温度对4种大型海藻氮磷吸收效率及光合生理特性的影响

研究以裂片石莼(Ulva fasciata)、肠浒苔(Ulva intestinalis)、龙须菜(Gracilaria lemaneaformis)、坛紫菜(Pyropia haitanensis)为实验材料, 分析了不同温度(15、20、25、30℃)下4种大型海藻对海水中N、P元素的吸收效率和光合特性的特点。结果显示: (1)4种大型海藻对水体N、P均有明显的吸收效果, 吸收能力高低依次为肠浒苔>裂片石莼>坛紫菜>龙须菜; (2)温度过高或过低都会限制藻类对N、P的吸收和正常生长, 同时降低4种藻的相对电子传递速率及光化学效率; (3)裂片石莼与肠浒苔的N、P吸收能力强, 且光合系统对温度耐受性高, 是实施养殖污水生物净化的良好材料; (4)4种海藻对水体中N、P营养盐的吸收在48h内基本完成, 实地应用中可考虑24—48h周期换水或采用流通循环式的培养模式, 以达到既促进藻类的生长又提高营养盐吸收效率的目的, 以避免藻体因营养缺乏引起负生长而造成二次污染。     

SEASONAL VARIATIONS OF PHOTOSYNTHETIC PIGMENTS, TOTAL C, N, AND P CONTENT, AND PHOTOSYNTHESIS IN PHYLLARIOPSIS PURPURASCENS: (PHAEOPHYTA) FROM THE STRAIT OF GIBRALTAR

Photosynthetic pigments, C, N, and P tissue composition, and photosynthetic rate were measured from April to October in the brown alga Phyllariopsis purpurascens (C. Agardh) Henry et South (Laminariales, Phaeophyta) growing at a 30-m depth in the Strait of Gibraltar. Ir-radiance reaching the population ranged from 13.5 to 27.5 mol.m^-2.mo^-1. The available light for this species, expressed as a percentage of the irradiance above the water, was 1.8%. Dissolved inorganic nitrogen forms, NO3-and NH₄+, were constant from April to October, whereas phosphate was depleted in August. Chlorophyll a decreased from 520.0 ± 165.0 to 199.6 ± 159.9 μg.g^-1 dry weight; in contrast, chlorophyll c and carotenoids did not change until September but increased threefold in October. C:N and N:P ratios changed in the same way and in the same range. They were constant until July but increased from 15–17 up to 42 (C:N) and from 14 to 40 (N:P) in October, suggesting a severe P limitation of growth of this species. The dark respiration rate and the light compensation point were constant from April to October (0.5 ± 0.1 μmol O₂. m^-2.s^-1 and 6.5 ± 0.2 μmol.m^-2. s^-1, respectively), whereas the maximum rate of apparent photosynthesis, light onset saturation parameter, and half saturation constant for light were maximum in April to May (3.7 μmol O₂. m^-2.s^-1and 40 and 41.5 μmol.m^-2. s^-1, respectively) and October (3.6 μmol O₂. m^-2.s^-1 and 50 and 53.7 μmol.m^-2. s^-1, respectively). They were minimum in August (1.2 μmol O₂.m^-2.s^-1 and 11.3 and 12 μmol.m^-2.s^-1, respectively). These minimum figures yielded a negative carbon budget in August and 0 in September, whereas it was positive the rest of the year. Photosynthetic efficiency, estimated by the ratio between maximum apparent photosynthesis and light half saturation constant, showed a strong agreement with productivity measured by means of an independent method. These results indicate that lamina expansion in this species is controlled by photosynthetic efficiency.     

Adaptation to Oxygen: ROLE OF TERMINAL OXIDASES IN PHOTOSYNTHESIS INITIATION IN THE PURPLE PHOTOSYNTHETIC BACTERIUM,RUBRIVIVAX GELATINOSUS*

The appearance of oxygen in the Earth''s atmosphere via oxygenic photosynthesis required strict anaerobes and obligate phototrophs to cope with the presence of this toxic molecule. Here we show that in the anoxygenic phototroph Rubrivivax gelatinosus, the terminal oxidases (cbb₃, bd, and caa₃) expand the range of ambient oxygen tensions under which the organism can initiate photosynthesis. Unlike the wild type, the cbb₃⁻/bd⁻ double mutant can start photosynthesis only in deoxygenated medium or when oxygen is removed, either by sparging cultures with nitrogen or by co-inoculation with strict aerobes bacteria. In oxygenated environments, this mutant survives nonphotosynthetically until the O₂ tension is reduced. The cbb₃ and bd oxidases are therefore required not only for respiration but also for reduction of the environmental O₂ pressure prior to anaerobic photosynthesis. Suppressor mutations that restore respiration simultaneously restore photosynthesis in nondeoxygenated medium. Furthermore, induction of photosystem in the cbb₃⁻ mutant led to a highly unstable strain. These results demonstrate that photosynthetic metabolism in environments exposed to oxygen is critically dependent on the O₂-detoxifying action of terminal oxidases.     

PARTICIPATION OF THE CYTOPLASMIC MEMBRANE IN THE GROWTH AND SPORE FORMATION OF BACILLI

A polyester embedding technique was used to study the early stages of spore formation in members of the genus Bacillus in order to investigate further the origin and nature of the initial spore septum and the resulting forespore envelope. Whereas previously, with a methacrylate procedure, this layer had appeared to be continuous with the cell wall, this study reveals it as a double layer of cytoplasmic membrane. Perisporal, membranous organelles connected both to the developing forspore envelope and to the cytoplasmic membrane were encountered in the four species studied. Similar organelles were prominent during growth at the sites of transverse septa formation. These were connected to, or continuous with, the cytoplasmic membrane and often adherent to the chromatin bodies of the dividing bacilli.