DEFINICIÓN DE LOS COMPONENTES DEL SISTEMA DE CAPTACIÓN 26

1.3. SISTEMAS DE CAPTACIÓN DE AGUA LLUVIA 26

1.3.1. DEFINICIÓN DE LOS COMPONENTES DEL SISTEMA DE CAPTACIÓN 26

The most extensive cellular structures seen in cyanobacteria with the electron microscope are series of flattened membranous sacs known as thylakoids. Structurally these vesicles appear tripartite having a typical unit membrane structure (Fogg et al., 1973) and have been shown to have a globular structure by freeze

etching techniques (Lang,

1968

). The thylakoids are predominately

peripheral in some species in which they are generally orientated parallel to the longitudinal cell wall, for exaunple, Synechococcus, Anacystis and Gloeocapsa (Ris and Sin#i, 1961), Anacystls montana f. minor (Echlin, 196ka), A. nidulans (Echlin, 196i+bj Allen,

1968

a) and S. lividus (Holt and Edwards, 1972> Golecki, 1979) but their more generally net-like permeation throughout the cytoplasm presents

a 3-dimensional maze of interlocking plates (Lang,

1968

). The

thylakoids contain the photosynthetic pigments, chlorophyll a and carotenoids, (Calvin and Lynch, 1952) and are the sites of photo synthesis. The ability to carry out photophosphorylation, photo synthetic oxygen evolution and the Hill reaction have all been demonstrated in cell-free extracts (Fogg et al.. 1973) and they

T h e t h y l á k o i d s s h o w c o n s i d e r a b l e v a r i a t i o n i n a r r a n g e m e n t a n d s t r u c t u r e a c c o r d i n g t o t h e sp e c i e s , p h y s i o l o g i c a l st a t e , d e v e l o p m e n t a l s t a g e a n d p r e p a r a t o r y p r o c edure. D i f f e r e n t m e t h o d s o f f i x a t i o n m a y l e a d t o d i f f e r e n c e s i n f i n e s t r u c t u r e . F o r e x ample, w h e n o s m i u m w a s u s e d a s t h e p o s t - f i x a t i v e t h e l a m e l l a e a p p e a r e d as a t y p i c a l tiiiartite s t r u c t u r e b u t w h e n p e r m a n g a n a t e w a s u s e d t h e l a m e l l a e a p p e a r e d as a f i v e o r e v e n s e v e n p a r t s t r u c t u r e c o m p o s e d o f a l t e r n a t e e l e c t r o n d e n s e a n d e l e c t r o n t r a n s p a r e n t b a n d s ( E c hlin,

196^a).

T h e m e m b r a n e s i n t h e f l a t t e n e d v e s i c l e s a r e u s u a l l y c l o s e l y apposed t o e a c h o t h e r b u t s o m e t i m e s the m e m b r a n e r a p p e a r t o b e s l i g h t l y s e p a r a t e d b y a n a r r o w i n t r a t h y l a k o i d a l s p a c e ( L a n g ,

1968

). T h e l u m e n w a s f o u n d t o b e d i l a t e d i n a g e d c e l l s ( E c h l i n , 196*»-a) a n d i n c e l l s g r o w n u n d e r u n f a v o u r a b l e c o n d i t i o n s , s u c h a s n i t r o g e n s t a r v a t i o n (P e a t a n d W h i t t o n ,

1967

» D e V a s c o n c e l o s a n d Fay, 197*0» T h y l a k o i d i r r e g u l a r i t y w a s a l s o f o u n d t o b e a s s o c i a t e d w i t h a g i n g i n A. m o n t a n a f. m i n o r ( E c h l i n , 196*ta), C. ffritschii ( P e a t a n d W h i t t o n , 1967)• A n a b a e n o p s i s sp. ( P e a t a n d W h i t t o n , 1968) a n d S c y t o n e m a sp. (W h i t t o n , u n p u b l i s h e d o b s e r v a t i o n s q u o t e d i n L a n g a n d W h i t t o n , 1973) a n d n i t r o g e n s t a r v a t i o n i n A. c y l i n d r i c a ( D e V a a c o n c e l o s a n d Fay, 197*0 • U n d e r t h e s e c o n d i t i o n s s t o r a g e p r o d u c t s w e r e f o u n d t o be a c c u m u l a t e d and, a c c o r d i n g t o L a n g a n d W h i t t o n (1973)» t h e p r e s e n c e o f n u m e r o u s s t o r a g e g r a n u l e s o f t e n l e a d s t o a m u c h le s s r e g u l a r a r r a n g e m e n t o f t h e t h y l a k o i d s . A s i m i l a r s i t u a t i o n wa s f o u n d b y V e n k a t a r a m a n , A m e l u n x e n a n d L o r e n z e n (

1969

) w h e n t h e e f f e c t o f t e m p e r a t u r e on t h e s y n c h r o n o u s g r o w t h o f A. n i d u l a n s was d e t e r m i n e d . C e l l s h a r v e s t e d f r o m t h e l o w t e m p e r a t u r e ph a s e o f t h e c y c l e a t 26°C

had -the individual identity of the thylakoids 'masked* as compared with the 2 or 3 parallel sheets of peripheral thylakoids at the higher temperature of 32°G. It was concluded that the difference was associated with the greater accumulation of photosynthetic products at the lower temperature filling the interlamellar spaces.

Light intensity has been found to affect the thylakoid content of cyanobacteria. For example, Allen (1968a) found an inverse relationship between light intensity and the thylakoid content or pigment concentration in A. nidulans. Also, Feat and Whitton (1967) found that in young filaments of C. fritschii. especially those grown at a low light intensity, the thylakoids were mainly parallel to the cell wall but at higher light intensities, and during later stages of cell development, they became scattered throughout the outer part of the cytoplasm. In cells grown hetero- trophically on sucrose in the dark the thylakoids were found to be evenly distributed throughout the cytoplasm. Wildon and Mercer

(

1963

) also showed some reduction in the numbers of lamellae present

in dark grown cells.

The effects of carbon dioxide deprivation in S. lividus were investigated by Miller and Holt (1977). A successive loss of thylakoid membranes with an increase in irregularity was found

during carbon dioxide starvation, the cells being bleached (containing no chlorophyll a or phycocyanin) after 120 hours of carbon dioxide deprivation and being devoid of detectable thylakoid membrane. It was concluded that the loss of thylakoid membrane^ after the exhaustion of pigment and storage materials (carbon and/or nitrogen sources) ,was the last logical step in the process of utilising cellular reserve materials in times of nutrient shortage. The maintenance of this

intricate membrane system in the absence of available substrate was presumed to be a waste of energy and carbon and thylakoids being composed of lipid and protein could serve as an excellent endogenxB source of carbon. The réintroduction of carbon dioxide enriched air into the bleached cultures led to a rapid resynthesis of thylakoid membrane and photosynthetic pigments. A full com plement of these components was, however, necessary before growth occurred, indicating that a morphological, chemical and physiological balance of the photosynthetic apparatus had to be attained prior to cell growth.

Certain cyanobacteria produce differentiated cells, akinetes and heterocysts, which also contain thylakoids. According to Lang and Whitton (1973), the arrangement of thylakoids in akinetes is

generally similar to veget ative cells prior to enlargement and

differentiation but in maturing heterocysts there is a pronounced increase in the amount of photosynthetic membrane.

Apart from the photosynthetic membrane system there have been a few reports of other membranous inclusions in cyanobacteria, for example, lamellasomes in A. nidulans (Echlin, 19#+b) and mesosome- like unit-membrane structures in Snirulina and three strains of Synechococcus (Allen, 1972).

1.3.6. Nuclear region

In many cyanobacterial species, particularly the smaller ones, the nuclear material is located in the centre of each cell or along its longitudinal axis (Fuhs, 1973). Echlin (196ka) found that the inner nucleoplasm of A. montana f. minor was an electron dense fibrous-granular material in an electron transparent matrix and

that the outer nucleoplasm seemed to contain ribonucleoprotein

particles as described by Ris and Singh (

1961

). As in bacterial

cells, the DNA fibrils are not localised in a membrane-limited nucleus, nor do they ever condense into cytologically demonstrable chromosomes as during mitosis in eukaryotic cells (Holm-Hansen,

1968

), n o r h a v e h i s t o n e - t y p e p r o t e i n s b e e n d e m o n s t r a t e d a s s o c i a t e d w i t h th e f i b r i l s ( R i s a n d S i n g h , 19&1; H o l m - H a n s e n ,

1968

; L a n g ,

1968

j F o g g et al.. 1973)*

In the best electron microscopy thin sections the nuclear

material of cyanobacteria is seen to be composed of D N A fibrils

of approximately 2 n a in diameter (Fuhs, 1973)* However, different fixation procedures have been shown to affect the degree of aggre gation of the finest D N A fibrils (Leak, 1967; Fogg et al. 1973»

Fuhs, 1973). Leak (

1967

) demonstrated three types of fibrils in

the nucleoplasm of A« variabilis.by using different fixation methods,

ranging in size from 2 - 3 m in diameter to aggregations from

10 to 35 m in diameter. A true fixation resulting in an almost

homogeneoiB fine-fibrillar appearance of the D N A plasm was obtained

using the Kellenberger method (Kellenberger, Ryter and Sechaud,

1958

) which is a modified osmium fixation technique, using osmium

tetroxide in a solution containing calcium ions and amino acids, followed by uranyl acetate treatment.

Evidence for the location of DNA was provided by the fwl g e n test plus autoradiographic techniques following the incorporation of ^H-labelled thymidine into rapidly growing cells of Anabaena sp. (Leak,

1965

) and plus U V fluorescence of acridine orange in

nucleoplasmic areas appeared in the central regions of the cells in addition to occupying various regions within the peripheral

cytoplasm. These results were substantiated by Leak (

1967

) who

found that cells previously treated with the enzyme desoxyribonuclease

or with trichloroacetic acid (both known to extract D N A ) did not

give the characteristic D N A reactions.

In document Diseño e implementación de un sistema de captación para el tratamiento de agua lluvia mediante ósmosis inversa para los Laboratorios de Biotecnología y Bromatología ESPOCH (página 52-66)