G LU C O SE FRUCTOSE - 6 - P G L U C O S E -6 - P G L U C O S E - 1 - P FRUCTOSE U D P - G LU C O S E A D P - G LU C O S E °C—(1,4)G LU C A N
F ig u r e 1.10 Some e n z y m e -c a ta ly s e d re a c tio n s t h a t c ould be in v o lv e d in th e c o n v e rs io n o f s u c ro s e to ( 1 - 4 ) - g l u c a n in d e v e lo p in g cereal e n d o s p e rm s , 1 , U D P ( A D P ) - d e p e n d e n t s u c ro s e s y n th a s e ; 2 , i n v e r t a s e ; 3, h e x a k in a s e ; 4, f r u c t o k i n a s e ; 5, glu co se p h o s p h a te isom erase; 6, p h o s p h o g lu c o m u ta s e ; 7, A D P ( U D P ) - g lu c o s e p y r o p h o s p h o r y la s e ; 8, n u c le o s id e - d i p h o s p h a te k in a s e ; 9, in o r g a n i c p y r o p h o s p h a t a s e ; 10, A D P ( U D P ) - g lu c o s e s ta rc h s y n t h a s e . - From D u ff u s and C o c h ra n e (1 9 8 2 ).
20.
G ra in d e v e lo p m e n t r e p r e s e n ts a n e t s y n t h e s is and d e p o s itio n of s t a r c h . T h e r e is e v id e n c e f o r th e p re s e n c e o f b o th g l y c o l y t i c and p e n to s e p h o s p h a te p a th w a y enzym e a c t i v i t y in d e v e lo p in g b a r le y end o sp e rm and o t h e r r e p o r t s o f s t a r c h - d e g r a d i n g enzymes ( D u f f u s and C o c h ra n e , 1982). The se asp e cts o f s t a r c h metabolism in w heat are r e le v a n t to p r e m a tu re s p r o u t i n g and th e e ffe c ts o f h ig h « -a m y la s e a c t i v i t i e s on b re a d m a k in g q u a l i t y .
G ord on (1980) and K in g (1983) re v ie w e d s p r o u t i n g in w h eat. G ra in p h o s p h o r u s c o n c e n tr a tio n has n o t been im p lic a te d in s p r o u t in g o r d o rm a n c y p ro b le m s in w h e a t b u t Jain e t al. (1982) and Q u ic k et a l. (1 9 8 2 /8 3 ) have noted n e g a tiv e c o r r e la t io n s between in o rg a n ic p h o s p h o r u s and th e d e p th o f d o rm a n c y in o a ts . 1 . 3 . 6 P h o s p h o ru s d e p o s itio n in g r a in Whole, m a tu re w h e a t g r a in s have a to ta l p h o s p h o ru s c o n c e n tr a t io n of b e tw e en 0.08% ( G . J . B l a i r , p e rso n a l co m m u n ic a tio n ) and 0.76% (S o fie ld et a l . , 1 97 7b). T h e m a jo r ity o f th e p h o s p h o r u s in m a tu re cereal g r a in is in th e fo rm o f p h y t a t e ( F i g u r e 1 .1 1 , 1 . 1 2 ) . P h y ta te re c e iv e d a tte n tio n d u r i n g World War II w hen i t was shown t h a t b ro w n b re a d was i n f e r i o r to w h ite b re a d as a so u rc e o f calcium in humans (M cC ance and W id d o w so n , 1942). R e c e n tly many n u t r i t i o n i s t s have s in g le d o u t p h y t i c acid and to a le sser e x t e n t f i b r e as th e cause o f low b i o a v a i l a b i l i t y o f m in e ra ls fro m p l a n t fo o d s , even a f t e r allow ance f o r th e lo w e r o v e r a ll d i g e s t i b i l i t y o f p l a n t food com pared to animal p r o d u c t s ( C h e r y a n , 1980).
Even some A m e ric a n d ie ts are d e f ic i e n t o r m a rg in a l in ions such as i r o n , z in c , calcium and m agnesium and t h e N ational Academ y o f
OPO-H, OPO-H,
OPO-H,
OPO_H,
F ig u r e 1.11 P h y tic acid o r m y o in o s ito l h e x a k is p h o s p h a te , t h e salts o f w h ic h are r e f e r r e d to as p h y t a t e ( C o s g r o v e , 1980a). T h e s t r u c t u r e p ro p o s e d b y A n d e r s o n (1914 ) is shown h e re . Q _ GO Z D Cd CD a _ oo o _ C D LlJ £ h — 0 0.1 0.2 0.3 0.4 0-5 T O T A L P HOS P HORU S ( % P ) F ig u r e 1.12 Examples o f th e r e la t io n s h i p betw e en to ta l p h o s p h o r u s ( T P ) and p h y t a t e b o u n d p h o s p h o r u s (P P ) in w h e a t. The t h e o r e tic a l 50 and 100% r e la t io n s h i p lines have been in c lu d e d to em phasize t h a t PP%TP in c re a s e s w i t h TP and is u s u a lly > 50%.
Lines 1, 2 and 3 f o r w h e a t g r o w n u n d e r d r y l a n d c o n d itio n s at Wagga Wagga ( B a t t e n and K h a n , u n p u b l is h e d d a t a ) , 4 and 5 w h e a t g r o w n in Ira n (N a h a p e ta in and B a s s i r i , 1976); 6 w h eat g r o w n in M ic h ig a n and Kansas (L o la s et a l . , 1976).
21.
Science has p ro p o s e d t h a t cereal fo o d s be f o r t i f i e d w i th th e s e ca tio n s ( N A S / N R C , 1974).
N u t r i e n t d e fic ie n c ie s du e to p h y t a t e are more e v i d e n t in societies w h ic h consume w holem eal, u n le a v e n e d g r a i n s . F a cto rs a f f e c t i n g th e d e s t r u c t i o n o f p h y t a t e d u r i n g b r e a d m a k in g and th e b i o a v a i l a b i l i t y o f ions are n o t well u n d e r s to o d ( T a n g k o n g c h i t r et a l . , 1981,1982; E rd m a n , 1981; R a n h o tra e t a l . , 1981). T h u s a b e t t e r u n d e r s t a n d in g o f f a c t o r s a f f e c t i n g th e f o rm a tio n o f p h y t a t e in g r a in s is r e q u i r e d .
P h y ta te is d e p o s ite d in d i s c r e t e r e g io n s (c a lle d g lo b o i d s ) o f c e l lu l a r o r g a n e lle s w h ic h are u s u a ll y r e f e r r e d to as p r o t e in bodies o r a le u ro n e p a r t ic le s (see Loewus and L o e w u s, 1983 f o r r e fe r e n c e s ; also T a n a k a et a l . , 1 9 7 4 a ,b ; Ogawa e t a l . , 1977). T h e f o rm a tio n and s u b s e q u e n t b re a k d o w n o f p h y t a t e a p p e a r to o c c u r o n l y in these s u b c e ll u la r r e g io n s , i . e . p h y t i n - c o n t a i n i n g p a r t ic le s are immobile (L o e w u s and L o e w u s , 1 98 3). T h e d i s t r i b u t i o n of p h y t a t e w i t h i n th e seed v a r ie s be tw e e n sp e c ie s . In o ilse e d s (e.g,soybeans') p h y t a t e o c c u rs t h r o u g h o u t th e k e rn e l ( M a r t in e z , 1977; Maga, 1982). Wada and Maeda (1980) d i v id e d g ra m in e o u s seeds in to tw o g r o u p s a f t e r e x a m in in g th e size and f r e q u e n c y o f g lo b o id s in a le u ro n e and s c u t e ll a r tis s u e s and th e to ta l p h o s p h o r u s c o n t e n t o f e m b ry o s and e n d o s p e rm s . G ro u p I F e a tu re s A la rg e p r o p o r t i o n o f P in th e a le u ro n e la y e r , b u t b o th a le u ro n e and s c u te llu m r ic h in P. Species B a r l e y , o a t, o r c h a r d g r a s s , r i c e , r y e , w h e a t. II B o th th e a m oun t and th e c o n c e n tr a t io n o f P in th e s c u te llu m w e re g r e a t e r th a n in th e a le u ro n e la y e r . M ille ts ( b a r n y a r d , common, f i n g e r ,
Ita lia n and P e a r l ) , maize, s o r g h u m , Job's t e a r (C o ix s p ) .
2 2
.
B io s y n t h e s is o f p h y t a t e
Loewus and Loewus (1983) p ro p o s e d th e r e la t io n s h ip s t h o u g h t to be in v o lv e d in p h y t a t e f o r m a t io n , a c c u m u la tio n and b re a k d o w n in s e e d - b e a r in g p la n ts ( F i g u r e 1 . 1 3 ) . T h e p r o d u c t s o f p h o to s y n th e s is lead to g lu c o s e - 6 - P , 1 L - m y o - i n o s i t o l - 1 - P and th e n to p h y t a t e v ia th e a c tio n s o f th e enzymes 1 L - M I- 1 - P s y n th a s e and p h o s p h o in o s ito l k in a s e .
Loewus and Loewus (1983) c ite d r e p o r t s w h ic h s u g g e s t t h a t M I-1 -P and M I - 2 - P a re p r e c u r s o r s o f p h y t a t e . T h e y c o n c lu d e d t h a t t h e r e is l i t t l e e v id e n c e as to th e f i r s t p h o s p h o r y la te d in te r m e d ia te le a d in g to p h y t a t e .
Loewus and Loewus (1983) re v ie w e d th e a v a ila b le in fo r m a tio n on t h e enzymes show n in F ig u re 1 .1 3 . B r i e f l y , th e a c t i v i t y o f s y n th a s e is s tim u la te d b y some io n s , e . g . ammonium, and p o ta s s iu m , and in h i b i t e d b y in o r g a n i c and p y r o p h o s p h a t e , sodium and a ra n g e o f p h o s p h o r y la t e d s u g a r s . T h e s y n th a s e is p r e s e n t in c y t o p la s t i c and c h l o r o p la s t i c f r a c t i o n s o f p l a n t s . In beans and in ric e g r a in s p h y ta s e show s a peak o f a c t i v i t y 14-16 d a y s a f t e r f l o w e r i n g .
C o s g ro v e (1980a) re v ie w e d th e f i v e p h y s io lo g ic a l roles s u g g e s te d