AUXOSPORE FORMATION AND THE MORPHOLOGY OF THE INITIAL CELL OF THE MARINE ARAPHID DIATOM GEPHYRIA MEDIA (BACILLARIOPHYCEAE)1

Recent studies have led to a rapid increase in knowledge of auxospore formation in diatoms. However, these studies have been limited to centric and raphid pennate diatoms, and there is still very little information for the araphid pennate diatoms. Using LM and SEM, we studied the development of the auxospore and the initial cell of the marine epiphytic diatom Gephyria media Arnott. Auxospores were bipolar and curved in side view, as in many other pennate diatoms. SEM revealed many transverse perizonial bands, all of which were incomplete rings. There was an elongate, sprawling, silicified structure beneath the ventral suture of the transverse perizonial bands. This structure is presumably equivalent to the longitudinal perizonial band in other pennate diatoms, although we could not determine the homologous relationship between the two features. Scales were found both in the inner wall of the perizonium and around the primary perizonial bands. The presence or absence of scales may be of phylogenetic significance in diatoms, only during the final stages of auxospore formation because scales are found in early spherical stages. The distinctive finger‐like structures observed throughout all stage of G. media have not been observed before in the other diatom taxa.     

Change in citrus leaf lipids during freeze-thaw stress

Fatty acids in the leaves of the citrus hybrid B5-9-68, a BC₁ progeny [(Citrus paradisi x Poncirus trifoliata) x C. sinensis], were compared with those in P. trifoliata and C. sinensis. Total lipid and triacylglycerol fatty acid profiles of the cold hardened hybrid were similar to the profiles of the hardy P. trifoliata and different from the profiles of the less hardy C. sinensis. When subjected to a freeze regime, the unhardened hybrid lost 22% leaf fatty acids during the freeze stage and 13% during the thaw stage. Linolenic acid accounted for 98% of the fatty acid decrease. Degradation was greatest in phosphatidylcholine (89%), phosphatidylglycerol (83%), monogalactosyldiglyceride (79%) and digalactosyldiglyceride (50%). Phosphatidic acid increased 4-fold over the two stress stages. Total leaf fatty acids during the freeze-thaw regime increased 12% in the cold hardened hybrid. Three molecular species of triacylglycerol which were rich in linolenic acid increased in the hardened hybrid during the freeze-thaw regime. The increase in highly unsaturated triacylglycerol species under freeze-thaw stress suggests that triacylglycerol has a role in maintaining the fluidity of biomembranes during freezing conditions.     

Role of habitat in determining macroinvertebrate production in an intermittent-stream system

1. The effect of channel drying on macroinvertebrate production was studied at the habitat and reach scale in a catchment drained by intermittent streams in Maine, U.S.A. The catchment includes two first‐order streams and their second‐order confluence. Six reaches were selected for study based on differences in channel slope and habitat cover (bedrock, riffle/run, debris dam and pool). Stream water in each reach was acidic and oligotrophic. 2. The study reaches had different degrees of channel drying. In the first‐order reaches, surface flow ceased earlier in the season and for longer periods than second‐order reaches. Regardless of reach, pool and debris dam habitats retained water longer than riffle/runs and bedrock. Unlike other habitats, debris dams retained moisture for relatively long periods following cessation of surface flow. 3. Reach‐specific macroinvertebrate production ranged from approximately 1.7 to 2.9 g AFDM m⁻² year⁻¹ which are among the lowest values ever reported. Habitat‐specific production ranged from approximately 0.5 to 5.0 g AFDM m⁻² year⁻¹ (bedrock and debris dams, respectively). 4. At the reach scale, quantities of stored benthic organic matter (range approximately 200–600 g AFDM⁻²) decreased in a downstream direction. 5. A combination of differences in the timing and duration of channel drying, habitat structure and detritus standing stocks appeared to influence levels of invertebrate production among the study reaches. 6. Our interpretation of a canonical correspondence analysis indicates that drying is more important than habitat in affecting macroinvertebrate production in this intermittent stream system.     

Design of a beneficial product for newborn calves by combining Lactobacilli,minerals, and vitamins

Diarrhea is one of the most frequent diseases affecting newborn calves in intensive systems. Several strategies were proposed to protect and improve health, such as probiotics. This work was directed to design a product containing freeze-dried bacteria, vitamins, and minerals, as well as to optimize conditions with lyoprotectors, combine strains and add vitamins, minerals, and inulin to the product. The lyoprotectors were milk, milk-whey, and actose, and products were stored for 6 months at 4°C. Combined bacteria were freeze-dried in milk and the final products were added with minerals, vitamins, and insulin. The viable cells were determined by the plate count assay and antibiotic profiles to differentiate strains. Lactobacillus johnsonii CRL1693, L. murinus CRL1695, L. mucosae CRL1696, L. salivarius CRL1702, L. amylovorus CRL1697, and Enterococcus faecium CRL1703 were evaluated. The optimal conditions were different for each strain. Milk and milk whey maintained the viability during the process and storage after 6 months for most of the strains, except for L. johnsonii. Lactose did not improve cell’s recovery. L. murinus was viable for 6 months in all the conditions, with similar results in enterococci. In strains combined before freeze-dried, the viability decreased deeply, showing that one-step process with bacteria mixtures, vitamins, and minerals were not adequate. Freeze-dried resistance depends on each strain and must be lyophilized individually.     

The relations of stomatal closure and reopening to xylem ABA concentration and leaf water potential during soil drying and rewatering

Two tropical tree species, Acacia confusa and Leucaena leucocephala, were used to study the relationships among stomatal conductance, xylem ABA concentration and leaf water potential during a soil drying and rewatering cycle. Stomatal conductance of both A. confusa and L. leucocephala steadily decreased with the decreases in soil water content and pre-dawn leaf water potential. Upon rewatering, soil water content and pre-dawn leaf water potential rapidly returned to the control levels, whereas the reopening of stomata showed an obvious lag time. The length of this lag time was highly dependent not only upon the degree of water stress but also on plant species. The more severe the water stress, the longer the lag time. When A. confusa and L. leucocephala plants were exposed to the same degree of water stress (around –2.0 MPa in pre-dawn leaf water potential), the stomata of A. confusa reopened to the control level 6 days after rewatering. However, it took L. leucocephala about 14 days to reopen fully. A very similar response of leaf photosynthesis to soil water deficit was also observed for both species. Soil drying resulted in a significant increase in leaf and xylem ABA concentrations in both species. The more severe the water stress, the higher the leaf and xylem ABA concentrations. Both leaf ABA and xylem ABA returned to the control level following relief from water deficit and preceded the full recovery of stomata, suggesting that the lag phase of stomatal reopening was not controlled by leaf and/or xylem ABA. In contrast to drying the whole root system, drying half of the root system did not change the leaf water relations, but caused a significant increase in xylem ABA concentration, which could fully explain the decrease of stomatal conductance. After rewatering, the stomatal conductance of plants in which half of the roots were dried recovered more rapidly than those of whole-root dried plants, indicating that the leaf water deficit that occurred during the drying period was related to the post-stress stomatal inhibition. These results indicated that the decrease in stomatal conductance caused by water deficit was closely related to the increase in xylem ABA, but xylem ABA could not fully explain the reopening of stomata after relief of water stress, neither did the leaf ABA. Some unknown physiological and/or morphological processes in the guard cells may be related to the recovery process.     

周期性土壤干旱和叶片水势对气孔响应木质部ABA灵敏度的影响

研究了周期性土壤干旱期间气孔对木质部ＡＢＡ响应的灵敏度的变化以及叶片水势对灵敏度的影响。实验结果证明了木质部ＡＢＡ浓度是反映根系周围土壤水分状况的一个指标的结论。土壤周期性干旱不影响木质部ＡＢＡ浓度对土壤水分状况的依赖关系,但显著地提高了气孔对木质部ＡＢＡ 响应的灵敏度。根据对实测数据的数学模拟结果显示,引起气孔导度下降５０％ 所需的木质部ＡＢＡ浓度从第一轮土壤干旱的７５０ ｎｍｏｌ／Ｌ降至第二轮土壤干旱的５５０ ｎｍｏｌ／Ｌ。分根实验的结果表明,叶片水分亏缺显著提高了气孔对木质部ＡＢＡ 的响应的灵敏程度,全根干旱中引起气孔导度下降５０ ％ 所需的木质部ＡＢＡ 浓度比半根干旱的小２ ～４ 倍。这表明,气孔对木质部ＡＢＡ响应的灵敏度不是一个固定的特性,可随植物生长环境及许多其他因素的变化而表现出很大的差异     

Spray drying of lipid-based systems loaded with Camellia sinensis polyphenols

In this work, spray-dried lipid systems based on soy phosphatidylcholine, cholesterol and lauroyl polyoxylglycerides for entrapping Green tea polyphenols were produced. The aim was to study the effects of the encapsulating composition and spray drying conditions on the system performance and physicochemical product properties. The spray dryer powder production yield falls around 50.7?±?2.8%, which is typical for lab scale spray dryers. Wrinkled and rounded particles, with low surface porosities were generated, independent of the drying carriers (trehalose or lactose) used. The product showed high encapsulation efficiency of Green tea polyphenols, which was promptly redispersible in water. It presented low density, and good compressive and flow properties. The results herein reported confirm the feasibility of the entrapment of Green tea polyphenols in lipid-based compositions by spray drying in presence of the drying carriers evaluated. The spray-dried microparticles show high potential to be used as additive in food, nutraceutical and pharmaceutical products.     

Growth,nutrient acquisition and ectomycorrhizae of <Emphasis Type="Italic">Eucalyptus regnans</Emphasis> F. Muell. seedlings in fertilized or diluted air-dried and undried forest soil

Seedlings of Eucalyptus regnans (mountain ash) grow poorly in undried forest soil, where they develop purple coloration in the foliage, but their growth is markedly improved when forest soil has been air dried. Whether this growth promotion is purely due to improved nutrient status of the soil, as a result of air drying, was investigated. In several pot experiments, E. regnans seedlings were grown (i) in air-dried and undried forest soil with addition of different levels of complete fertiliser, (ii) in air-dried or undried soil diluted to different extents with sand, or (iii) in undried soil mixed with different amounts of air-dried soil. Seedling dry weight, P content and incidence of ectomycorrhizal root tips were determined.In all experiments, the dry weights of seedlings were 3–6 times greater in 100% air-dried soil than in 100% undried soil. Fertiliser application resulted in a significant increase in dry weight of seedlings in both air-dried and undried soil, but the dry weights in air-dried soil were always significantly greater than those in undried soil at the same level of fertiliser application. Even at the highest level of fertiliser application, the growth difference between seedlings in air-dried and undried soil remained. When air-dried soil was diluted with sand, there was a significant reduction in seedling dry weight only when soil was diluted to 20% or less (air-dried soil:total mix). Conversly, when air-dried soil was mixed with undried soil, there was a proportional decrease in seedling dry weight with increasing amounts of undried soil. In all experiments, the dominant ectomycorrhizal morphotypes in 100% air-dried soil were different from those in undried soil. Fertilisation and dilution of air-dried and undried soil did not result in a reduction in the overall incidence of ectomycorrhizal root tips, although the frequency of occurrence of different ectomycorrhizal morphotypes was affected.It is concluded that the growth difference between seedlings in air-dried and undried forest soils is not due solely to differences in the direct availability of nutrients in the soils, and different ectomycorrhizae may indirectly affect nutrient availability to the plant.     

Partial Root Drying Effects on Biomass Production in Brassica napus and the Significance of Root Responses

Partial root drying (PRD) has been shown to stimulate stomatal-closure response and improve water-use efficiency and thus biomass production and grain yield under water deficiency. While most studies focus on above-ground responses to PRD, we examined how root responses contributed to effects of partial root drying. In particular, in two experiments with oilseed rape (Brassica napus L.) we investigated whether roots were able to forage for patchily distributed water, and how this affected plant growth compared with uniform watering and alternate watering (in which different parts of the roots receive water alternately). The first pot experiment was carried out in the greenhouse and the second outside under a rain-shelter in which also the watering amount was varied. The results indicate that B. napus roots were able to forage for fixed water patches by selective root placement. In the first experiment with small plants, root foraging was equally effective as enhanced water-use efficiency under alternate watering. Both treatments resulted in about 10% higher shoot biomass compared with uniform watering. Alternate watering generally outperformed uniform watering in the second experiment, but the success depended on the time of harvest and the water supply level. Measurements indicated that only the alternate watering regime effectively reduced stomatal conductance, but lead to a higher shoot biomass only under more severe (50%) rather than under milder water deficiency (70% of a well watered control). Water deficiency strongly reduced leaf initiation rates and leaf sizes in B. napus, but for a given level of water supply the supply pattern (uniform control, fixed patchy or alternate watering) hardly influenced these growth parameters. Although also in the second experiment, the plants selectively placed their roots in the wet parts of the pot, root foraging was not as effective as in the first experiment. Possible reasons for these discrepancies are discussed as well as their implications for the application of PRD effects for crop growth.