commonly increase and decrease, respectively, under µg conditions in space. Venn analysis revealed six auxin-related genes and three water channel AQUAPORIN genes that were responsive to gravity. Among 6 auxin-related genes, the accumulation of transcripts of Auxin-induced protein 5NG4 and Indole-3-acetic acid-amido synthetase GH3.3 tended to increase, and that of Auxin-induced protein, Auxin response factor, SAUR-like auxin-responsive family protein and Auxin response factor tended to decrease under µg conditions, whereas there were no statistic differences between under µg and artificial 1 g conditions. Similarly there were no statistic differences between under µg conditions and artificial 1 g, but the accumulation of NIP3-1 and Plasma membrane intrinsic protein11, and AQUAPORIN1/Tonoplast intrinsic protein tended to increase and decrease, respectively. A possible role of auxin-related genes and AQUAPORIN genes in regulating growth of etiolated pea seedlings grown under µg conditions in space is discussed.
Phospho-glycoproteins (PGPs) belong to the ATP-binding cassette protein subfamily B (ABCB) subgroup of the ATP-binding cassette (ABC) transporter superfamily. The involvement of ABCB proteins in ...auxin transport is first suggested base on the results of expression levels of PGP1/ABCB1. PGPs have also been shown to mediate the cellular and long-distance transport of auxin. Interactions among PIN-formed and P-glycoprotein in auxin transport have been shown although PINs and PGPs characterize coordinated and independent auxin transport mechanisms. ABC (ABCB)/PGP is also suggested to have an important role in a graviresponse in plants. This review is describing auxin transport and a graviresponse in plants focused on structures and functions of ABC proteins.
Etiolated plants show automorphosis (automorphogenesis), spontaneous growth responses under a stimulus-free environmental condition, under microgravity conditions in space as well as simulated ...microgravity (or weightlessness) ones on a 3-dimensional clinostat. Although the mechanism to regulate automorphosis has been unclear yet, in STS-95 space experiments a close relationship between automorphosis and reduced auxin polar transport in etiolated Alaska pea seedlings has been suggested. Induction of automorphosis-like epicotyl bending by auxin polar transport inhibitors strongly supports causal relationship of auxin polar transport to induce automorphosis. Genetic and molecular biological studies of Arabidopsis have demonstrated an importance of PIN-FORMED (PIN) proteins as carrier (or facilitator) subcellularly localized at the polar side of the plasma membrane for auxin polar transport. This review is describing automorphosis and auxin polar transport focused on structure and functions of PIN proteins together with hormonal regulation of automorphosis in etiolated Alaska pea seedlings.
Abstract
A
zolla
, a small water fern, abscises its roots and branches within 30 min upon treatment with various stresses. This study was conducted to test whether, in the rapid abscission that ...occurs in
A
zolla
, breakdown of wall components of abscission zone cells by
●
OH
is involved. Experimentally generated
●
OH
caused the rapid separation of abscission zone cells from detached roots and the rapid shedding of roots from whole plants. Electron microscopic observations revealed that
●
OH
rapidly and selectively dissolved a well‐developed middle lamella between abscission zone cells and resultantly caused rapid cell separation and shedding. Treatment of abscission zones of
I
mpatiens
leaf petiole with
●
OH
also accelerated the separation of abscission zone cells. However, compared with that of
A
zolla
roots, accelerative effects in
I
mpatiens
were weak. A large amount of
●
OH
was cytochemically detected in abscission zone cells both of
A
zolla
roots and of
I
mpatiens
leaf petioles. These results suggest that
●
OH
is involved in the cell separation process not only in the rapid abscission in
A
zolla
but also in the abscission of
I
mpatiens
. However, for rapid abscission to occur, a well‐developed middle lamella, a unique structure, which is sensitive to the attack of
●
OH
, might be needed.
A
zolla, a small water fern, abscises its roots and branches within 30 min upon treatment with various stresses. This study was conducted to test whether, in the rapid abscission that occurs in
A
zolla, the breakdown of wall components of abscission zone cells by
●
OH
is involved. Furthermore, the effects of
●
OH
on the cell separation of abscission zone cells of
I
mpatiens leaf petioles were also examined and compared with those of
A
zolla. The results suggest that
●
OH
is involved in the cell separation process not only in the rapid abscission in
A
zolla but also in the abscission of
I
mpatiens.
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