This article reviews the current knowledge of the Zucchini yellow mosaic virus (ZYMV) specific physiological alterations within Styrian oil pumpkin plants with respect to glutathione metabolism. Reactive oxygen species (ROS), whose formation is accelerated under the virus infection, must be rapidly processed by antioxidants if oxidative damage is to be averted. Coupled with carbon, nitrogen and sulfur metabolism the reduced form of glutathione is known to play important protective roles in responses against viral pathogen infections, acting as an antioxidant, signal molecule and redox buffer. Biochemical analysis and immunocytochemical techniques were used, in order to demonstrate the alterations in the concentration and the distribution of glutathione in organs, tissues and within single cells of ZYMV infected Styrian oil pumpkin plants. The symptoms were preceded by a decline in total glutathione levels within whole leaves, whereas in single cells of dark-green leaf parts, close to the main leaf vein, increased glutathione concentrations were observed. Besides genetic engineering, possibilities to increase cellular glutathione contents in plants are the use of glutathione precursors or chemicals, which are stimulating glutathione synthesis. Experiments with L-2-oxothiazolidine-4-carboxylic acid (OTC) and salicylic acid (SA) demonstrated, that both chemicals were rapidly taken up by the plants since cotyledons, roots, leaf protoplasts and callus cells possessed a high affinity to assimilate these chemicals into thiol compounds. Furthermore, treatment with OTC and SA provided an enhanced tolerance against ZYMV induced symptoms and stimulated the synthesis, conversion and translocation of glutathione during advanced ZYMV infection in seedlings and regenerated plants. Since the characteristically thin, coated seed character of the Styrian oil pumpkin is a genetically recessive trait somatic embryogenesis discussed in this article would be important not only to obtain virus resistance by modulating the physiological properties of the plantlets, but also for the conservation of this local cultivar.

Key words: Cucurbita pepo, Styrian oil pumpkin, ZYMV, reactive oxygen species, systemic acquired resistance, glutathione, L-2-oxothiazolidine-4-carboxylic acid, salicylic acid, somatic embryogenesis, virus tolerance Abbreviations: GR, glutathione reductase; GSH, reduced glutathione; GSSG, oxidized glutathione; HIV, human immunodeficiency virus; H2O2, hydrogen peroxide; OTC, L-2-oxothia zolidine-4-carboxylic acid; ROS, reactive oxygen species; SA, salicylic acid; SAR, systemic acquired resistance; ZYMV, Zucchini yellow mosaic virus;

Slovenian:

Vpogled v obrambne mehanizme in vloga glutationa med napredno okužbo Štajerske oljne buče s ZYMV

Članek je pregled dosedanjih raziskav o fizioloških spremembah povezanih s presnovo glutationa na štajerski olji buči po okužbi z virusom rumenega mozaika buč (Zucchini yellow mosaic, ZYMV). Po okužbi z virusom se aktivira sinteza antioksidantov, ki prestrežejo reaktivne kisikove vrste in tako preprečujejo nastanek oksidativnih poškodb. Glutation je pomembna žveplova organska spojina, ki povezuje metabolizem ogljika, dušika in žvepla. Deluje kot antioksidant, signalna molekula in redoks pufer in igra pomembno zaščitno vlogo pri okužbi z virusi. V okviru raziskav smo uporabili biokemične analize in imunocitokemične tehnike z namenom prikaza sprememb v razporeditvi in vsebnosti glutationa v organih, tkivih in na nivoju posameznih celic po okužbi Štajerske oljne buče s ZYMV. Simptomi na listih so sovpadali z nižjo vsebnostjo glutationa v primerjavi s kontrolnimi listi, medtem ko smo na temno zelenih področjih lista blizu osrednje listne žile na nivoju posameznih celic izmerili povišano vsebnost glutationa.
Poleg genskega inženiringa je uporaba prekurzorjev sinteze glutationa in spojin, ki stimulirajo sintezo te molekule, učinkovita možnost za povečanje vsebnosti glutationa na celičnem nivoju kot tudi na nivoju celih listov. Poskusi tretiranja z L-2-oksoothiazolidin-4-karboksilno kislino (OTC) in salicilno kislino (SA) so pokazali, da se obe spojini učinkovito privzameta v rastlino. Klični listi, korenine, protoplasti in kalusne celice so imeli veliko afiniteto do pretvorbe le-teh v glutation. Poleg tega je tretiranje z OTC in SA izboljšalo odpornost proti okužbi s ZYMV, omilijo simptome in med napredujočo okužbo spodbudilo sintezo, pretvorbo in translokacijo glutationa v sejančkih in regeneriranih rastlinah. Ker je karakteristično tanka semenska lupina Štajerske oljne buče genetsko recesivna lastnost, je somatska embriogeneza pomembna možnost razmnoževanja štajerske oljne buče, ne samo za zviševanje odpornosti pred okužbo z virusi z moduliranjem fizioloških lastnosti ampak tudi za ohranjanje te lokalne sorta.

Ključne besede: Cucurbita pepo / Štajerska oljna buča / ZYMV / reaktivne kisikove vrste / sistemsko pridobljena odpornost / glutation / L-2-oksothiazolidin-4-karboksilna kislina / salicilna kislina / somatska embriogeneza / toleranca na viruse

Okrajšave: GR, glutation reduktaza; GSH, reduciran glutation; GSSG, oksidiran glutation; HIV, virus človeške imunske pomanjkljivosti; H2O2, vodikov peroksid; OTC, L-2-oksothiazolidin-4-karboksilna kislina; ROS, reaktivne kisikove vrste; SA, salicilna kislina; SAR, sistemsko pridobljena odpornost; ZYMV, virus rumenega mozaika buč.

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