On embedding curves in surfaces

summary:Contrary to a statement of Borsuk the author proves that every locally plane Peano continuum is embeddable into a 2-manifold

Disconnections of plane continua

summary:The paper deals with locally connected continua $X$ in the Euclidean plane. Theorem 1 asserts that there exists a simple closed curve in $X$ that separates two given points $x$, $y$ of $X$ if there is a subset $L$ of $X$ (a point or an arc) with this property. In Theorem 2 the two points $x$, $y$ are replaced by two closed and connected disjoint subsets $A$, $B$. Again -- under some additional preconditions -- the existence of a simple closed curve disconnecting $A$ and $B$ is stated

The chemical characteristic and distribution of brassinosteroids in plants

Brassinosteroids represent a class of plant hormones with high-growth promoting activity. They are found at low levels in pollen, anthers, seeds, leaves, stems, roots, flowers, grain, and young vegetative tissues throughout the plant kingdom. Brassinosteroids are a family of about 60 phytosteroids. The article gives a comprehensive survey on the hitherto known brassinosteroids isolated from plants. The chemical characteristic of brassinosteroids is also presented

Fitoremediacja - alternatywa na czyste środowisko

Postęp przemysłowy i cywilizacyjny, oprócz bezsprzecznych korzyści, niesie za sobą degradację środowiska. Obiecujące możliwości w procesach remediacji – usuwania różnego rodzaju zanieczyszczeń z atmosfery, gleby i wody daje zastosowanie roślin. W fitoremediacji wykorzystuje się naturalną zdolność wybranych gatunków roślin do wzrostu i rozwoju w ekosystemach skażonych substancjami organicznymi i nieorganicznymi, a także ich pobierania i detoksykacji. Naturalne fitoremediatory powinny charakteryzować się rozwiniętym systemem korzeniowym, szybkim wzrostem, dużą produkcją biomasy, tolerancją na skażenia oraz zdolnością akumulowania kilku zanieczyszczeń jednocześnie. Ze względu na sposób, w jaki rośliny wpływają na oczyszczanie skażonych ekosystemów, wyróżnia się główne techniki fitoremediacji: fitoekstrakcję, fitodegradację, fitostabilizację, fitoewaporację i ryzofiltrację. W rzeczywistości jednak mechanizmy usuwania czy detoksykacji zanieczyszczeń są bardziej złożone i często wynikają z połączenia różnego rodzaju metod. Fitoremediacja – jak każda metoda – posiada niewątpliwe zalety, jak również pewne ograniczenia, ale generalnie uważana jest za metodę przyjazną środowisku, tanią, mało inwazyjną i akceptowalną społecznie. Technika ta jest powszechnie postrzegana jako alternatywa dla ingerujących w środowisko metod fizyko-chemicznych, które mogą przyczyniać się do wtórnych zanieczyszczeń gleby, wody oraz powietrza. Fitoremediacja znajduje szerokie zastosowanie na zdegradowanych terenach poprzemysłowych, gdzie pomaga przywrócić je do takiego stanu, aby mogły być użytkowane jako obszary rekreacyjne lub mieszkalne.Wojewódzki Fundusz Ochrony Środowiska i Gospodarki Wodnej w Białymstok

Comprehensive Overview of the Brassinosteroid Biosynthesis Pathways: Substrates, Products, Inhibitors, and Connections

Brassinosteroids (BRs) as a class of steroid plant hormones participate in the regulation of numerous developmental processes, including root and shoot growth, vascular differentiation, fertility, flowering, and seed germination, as well as in responding to environmental stresses. During four decades of research, the BR biosynthetic pathways have been well studied with forward- and reverse genetics approaches. The free BRs contain 27, 28, and 29 carbons within their skeletal structure: (1): 5a-cholestane or 26- nor-24a-methyl-5a-cholestane for C27-BRs; (2) 24a-methyl-5a-cholestane, 24b-methyl- 5a-cholestane or 24-methylene-5a-cholestane for C28-BRs; (3) 24a-ethyl-5acholestane, 24(Z)-ethylidene-5a-cholestane, 25-methyl-5a-campestane or 24- methylene-25-methyl-5a-cholestane for C29-BRs, as well as different kinds and orientations of oxygenated functions in A- and B-ring. These alkyl substituents are also common structural features of sterols. BRs are derived from sterols carrying the same side chain. The C27-BRs without substituent at C-24 are biosynthesized from cholesterol. The C28-BRs carrying either an a-methyl, b-methyl, or methylene group are derived from campesterol, 24-epicampesterol or 24-methylenecholesterol, respectively. The C29-BRs with an a-ethyl group are produced from sitosterol. Furthermore, the C29 BRs carrying methylene at C-24 and an additional methyl group at C-25 are derived from 24- methylene-25-methylcholesterol. Generally, BRs are biosynthesized via cycloartenol and cycloartanol dependent pathways. Till now, more than 17 compounds were characterized as inhibitors of the BR biosynthesis. For nine of the inhibitors (e.g., brassinazole and YCZ-18) a specific target reaction within the BR biosynthetic pathway has been identified. Therefore, the review highlights comprehensively recent advances in our understanding of the BR biosynthesis, sterol precursors, and dependencies between the C27-C28 and C28-C29 pathways

Suppression of Chlorella vulgaris Growth by Cadmium, Lead, and Copper Stress and Its Restoration by Endogenous Brassinolide

Brassinosteroids play a significant role in the amelioration of various abiotic and biotic stresses. In order to elaborate their roles in plants subjected to heavy metals stress, Chlorella vulgaris cultures treated with 10−8 M brassinolide (BL) were exposed to 10−6–10−4 M heavy metals (cadmium, lead and copper) application. Under heavy metals stress, the growth and chemical composition (chlorophyll, monosaccharides, and protein content) have been decreased during the first 48 h of cultivation. The inhibitory effect of heavy metals on C. vulgaris cultures was arranged in the following order: copper > lead > cadmium. C. vulgaris cultures treated with BL in the absence or presence of heavy metals showed no differences in the endogenous level of BL. On the other hand, treatment with heavy metals results in BL level very similar to that of control cell cultures. These results suggest that the activation of brassinosteroids biosynthesis, via an increase of endogenous BL, is not essential for the growth and development of C. vulgaris cells in response to heavy metals stress. Simultaneously, BL enhanced the content of indole-3-acetic acid, zeatin, and abscisic acid in cultures treated with heavy metals. Levels per cell of chlorophylls, protein, and monosaccharides are all increased by BL treatment when compared to nontreated control cells. Application of BL to C. vulgaris cultures reduced the accumulation of heavy metals stress on growth, prevented chlorophyll, monosaccharides, and protein loss, and increased phytochelatins content. The arrested growth of C. vulgaris cells treated with heavy metals was restored by the coapplication of BL. It suggested that BL overcame the inhibitory effect of heavy metals. From these results, it can be concluded that BL plays the positive role in the alleviation of heavy metals stress