Photoregulated or Energy Dependent Process of Hormogonia Differentiation in Nostoc sphaeroides Kützing (Cyanobacterium)

Hormogonium, which was thought to play an important role in the dispersal and survival of these microorganisms in their natural habitats, is a distinguishable developmental stage of heterocystous cyanobacteria. The present study examined the effects of different light conditions and sugars on the of hormogonia was light dependent in the absence of sugar, but that close to 100% of cyanobacteria differentiated to hormogonia in the presence of glucose or sucrose, irrespective of the light conditions. This differentiation was inhibited, even in the presence of sugars, upon application of an inhibitor of respiration.Following the testing of different sugars, the effects of different lights were examined. It was found that 5-10 μmol.m-2.s-1 photon flux density was optimal for hormogonia differentiation. One hundred percent differentiation was obtained with white light irradiation, in contrast with irradiation with green light (80%differentiation) and red light (0-10% differentiation). Although they showed different efficiencies in induc ing hormogonia differentiation in N. sphaeroides, the green and red radiation did not display antagonistic effects. When the additional aspect of time dependence was investigated through the application of different light radiations and an inhibitor of protein synthesis, it was found that the initial 6 h of the differentiation process was crucial for hormogonia differentiation. Taken together, these results show that hormogonia differentiation in N. sphaeroides is either a photoregulated or an energy dependent process.     

Electron Transport Regulates Cellular Differentiation in the Filamentous Cyanobacterium Calothrix

Differentiation of the filamentous cyanobacteria Calothrix sp strains PCC 7601 and PCC 7504 is regulated by light spectral quality. Vegetative filaments differentiate motile, gas-vacuolated hormogonia after transfer to fresh medium and incubation under red light. Hormogonia are transient and give rise to vegetative filaments, or to heterocystous filaments if fixed nitrogen is lacking. If incubated under green light after transfer to fresh medium, vegetative filaments do not differentiate hormogonia but may produce heterocysts directly, even in the presence of combined nitrogen. We used inhibitors of thylakoid electron transport (3-[3,4-dichlorophenyl]-1,1-dimethylurea and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone) to show that the opposing effects of red and green light on cell differentiation arise through differential excitations of photosystems I and II. Red light excitation of photosystem I oxidizes the plastoquinone pool, stimulating differentiation of hormogonia and inhibiting heterocyst differentiation. Conversely, net reduction of plastoquinone by green light excitation of photosystem II inhibits differentiation of hormogonia and stimulates heterocyst differentiation. This photoperception mechanism is distinct from the light regulation of complementary chromatic adaptation of phycobilisome constituents. Although complementary chromatic adaptation operates independently of the photocontrol of cellular differentiation, these two regulatory processes are linked, because the general expression of phycobiliprotein genes is transiently repressed during hormogonium differentiation. In addition, absorbance by phycobilisomes largely determines the light wavelengths that excite photosystem II, and thus the wavelengths that can imbalance electron transport.     

Cytochemical changes in the developmental process of Nostoc sphaeroides (cyanobacterium)

There are several apparent developmental stages in the life cycle of Nostoc sphaeroides Kützing, an edible cyanobacterium found mainly in paddy fields in central China. The cytochemical changes in developmental stages such as hormogonia, aseriate stage, filamentous stage and colony in N. sphaeroides were examined using fluorescent staining and colorimetric methods. The staining of acidic and sulfated polysaccharides increased with development when hormogonia were used as the starting point. Acidic polysaccharides (AP) were most abundant at the aseriate stage and then decreased, while the sulfated polysaccharides (SP) were highest at the colony stage. Quantitatively, along the developmental process from hormogonia to colony, total carbohydrates first increased, then became stable, and then reached their highest level at the colony stage, while reducing sugars were highest at the hormogonia stage and then decreased sharply once development began. SP were not detectable in the hot water soluble polysaccharides (HWSP), and hormogonia had the lowest content of AP, while old colonies had the highest. The AP content of the aseriate stage, filamentous stage and young colony stage were very similar. The evolutionary relationships reflected in the developmental stages of N. sphaeroides are discussed.     

Hormogonia mass differentiation from Nostoc sphaeroides Kütz. (cyanobacterium) and the comparison of structural characteristics between hormogonia and vegetative filaments

It was found that, after colonies of Nostoc sphaeroides Kütz. in exponential phase of growth were transferred to fresh complete BG‐11₀ medium, the hormogonia differentiated independent of the type of preculture used. This provided evidence that the hormogonia differentiation was not directly related to phosphorus and potassium status, nor to the osmotic effect of the media. In contrast, all the cultures in the stationary growth phase had no hormogonium differentiation after being transferred to fresh medium. However, the incomplete media for preculture seemed to favor the liberation of hormogonia from colonies to the medium. The result showed that the morphology and ultrastruc‐tures of the vegetative filament, the main stage of Nostocacean life history, determine its adaptability in changing environments, while the hormogonium remains as a propagule of the species.     

丝状体蓝藻藻殖段的分化及其调节机制

本文介绍了丝状体蓝藻(亦称蓝细菌) 的藻殖段的分化及其调节机制。藻殖段与正常藻丝体的区别在于细胞形状、细胞内存有气囊和可移动的短而直的藻丝链等。本文对许多环境因子包括光和营养因素等促进或抑制藻殖段的分化进行了讨论;还介绍了念珠藻(Nostoc) ,单歧藻(Tolypothrix) 和眉藻(Calothrix)所具有复杂的细胞发育过程,即具气囊又可移动的藻殖段分化,异形胞分化以及营养细胞的补偿性色适应。这三种细胞类型的适应形成取决于两种不同的光受体系统。藻殖段和异形胞两者的分化可能取决于光合电子传递链;而营养细胞的补偿性色适应则受光敏色素的调节。此外,谷酰胺合成酶合成和活性调节的PII蛋白,在协同藻殖段分化、异形胞分化及营养细胞的补偿色适应中起重要作用。由于蓝藻藻殖段分化及其调节机制是一个新的研究领域,关于它的知识尚不完整,亟待人们加强研究。     

Photomophogenesis in the Blue-green Alga Nostoc commune 584

The blue-green alga Nostoc commune 584 displays a photocontrolled developmental cycle similar to that described for N. muscorum A by Lazaroff and Vishniac (1961). In both species white fluorescent light acts at the same stage, ragulating the development of motile trichomes from sheathed aseriate colonies. However white light blocks this step in N. commune 584, whereas the formation of motile trichomes is promoted by white light in N. muscorum A. Light-grown (aseriate) cultures in N. commune 584 were used to determine the action spectra for photomorphogenesis. Green light (max 520 nm) inhbited aseriate colony breakage, and red light (max 640 nm) promoted colony breakage and the differentiation of motile trichomes. On a quantum basis green light was about 3 times more effective than red light. The morphogenetic effects of either red or green light were reversible by irradiation with the other color of light. Repeated photoreversibility was observed, and the algal culutres responded only to the color of the last irradiation in a sequence. An unidentified substance is excreted into the media of motile cultures of both N. commune 584 and N. muscorum A which promotes motility in non-motile cultures. The motility-promoting substances from both species are reciprocally active. Activity is lost when the media are autoclaved.     

丝状体蓝藻藻殖段的分化及其调节机制

本文介绍了丝状体蓝藻（亦称蓝细菌）的藻殖段的分化及其调节机制。藻殖段与正常藻丝体的区别在于细胞开状、细胞内存有气囊和可移动的短而真的藻丝链等。本文对许多环境因子包括光和营养因素等促进或抑制藻殖段的分化进行一讨论;还介绍了含球藻（Ｎｏｓｔｏｃ）,单歧藻（Ｔｏｌｙｐｏｔｈｒｉｘ）和眉藻（Ｃａｌｏｔｈｒｉｘ）所具有复杂的细胞发育过程,即具气囊又可移动的藻殖段分化,异形胞分化以及营养细胞的被偿性色适应。这     

NOSTOCACEAN MACRO‐MORPHOGENESIS

A poorly understood feature of nostocacean growth and development is the formation of ordered macroscopic structures from microscopic cells, trichomes, and filaments. Using macro‐photography, time‐lapse micro‐cinematography, light and electron microscopy of Nostoc species in pure culture, it has been possible to demonstrate how motility, adhesion and aggregation of photo‐induced hormogonia result in macro‐morphogenesis of dendroid forms. Red‐light induced hormogonia from synchronized cultures aggregate rapidly on agar as tight flowing streams, in patterns responsive to the direction and quality of incident light. Unlike the even textured cell surfaces of heterocystous filaments, the cell walls of swarming hormogonia are covered with a striate mucoid layer containing pili attached to cells of adjacent hormogonia. During differentiation to an aseriate phase, cell wall fusions occur and a gelatinous matrix forms around the enlarging sub‐globose cells. Liquid suspensions of hormogonia aggregate in a solid mass following the net centripetal movement of interlaced loops of curved hormogonia attached by adhesive pili. In darkness or dim white light, compressed hormogonial aggregates form erect tree‐like (dendroid) macro‐structures by photo‐tactic reversal of streaming motility. Hormogonia within the aggregates re‐organize into streams that push upward into the light, forming structured, positively phototropic protuberances, several millimeters in length. Under weak illumination, the structures become branched with crowns of waving hormogonia. The dendroid morphology is stabilized by deposit of gelatinous material derived from successive cycles of cell‐filament development, liberation of heterocysts and formation of dormant cells and trichomes.