The roles of abscisic acid, CO2, and the cuticle in the regulation of plant transpiration
Kuupäev
2017-02-16
Autorid
Ajakirja pealkiri
Ajakirja ISSN
Köite pealkiri
Kirjastaja
Abstrakt
Veatu gaasivahetuse regulatsioon on äärmiselt oluline taimele elus püsimiseks ning aluseks põllumajandustaimede kõrgele saagikusele. Gaasivahetuse all peetakse silmas süsihappegaasi sisenemist taime lehte ning vee väljumist lehest atmosfääri. Süsihappegaasi on taimel vaja fotosünteesi käimas hoidmiseks, kuid veekadu peab taim võimalusel piirama, et vältida kuivale jäämist ja põua tõttu suremist. Enamik taime veekaost toimub läbi taime pinnal olevate väikeste pooride, õhulõhede, kuna epidermiserakke katab vett hülgav lipiidne kutiikula kiht. Selleks, et saaksime tõsta saagikust või parandada taimede ellujäämust ekstreemsetes oludes, on oluline mõista molekulaarseid mehhanisme, millega kontrollitakse taime gaasivahetust nii õhulõhede kui kutiikula kaudu.
Käesoleva doktoritöö raames kinnitati, et taimehormooni abstsiishappe signaaliraja komponendid omavad olulist rolli madala õhuniiskuse, pimeduse ja õhusaasteaine osooni toimel õhulõhede sulgumise reaktsioonides. Kuid kõrge süsihappegaasi mõjul toimuvas õhulõhede sulgumises osalevad vaid mõned abstsiishappe signaaliraja komponendid ning tõenäoliselt esineb ka paralleelne signaalirada. Lisaks pakuti välja mudel, mille kohaselt signaal süsihappegaasi kontsentratsiooni tõusust edastatakse harilikus müürloogas (Arabidopsis thaliana) läbi MAP kinaasvalkude MPK12 ja MPK4. Aktiveeritud MPK12 ja MPK4 on võimelised inhibeerima CO2-spetsiifilist kinaasi HT1 ning seeläbi võimaldatakse anioonkanali SLAC1 aktivatsioon sulgrakkudes ja selle tulemusena ka õhulõhede sulgumine.
Leidmaks uusi molekulaarseid komponente, mis reguleerivad taime gaasivahetust, on mutantide analüüs panustanud tähelepanuväärselt palju teadusmaailma varasalve. Seega, töötati välja uus taimemutantide skriiningmeetod, mis võtab arvesse taimelehtede temperatuuri, lõikamisjärgset närtsimist ning kaalukaotust. Üks skriiningust isoleeritud mutantidest, cool breath 5 oli defektse BODYGUARD geeni ekspressiooniga. BODYGUARD valk on oluline faktor C18 küllastumata kutiikula rasvhapete normaalse hulga saavutamisel eelkõige noortes lehtedes ja õites. Tulemuste põhjal pakuti välja, et BODYGUARD võiks kaasa aidata endoplasmaatilises retiikulumis toimuvale kutiikula monomeeride biosünteesile.
Kokkuvõtteks, abstsiishape, MPK-d ja kutiikula on kõik olulised faktorid reguleerimaks taime transpiratsiooni ja gaasivahetust.
Flawless coordination and regulation of gas exchange is highly important for the survival of land plants and for maintaining high agricultural crop yield. Plants need to ensure the entrance of carbon dioxide to feed photosynthesis, but at the same time water loss must be minimized to avoid desiccation and eventually death. Water loss through the epidermal cells is inhibited by the water-repellent layer called cuticle, which is covering all the aboveground parts of plants. Thus, most of the water exits plants through the small pores in the epidermis called stomata. In order to be able to increase crop yield or viability of plants in extreme conditions, it is important to understand the molecular mechanisms controlling the gas exchange between the plant and the atmosphere both through the stomata and the cuticle. The current thesis confirmed that the signaling pathway of plant hormone abscisic acid controls the closure of stomata in response to reduced air humidity, darkness, and air pollutant O3. Elevated CO2-induced stomatal closure involves only partially the abscisic acid pathway and the presence of a parallel signaling pathway is possible. Furthermore, a model for stomatal CO2 signaling is suggested, where the signal of elevated CO2 is conducted via novel players, MAP kinases MPK12 and MPK4, in Arabidopsis thaliana. Activated MPK12 and MPK4 are able to inhibit the CO2-specific kinase HT1, which results in activation of the anion channel SLAC1 in the guard cells and eventually in stomatal closure. In order to find new molecular components determining the rate of gas exchange between the plant and the atmosphere, reverse genetics approaches have contributed remarkably to it. Hence, a new screening method for screening mutants for impaired transpiration was introduced, which was based on temperature-dependent water spot condensation, visual wilting and weight loss of excised leaves. One of the mutants from this screen, named cool breath 5 was defective in the expression of BODYGUARD gene. BODYGUARD protein plays a crucial role in determining the occurrence of C18 unsaturated fatty acids in the cuticle, especially in young developing leaf tissues and flowers. It was hypothesized that BODYGUARD could facilitate a biosynthetic step of these cuticular monomers in the endoplasmic reticulum. All-in-all, abscisic acid, MPKs and cuticle all have their distinct role in regulating plant transpiration and coordinating gas exchange of plants.
Flawless coordination and regulation of gas exchange is highly important for the survival of land plants and for maintaining high agricultural crop yield. Plants need to ensure the entrance of carbon dioxide to feed photosynthesis, but at the same time water loss must be minimized to avoid desiccation and eventually death. Water loss through the epidermal cells is inhibited by the water-repellent layer called cuticle, which is covering all the aboveground parts of plants. Thus, most of the water exits plants through the small pores in the epidermis called stomata. In order to be able to increase crop yield or viability of plants in extreme conditions, it is important to understand the molecular mechanisms controlling the gas exchange between the plant and the atmosphere both through the stomata and the cuticle. The current thesis confirmed that the signaling pathway of plant hormone abscisic acid controls the closure of stomata in response to reduced air humidity, darkness, and air pollutant O3. Elevated CO2-induced stomatal closure involves only partially the abscisic acid pathway and the presence of a parallel signaling pathway is possible. Furthermore, a model for stomatal CO2 signaling is suggested, where the signal of elevated CO2 is conducted via novel players, MAP kinases MPK12 and MPK4, in Arabidopsis thaliana. Activated MPK12 and MPK4 are able to inhibit the CO2-specific kinase HT1, which results in activation of the anion channel SLAC1 in the guard cells and eventually in stomatal closure. In order to find new molecular components determining the rate of gas exchange between the plant and the atmosphere, reverse genetics approaches have contributed remarkably to it. Hence, a new screening method for screening mutants for impaired transpiration was introduced, which was based on temperature-dependent water spot condensation, visual wilting and weight loss of excised leaves. One of the mutants from this screen, named cool breath 5 was defective in the expression of BODYGUARD gene. BODYGUARD protein plays a crucial role in determining the occurrence of C18 unsaturated fatty acids in the cuticle, especially in young developing leaf tissues and flowers. It was hypothesized that BODYGUARD could facilitate a biosynthetic step of these cuticular monomers in the endoplasmic reticulum. All-in-all, abscisic acid, MPKs and cuticle all have their distinct role in regulating plant transpiration and coordinating gas exchange of plants.
Kirjeldus
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Märksõnad
taimed, gaasivahetus, abstsiishape, süsinikdioksiid, kutiikula, transpiratsioon, plants (botany), gas exchange, abscisic acid, carbon dioxide, cuticula, transpiration