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インド・ハイデラバード大学の生命科学部長であるAgepati S. Raghavendra教授の来日に伴い、東京理科大学 野田キャンパスにおいて以下のセミナーを開催することになりました。

日時: 2007年7月4日(水) 9:00-

講演者:Agepati S. Raghavendra教授 (インド・ハイデラバード大学 生命科学部長)
Department of Plant Sciences&s_comma; School of Life Sciences&s_comma; University of Hyderabad&s_comma; Hyderabad 500 046&s_comma; India

"Regulatory mechanisms of stomatal closure by environmental signals and plant hormones: Applications of mathematical modeling and bioinformatic tools".
"Signaling components in guard cells during stomatal closure induced by abscisic acid or methyl jasmonate"

場所: 東京理科大学 野田キャンパス 講義棟3階K309教室 (東武野田線運河駅下車徒歩5分)
(JR常磐線 柏駅から運河駅まで東武野田線で12分)


"Regulatory mechanisms of stomatal closure by environmental signals and plant hormones: Applications of mathematical modeling and bioinformatic tools".

A pair of very specialized cells called “guard cells” forms each stoma. The guard cells are metabolically very active&s_comma; possess ion-channels and allow selective influx/efflux of not only potassium but also calcium ions&s_comma; depending on the stimulus. The characteristics of these potassium and ion channels in guard cells&s_comma; in comparison with those in xylem tissue&s_comma; have attracted attention of scientists. Similarly&s_comma; guard cells are also extremely sensitive to environmental signals such as light&s_comma; particularly blue light&s_comma; and hormones such as abscisic acid (ABA). The nature and gene expression profile in response to ABA of cryptochrome&s_comma; a typical receptor of blue light is studied extensively using guard cells and form an essential component of research in signal transduction. Bioinformatic tools involving gene mining&s_comma; sequence alignment&s_comma; assessment of gene evolution and prediction of gene function are frequently done on guard cells. In several instances novel genes were ident!
ified and mutants were created and studied further. Some of these studies revealed also the occurrence and function of novel proteins in guard cells. Because of the interesting complex net works of perception and transduction of signals&s_comma; the guard cells have become model systems to construct and validate the signaling networks in plant tissues. This topic is be of great interest to study further the systems biology of plant tissues. A case study would be presented to indicate the signaling network in guard cells illustrating the interacting events on exposure to ABA.
Guard cells have also been the subject of dynamic modeling as the influx/efflux of osmotic solutes and subsequent swelling/shrinkage of guard cells illustrate an interesting interaction of biomechanics with biochemical and biophysical events. The regulation of transpiration by stomatal conductance&s_comma; kinetics of stomatal opening in response to light and/or CO2 and the physical changes in guard cells are all subjects of mathematical modeling&s_comma; since the past several years. Some of these models are extremely efficient&s_comma; popular and are integrated into simulation models of crop production. A few examples of mathematical modeling of function&s_comma; components and events in guard cells would be elaborated.

"Signaling components in guard cells during stomatal closure induced by abscisic acid or methyl jasmonate"

Signaling events during abscisic acid (ABA) or methyl jasmonate (MJ)-induced stomatal closure were examined in Arabidopsis thaliana wild type&s_comma; and its selected mutants. Some of the experiments were performed on epidermal strips of Pisum sativum and Nicotiana glauca. Both MJ and ABA promoted H2O2 production in wild-type guard cells&s_comma; while diphenylene iodonium (DPI) chloride&s_comma; an inhibitor of NAD(P)H oxidases&s_comma; prevented ABA- and MJ-induced stomatal closure. MJ-induced stomatal closure was suppressed in the NAD(P)H oxidase double mutant atrbohD/F and in the outward potassium channel mutant gork1. Further&s_comma; MJ induced alkalization in guard cell cytosol and MJ-induced stomatal closure were inhibited by butyrate. The kinetics of cytosolic pH changes and reactive oxygen species (ROS) production revealed that the alkalization of cytoplasm preceded ROS production during the stomatal response to both ABA and MJ.
The presence of 10 M MJ&s_comma; induced a striking increase of NO in guard cells&s_comma; while inducing stomatal closure in epidermis of Nicotiana glauca. The MJ induced increase in NO of guard cells and stomatal closure were prevented to a large extent by cPTIO&s_comma; a NO scavenger and L-NAME&s_comma; an inhibitor of NO synthase (NOS)&s_comma; suggesting that guard cells generate NO in response to MJ and that a NOS like activity is partially involved in such NO production. Time course experiments revealed that on exposure to MJ&s_comma; the rise in guard cell pH peaked at 15 min&s_comma; while NO production peaked at 18 min and the ROS production much later at about 30 min. Butyrate&s_comma; a weak acid that reduces the cytosolic pH&s_comma; restricted the NO increase and stomatal closure induced by MJ. In contrast&s_comma; EGTA (Ca2+ chelator) or nicotinamide (the blocker of Ca2+ release) reversed the stomatal closure in presence of MJ&s_comma; despite the increase of NO in guard cells. In summary&s_comma; we conclude that H2O2&s_comma; NO and cytosolic pH are all !
essential secondary messengers during stomatal closure in response to not only ABA or MJ. Changes in pH are upstream of NO production while calcium signaling is located downstream of NO effects.

Recent References:
V. A. Kolla&s_comma; A. Vavasseur and A. S. Raghavendra. 2007. Hydrogen peroxide production is an early event during bicarbonate induced stomatal closure in abaxial epidermis of Arabidopsis. Planta 225: 1421-1429.
V. A. Kolla and A. S. Raghavendra. 2007. Nitric oxide is a signaling intermediate during bicarbonate-induced stomatal closure in Pisum sativum. Physiol. Plant. 130: 9198.
A. Vavasseur and A.S. Raghavendra. 2005. Tansley Review: Guard cell metabolism and CO2 sensing. New Phytol. 165: 665-682.
D. Suhita&s_comma; A.S. Raghavendra&s_comma; J.M. Kwak and A. Vavasseur. 2004. Cytoplasmic alkalization precedes reactive oxygen species production during methyl jasmonate- and abscisic acid-induced stomatal closure. Plant Physiol. 134: 1536-1545.

朽津 和幸 (Prof. Dr. Kazuyuki KUCHITSU)
東京理科大学 大学院 理工学研究科 応用生物科学専攻
 ゲノム創薬研究センター 細胞シグナル制御部門 併任
〒278-8510 千葉県野田市山崎2641
FAX 04-7123-9767
E-mail: kuchitsu@rs.noda.tus.ac.jp