Biljana Filipović

Hairy root exudates of allelopathic weed Chenopodium murale L. induce oxidative stress and down-regulate core cell cycle genes in Arabidopsis and wheat seedlings

The effects of Chenopodium murale root exudates, applied as phytotoxic medias (PMs), were tested on Arabidopsis thaliana and Triticum aestivum. The effects of PMs, where wild-type roots (K), hairy roots derived from roots (R clones) or from cotyledons (C clones) were cultured, were different. K medium suppressed Arabidopsis germination, while other PMs reduced root and leaf elongation and the number of rosette leaves. R media were more phytotoxic than C media. Treatment of Arabidopsis with R8 down-regulated expression of core cell cycle genes: cyclin-dependent kinase (CDK) A1;1, four B-class CDKs, and cyclins CYCA3;1, CYCB2;4, CYCD4;2 and CYCH1 in root and shoot tips. Only CYCD2;1 transcript was elevated in treated shoots, but down-regulated in roots. Wheat Ta-CDC2 and Ta-CYCD2 genes showed the same expression profiles as their Arabidopsis counterparts, CDKA1;1 and CYCD2;1. PMs also caused increase of antioxidative enzyme activities in both plants. Exposure of Arabidopsis to PMs induced one catalase isoform, but repressed another, resulting in no net change of catalase activity. Wheat seedlings treated with PMs had catalase activity significantly elevated in all treatments, particularly in shoots. In both plants, PMs induced the activity of different peroxidase isozymes and total peroxidase activity. Both plants responded to phytotoxic treatments by induction of CuZn-superoxide dismutase. Thus, the phytotoxicity of C. murale root exudates is, at least partially, based on down-regulation of the cell cycle regulators and on generation of oxidative stress in the affected plants. We propose that C. murale root exudates should be considered as means of biological weed control.

Plant regeneration in leaf culture of Centaurium erythraea Rafn. Part 1: The role of antioxidant enzymes

Centaurium erythraea Rafn. is a medicinal plant rich in secoiridoids and xanthones and used for gastrointestinal disorders, fever, anemia and many other conditions. C. erythraea is characterized with extraordinary developmental plasticity and manageability in vitro; thus we propose it as an excellent experimental model system for studies in developmental biology. Hereby we describe regeneration of centaury from leaf explants that can proceed via somatic embryogenesis or organogenesis on inductive media containing 2,4-D and CPPU. In the absence of growth regulators, shoots and roots appeared without callusing, on light or in darkness, respectively. Indirect somatic embryogenesis was induced in the presence of growth regulators occurring both on light and in darkness. Light was obligatory for indirect shoot development, where adventitious buds formed simultaneously with somatic embryos. Dynamic changes of antioxidative activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POX) in response to morphogenetic changes were followed during developmental pathways in vitro. Wounding of centaury leaves immediately induced all SOD and CAT isoforms but caused a decrease in POX activity. In control leaves and leaf explants, three Cu/Zn-SOD activities were detected, which gradually decreased on inductive treatments on light, but remained unchanged during growth in darkness. Morphogenetic paths on all hormonal and light treatments where characterized with dynamic changes of CAT activity (comprised of three major CAT isoforms), but generally CAT was reduced during morphogenesis induction. POX activity was strongly induced during morphogenesis in all treatments.

ECOPHYSIOLOGICAL AND ANATOMICAL CHARACTERISTICS OF THE SUBTROPICAL SHRUB ZANTHOXYLUM ACANTHOPODIUM (RUTACEAE) IN CONDITIONS OF A TEMPERATE CONTINENTAL CLIMATE (SERBIA)

The evergreen shrub Zanthoxylum acanthopodium DC. (Rutaceae), originating from warm temperate and subtropical Asia, has existed successfully in the Jevremovac Botanical Garden in Belgrade for more than 80 years. The seasonal pattern of water management in leaves, electrolyte leakage, essential oil composition, and leaf anatomy were examined in order to understand the resistance and viability of this subtropical shrub in the temperate continental cli- mate of Belgrade, Serbia.

Organ-specific and genotype-dependent constitutive biosynthesis of secoiridoid glucosides in Centaurium erythraea Rafn, and its elicitation with methyl jasmonate

While bioactive properties of Centaurium erythraea Rafn secoiridoid glucosides (SG) are widely recognized, many aspects related to their biochemistry, metabolism and relationship to the overall plant physiology are not yet understood. Here we present for the first time an insight into the molecular background of organ-specific and genotype-dependent constitutive biosynthesis of secoiridoids in C. erythraea, by comparing chemical profiles and secoiridoid glucosides-related gene expression. Genes encoding enzymes for intermediate steps of secoiridoids biosynthesis up to secologanin have been identified by analysing transcriptomic data from C. erythraea leaves. Results suggest an organ-specific capacity for the production and accumulation of secoiridoid glucosides, and highlight leaves as the main biosynthesis site. They also point out that significant differences in SG content among various C. erythraea genotypes, are, at least partially, determined by different expression patterns of SG-related genes. The biosynthesis of SG in C. erythraea leaves is enhanced upon treatments with methyl jasmonate (MeJA), which causes reprogramming of SG-related gene expression, leading to an increased production of valuable bioactive compounds. The present study unveiled several rate-limiting genes (encoding GES, G8O, 8HGO, IS and 7DLGT) in SG biosynthesis. SLS and CPR are highlighted as important genes/enzymes that might regulate biosynthetic flux through SG pathway. Information gathered within this study will help us gain deeper insight into the SG metabolism and develop strategies for enhanced biosynthesis of specific secoiridoid glucosides in homologous or heterologous systems.