Acquisition of desiccation tolerance by isolated maize embryos exposed to different conditions: the questionable role of endogenous abscisic acid

The effect of exogenous ABA on acquisition of desiccation tolerance has been well documented for the embryos of several species. including maize ( Zea mays L.). It has also been suggested that endogenous ABA plays a role in regulating the same phenomena. To test this hypothesis, endogenous ABA was quantified by radioimmunoassay. Our results show that: (1) during embryogenesis in maize, endogenous ABA increase-concomitantly with the acquisition of desiccation tolerance: (2) ABA deficient embryos of the vp 5 mutant are desiccation intolerant, but tolerance can he induced by exogenous ABA: and (3) desiccation tolerance is acquired if desiccation sensitive embryos undergo a slow drying treatment, during which ABA increases. However, when embryos were preincubated in fluridone to prevent ABA accumulation during slow drying, desiccation tolerance was induced in spite of the low level of endogenous ABA in the embryo. Our results cast doubts on an exclusive role of ABA in the acquisition of desiccation tolerance in maize embryo.     

Natural dibenzoxazepinones from leaves of Carex distachya: Structural elucidation and radical scavenging activity

Two new dibenzoxazepinones have been isolated from the leaves of Carex distachya, an herbaceous plant growing in the Mediterranean area. The structures have been elucidated on the basis of their spectroscopic properties. Bidimensional NMR (DQ-COSY, TOCSY, NOESY, ROESY, HSQC, and HMBC) furnished important data useful for the characterization of the molecules. The compounds have been assayed, for the antioxidant activity, by measuring its capacity to scavenge the DPPH, the superoxide anion, and nitric oxide radicals.     

Natural feruloyl monoglyceride macrocycles as protecting factors against free-radical damage of lipidic membranes

Nine novel natural feruloyl monoglyceride (MGs) macrocycles have been isolated from the leaves of Carex distachya, an herbaceous plant growing in the Mediterranean maquis. All the structures have been elucidated on the basis of their spectroscopic features, especially two-dimensional NMR (DQ-COSY, TOCSY, NOESY, ROESY, HSQC, HMBC, HSQC-TOCSY) and ESI-MS. All the compounds have been assayed as protecting factors against the radical damage of the lipids by using different antioxidant tests.     

Structural characterization of phytotoxic terpenoids from Cestrum parqui

Isolation, chemical characterization and phytotoxicity of nine polyhydroxylated terpenes (five C13nor-isoprenoids, two sesquiterpenes, a spirostane and a pseudosapogenin) from Cestrum parqui L'Herr are reported. In this work we completed the phytochemical investigation of the terpenic fraction of the plant and described the structural elucidation of polar isoprenoids using NMR methods. All the configurations of the compounds have been assigned by NOESY experiments. Four new structures have been identified as (3S,5R,6R,7E,9R)-5,6,9-trihydroxy-3-isopropyloxy-7-megastigmene, 5alpha-spirostan-3beta,12beta,15alpha-triol, and 26-O-(3'-isopentanoyl)-beta-d-glucopyranosyl-5alpha-furost-20(22)-ene-3beta,26-diol, and as an unusual tricyclic sesquiterpene. The compounds have been assayed for their phytotoxicity on lettuce at the concentrations ranging between 10(-4) and 10(-7)M. The activities of some compounds were similar to that of the herbicide pendimethalin.     

Radical-scavenging activities of new hydroxylated ursane triterpenes from cv. Annurca apples

Two new ursolic acid triterpene derivatives, compounds 2 and 3, have been isolated from cv. Annurca apple fruit, a high-quality apple variety widely cultivated in southern Italy, together with the known 2-oxopomolic acid (1). The new compounds were identified by means of different spectroscopic techniques as 3-epi-2-oxopomolic acid (= (3alpha)-3,19-dihydroxy-2-oxours-12-en-28-oic acid; 2) and (1alpha)-1-hydroxy-3-oxours-12-en-28-oic acid (3). Compounds 1-3 were tested for their radical-scavenging activities with the aid of a 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay (Fig. 2). All three constituents showed activities similar to that of the reference antioxidant alpha-tocopherol (vitamin E).     

Structures of bioactive carexanes from the roots of Carex distachya Desf

Four metabolites, named carexanes I-L, have been isolated from the roots of Carex distachya Desf, an herbaceous plant living in the Mediterranean maquis, together with three known compounds, already isolated from the aerial part of the plant. All the compounds have been characterized on the basis of their spectroscopic properties. Carexane I derived from the lose of a proton from the C-18 carbon of an intermediate isopropyl cation. Its stereostructure has been elucidated by Mosher's method, NOESY/ROESY experiments and computational calculations. The bioactivity on seed germination and root/shoot growth of Lactuca sativa L. of all the isolated compounds is also reported.     

Characterization of two chemotypes of <Emphasis Type="Italic">Pinus pinaster</Emphasis> by their terpene and acid patterns in needles

The existence of two chemotypes of Pinus pinaster, on the basis of the chemical composition of the resin acids in their needles, is known. An investigation was performed on 54 samples of needles of Spanish Pinus pinaster to study the differences between these chemotypes on the basis of monoterpene, sesquiterpene, neutral diterpene, fatty acid, and resin acid composition. One-hundred and twelve compounds were identified by GC–FID and GC–MS. Statistical analysis of the results established the existence of two groups or chemotypes, in the ratio of 5:1. In one chemotype, total acid compounds were more abundant than neutral compounds, whereas in the other the concentrations of both neutral and acid compounds were similar. Distinction of the chemotypes was based on the presence/absence of a sesquiterpene (germacrene d-4-ol acetate), neutral diterpenes (8(14),13(15)-abietadiene, anticopalol, an isomer of anticopalol, and pimarol), fatty acids (10-octadecenoic, 14-hydroxy-10-octadecenoic, and 13-hydroxy-9-octadenoic acids and an unidentified fatty acid), and resin acids (levopimaric + palustric, eperuic, and anticopalic acids, and three isomers of anticopalic acid); and on the different relative percentages of other compounds of these types. This study gives a wide view of the composition of the needles of Pinus pinaster, improving the differentiation of chemotypes on the basis of terpene and acid composition.     

Changes in leaf hexokinase activity and metabolite levels in response to drying in the desiccation-tolerant species Sporobolus stapfianus and Xerophyta viscosa.

The phosphorylation of glucose and fructose is an important step in regulating the supply of hexose sugars for biosynthesis and metabolism. Changes in leaf hexokinase (EC 2.7.1.1) activity and in vivo metabolite levels were examined during drying in desiccation-tolerant Sporobolus stapfianus and Xerophyta viscosa. Leaf hexokinase activity was significantly induced from 85% to 29% relative water content (RWC) in S. stapfianus and from 89% to 55% RWC in X. viscosa. The increase in hexokinase corresponded to the region of sucrose accumulation in both species, with the highest activity levels coinciding with region of net glucose and fructose removal. The decline of hexose sugars and accumulation of sucrose in both plant species was not associated with a decline in acid and neutral invertase. The increase in hexokinase activity may be important to ensure that the phosphorylation and incorporation of glucose and fructose into metabolism exceeded production from potential hydrolytic activity. Total cellular glucose-6-phosphate (Glc-6-P) and fructose-6-phosphate (Fru-6-P) levels were held constant throughout dehydration. In contrast to hexokinase, fructokinase activity was unchanged during dehydration. Hexokinase activity was not fully induced in leaves of S. stapfianus dried detached from the plant, suggesting that the increase in hexokinase may be associated with the acquisition of desiccation-tolerance.