Uticaj citokinina na otpornost pšenice prema oksidativnom stresu u uslovima nedostatka azota

Abstract

<p>Starenje biljnog tkiva je prirodan proces koji se u uslovima stresa ubrzava. Sa starenjem se smanjuje sadržaj citokinina i aktivnost antioksidantnih enzima (superoksid dismutaza, katalaza, peroksidaza i dr.) &scaron;to dovodi do intenzivnijeg nastajanja i povećanja količine slobodnih radikala u ćelijama. Povećane količine kiseoničnih i drugih slobodnih radikala ubrzavaju procese starenja razaranjem makromolekula i naru&scaron;avanjem metabolizma biljaka. Stoga povećana aktivnost antioksidantnih enzima, smanjujući količine slobodnih radikala, usporava odvijanje procesa starenja. Slično drugim činiocima stresa, nedostatak azota, izme&ntilde;u ostalog, povećava količinu kiseoničnih radikala i ubrzava starenje biljnih tkiva. Sa druge strane, jedna od osobina citokinina je da odlažu starenje biljnih tkiva u kojima se nalaze u povećanoj količini. Suprotni efekti kiseoničnih radikala i citokinina na integritet ćelijskih makromolekula i starenje nameću pitanje da li i kako citokinini utiču na količinu kiseoničnih radikala u biljnim tkivima u uslovima stresa.&nbsp; Da bi se utvrdila veza izme&ntilde;u citokinina i aktivnosti antioksidantnih enzima u uslovima nedostatka azota, biljke p&scaron;enice su u polukontrolisanim i poljskim uslovima folijarno tretirane rastvorima jedinjenja sa citokininskom aktivno&scaron;ću (trans zeatin, benzil adenin i fenil urea). Analizirana je aktivnost superoksid dismutaze i peroksidaze, količine nastalog superoksid radikala (O2&middot;&oline;), hidroksil radikala (&bull;OH) i malonil dialdehida (MDA), masa i lisna povr&scaron;ina biljaka, kao i sadržaj proteina i pigmenata. U poljskom ogledu, osim pomenutih parametara, analiziran je broj zrna u klasu, masa 1000 zrna i prinos.&nbsp; Primena trans zeatina značajno je smanjila količinu &bull;OH i MDA u odnosu na kontrolu u polukontrolisanim i u poljskim uslovima. Tretiranje p&scaron;enice rastvorima jedinjenja sa citokininskom aktivno&scaron;ću ispoljilo je značajan uticaj na količinu O2&middot;&oline; i aktivnost superoksid dismutaze i peroksidaze. Folijarno tretiranja biljaka rastvorima trans zeatina u poljskom ogledu, i pored pozitivnog uticaja na smanjenje lipidne peroksidacije, nije dovelo do značajne promene broja zrna u klasu, mase 1000 zrna ili prinosa.</p>

<p>Senescence of plant tissues is a natural process, which is accelerated by stress. During senescence, the content of cytokinins and the activity of antioxidative enzymes (superoxid dismutase, peroxidase, and catalase) are declining, which leads to an increase in the concentration of free radicals in the cell. Augmented amounts of free radicals, including oxygen radicals, promote senescence because they are destructive for cellular macromolecules and can impair cell metabolism. Therefore, an increase in the activity of antioxidant enzymes delays senescence, by reducing the amount of free radicals in the cell. Similar to the other stress factors, nitrogen deficiency also increases the amount of free radicals and accelerates senescence of plant tissues. On the other hand, cytokinins can delay senescence of tissues in which they are present in higher amounts. The opposite effects of oxygen radicals and cytokinins on the integrity of cell membranes and senescence raise the question whether and how cytokinins affect the amount of reactive oxygen species in plant tissues exposed to stress.&nbsp;&nbsp;&nbsp; With the aim to study relationship between cytokinins and the activity of antioxidant enzymes under nitrogen deficiency, wheat plants, grown under semi-controlled and field conditions, were treated with cytokinins (trans-zeatin, benzyl adenine and phenyl urea). Activities of superoxid dismutase and peroxidase were analyzed as well as amounts of superoxid radical (O2&middot;&oline;) and hydroxyl radical (&bull;OH), plant weight, total leaf area, contents of proteins and concentration of chloroplast pigments. In the plants grown in the field, besides already mentioned parameters, number of seeds per spike, mass of 1000 seeds and yield were determined.&nbsp; Application of trans-zeatin significantly reduced amounts of &bull;OH and MDA both under semicontrolled and field conditions. Treatment with cytokinins significantly affected the amount of O2&middot;&oline; and activities of superoxid dismutase and peroxidase. Although foliar application of cytokinins reduced lipid peroxidation in wheat grown in the field, it did not significantly change number of seeds per spike, mass of 1000 seeds and yield.</p>