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Common duckweed (Lemna minor L.), a small floating macrophyte with a high phytoremediation and bioaccumulation capacity, is characterized by high dry matter yield, cellulose, and starch content. Appropriate manipulation of growing conditions can provide a substantial increase in starch accumulation. Hence, this study aimed to investigate the impact of individual and simultaneous exposure to phytohormone 6- benzylaminopurine (1 μM 6-BA) and increased salinity (50, 100, 150 mM NaCl) on starch and phenolics accumulation, as well as on the antioxidant capacity of common duckweed. After ten days of exposure, increased salinity inhibited duckweed's growth rate and frond size, while 6-BA stimulated it. Simultaneously, the progressive accumulation of starch due to increased salinity was measured and localized on semi-thin microscopic sections in the mesophyll layer. The content of polyphenolic acids (chlorogenic, ferulic, p-coumaric, and syringyl acid), determined by HPLC, differed depending on salinity level. Higher salinity caused a significant decrease in the total phenolic content, indicating salt's negative effect. However, high phenolic content and potent antioxidant activity were observed in the combination of salt and phytohormone. These results suggest an effective tolerance mechanism to increased salinity, making duckweeds an excellent potential feedstock for bioethanol production in moderately saline ecosystems.

Svržnica is a small lowland drainage canal that flows into the river Biđ. To raise public interest in adequately managing water resources, the monitoring of biological, physical, and chemical elements of water quality was carried out, from spring to winter, at four sites of the canal: S1 - a pre- discharged site characterized by the high representation of macrophytes ; S2 - immediately after the discharge of municipal wastewaters characterized by the complete absence of macrophytes ; S3 - the oak forest site with ruderal plants and poorly represented macrophytes ; S4 - at the mouth of the canal into the Biđ river, with large macrophyte cover. The water quality was mainly moderate based on physical and chemical elements, with high phosphorus and organic nitrogen load throughout the year of sampling, except on the S1 site. The highest representation of algae was established in late spring at all locations. At the same time, their presence was negligible in other seasons. Indicators of faecal contamination were determined in water samples at S2 and S3, and the microbiological load was more significant in the winter. Screening phytotoxicity tests with Lemna minor were conducted using undiluted water samples. Chlorosis, colony structure breakup, and buoyancy loss were noted in all water samples, and the most significant phytotoxicity effect in waters from the S1 site was due to deficient nutrients.

Zaslanjivanje tla abiotički je stres koji uvelike ograničava poljoprivrednu proizvodnju. Cilj rada bio je istražiti utjecaj solnog stresa na klijance ječma (Hordeum vulgare L.) te utvrditi mehanizme tolerancije koji se primarno aktiviraju u ranoj fazi razvoja. Sedam dana stare biljke uzgajane u kontroliranim uvjetima izložene su različitim koncentracijama natrijevog klorida (50, 100, 200 i 400 mM). Utjecaj solnog stresa praćen je nakon 3, 6, 12 i 24 sata. Fiziološka i biokemijska mjerenja izvršena su na prvim potpuno razvijenim listovima. Primijenjeni stres uzrokovao je smanjenje sadržaja fotosintetskih pigmenata i nije inducirao oksidativna oštećenja, što je pokazala smanjena razina malondialdehida. Niska razina malondialdehida obilježje je tolerantnih biljaka na stresne uvjete. Parametri fluorescencije klorofila a (L- i K- stupanj ; indeks vitalnosti - PIABS) potvrdili su izrazito dobru funkcionalnost fotosintetskog aparata. Povećanje razine solnog stresa i poboljšane performanse klijanaca ječma praćene su povećanim sadržajem prolina i relativnog sadržaja vode. Rezultati pokazuju da osmotska prilagodba pridonosi poboljšanju tolerancije na povišeni salinitet u ranim fazama rasta klijanaca, dok niti jedan pojedinačni parametar ne može biti izdvojen kao primarno odgovoran čimbenik osjetljivosti i/ili tolerancije. Kombinacija parametara bolje objašnjava doprinos komponenata osmotskog, ionskog i oksidativnog stresa ukupnoj toleranciji na povišeni salinitet komercijalno značajnih žitarica.

Duhan (Nicotiana tabacum L.) je gospodarski značajna kultura, a ujedno i često korišteni modelni organizam u biološkim istraživanjima. U ovom radu cilj je bio istražiti dinamiku razvoja fotosintetskog aparata tijekom ontogeneze listova duhana određivanjem koncentracija fotosintetskih pigmenata ključnih za apsorpciju svjetlosti (Chl a, Chl b) i mjerenjem fluorescencije klorofila a u svrhu procjene funkcionalnosti fotosintetskog aparata. Početna mjerenja izvršena su na listovima 14 dana starih presadnica, a sljedeća su obuhvatila pet insercija odnosno pet parova listova starosti 20, 24, 29, 32 i 37 dana. Rezultati su pokazali konstantni porast maksimalnog kvantnog prinosa fotosustava II (TR0 /ABS) i indeksa fotosintetske učinkovitosti (PIABS) tijekom razvoja, potvrđujući kompetentnost ispitivanih skupina listova za učinkovito apsorbiranje i iskorištavanje energije u fotokemijskim procesima, unatoč različitoj dinamici akumulacije fotosintetskih pigmenata (Chl a, Chl b, Chl a+b). Porast gustoće aktivnih reakcijskih središta (RC/CS0 ) i smanjenje apsorpcije (ABS/RC) osigurali su porast učinkovitosti fotosustava II tijekom razvoja listova. Najviše koncentracije pigmenata izmjerene u insercijama 2 i 3 ukazuju na maksimum eksponencijalnog rasta listova u toj fazi razvoja. Degradacija pigmenata u insercijama 4 i 5 nije utjecala na funkcionalnost fotosintetskog aparata što je utvrđeno visokim vrijednostima parametara TR0 /ABS i PIABS, ali ipak ukazuje na početak senescencije listova.

Global warming and climate changes have enormous negative impact on crop production in affected areas. Increased soil salinity and drought are abiotic stresses particularly pronounced in Mediterranean, semi-arid, and arid climates. The abiotic stress tolerance of Brassica crops correlated with certain changes in plant hormones such as salicylic acid (SA), abscisic acid (ABA), auxins (IAA), cytokinins (CS) and brassinosteroids (BR). The effect of salinity stress and drought was evaluated on selected Brassica crops: Chinese cabbage (Brassica rapa ssp. pekinensis), white cabbage (B. oleracea var. capitata forma alba) and kale (B. oleracea var. acephala) with particular focus on the role of plant hormones in abiotic stress tolerance. Based on the physiological and biochemical markers the Chinese cabbage exhibited the lowest tolerance, followed by the white cabbage, while the kale appeared to be the most tolerant to drought and salinity stress in aplied experimental conditions.

Biljke su tijekom rasta i razvoja često izložene različitim stresnim čimbenicima. Budući da je ječam jedna od glavnih žitarica koja se koristi u ljudskoj i životinjskoj ishrani nužno je razumjeti strategije prilagodbe na stres i kreirati tolerantne kultivare. Cilj ovog istraživanja bio je odrediti sadržaj ukupnih topljivih šećera (TSS) u listovima dvadeset kultivara ozimog ječma tijekom razvoja u varijabilnim vremenskim uvjetima. Kultivari su rasli na eksperimentalnim poljimaPoljoprivrednog instituta Osijek. Uzorkovanja su izvršena tijekom tri fenološke faze. Prosječne vrijednosti TSS izmjerene tijekom vlatanja, cvatnje i nalijevanja zrna su iznosile 37, 18, 43, 44 i 46, 17 mg g-1 suhe tvari. Porast količine izmjerenih šećera može se povezati sa blagom sušom koja je zabilježena tijekom cvatnje i nalijevanja zrna. U istraživanim kultivarima zabilježena je različita akumulacija šećera. U pet kultivara ('Zlatko’, ‘Casanova’, ‘Maxim’, Osk.5.87/1-13 i ‘Lord’) sadržaj šećera nije se mijenjao tijekom razvoja. U dva kultivara ('Barun' i 'Bravo') akumulacija ukupnih šećera započela je u fazi nalijevanja zrna, dok je u ostalima akumulacija šećera zabilježena već tijekom cvatnje. Rezultati ovog istraživanja ukazuju na prisutnost različitih mehanizama prilagodbe na blagu sušu. Brojna dosadašnja istraživanja također su pokazala osjetljivost TSS na stres izazvan sušom. Nadalje, razlike u sadržaju ukupnih topljivih šećera mogle bi se koristiti tijekom selekcije kultivara tolerantnih na sušu.

Aleppo pine (Pinus halepensis L.) is widely spread Mediterranean woody species. Its natural and cultivated populations can be frequently found in the coastal area of the Adriatic Sea. Usually, needles fall down after the second year, what can be the reason for substantial crown defoliation under extreme environmental stress. The aim of this investigation was to compare the chlorophylls content and photosynthetic performance in current- year (CY) and previousyear (PY) A. pine needles. Chlorophylls concentrations were determined spectrophotometrically and the photosynthetic performance was determined by measuring the increase in chlorophyll a fluorescence (JIP test). Results revealed that concentrations of chlorophylls a and b were almost two folded in PY needles compared to CY ones, what was statistically significant. Chlorophylls a to b ratio and values of the maximum quantum yield of the photosystem II (Fv/Fm) showed no statistical significance between CY and PY needles. However, performance index (PIABS) was significantly higher in CY needles compared to PY ones. Based on the presented results it can be concluded that despite of considerably lower chlorophylls content, CY needles reveled enhanced photosynthetic performance than older needles. The analysis of JIP test parameters showed that the main reason for this was better utilization of absorbed light energy in CY needles due to their more competent photosynthetic electron transport, in comparison to PY needles.

Prijašnja istraživanja pokazala su da manjak vode i teški metali, poput kadmija (Cd), imaju snažan učinak na biosintezu lignina u korijenu kukuruza. U ovom radu istraživan je utjecaj manjka vode i kadmija na sadržaj lignina u korijenu dvije roditeljske linije (B73, Mo17) i njihovog hibrida (B73xMo17). Biljke su bile izložene manjku vode, kadmiju (otprilike do 5 mg Cd/ kg tla) i kombiniranom tretmanu kadmija i manjka vode. U dobro navodnjavanim biljkama (kontrola), B73, Mo17 i B73xMo17, ukupni sadržaj lignina iznosio je 131, 96, 103, 19 i 212, 56 mg/g suhe tvari. U linijama B73 i Mo17 nije zamijećeno značajno smanjenje sadržaja ukupnog lignina u odnosu na kontrolu bez obzira na tretman. Međutim, u hibridu (B73xMo17) sadržaj lignina značajno se smanjio nakon tretmana kadmijem (182.26 mg/g suhe tvari) u usporedbi s kontrolom. Najmanji sadržaj lignina izmjeren je u hibridu izloženom manjku vode (154, 34 mg/g suhe tvari), a također i u biljkama podvrgnutim kombiniranom tretmanu manjka vode i kadmija (162, 98 mg/g suhe tvari). Dobiveni rezultati pokazuju da korijen hibrida kukuruza (B73xMo17) ima generalno niži sadržaj lignina bez obzira na tretman u usporedbi s dobro navodnjavanim biljkama (kontrolom). Objašnjenje za ovo smanjenje ukupnog sadržaja lignina moglo bi se pripisati adaptivnom odgovoru hibrida budući da je sličan efekt zabilježen u listovima kukuruza izloženih suši.

Cadmium exposure and water deficit are among the most powerful abiotic stress factors affecting crop growth and productivity. Present study was conducted to evaluate the oxidative damage and the antioxidative response management in the leaves of two maize inbred lines (A: B84, B: Os6-2) and their hybrid (AxB: B84xOs6-2) subjected to excess Cd and or no water limitation in the greenhouse experiment during flowering phase. In well- watered conditions, the increase of lipid peroxidation level (LP) in A and AxB affected by Cd indicates its toxicity, while in B higher amount of accumulated proline could be the reason of maintained LP. In A increased activities of guaiacol peroxidase (POD), ascorbate peroxidase (APX) and catalase (CAT) were shown while in B POD and APX were increased. Water limitation caused decrease in RWC in A, B and AxB. Higher decrease of RWC was observed in combination of stress factors in A and B but not in AxB. The increase of LP and proline content as well as higher activity of POD and APX was observed in A. In B only POD and APX were increased. Increased APX and higher proline accumulation in AxB might be the reason of decreased LP and unchanged POD. Inhibition of CAT activity was observed in A, B and AxB. Obtained results showed different strategies of antioxidative mechanisms in maize inbred lines and their hybrid subjected to investigated stress factors. It seems that hybrid is more tolerant than its parental lines probably due to heterosis and dilution effect.

In order to investigate early photosynthetic responses of Chinese cabbage (B. rapa ssp. pekinensis) and kale (B. oleracea var. acephala) to the increased salinity, photosynthetic performance, chlorophylls concentration and relative accumulation levels of the photosynthetic proteins (Rubisco LSU, Cyt f, LHC b II and D1) were analyzed. Plants were grown hydroponically, treated with NaCl in a range of conc. 0-200 mM for a short-term (24 hours). Results showed that investigated species had different tolerance to the salt stress what was based on their different photosynthetic adjustment strategies. Kale, as a more salt tolerant species, revealed considerably better photosynthetic performance under increased salinity conditions due to more competent electron transport, in comparison to the moderately sensitive Chinese cabbage. On the other hand, Chinese cabbage plants decreased considerably their photosynthetic performance under the salt stress conditions. This was due to the less competent electron transport as well as increased light harvesting and trapping properties of PSII. This led to the increase in dissipation flux and the modification of a certain number of RC from active to dissipative ones. The observed differences in the photosynthetic performance of two investigated species corresponded to the differential accumulation of chlorophylls and photosynthetic proteins that regulate electron transport and light harvesting.

Cadmium (Cd) toxicity in soil and water deficit are causing serious problems in natural and agricultural ecosystems. The aim of this study was to investigate the influence of Cd and/or drought on photosynthetic performance of maize. Two maize lines (B84 and Os6-2) as well as their hybrid (B84xOs6-2) were subjected to Cd- induced stress (Cd), drought (D) and combined stress (Cd+D). To evaluate photosynthetic performance, chlorophyll a fluorescence was measured. Total performance index (PItot) is the most sensitive parameter of JIP-test that includes functional activity of photosystem II (PSII), photosystem I and intersystem electron transport chain. The line Os6-2 showed significant decline of PItot subjected to D and Cd+D treatments. In addition, both treatments showed positive L and Kbands, indicating lower PSII stability and destabilization of oxygen evolving center of PSII, respectively. The PItot in the line B84 declined only at D treatment with parallel increase in L-band and positive inflection of K-band. The hybrid showed decrease of PItot at Cd+D treatment with corresponding positive L and K- bands. Decline of the PItot parameter indicated that drought is the main reason for photoinhibition in Os6-2 and B84 lines. Photoinhibition due to the combination of Cd and drought occurred in hybrid and also in line B84. Our results suggested that both investigated maize lines and their hybrid have different strategies to cope with Cd-induced stress and/or drought.

Chlorophyll fluorescence (ChlF) parameters of JIP-test are considered as early indicators of stress in photosynthetic tissues. The JIP-test is particularly useful for crop plants when applied in vivo under mild drought stress under control and field conditions. However, due to increasing intrinsic photosynthetic heterogeneity affected by increasing drought stress severity, the usefulness of the classical ChlF parameters is in question. Objective of this study was to monitor changes in values of the maximum efficiency of photosystem II (Fv/Fm) parameter and its corresponding standard deviations during increasing water deficit in barley measured in 25 replications and conducted in three independent pot experiments. After ten days of growing, drought stress was induced by withholding water and monitored for the next ten days. During the 10-days interval, Fv/Fm values decreased from 0.80 to 0.48, 0.53 and 0.54 in three experiments, respectively. However, standard deviations of Fv/Fm values increased successively being from 0.005 on the day 1 to 0.18, 0.19 and 0.26 on the day 10 in the respective three experiments. The consistent sharp increase of the corresponding standard deviation of about 0.02 occurred at the Fv/Fm value of 0.75 indicating considerable increasing of photosynthetic heterogeneity. Therefore, we propose a threshold Fv/Fm level of 0.75 that would reflect a point at which the spatio-temporal heterogeneity of Fv/Fm should be considered since it represents a boundary value for fully functional photosystem II. In our studies in the field environments in maize though, we found that even under moderate drought stress, Fv/Fm values were rarely lower than 0.75 with small standard deviations corroborating the use of classical ChlF parameters.

Drought tolerance is one of the most studied features considering the global problem of water deficit. Here we investigated recovery of dehydrated and poorly viable barley seedlings upon re‐watering. Barley seedlings (Hordeum vulgare L. cv. Bravo) were cultivated in the growth chamber (16 h day, ~65 μmol m‐2 s‐1, 22±1 oC ; 8 h night, 19 oC) for ten days and then subjected to drought induced by withholding water. After 8 days, when leaf relative water content (RWC) was about 20% seedlings were watered daily with the same amount of water as controls. For all measurements, first fully developed leaves were sampled before stress (0th day), 8th day of drought and every 24 h during rehydration period of four days. Increased performance index (PIABS), the parameter of chlorophyll a fluorescence called index vitality, and immunodetection of Rubisco LSU revealed efficient photosynthetic apparatus after re‐watering period. Increasing of RWC, decreasing the lipid peroxidation level, and degradation of accumulated proline indicated high tendency for the establishment of homeostasis previously disrupted by drought. We can conclude that despite the low RWC and downregulated photosynthesis under severe drought, seedlings were able to recover their overall photosynthetic efficiency (PIABS) at the end of rehydration period. Obtained results might be helpful to barley breeders during selection of cultivars in order to create a new generation of genotypes better adapted to water deficit.

Photoinhibitory implications in photosynthetic apparatus of two developmental stages of Norway spruce (Picea abies L. Karst.) needles, current-year (CY, three months old) and previous-year (PY, one year older), were investigated. Chlorophyll a fluorescence of young (CY) and mature (PY) needles, collected early in the morning, was measured after acclimatization to the room temperature and after the stress treatment (HL, ~850 μmolm-2s-1 ; 291 0C ; 1 hour) conducted in growth chamber. The maximum quantum yield of photosystem II (PSII), Fv/Fm, measured before stress application showed fully functional PSII in both CY and PY needles. Increased performance index on absorption basis (PIABS) in PY revealed their higher overall photosynthetic efficiency. Light stress (HL) slightly decreased Fv/Fm in both, CY and PY needles, but remained high above limited value for PSII functionality (Fv/Fm>0.75). Specific fluxes per active reaction center (RC) including absorption (ABS/RC) and trapping of excitation energy (TR0/RC), electron transport (ET0/RC) and dissipation of excessive absorbed energy (DI0/RC) were also analyzed. CY needles had decreased PIABS and ET0/RC after stress treatment. Other fluxes per RC showed significantly higher values in CY, if compared with PY needles. In conclusion, we can highlight better acclimation response of mature needles under photoinhibitory light. In spite of the same primary photochemistry, young needles were strongly affected by light stress what was related to inhibited electron transport in thylakoid membranes.