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Speeialia 1483I t should be p o i n t e d out t h a t in so-called physiological conditions of p H and concentration, the N A D H signal is m u c h larger t h a n t h a t p r o d u c e d b y t h e Schiff-base.Indeed, N A D H 10 .5 21/I in Tris buffer 20 mlVI p H 7.4gives a fluorescence signal of 137% of t h a t of t h e s t a n d a r d quinine sulfate solution, while the emission of a m i x t u r e of P -5 -P 3 ~xg/ml and g l u t a m a t e 3.75 m M is only 19.5% of t h e emission of t h e reference solution. Nevertheless, not only g l u t a m a t e b u t also the other amino acids can p a r t i c i p a t e in t h e f o r m a t i o n of Schiff-bases, and care should be t a k e n in t h e i n t e r p r e t a t i o n of t h e results of e x p e r i m e n t s which are not inducing changes in tissue fluorescence emission large enough to be safely a t t r i b u t e d to a modification in the r e d o x state of the p y r i d i n e nucleotides.In the course of our experiments, a good correlation b e t w e e n t h e emission i n t e n s i t y at 468 n m a n d t h e con-c e n t r a t i o n of P -5 -P in the c o n c e n t r a t i o n r a n g e b e t w e e n 0.01 vg to 1 ~g/ml has been observed in a reaction m e d i u m h e a t e d at 50 ~ for 5 m i n and containing g l u t a m a t e 5 m M and A1C1 a 2 m M in acetate buffer 20 m M at p H 5. This indicates the possibility of the use of t h e fluorescence characteristics of t h e Schiff-base for t h e d e v e l o p m e n t of a specific t e c h n i q u e of d e t e r m i n a t i o n of free p y r i d o x a l p h o s p h a t e c o n c e n t r a t i o n in biological material. Rdsumd. La base de Schiff form6e ~ p a r t i r de pyridoxalp h o s p h a t e et d ' u n acide amin@ pr6sente une fluorescence d o n t les caract6ristiques spectrMes sont similaires ~ celles du N A D H . Les possibilit6s @ventuelles de faire la distinction entre le signal 6mis par la base de Schiff et le N A D H au cours de t r a v a u x r6alis@s avec les microfluorim@tres utilis@s pour 6tudier les modifications du niveau d ' o x y d o -r6duction des nucl@otides de la p y r i d i n e sont discut6es. This is to r e p o r t a new t e c h n i q u e w h i c h enabled us to d o c u m e n t the presence of h e t e r o c h r o m a t i n in Nigella, a species in which a lack of d e m o n s t r a t a b l e h e t e r o c h r o m a t i n was r e p o r t e d previously :. The t e c h n i q u e is a modification of t h e cytological procedures used for the d e m o n s t r a t i o n of h e t e r o c h r o m a t i n in rye chromosomes 2. Actively growing p r i m a r y root tips of Nigella damascena var Miss. Jekyl, were p r e t r e a t e d in m o n o b r o m o n a p h t a l e n e solution for 3 h at r o o m t e m p e r a t u r e and fixed in glacial acetic acid o v e r n i g h t (22-24 h). After fixation, the root tips were softened by i m m e r s i n g in an e n z y m e solution * for 1/~ h at r o o m t e m p e r a t u r e . The r o o t t i p s were t h e n squashed. The cover slips were s e p a r a t e d f r o m t h e ...

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