Light filtering by epidermal flavonoids during the resistant response of cotton to Xanthomonas protects leaf tissue from light-dependent phytoalexin toxicity

2,7-Dihydroxycadalene and lacinilene C, sesquiterpenoid phytoalexins that accumulate at infection sites during the hypersensitive resistant response of cotton foliage to Xanthomonas campestris pv. malvacearum, have light-dependent toxicity toward host cells, as well as toward the bacterial pathogen. Adaxial epidermal cells surrounding and sometimes covering infection sites turn red. The red cells exhibited 3-4-fold higher absorption at the photoactivating wavelengths of sunlight than nearby colorless epidermal cells. Red epidermal cells protected underlying palisade mesophyll cells from the toxic effects of 2,7-dihydroxycadalene plus sunlight, indicating a role for epidermal pigments in protecting living cells that surround infection sites from toxic effects of the plant’s own phytoalexins. A semi-quantitative survey of UV-absorbing substances extracted from epidermal strips from inoculated and mock-inoculated cotyledons indicated that the principal increase in capacity to absorb the photoactivating wavelengths was due to a red anthocyanin and a yellow flavonol, which were identified as cyanidin-3-O-β-glucoside and quercetin-3-O-β-glucoside, respectively.     

Effects of methyl jasmonate on phytoalexin production and aflatoxin control in the developing cotton boll

Artificially wounded 22–27-day old developing cotton bolls were initially inoculated with, (1) a cell-free, hot water-soluble mycelial extract (CFME) of an atoxigenic strain of Aspergillus flavus or with, (2) chitosan lactate (CHL) or with, (3) CFME or CHL and then exposed to gaseous methyl jasmonate (MJ) or, (4) exposed to MJ alone. Five days after these treatments, the induction of the sesquiterpenoid naphthol phytoalexins, 2,7-dihydroxycadalene (DHC) and 2-hydroxy-7-methoxy cadalene (HMC), lacinilene C, lacinilene C7-methyl ether, and the coumarin phytoalexin-scopoletin was determined on the excised carpel discs surrounding the inoculated surfaces of the developing cotton bolls. The results indicated a two- or three-fold increase in the production of the phytoalexins when gaseous MJ was added in combination to the CFME or the CHL elicitors. In a separate experiment, 22–27-day old developing cotton bolls were pretreated for a five-day period as described above and then a spore suspension of a toxigenic strain of A. flavus was introduced into a second artificial wound which was produced adjacent to the first wound. On boll maturity, the cottonseeds located within the locules underlying the areas that were pretreated with both elicitors and MJ then later infected with toxigenic A. flavus exhibited a 75–95% aflatoxin B₁ inhibition. These results suggest a host defense mechanism which may be triggered by both elicitors and MJ.     

A possible relationship between chitinozoa and tintinnids

The biological affinity of the extinct microfossil order chitinozoa has been the source of much discussion in the fifty years since they were first discovered. Within this period these flask-shaped, organic-walled organisms have been variously attributed to rhizopods, flagellates, tintinnids, chrysomonads, metazoan eggs, dinoflagellates, and fungi. Most of these suggested relationships were made before it was recognised that chitinozoans were encapsulated and must therefore be resting cysts or eggs and not active individuals.There are no living organisms which combine all the characteristics of the chitinozoa. Of all the possibilities, a grouping of flask-shaped cysts which have been found in present-day marine plankton and sediment comes closest to characterising the morphology of chitinozoa. This grouping of flask-shaped cysts includes forms which have been found within tintinnid loricae. Another modern cyst type Pacillina arctica, which is believed to be a ciliate cyst, comes close to replicating the morphology of the chitinozoan genus Hoegisphaera. This paper discusses the structure of tintinnid, other flask-shaped cysts and Pacillina arctica in relation to chitinozoan morphology, drawing attention to similarities and differences. The occurrence and distribution of these cyst forms in present-day plankton is also described and interpreted.     

A relationship between leaf structure and growth potential in apple

The number of palisade mesophyll cells per unit area leaf lamina was related to the growth potential of apple rootstocks covering a wide range of vigour. The number of these cells per unit leaf surface depends on cell diameter, the number of layers of palisade, and the amount of intercellular airspace. In composite, grafted trees rootstock influence was observed on the leaf structure of scions of low, or intermediate, growth potential.     

Nitrogen fertility and leaf age effect on ethylene production of cotton in a controlled environment

The effect of nitrogen (N) fertility and its subsequent impact on ethylene production varies with plant species. Additionally, ethylene production reportedly increases or decreases with leaf age for several species. We examined leaf age and N fertility effects on ethylene production of cotton (Gossypium hirsutum L.) during the early vegetative stages of development (14 to 42 days after emergence) in a controlled environment. Ethylene production was determined by sampling leaf discs from the topmost fully expanded, middle, and bottom leaves of the canopy at 14, 21, 28, 35, and 42 days after emergence. Ethylene was collected from leaf discs in sealed test tubes and quantified by gas chromatography. Early in development, a N deficiency was associated with elevated levels of ethylene, suggesting stress ethylene production was occurring in response to a N-deficiency stress. As plant development progressed, however, increased ethylene production was associated with higher levels of applied N. Additionally, higher ethylene production was linearly associated with higher chlorophyll levels in all three leaves sampled. Ethylene production within plants receiving any given rate of N initially increased and then decreased with leaf age. The dynamics of this relationship suggest that as the N status of the plant changes during plant development, the relative rate of ethylene production, with regard to leaf age, is significantly influenced.     

植物叶片最大羧化速率与叶氮含量关系的变异性

叶片最大羧化速率是表征植物光合能力的关键参数, 受到光照、温度、水分、CO₂浓度、叶片氮含量等多个要素的控制。准确地模拟植物叶片最大羧化速率对环境因子的响应是预测未来植被生产力和碳循环过程的前提。目前大多数陆地碳循环过程模型以Farqhuar光合作用模型为基础模拟植物的光合作用, 关于植物叶片的最大羧化速率与叶氮含量关系的模拟方法却各不相同。该文汇总了1990-2013年国内外植物叶片光合速率观测研究文献中叶片最大羧化速率与叶氮含量的关系式及相关数据, 分析了叶片最大羧化速率与叶氮含量关系随不同植被功能型和时间的变化特征, 以及环境因子变化条件下最大羧化速率与叶氮含量关系的变化特征, 探讨了二者关系变异性的可能原因以及影响因子。结果表明: 1)不同功能型植物叶片的最大羧化速率和叶氮含量的关系存在较大差异, 二者线性关系式的斜率平均值变化范围为16.29-50.25 μmol CO₂·g N^-1·s^-1。落叶植被叶片的最大羧化速率随叶氮含量的变化率和光合氮利用效率一般都高于常绿植被, 其变异主要源于植物的比叶重和叶片内部氮素分配的差异。2)叶片最大羧化速率随叶氮含量的变化存在季节和年际变异。在没有受到水分胁迫的年份中, 叶片最大羧化速率随叶氮含量变化的速率一般在春季或夏季最高, 其季节变异与比叶重和叶氮在Rubisco的分配比例的季节变化有关。受到干旱的影响, 叶片最大羧化速率随叶氮含量的变化率会升高。3)当大气CO₂浓度增加时, 由于叶片中Rubisco含量的降低, 多年生针叶叶片最大羧化速率和叶氮关系斜率值会出现降低; 当供氮水平增加时, 叶片最大羧化速率和叶片氮含量均表现出增加趋势, 二者线性关系的斜率也相应增加。在此基础上, 该文指出在模拟叶片最大羧化速率与叶氮含量的关系时, 应考虑叶片比叶重和叶氮在Rubisco中的分配比例的季节变异、水分胁迫、大气CO₂浓度和供氮水平变化对二者关系的影响。囿于数据的有限性, 今后应进一步加强多因子控制实验研究, 深入探讨叶片最大羧化速率与叶氮含量关系的变异性机理, 并获得更系统的观测数据, 以助生态系统过程模型的改进, 提高模型的模拟精度。     

Variations in the relationship between maximum leaf carboxylation rate and leaf nitrogen concentration

叶片最大羧化速率是表征植物光合能力的关键参数, 受到光照、温度、水分、CO₂浓度、叶片氮含量等多个要素的控制。准确地模拟植物叶片最大羧化速率对环境因子的响应是预测未来植被生产力和碳循环过程的前提。目前大多数陆地碳循环过程模型以Farqhuar光合作用模型为基础模拟植物的光合作用, 关于植物叶片的最大羧化速率与叶氮含量关系的模拟方法却各不相同。该文汇总了1990-2013年国内外植物叶片光合速率观测研究文献中叶片最大羧化速率与叶氮含量的关系式及相关数据, 分析了叶片最大羧化速率与叶氮含量关系随不同植被功能型和时间的变化特征, 以及环境因子变化条件下最大羧化速率与叶氮含量关系的变化特征, 探讨了二者关系变异性的可能原因以及影响因子。结果表明: 1)不同功能型植物叶片的最大羧化速率和叶氮含量的关系存在较大差异, 二者线性关系式的斜率平均值变化范围为16.29-50.25 μmol CO₂·g N^-1·s^-1。落叶植被叶片的最大羧化速率随叶氮含量的变化率和光合氮利用效率一般都高于常绿植被, 其变异主要源于植物的比叶重和叶片内部氮素分配的差异。2)叶片最大羧化速率随叶氮含量的变化存在季节和年际变异。在没有受到水分胁迫的年份中, 叶片最大羧化速率随叶氮含量变化的速率一般在春季或夏季最高, 其季节变异与比叶重和叶氮在Rubisco的分配比例的季节变化有关。受到干旱的影响, 叶片最大羧化速率随叶氮含量的变化率会升高。3)当大气CO₂浓度增加时, 由于叶片中Rubisco含量的降低, 多年生针叶叶片最大羧化速率和叶氮关系斜率值会出现降低; 当供氮水平增加时, 叶片最大羧化速率和叶片氮含量均表现出增加趋势, 二者线性关系的斜率也相应增加。在此基础上, 该文指出在模拟叶片最大羧化速率与叶氮含量的关系时, 应考虑叶片比叶重和叶氮在Rubisco中的分配比例的季节变异、水分胁迫、大气CO₂浓度和供氮水平变化对二者关系的影响。囿于数据的有限性, 今后应进一步加强多因子控制实验研究, 深入探讨叶片最大羧化速率与叶氮含量关系的变异性机理, 并获得更系统的观测数据, 以助生态系统过程模型的改进, 提高模型的模拟精度。     

A possible evolutionary lag in the relationship between freshwater mussels and European bitterling

The coevolutionary dynamics between European bitterling Rhodeus amarus and freshwater unionid mussels, which the former parasitize by laying eggs on their gills, were tested. In a series of experiments fish preferences and mussel responses were compared in parasites and hosts of recent (Europe) and ancient (Asia) sympatry. Rhodeus amarus readily oviposited on the gills of all mussel species tested. Fish that laid their eggs on the gills of Asian Anodonta woodiana, however, suffered a dramatic reduction in reproductive success compared to fish that oviposited on the gills of European mussels: Unio pictorum , Unio tumidus , Anodonta anatina and Anodonta cygnea . This difference was the result of egg ejection behaviour by mussels rather than the unsuitability of the internal gill environment for European bitterling embryo development. The ejection response of mussels with a long sympatry with European bitterling was considerably more pronounced than that of mussels with a substantially shorter sympatry. The data support a coevolutionary arms race between bitterling and mussels and point to an evolutionary lag in the relationship between R. amarus and its European mussel hosts.     

The relationship between leaf growth and ABA accumulation in the grass leaf elongation zone

Detached barley (Hordeum vulgare L.) shoots, maintained at different air temperatures and VPDs, were fed ABA via the sub-crown internode in a leaf elongation assay. Analysis of variance of leaf elongation rate (LER) showed significant effects of temperature (T), fed [ABA] and the interaction T × [ABA]. However, the interaction became non-significant when LER was modelled against the [ABA] of the elongation zone, [EZ-ABA] When detached barley shoots were fed sap from droughted maize (Zea mays L.) plants, sap [ABA] could not explain the growth inhibitory activity. Measurement of [EZ-ABA] accounted for this ‘unexplained’ growth inhibition. The detached shoot experiments indicated that [EZ-ABA], and not xylem sap [ABA], was an appropriate explanatory variable to measure in droughted plants. However, ABA accumulation in the elongation zone could not explain a 35% growth reduction in intact droughted plants; thus we considered an interaction of water status and ABA. Using a coleoptile growth assay, we applied mild osmotic stresses (ψ=0 to ?0.06 MPa) and 10^?4 mol m^?3 ABA. Individually, these treatments did not inhibit growth. However, osmotic stress and ABA applied together significantly reduced growth. This interaction may be an important mechanism in explaining leaf growth inhibition of droughted plants.     

Methylation reactions and the phytoalexin response in alfalfa suspension cultures

 In order to determine why the activated methyl cycle is up-regulated in plants undergoing defence responses to fungal pathogens we have monitored the utilisation of methyl groups derived from methionine in cell-suspension cultures of alfalfa (Medicago sativa L.) treated for various times with fungal elicitor, by carrying out a parallel labelling study with [³⁵S]methionine and [methyl-³H]methionine. The distribution of the two radiolabels among the medium, soluble cellular components and cell wall was then determined. In the absence of elicitor the utilisation of the two radiolabels was similar. However, in the presence of the elicitor the total incorporation of radioactivity from [methyl-³H]methionine into metabolites was far greater than from [³⁵S]methionine, indicating that the methyl label had been utilised in methylation reactions. Elicitor treatment resulted in up to a sixfold increase in the use of ³H-methyl groups in the methylation of hydrophobic metabolites. In the period 0–24 h after elicitor treatment, increased methylation was directed largely into the synthesis of the isoflavonoid phytoalexin medicarpin and related metabolites. Newly synthesized phytoalexins were exported into the medium, while a significant proportion of the medicarpin accumulating in the cell in the early stages of elicitation was derived from the hydrolysis of its respective conjugate. Elicitor treatment also modified the incorporation of ³H-methyl groups into the cell wall. Between 0 and 24 h after elicitor treatment the methylation of pectin in the cell wall declined. After 24 h, pectin methylation recovered and was associated with an increase in the methylation of other wall-bound polysaccharide components. Since no other major metabolic sink for the increased methylation was determined we conclude that the increased activity of the activated methyl cycle during defence interactions in alfalfa is required to support phytoalexin synthesis and cell wall modifications. Received: 1 August 1996 / Accepted: 24 October 1996     

An evaluation of a possible phylogenetic relationship between the Euglenophyta and Kinetoplastida

Winthout close phylogenetic ties to any of the other algae, the Euglenophyta are a taxonomic enigma. The argument is made here that the euglenophytes have extensive morphological homology with the zooflagellte trypanosomatids, bodonids, andIsonema. A phylogenetic sequence is postulated linking these group; the available data suggest that the euglenophytes had their origin in these zooflagellates and that the introduction of the chloroplast and a phototrophic mode of nutrition was a relatively late step in this evolutionary process.     

A possible relationship between cord blood transferrin and birth length in infants

Cord blood levels of transferrin (Tf) and insulin-like growth factor I (IGF-1) were measured in 33 normal and 12 preterm infants. Tf was measured by the single radial immunodiffusion technique, while IGF-1 was measured by specific RIA. Tf levels in normal term infants (195 +/- 27 mg/dl) were significantly below normal adult levels (261 +/- 12 mg/dl). Tf levels in preterm infants (159 +/- 30 mg/dl) were lower than those in normal term infants. Tf levels showed a positive correlation with birth length, weight, gestational age and albumin levels in all infants. There was no correlation between Tf and IGF-1 levels in term and preterm infants.     

Inhibition of elicitor-induced phytoalexin formation in cotton and soybean cells by citrate

Addition of an elicitor preparation from Verticillium dahliae to soybean or cotton cell suspension cultures induces the formation of the phytoalexins, glycelollin or sesquiterpene aldehydes, respectively. Recent work (PS Low, PF Heinstein 1986 Arch Biochem Biophys 249: 472-479) has shown that the induction of phytoalexin biosynthesis in these cells is preceded by rapid changes in the plant cell membrane which can be conveniently monitored by membrane associated fluorescent probes. Using this elicitation assay, we have found that citrate, a common metabolite of higher plants, acts as a potent inhibitor of elicitation when added prior to treatment with elicitor. The citrate concentration required to obtain a 50% inhibition of the elicitor-induced fluorescence transition in cultured cotton cells was found to be about 2 millimolar, while the concentration of citrate observed to inhibit elicitor-induced sesquiterpene aldehyde formation in the same cell suspensions was also 2 millimolar. Curiously, in the presence of elicitor, citrate at less than ID₅₀ concentrations increased cell mass accumulation significantly above control incubations without elicitor. A similar inhibition of glyceollin formation with an increase in cell mass accumulation was also observed upon addition of 1 to 5 millimolar citrate to soybean cell suspension cultures. The physiological significance of the inhibition by citrate of phytoalexin formation in plant cell suspensions was supported by the observation that a similar inhibition of sesquiterpene aldehyde formation occurs in cotton plantlets elicited by cold shock or V. dahliae stress. The specificity of citrate as an inhibitor of phytoalexin formation was demonstrated by data showing that other di- and tricarboxylic-hydroxy acids did not inhibit, with the exception of malate which inhibited phytoalexin formation in soybean cells with roughly half the potency of citrate. These experiments not only demonstrate that citrate can act as a specific inhibitor of elicitation, but they further confirm the validity of monitoring elicitation and its modulation with fluorescent probes.