Zeolite effect on antioxidative status parameters in tomato (Solanum lycopersicum L.) and maize (Zea mays) under drought conditions

Uzimajući u obzir klimatske promjene koje podrazumijevaju smanjenje količine padavina i porast temperatura, suša je postala globalni problem za koji se smatra da će biti aktuelan još dugo vremena u budućnosti. Osim problema koje stvara u brojnim životnim sferama, suša je jedan od najozbiljnijih faktora koji negativno utiče na poljoprivredu, s obzirom da nedovoljno vodosnabdijevanje negativno utiče na rast i razvoj biljaka. U uslovima suše povećana produkcija reaktivnih vrsta kiseonika može da izazove pomjeranje ravnoteže u ćelijskim oksidoredukcionim reakcijama u smjeru oksidacije te da dovede do nastanka oksidativnog stresa. Posljedice oksidativnog stresa su strukturna i funkcionalna oštećenja ćelijskih komponenti koja dovode do poremećaja u metabolizmu i funkcionisanju ćelije.Veoma važnu ulogu u toleranciji biljaka na stres izazvan sušom ima antioksidativni sistem zaštite koji neizbježno uključuje enzime superoksid dismutazu, katalazu, peroksidaze Klase III i askorbat peroksidazu, ali takođe i niskomolekularne antioksidante poput askorbata, glutationa, fenola i karotenoida. Posljednjih godina se naglo povećao interes za korištenje ekološki opravdanih i neinvazivnih sredstava kojima se unaprijeđuje problem vodosnabdijevanja biljaka, a velika pažnja je posvećena primjeni prirodnih aluminosilikata, od kojih je najpoznatiji zeolit. Iako nisu mnogobrojni, postoje radovi koji upućuju da ovaj prirodni mineral može značajno da doprinese poboljšanju vodnog režima biljaka zbog osobine vezivanja te uravnoteženog otpuštanja vode. U ovoj doktorskoj disertaciji predmet istraživanja je uključio dvije biljne vrste različite po tipu fotosintetičkog metabolizma i adaptivnim strategijama na prilagođavanje na sušu, a to su paradajz (Solanum lycopersicum L.) i kukuruz (Zea mays L.). Fokus istraživanja bio je ispitivanje mogućnosti primjene zeolita u svrhu sprječavanja ili ublažavanja posljedica stresa izazvanog sušom kod biljaka paradajza i kukuruza, ali i ispitivanje mogućeg različitog odgovora u odnosu na biljnu vrstu. Intenzitet oksidativnog stresa analiziran je na osnovu indirektnih pokazatelja, analizom biohemijskih parametara antioksidativnog metabolizma. Osim toga, analize su uključile i fiziološke parametre povezane sa fotosintetičkim metabolizmom (strukturne karakteristike stoma, intentzitet fotosinteze i transpiracije, sadržaj enzima Rubisco,koncentracije fotosintetičkih pigmenata, relativni sadržaj vode) te anatomsko-histološke karakteristike listova imorfološke osobine izdanka. Za istraživanje na biljkama paradajza zeolit je dodat u supstrat u tri različite koncentracije (5%, 10% i 20%). Kontrolne biljke su optimalno navodnjavane tokom cijelog eksperimentalnog perioda, bez zeolita u supstratu, ali i sa svim primjenjenim koncentracijama. Biljke u uslovima suše nisu navodnjavane, a bile su podijeljene u grupu koja nije imala zeolit te u grupe sa tri koncentracije zeolita. Dobijeni rezultati su pokazali da se sa dodatkom 5% zeolita u supstrat može značajno doprinijeti ublažavanju negativnih posljedica stresa, iako nije ostvareno potpuno sprečavanje uticaja suše. Dodatak 10% zeolita u supstrat nije imao pozitivan efekat, dok je dodatak 20% zeolita dodatno pogoršao uslove prouzrokovane sušom. U tom smislu zaključeno je da je efekat zeolita na antioksidativni status biljaka paradajza u uslovima suše uslovljen njegovom koncentracijom u zemljištu, te da u zavisnosti od nje može biti i pozitivan i negativan. Kod eksperimenta na biljkama kukuruza primjenjene su dvije koncentracije (5% i 10%) zeolita. Kontrolne biljke su navodnjavane bez zeolita i sa primjenjenim koncentracijama, dok su biljke podvrgnute uticaju suše bile bez navodnjavanja, takođe bez zeolita, ali i sa odabranim koncentracijama. Rezultati su pokazali da primjena zeolita ni u jednoj koncentraciji ne može da spriječi niti da ublaži posljedice oksidativnog stresa izazvanog sušom kod biljaka kukuruza. Osim toga fiziološki pokazatelji i parametri enzimskog antioksidativnog metabolizma ukazali su da prisustvo 10% zeolita dodatno pogoršava stresno stanje izazvano sušom.Prisustvo zeolita u supstratu biljaka kukuruza se pokazalo štetnim čak i u uslovima optimalnog navodnjavanja, zbog nastale razmjene katjona sa okolnim supstratom i redistribucije hemijskih elemenata koja je uslovila toksičan efekat pojedinih jona, ali i deficit onih koji su neophodni za nesmetan metabolizam. Zaključeno je da su se biohemijsko-fiziološki putevi u metaboličkim strategijama prilagođavanja na sušu donekle razlikovali kod biljaka paradajza i kukuruza, a takođe da je i sam efekat zeolita u sprečavanju posljedica stresa bio specifičan u odnosu na vrstu i zavisi od primjenjene koncentracije zeolita.Taking into account climate change, which implies a precipitation decreasing and temperatures rising, drought has become a global problem that is considered to be relevant for a long time to come. In addition to the problems it creates in many spheres of life, drought is one of the most serious factors that negatively affects agriculture, given that insufficient water supply disrupts the growth and development of plants. The production of reactive oxygen species in drought conditions can cause an inbalance of cellular redox homeostasis in the direction of oxidation and lead to the formation of oxidative stress. The consequences of oxidative stress are structural and functional damages of cellular compartments which leads to disturbance of metabolism and cell function. A very important role in plant tolerance to drought stress has the antioxidant protection systems that inevitably include theenzymes superoxide dismutase, catalase, Class III peroxidases and ascorbate peroxidase, but also low molecular weight antioxidants such as ascorbate, glutathione phenol and carotenoids. In recent years, there has been a sharp increase in interest in the use of environmentally sound and non- invasive means to improve the water supply of plants, and much attention has been paid to the use of natural aluminosilicates, the most famous of which is zeolite. Although not numerous, there are studies that suggest that this natural mineral can significantly contribute to the improvement of the water regime of plants due to the binding properties and balanced release of water. In this PhD thesis, the subject of research included two plant species different in type of photosynthetic metabolism and adaptive drought adaptation strategies, namely tomatoes (Solanum lycopersicum L.) and maize (Zea mays L.). The focus of research was to examine the possibility of using zeolite to prevent or mitigate the effects of drought stress in tomato and maize plants, but also to examine the possible different response in relation to the plant species. The intensity of oxidative stress was analyzed on the basis of analysis of biochemical parameters of antioxidant metabolism. In addition, analyzes included physiological parameters related to photosynthetic metabolism (structural characteristics of stoma, photosynthesis and transpiration intensity, Rubisco content,photosynthetic pigment concentrations, relative water content) and anatomical- histological characteristics of leaves and shoot morphological properties. For the research with tomato plants zeolite was applied with three different concentrations (5%, 10% and 20%). Control plants were optimaly irrigated during the entire experimental period, without zeolite in substrate, but also with all applied zeolite concentrations. The plants in drought conditions were not irrigated and they were divided into group without zeolite and with 5%, 10% and 20% zeolite respectively. The obtained results showed that the addition of 5% zeolite to the substrate can significantly contribute to the mitigation of the negative effects of stress, although complete drought prevention has not been achieved. The zeolite application of 10% did not have a positive effect, while the application of 20% caused additional deteriotation of drought consequences. In that sense, it was concluded that the effect of zeolite on the antioxidant status of tomato plants in drought conditions is conditioned by its concentration in the soil, and that depending on it, it can be both positive and negative. In experiment with maize plants, two zeolite concentrations (5% and 10%) were applied. Control plants were irrigated without zeolite and with applied 5% and 10% zeolite respectively, while plants submitted to drought were not irrigated and they also were without zeolite and with selected concentrations. The results showed that the application of zeolite in any concentration cannot prevent or mitigate the effects of oxidative stress caused by drought in maize plants. In addition, physiological indicators and parameters of enzymatic antioxidant metabolism indicated that the presence of 10% zeolite further exacerbates drought-induced stress. The presence of zeolite in the substrate of maize plants was harmful even in conditions of optimal irrigation as a result of cation exchange with surrounding substrate and redistribution of chemical elements which conditioned the toxic effects of certain ions, but also the defficite of necessary ions for undisturbed metabolism. It was concluded that the biochemicalphysiological pathways in metabolic drought adaptation strategies differed somewhat in tomato and maize plants, and also that the effectof zeolite in preventing the effects of stress was species-specific and concentration dependent