Chlorophyll fluorescence in the resurrection plant Selaginella lepidophylla (Hook. & Grev.) Spring during high-light and desiccation stress,and evidence for zeaxanthin-associated photoprotection

The function of photosystem (PS)II during desiccation and exposure to high photon flux density (PFD) was investigated via analysis of chlorophyll fluorescence in the desert resurrection plant Selaginella lepidophylla (Hook. and Grev.) Spring. Exposure of hydrated, physiologically competent stems to 2000 mol · m^–2 · s^–1 PFD caused significant reductions in both intrinsic fluorescence yield (F_O) and photochemical efficiency of PSII (F_V/F_M) but recovery to pre-exposure values was rapid under low PFD. Desiccation under low PFD also affected fluorescence characteristics. Both F_V/F_M and photochemical fluorescence quenching remained high until about 40% relative water content and both then decreased rapidly as plants approached 0% relative water content. In contrast, the maximum fluorescence yield (F_M) decreased and non-photochemical fluorescence quenching increased early during desiccation. In plants dried at high PFD, the decrease in F_V/F_M was accentuated and F_O was reduced, however, fluorescence characteristics returned to near pre-exposure values after 24-h of rehydration and recovery at low PFD. Pretreatment of stems with dithiothreitol, an inhibitor of zeaxanthin synthesis, accelerated the decline in F_V/F_M and significantly increased F_O relative to controls at 925 mol · m^–2 · s^–1 PFD, and the differences persisted over a 3-h low-PFD recovery period. Pretreatment with dithiothreitol also significantly decreased non-photochemical fluorescence quenching, increased the reduction state of Q_A, the primary electron acceptor of PSII, and prevented the synthesis of zeaxanthin relative to controls when stems were exposed to PFDs in excess of 250 mol · m^–2 · s^–1. These results indicate that a zeaxanthin-associated mechanism of photoprotection exists in this desert pteridophyte that may help to prevent photoinhibitory damage in the fully hydrated state and which may play an additional role in protecting PSII as thylakoid membranes undergo water loss.Abbreviations and Symbols DTT dithiothreitol - EPS epoxidation state - F_O yield of instantaneous fluorescence at open PSII centers - F_M maximum yield of fluorescence at closed PSII centers induced by saturating light - F_M F_M determined during actinic illumination - F_V yield of variable fluorescence (F_M-F_O) - F_V/F_M photochemical efficiency of PSII - q_P photochemical fluorescence quenching - q_NP non-photochemical fluorescence quenching of Schreiber et al. (1986) - NPQ non-photochemical fluorescence quenching from the Stern-Volmer equation - PFD photon flux density - RWC relative water content This paper is based on research done while W.G.E. was on leave of absence at Duke University during the fall of 1990. We would like to thank Dan Yakir, John Skillman, Steve Grace, and Suchandra Balachandran and many others at Duke University for their help and input with this research. Dr. Barbara Demmig-Adams provided zeaxanthin for standard-curve purposes.     

Conservation of Cell Order in Desiccated Mesophyll of Selaginella lepidophylla ([Hook and Grev.] Spring)

Understanding of the basis of desiccation tolerance in matureplant tissues that survive extreme dehydration requires knowledgeof the degree of cellular order in the dry state. Generally,aqueous fixatives have been used in ultrastructural studiesof such material, and these are known to be inadequate in thepreservation of dry material. Cryopreservation provides a moreassured level of fixation fidelity than aqueous fixatives, particularlywith dry material. Using freeze substitution and electron microscopy,we examined the ultrastructure of dry mesophyll cells ofSelaginellalepidophylla ([Hook and Grev.] Spring). In this material thecells were condensed and had highly folded walls. The plasmalemmawas bounded on both sides by layers of granular material, andthe membrane was in close and continuous apposition to the walls.The conformation and position of organelles and their structureappeared to be influenced by being compacted within the shrunkencells, but the ultrastructural integrity of all organelles andcellular membranes, including mitochondria, chloroplasts andvacuoles, was maintained in the dry state. These cells had numeroussmall vacuoles clustered in aggregates, and the tonoplast membranesappeared to be coated on the internal side by a fine granularlayer. The vacuoles contained osmiophilic material of varyingdegrees of condensation and had embedment holes suggesting thepresence of salt crystals within the vacuoles. The general conclusionsfrom these studies are that a critical level of cell order ismaintained in the dry state in these desiccation-tolerant plants,and a high degree of effective packing and shape fitting ofcellular constituents with the compaction forces of dehydrationunderlies this conservation of cell order. Freeze substitution; Selaginella lepidophylla ([Hook and Grev.] Spring); ultrastructure; membrane structure; desiccation tolerance; resurrection plants     

Protein Synthesis and Photosynthetic Recovery in the Resurrection Plant, Selaginella lepidophylla

The effects of inhibition of protein synthesis on whole-plant CO(2) exchange and on protein synthesis during hydration of the resurrection plant Selaginella lepidophylla (Hook and Grev.) were examined. Both chloramphenicol and cycloheximide inhibited the redevelopment of photosynthetic capacity which normally occurs within 24 hours of hydration in the light. The inhibitory effect of chloramphenicol was greater than that of cycloheximide. The onset of chloramphenicol inhibition of net photosynthesis occurred only after 12 hours of hydration. Cycloheximide stimulated net CO(2) influx early after rehydration and inhibited net CO(2) influx after 14 hours of hydration. Total protein synthesis, as measured by l-[(35)S]methionine incorporation, increased through 24 hours of hydration. Based upon the results obtained with the protein synthesis inhibitors, most protein synthesis within the first 12 hours of hydration was cytoplasm-directed, whereas the rate of organelle-directed protein synthesis remained low until 12 hours of hydration and increased rapidly thereafter. These data suggest that both organelle- and cytoplasm-directed protein synthesis are necessary for full photosynthetic recovery during rehydration of S. lepidophylla.     

Chlorophyll Fluorescence during Drying and Rehydration in the Mosses Rhytidiadelphus loreus (Hedw.) Warnst.,Anomodon viticulosus (Hedw.) Hook. & Tayl. and Grimmia pulvinata (Hedw.) Sm.

Chlorophyll-fluorescence parameters of three mosses, Rhytidiadelphusloreus (Hedw.) Warnst.,Anomodon viticulosus (Hedw.) Hook &Tayl. and Grimmia pulvinata (Hedw.) Sm. were measured duringdrying, and following remoistening after a period of desiccation.Most changed little with drying until the full-turgor pointwas approached, when rapid changes accompanied loss of cellwater. In R. loreus all parameters decreased together down toa water content of about 30% d.wt (RWC approx. 0.15). At lowwater contents (5–16% d.wt; RWC approx. 0.02–0.08)saturating pulses tended to suppress rather than stimulate fluorescence.In A. viticulosus F_v/F_m, q_Pand     

Dynamics of Endogenous Phytohormones during Desiccation and Recovery of the Resurrection Plant Species Haberlea rhodopensis

Drought is one of the most significant threats to world agriculture and hampers the supply of food and energy. The mechanisms of drought responses can be studied using resurrection plants that are able to survive extreme dehydration. As plant hormones function in an intensive cross-talk, playing important regulatory roles in the perception and response to unfavorable environments, the dynamics of phytohormones was followed in the resurrection plant Haberlea rhodopensis Friv. during desiccation and subsequent recovery. Analysis of both leaves and roots revealed that jasmonic acid, along with and even earlier than abscisic acid, serves as a signal triggering the response of the resurrection plants to desiccation. The steady high levels of salicylic acid could be considered an integral part of the specific set of parameters that prime H. rhodopensis desiccation tolerance. The dynamic changes of cytokinins and auxins suggest that these hormones actively participate in the dehydration response and development of desiccation tolerance in the resurrection plants. Our data contribute to the elucidation of a global complex picture of the resurrection plant’s ability to withstand desiccation, which might be successfully utilized in crop improvement.     

Relationships among membranes in plastids of the red algaNitophyllum punctatum (Stackh.) Grev.

Summary The fine structure of plastids in the early stages of differentiation has been studied during the carposporogenesis of the red algaNitophyllum punctatum (Stackh.) Grev. A membranous body has been found in the plastidial matrix, which shows connections either with thylakoids, or with the plastidial genophore. More than one membranous body may be present and in some instances they show a morphological relationship also with the plastidial limiting membranes. The presence of such bodies has been observed also in fully differentiated plastids in a number of other red algae currently under study.It has been shown that the plastidial envelope may release in the matrix vesicles that give rise to the single thylakoids typical of the red algal plastids.The research project received the financial support of Ministero della Pubblica Istruzione (Roma).     

Karyotype Analysis of Speirantha gardenii (Hook.) Baill.

This paper reports the chromosome numbers and karyotype analysis of Speirantha gardenii, which is endemic to China. The material was collected from Huang Shan, Anhui. It is a diploid species. Its somatic chromosome is 2n=38=22m+6sm+10st. The 9th pair is submedian centromere chromosomes, but it has two constrictions. The secondary constriction is on the short arm near centromere. Of the 19 chromosome pairs,secondary constriction is present only in this pair.     

高斑叶兰的组织培养

1植物名称高斑叶兰[Goodyera procera(Ker- Gaw1.)Hook.]。2材料类别茎段。3培养条件(1)芽诱导培养基:MS 6-BA 0.5 mg·L~(-1)(单位下同) NAA 0.05;(2)增殖培养基:1/ 2 MS 6-BA 2.0 NAA 0.2 100 g·L~(-1)椰汁:(3)生根培养基:1/2Ms IBA 1.0 NAA 0.5 0.5 g·L~(-1)活性     

卷柏总蛋白质提取方法及双向电泳条件的建立

目的:建立复苏植物——卷柏总蛋白质的提取方法,以及可以对其蛋白质组进行阵列分离的双向电泳条件。方法:通过多种条件的组合与优化,建立了以物理和化学2种方法充分裂解植物组织细胞,并采用低温操作、加入PVP等去除植物组织中大量的酚类物质,最后离心去除不溶性杂质的卷柏蛋白质组双向电泳(2-DE)样品制备方法。第1向电泳为固相pH梯度等电聚焦,第2向电泳为垂直平板SDS-PAGE。结果:通过对样品制备、蛋白定量、第1向和第2向电泳、染色方法等各实验环节进行控制和优化,凝胶经考马斯亮蓝染色后,可分辨蛋白质斑点数约600个。结论:建立了卷柏总蛋白质的提取方法及蛋白质组双向电泳技术,为后续研究卷柏在干旱胁迫下的差异表达奠定了基础。     

一株阿尔泰虫草内生菌的分离及抑菌活性

目的:从采自阿尔泰山脉的虫[ Ophiocordyceps gracilis( Grev.)G.H Sung,J.M.Sung,Hywel- Jones&Spatafora]体内分离出1株出现频率较高的真菌(命名为SFY00C3)进行了研究.方法:经形态学和ITS序列分析鉴定,对SFY00C3菌株及其发酵液采用滤纸片法,同时对6种供试菌株不同程度进行了抑制作用的研究.结果:SFY00C3菌株为青霉属(Penicillium)真菌变灰青霉(Penicillium canescens);对大肠杆菌和金黄色葡萄球菌的抑制作用较强,抑菌圈均大于10 mm.结论:虫草内生菌变灰青霉的抑菌活性成分值得进一步研究,为研究新的天然产物抑菌药物提供思路.     

Chemical and physical-chemical characteristics of dietary fibres from Ulva lactuca (L.) Thuret and Enteromorpha compressa (L.) Grev.

Dietary fibres from Ulva lactuca (L.) Thuret (sea lettuce) and Enteromorpha compressa (L.) Grev. (A.O. nori) were measured according to a ‘standard’ method and a ‘physiological’ protocol simulating the gastric and intestinal environments. U. lactuca contained 15.8–8.0% soluble and 24.2–32.6% insoluble fibres according to the ‘standard’ and ‘physiological’ methods, respectively. For E. compressa, these values were 14.9–15.9 and 21.6–28.7%, respectively. For both algae, the composition suggests that the soluble fibres were xylorhamnoglycuronans sulphates and insoluble fibres were essentially composed of glucans. No marked chemical compositional variation was observed between soluble fractions extracted under the simulated gastric and intestinal conditions. Fibres in both algae are hydrophilic but the water holding capacities were higher after extraction of soluble fibres (5.5–9.5 g g⁻¹ for the dry algae; 14.0–16.0 g g⁻¹ for the standard insoluble fibres). Water soluble fibres demonstrated low intrinsic viscosities at 37 °C in buffers, particularly those from E. compressa (36.0–36.5 ml g⁻¹), and was affected by pH for those of U. lactuca (147.5 ml g⁻¹ at pH 3.0 and 175.0 ml g⁻¹ at pH 7.3).