CANALES DE COMERCIALIZACIÓN

W hile c o n sid e rin g th e e f f e c t o f flo o d in g -in d u c e d a n a e ro b io s is on th e o rg an ic a c id component o f ro o t tis s u e m etabolism , i t i s

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a ls o im p o rtan t to c o n s id e r any o th e r f a c to r s which m ight he a f f e c tin g th e a c id l e v e ls . One such f a c to r i s th e c a tio n -a n io n b alan ce in th e ro o t t is s u e s .

The a b s o rp tio n o f c a tio n s and an io n s by p la n t ro o ts does n o t n e c e s s a r ily o ccu r a t e q u al r a te s from even a s in g le s a l t s o l­ u tio n , and p r e f e r e n t i a l a b s o rp tio n o f io n s from th e e x te rn a l en­ vironm ent i s n o t an uncommon phenomenon (Jaco b so n & O rdin 1954). S ince th e t o t a l charge o f th e io n s in s id e p la n t c e l ls must be e l e c t r i c a l l y e q u al to z ero , th e r e must be mechanisms a v a ila b le f o r m a in ta in in g c a tio n -a n io n eq u iv alo n cc fo llo w in g unequal io n a b s o rp tio n . N o tw ith stan d in g exchange f o r p re v io u s ly ab so rb ed io n s , th e raain tain an ce o f io n b a lan ce may depend upon m etab o lic changes w ith in th e r o o t, and th e re i s evidence t h a t th e most im­ p o r ta n t means o f io n com pensation l i e s w ith in a l t e r a t i o n s to th e m alic a c id f r a c tio n o f th e o rg an ic a c id s o f th e ro o ts (Jaco b sen & O rdin 1954). E xcess c a tio n u p tak e , r e l a t i v e to an io n u p tak e, has been shown to r e s u l t in an in c re a s e in TCA c y c le a c id s (Jo h n ­

son, Jack so n ,1 Adams 1963)? and when ex cess an io n uptake o ccu rs th e re i s lik e w is e a d e c re a se in th e a c id s . Changes in c e l l sap pH, which wore p ro p o rtio n a l to o rg an ic a c id changes in th e r o o ts , were induced by unbalanced io n uptake in e x c is e d b a rle y r o o ts w ith in 15 m inutes ( H ia tt I9 6 7).

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uptake p ro b ab ly ooour w ith in c e l l v acu o les (T o r ii & L a tie s I966) . C e rta in ly , th e norm al fu n c tio n in g of th e TCA c y cle cannot account f o r th e changes, as m alic a c id i s a member o f th e c y c le , and some p o o l system has to be v is u a lis e d to accommodate th e m alate in c re a s e s and d e c re a se s which have beon o b serv ed . I t i s a ls o u n lik e ly t h a t o rg a n ic a c id p ro d u c tio n upon excess c a tio n u ptake o ccu rs th rough th e o x id a tiv e d eam in atio n o f amino a c id s , f o r in e x c ise d b a rle y r o o ts th e re vras no c o r r e la tio n betw een th e fo rm a tio n o f o rg an ic a c id s and th a t o f ammonia o r am ides, as would have been n e c e ssa ry to su p p o rt t h i s th e o ry ( U lric h 1941).

I t co u ld be arg u ed t h a t , sin c e ex cess c a tio n u p tak e can le a d to in c re a s e d m alic a c id c o n te n t in th e r o o ts , th e observed r i s e in m alate le v e l in th e r o o ts o f flo o d ed h e lo p h y te s may be a rc f - l e c ti o n o f in c re a s e d c a tio n uptake fo llo w in g th e p ro v is io n o f H o ag lan d 's s o lu tio n . However, i t must be p o in te d out t h a t am.

in c re a s e in th e r a t e o f c a tio n uptake in tu rn su g g e sts t h a t tl 3

r a t e o f re s i r a t i o n in th e ro o t tis s u e s h as in c re a s e d . F u rth e r­ more, t h i s in c re a s e in tis s u e r e s p ir a tio n upon flo o d in g in the h e lo p h y te s can be compared w ith th e s itu a t i o n in th e flo o d e d > 3n- h e lo p h y te s , where th e re h as been no in c re a s e in m alic a c id , he nee no in c re a s e d c a tio n u p tak e and hence no in c re a s e in th e r a t e c f r e s p i r a t io n . In o th e r w ords, th e v a li d i ty o f th e th e o ry t h a t flo o d to le ra n c e in r o o ts can be r e la te d to a s p e c ts o f th e o rg an ic a c id m etabolism i s n o t a f f e c te d by any a c id change b ro u g h t about

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by unbalanced io n a b s o rp tio n .

A f u r th e r in flu e n c in g f a c to r on th e o rg an ic a c id le v e ls h as been m entioned e a r l i e r , nam ely t h a t o f a r o le in c arb o h y d rate s to ra g e . Tho h ig h l e v e ls o f sh ik im ic a c id in th e la r g e , f le s h y rhizom es o f I r i s p seu d aco ru s and Nuphar l u te a su g g e st th a t changes in le v e ls o f t h i s a o id , and u ro b ab ly of m alate a ls o , a re more

r e la te d to th e u t i l i s a t i o n o f carb o h y d rate, re s e rv e s th a n to p a th ­ ways concerned w ith flo o d to le r a n c e .

O rganic a c id f lu c tu a tio n s in p la n t t is s u e s may be a ls o a t t r i b ­ u te d to ’com partm entation* o f th e s e a c id s in to 'p o o ls ' w ith in th e c e l l s . The p resen c e o f such p o o ls , where la r g e amounts o f in d iv id ­ u a l a c id s a re p h y s ic a lly rem ote from th e r e s p ir a to r y c e n tr e s , h as been d em o n strated in ro o t tis s u e s in m aize, c a r r o t and b e e t (T ab le 12)

Table 12. Amounts o f in d iv id u a l a c id s e s tim a te d to be in tu r n ­ o v er p o o ls (jj mole / g fre s h w e ig h t). (From HacLennan, B eovers & H arley 1963)»

A cid m aize r o o t c a r r o t r o o t b e e t ro o t w heat l e a f (1s t cm)

C itr ic 0.35 0 .6 0 0.86 0.09

S u c c in ic 0 .1 8 - - 0.15

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I n th e p re s e n t work th e la r g e changes w hich were found in s e v e ra l of th e a c id s in d ic a te t h a t th e y could n o t be sto ra g e p ro d ­ u c ts is o la te d from a c tiv e c e l l m etabolism , and th e fo rm a tio n o f new a c id s must have been in th e cytoplasm and n o t is o la te d from

enzyme s ,

ÎÆSTABOLIC ADAPTATIONS WITH REGARD TO ECOLOGICAL AMPLITUDE

P la n t s p e c ie s which a re m e ta b o lic a lly ad ap ted to w ith sta n d p e rio d s o f a d v erse c o n d itio n s , such as flo o d in g , a re a t an advan­ ta g e over th o se in whom th e re i s no such a d a p ta tio n . The form er ty p e o f p la n t may su rv iv e and even f lo u r is h in a h a b it a t where a tem porary, s h o rt-te rm p e rio d o f flo o d in g ex clu d es th o se non­ a d ap ted , n o n - to le r a n t s p e c ie s . The d i s t r ib u t i o n o f sp e c ie s ii and around such s i t e s i l l u s t r a t e s t h e i r e c o lo g ic a l am plitude j n re s p e c t o f flo o d in g . For exam ple, w ith in th e genus E r ic a, e x p e ri­ m ental flo o d in g r e ta r d s th e grow th and may even k i l l E. c in e rc a , b u t does n o t a f f e c t E. t e t r a l i x , and in th e f i e l d th o se s i t e s

su p p o rtin g E. t e t r a l i x te n d to be w aterlo g g ed , y e t th o se s u p p c rt- in g E. c in e re a much d r i e r (B a n n is te r 1964a , 1964b ) . In a d d itio n to i n te r s p e c i f i c d if f e r e n c e s th e r e may a ls o be i n tr a s p e c i f i c ones, f o r in S enecio v u lg a r is th e flo o d in g to le ra n c e o f a garden ra c e was found to be g r e a te r th a n t h a t o f a sand-dune ra c e (C raw ford

83.