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排序方式: 共有485条查询结果,搜索用时 31 毫秒
81.
82.
83.
Sharon A. Robinson Catherine E. Lovelock C. B. Osmond 《Plant biology (Stuttgart, Germany)》1993,106(4):307-312
The leaves of the Crassulacean acid metabolism plant Cotyledon orbiculata have a waxy coating which is highly reflective but can be easily removed by brushing. This provided an ideal system in which to investigate the role of epidermal wax as a possible photoprotectant. Removal of the wax, prior to exposure to natural sunlight, resulted in substantial decreases in Fv/Fm and in severe cases evidence of photoinhibitory damage, as indicated by a rise in Fo. Leaves from which wax had been removed also showed higher conversion of violaxanthin to zeaxanthin than waxed leaves. Recovery of brushed leaves over a 12 day period was correlated with an increase in the total pool of xanthophyll cycle components. This study suggests that the presence of highly reflective wax on the epidermis may confer significant photoprotection to plants exposed to high solar radiation environments. 相似文献
84.
Sj?gren-Larsson syndrome (SLS) is an inherited neurocutaneous disorder characterized by ichthyosis, mental retardation, spasticity, and deficient activity of fatty aldehyde dehydrogenase (FALDH). FALDH is an enzyme component of fatty alcohol:NAD oxidoreductase (FAO), which is necessary for fatty alcohol metabolism. To better understand the biochemical basis for the cutaneous symptoms in this disease, we investigated lipid metabolism in cultured keratinocytes from SLS patients. Enzyme activities of FALDH and FAO in SLS cells were <10% of normal. SLS keratinocytes accumulated 45-fold more fatty alcohol (hexadecanol, octadecanol, and octadecenol) than normal, whereas wax esters and 1-O-alkyl-2,3-diacylglycerols were increased by 5.6-fold and 7.5-fold, respectively. SLS keratinocytes showed a reduced incorporation of radioactive octadecanol into fatty acid (24% of normal) and triglyceride (13% of normal), but incorporation into wax esters and 1-O-alkyl-2,3-diacylglycerol was increased by 2.5-fold and 2.8-fold, respectively. Our results indicate that FALDH deficiency in SLS keratinocytes causes the accumulation and diversion of fatty alcohol into alternative biosynthetic pathways. The striking lipid abnormalities in cultured SLS keratinocytes are distinct from those seen in fibroblasts and may be related to the stratum corneum dysfunction and ichthyosis in SLS. 相似文献
85.
The outermost layer of the skin, the stratum corneum (SC), comprises the main barrier function between body and environment. The SC features a highly structured lipid organization: a short periodicity phase and a long periodicity phase (LPP) with a repeat distance of 6 and 13 nm, respectively. Like SC, vernix caseosa (VC), the creamy white skin-surface biofilm of the newborn, also contains barrier lipids, i.e. ceramides, cholesterol and free fatty acids. Aim of this study was to investigate whether isolated VC lipids also form the characteristic LPP. Several preparation methods were examined and only when the solution of the lipid mixture, isolated either from VC or SC, was dried under nitrogen at 37 °C and subsequently spread onto a support, the LPP was formed. When VC barrier lipids were first exposed to elevated temperatures and subsequently cooled down, the LPP was formed at around 34 °C, which is at a much lower temperature than observed with the lipids in SC. In conclusion, we showed for the first time that depending on the preparation method, (i) VC lipids also form the LPP and (ii) the LPP in VC lipids and SC lipids was obtained at a low equilibration temperature, mimicking the physiological condition. 相似文献
86.
Lee SH Ahn SJ Im YJ Cho K Chung GC Cho BH Han O 《Biochemical and biophysical research communications》2005,330(4):1194-1198
Previous studies show that low temperature strongly induces suberin layers in the roots of chilling-sensitive cucumber plants, while in contrast, low temperature produces a much weaker induction of suberin layers in the roots of the chilling-tolerant figleaf gourd [S.H. Lee, G.C. Chung, S. Steudle, Gating of aquaporins by low temperature in roots of chilling-sensitive cucumber and -tolerant figleaf gourd, J. Exp. Bot. 56 (2005) 985-995; S.H. Lee, G.C. Chung, E. Steudle, Low temperature and mechanical stresses differently gate aquaporins of root cortical cells of chilling-sensitive cucumber and figleaf gourd, Plant Cell Environ. (2005) in press; S.J. Ahn, Y.J. Im, G.C. Chung, B.H. Cho, S.R. Suh, Physiological responses of grafted-cucumber leaves and rootstock roots affected by low root temperature, Scientia Hort. 81 (1999) 397-408]. Here, the effect of low temperature on fatty acid unsaturation and lipoxygenase activity was examined in cucumber and figleaf gourd. The double bond index demonstrated that membrane lipid unsaturation shows hyperbolic saturation curve in figleaf gourd roots while a biphasic response in cucumber roots to low temperature. In figleaf gourd, the hyperbolic response in the double bond index was primarily due to accumulation of linolenic acid. Chilling stress also significantly induced lipoxygenase activity in figleaf gourd roots. These results suggest that the degree of unsaturation of root plasma membrane lipids correlates positively with chilling-tolerance. Therefore, studies that compare the effects of chilling on cucumber and figleaf gourd may provide broad insight into stress response mechanisms in chilling-sensitive and chilling-tolerant plants. Furthermore, these studies may provide important information regarding the relationship between lipid unsaturation and lipoxygenase function/activity, and between lipoxygenase activity and water channeling during the response to chilling stress. The possible roles of these processes in chilling tolerance are discussed. 相似文献
87.
Peter J. Holloway 《Phytochemistry》1974,13(10):2201-2207
The cuticular wax and cutin components of the cuticular membranes isolated from the leaves of two spinach cultivars have been determined. The membranes contain about 0·007 mg/cm2 of cuticular wax which comprises monobasic acids (C16–C38) with hexadecanoic as the major component. The amounts of cutin are comparable with those of cuticular wax and the monomeric constituents are predominantly C18 epoxy compounds. The most abundant monomer is 9,10-epoxy-18-hydroxyoctadecanoic acid (up to 63%) together with substantial amounts of 9,10,18-trihydroxyoctadecanoic acid (up to 22%). Also present are 9,10-epoxyoctadecane-1,18-dioic acid (6–7%) dihydroxyhexadecanoic acid (3–4%) and ω-hydroxymonobasic and fatty acid fractions. The tentative identification of two minor components, 18-hydroxyoxooctadecanoic and 9,10-epoxy-12,18-dihydroxyoctadecanoic acids, is also made. Although spinach membranes have a delicate structure their cutin composition is essentially similar to that of much more substantial membranes. 相似文献
88.
M.J.K. Macey 《Phytochemistry》1974,13(8):1353-1358
Two different mutations in Brassica oleracea, gl5 and gl4 have been re-investigated using acetate-1-14C labelling in an attempt to define more closely the nature of the genetic blocks to wax synthesis. It has been found that gl5 is a mutation which blocks elongation in the Step C28–C30. The mutation gl4 exhibits no elongation block and could be blocked in the decarboxylation Step C30–C29. 0·1 mM TCA supplied in the culture solution of cauliflower seedlings affected the leaf surface by producing a glossy appearance similar to that induced by gl3 and gl4. At this concentration growth was not inhibited and the appearance of the plants was normal except for the surface wax. The amount of surface wax produced was about 40% of that in untreated seedlings on a leaf area basis. Slight, but significant changes in wax composition were noted, mainly involving a reduction in C30 acids and aldehydes, a slight reduction (33–29%) in alkane content, and a marked difference in chain length composition of the alkanes with C27 increased relative to C29. Over a range of concentrations from 0·1–1 mM, TCA inhibited incorporation of label from acetate-1-14C into C30 acids and aldehydes more than into C28 at concentrations 0·4–0·8 mM while label tended to accumulate in C24 and C26 acids; thus elongation C28–C30 was especially sensitive to TCA. TCA also inhibited incorporation into primary alcohols and esters almost as much as into C29 compounds. In spite of relatively specific effects on incorporation of label into longer chain lengths, the resulting block to C30 synthesis is not sufficient to make much difference to the overall rate of C29 synthesis. Both results of analysis of wax from whole plants and experiments with tissue slices in vitro indicated that the effect of TCA in reducing the glaucousness of the leaf surface is a combination of overall reduction of wax synthesis together with slight but significant changes in wax composition. 相似文献
89.
Kouichi Yamazaki Tsukasa Iwashina Junichi Kitajima Yasushige Gamou Akira Yoshida Takashi Tannowa 《Biochemical Systematics and Ecology》2007
External and internal flavonoids were isolated from 12 Uncarina taxa (Pedaliaceae), endemic to Madagascar. Four flavone aglycones, tricetin 7,3′,5′-trimethyl ether, tricetin 7,4′,5′-trimethyl ether, 5,3′-dihydroxy-6,7,4′,5′-tetramethoxyflavone and eupatorin were isolated from leaf wax of seven Uncarina taxa, Uncarina grandidieri, Uncarina decaryi, Uncarina abbreviata, Uncarina turicana, Uncarina platycarpa, Uncarina leandrii var. leandrii and Uncarina peltata, but not Uncarina stellulifera, Uncarina perrieri, Uncarina sakalava, Uncarina leptocarpa and U. leandrii var. rechbergeri. Furthermore, eight flavonoid glycosides were isolated from the leaves. Major glycosides were apigenin and luteolin 7-O-glucuronides and occurred in all the Uncarina taxa examined, except the absence of the former compound in U. peltata. Other glycosides were identified as hispidulin, jaceosidin, chrysoeriol and tricin 7-O-glucuronides, and luteolin 7,4′-di-O-glucuronide and a flavonol, isorhamnetin 3-O-diglucoside. From the results described above, methylated flavone aglycones and glucuronides were chemical characters of the leaves of Uncarina species, and also may be those of the family Pedaliaceae. Besides, an anthocyanin, two flavonols and three flavones were isolated from the flowers of U. grandidieri, and identified as cyanidin 3-O-rutinoside (anthocyanin), quercetin and isorhamnetin 7-O-glucuronides (flavonols) and apigenin, luteolin and jaceosidin 7-O-glucuronides (flavones). 相似文献
90.