Ratios de endeudamiento parcial del total de empresas

7 6 5 4 3 2 1 IAA-asp. I AA. 1---4 1---4 IAA-asp. 1---4 Rf F I G U R E 25 - EM X I I . 7 6 5 4 3 2 1 IAA-asp. IAA. 1---1 1---i I AA -asp. _{I AA.} 1---4 t----1 Rf Rf MM 1 06 - IBA. E M X I I . - I BA.

Histograms of chromatogram segments of the 2 -_{14c -}IAA external solution . The solvent system was isopropanol : N H40 H : water (8 : 1 : 1 .5 v/v ) .

c ompounds des cribed by Leopold and Plummer (1961 ), rel eased from the cut ends of the cutt ings and l e ached from the cut ting base s. The activi ty i n thi s zone was not cons i dered to be of any real signi fi cance in the me tabolism o f

14c-IAA.

No maj or me taboli te was l ocated in the external media , sugge s t ing that they are not free ly mobi l e once formed.

In external s oluti ons o f bo th 1 - 1 4c-IAA and 2-1 4c-IAA experiments, the level of remaining 1 4c-IAA in the external s oluti on was always higher in treatment s which had included an IBA pre-treatment of the cuttings. Thi s was much more evident i n MM 1 06 than in EM XII.

( 3 ) Al c ohol Extracts of

Two maj or zones of ac tivi ty were located on chromatograms o f the al c o ­ h o l extrac ts , one corresponding t o IAA and one c orres ponding t o indoleace tyl aspartic acid (IAA-asp.). Fi gure 26 pre sents radi ochromatograms of al c oho l i c extrac ts o f the two roots tocks treated wi th 1 -1 4c-IAA . Cuttings o f both MM 1 06 and EM XI I pre treated wi th IBA retained a higher level of ac tivi ty i n

the IAA z one than untreated cut t ings. !n both cases the rati o of IAA l evel between IBA-treated cuttings and untreated cut tings was approximately 2 : 1 .

In MM 1 06 cuttings the degree of IAA-asp. conjugate formation i s very

different be tween IBA-treated and untreated cuttings. The l evel of IAA-asp . i n IBA-treated cut t ings i s only one �uarter o f the free IAA level , whereas in unt reated cuttings, c onjugati on has pro ceeded to a much greater degree, so that twice as much activity re sides in the IAA-asp . zone c ompared t o

free IAA .

In EM XII cuttings , tho s e treated with IBA show no devel opment o f IAA-asp. c onjugation, whereas untreated cuttings show only a l ow devel o pment of IAA-asp. In gene ral the c onjugation reaction s eems to be much slower i n

g 0 )( E ri u d

�

)( _{. 3} E � t.l IAA-asp. t--1 I AA -asp. .-.--. IAA 1---i Rf IAA � MM 106 + I BA. EM X I I . + I BA. 1 ci 0 0 IAA-asp. 1---i I AA -asp. .-.--. IAA .-.--. Rf IAA � MM 106 - IBA. EM X I I. - IBA. ,... 5 F IGURE 26. )( e ri u 3 2 Rf Rf

H istograms of chromatogram segments of the alcoholic extracts of MM 106 and EM X I I

hardwood cuttings treated with 1 - 1 4c -IAA. The solvent system was isopropanol : N H40H : water (8 : 1 : 1 .5 v/v).

Figure 27 shows radi ochromatograms of al coholic extrac ts of EM XII and

MM 1 06 cut tings after exposure to 2 -1 4c-IAA . A s imilar pattern emerges with

2 -1 4c-IAA as was evident in cut tings treated wi th 1 -1 4C-IAA. In IBA-treated

MM 1 06 cuttings, the IAA-as p. activity is restricted to approximately one third o f the act ivi ty of IAA , but in untreated cut tings, 2.5 time s the ac t ivi ty of IAA was located in the IAA-asp. z one. More than twice as much ac tivi ty in the free IAA z one was pres ent in the I BA-treated cutt ings c om­ pared wi th untreated MM 1 06 cuttings.

EM XI I cut tings pre -treated wi th IBA show only minimal IAA-asp. c onju­ gat i on , but untreated cuttin,'·s have an IAA-ASP. ac tivity approaching one half the activi ty of free IAA. As was found in MM 106, the activi ty found in the free IAA zone was twice as high for IBA-treated cut tings than

untreated EM XI I cuttings.

( 4 ) Alcohol Insoluble

T i s sue remaining after alcohol extraction underwent alkaline hydrolysis and e ther extraction. In both MM 1 06 and EM XI I tissue treated wi th both carboxyl and me thyl ene l abelled IAA , very little ac tivi ty was obtained after hydrolysis. ChromatogTams showed that any activi ty pre s ent was l ocated at Rfs 0 . 0-0. 1 and Rf 0.5-0.6 ( IAA ) . The ac tivi ty ob tained was only minimally above background l evel s and was not consi dered to be s i gnifi cant in the met abolism of 1 4C-IAA . Thi s was veri fied by analysis o f activi ty budget s whi ch showed that almos t al l the activity was accounte d f o r i n the 1 4co2 ,

1 0 _{IAA-asp. IAA}

9 IAA-asp. IAA MM 1 06 1---1 1---i MM 1 06

8 1----1 1--1 + IBA. - IBA. 7 7 0 6 0 6 0 0 0 0 ,... 5 .... 5 )( )( E 4 E 4

� 3

� 3

2 2 1 1 Rf 1 0 1 0 EM X I I. EM X I I .

IAA-asp. IAA _{+· I BA.} - I AA-asp. I AA _{- IBA.}

1---1 1---1 1---1 1---1 8 8 7 7 0

_g

₆ g 6 .... 0 )( 5 .... ₎₍ E _{4 E 4} ci. _ci. t.i t.i

3

3

2 2 1 1 Rf Rf F I G U R E 27

Histograms of chromatogram segments of the alcoholic extract of MM 1 06 and EM X I I

hardwood cuttings treated with 2 - 1 4c - IAA. The solvent system was isopropanol :

DISCUSSION

The concept of promo tion o f root ini tiation by IAA i s now general ly accepted. Exogenous appli cati ons of IAA or synthetic auxins ( IBA , NAA , 2 , 4- D ) have been shown to promote root ini t i at i on on cuttings of fruit tree rootstocks ( Cooper , 1 9 3 5 ; Hatcher and Garner , 1 947 ; Hartmann � al . , 1 96 5 ; Howard , 1 966 , 1 96 8a; Callson, 1 966 ; Nahlawi and Howard , 1 97 1 ;

Doud and Carl son , 1972). A tradi ti onal interpre tation has been that exo­ genous auxin applications increase the to tal auxin pool to a level -v�hich wi l l promo te root ini t iat ion. Resul ts from Sections I and II demons trated that roo ting was promoted by endogenous IAA and that IBA could only further promo te root ini tiation in the presence of a thre shold l evel of IAA ; a s imi lar situation was observed by Lanphear and Meahl (1 96 3 ).

Treatments of IAA , IBA or both promo ted roo ting in MM 1 06 rootstock ( s e e Table 4 ) , when compared wi th the control in terms of the numbe r o f cut tings rooted. When c ompared on the bas i s o f average number o f roo t s per cut ting, the IAA treatment was not significantly different from the c ontrol but the lack of s tati s t i c al signifi cance was only marginal. Simi la�ly the IBA t reatment was no t s i gnificantly different from the IAA treatment but this lack of signifi canc e was al so marginal. A combined treatment was s i gni ficantly better than al l other treatments. With EM XII roots tock, the only treai _:.�ent to induce roo t ini tiation was the IAA/IBA combined t reatment ( Tabl e 5 ) . Root ini tiat i on on MM 1 06 appeared t o be promoted more readily by IBA than IAA , the c ombinati on producing an addi tive promotion. Thi s sugges ted that both IAA and IBA have a role in the same physiologi cal pro c e s s but that they do not both act on the s ame process. In EM ;ai

roo t s tock , neither exogBnous auxin stimulated root ini tiation when applied

148.

Thi s indicated that ne i ther IAA nor IBA al one c ould reach an optimum l evel for promo ting rooting· , bu t in combination , ei ther the total auxin l evel or the c ombined reac tions o f IAA and IBA , served t o promo te roo t ini tiat ion.

Knowledge of the endogenous l evels o f IAA i n the two roo t s tocks l e d to the c onclus ion that confounding of the resul t s had occurred. Since MM 1 06

had a l evel o f endogenous IAA which fac i l i tated the roo t ing of a high percentage of the cu ttings throughout the season, marked promo tion by the addi t i on of further IAA was not likely to be forthcoming. Furthermore, the addi t i on of IBA would be expected to give a cons iderable degree of roo ting promo ti on. EM XI I was found to re tai n a very l ow level of endogenous IAA through the seas on, so t he concentrat ion appl i e d (0.1%) di d no t necessarily rai se IAA l evel s to an optimum level. The fai l ure of IBA al one , t o promo te ro oting in EM XI I no ted in Sec tions I and I I , was again evident.

Treatments de signed to overcome the respe c t ive complicating fact o rs were used to modi fy the experiments. A spec tacular removal of the roo ting abi l i ty of MM 1 06 was achi eved using centrifugat ion and cut ting bas e removal.

Examination of centri fugates and tissue samples indi cated that a raduc t i on in the endogenous IAA l eve l wi thin the cut tings ac counted for the dec reased roo ti ng abi l i ty. Re s to rati on of the roo ting abi l i ty of MM _{1 06} in terms of numbers rooted and the average number of ro o t s per cutting was achi eved by both IAA and IBA appl i cation; the combined t reatment again showed an

addi tive promo t i on effect (Table 7 ) . A ten-fo l d increase in the IAA c oncen­ tration applied to �[ XI I cut tings did no t promo te roo ting in the IAA t reat­ ment. An effective IJrorr.o t i on of rooting of 5afo

(

i .e. from 4o% to

6Cf/o

o f the cut t ings roo ted) was observed in the combined t reatment, i . e . by increasing the IAA level, rooting was promoted in the IAA/IBA treatment (Table 6 ) .

and the increased s timulation o f rooting i n a difficul t-to-root speci e s , were related to the changes in level of endogenous and exogenously supplied

IAA . Since IBA also res tored the ability o f MM 1 06 cuttings to roo t , the

e ffect of changing IBA c oncentrati ons on roo t i nitiation was evaluated.

Changes in IBA c oncentration from 2 , 500 ppm to 20,000 ppm had no

s i gnificant effect on the number of cuttings rooted or the average number

of roots per cutting in MM 1 06 and EM XI I ( Tabl e s 8 and 9 ). Thi s indi cated

that once an optimum l evel was achi eved in the cutting base , no further

promot ion was obtained by increas ing the IBA concentration. Because the

I BA-promoted rooting s t imulus could easily be s aturate d , the postulation

that IBA promo tes rooting by the same mechani sm as IAA does no t seem t enable.

An effect on s ome supporting mechani sm of IAA-induced roo t ini tiation,

appeare d to be the mo s t likely role of IBA in promoting root formation.

IAA appeared to be the fundamental promot er of root ini tiation i n apple roots tock hardwood cut tings. The mo s t recent research reports on the physiolo�- of root ini t iat ion indicated that root ini tiation was an IAA­ specific mechani sm and that IAA influence d the first " initiation of root meri stems '! phase of adventi tious roo t regeneration ( Greenwood and Gol dsmi th , 1 97 0 ; Hais sig, 1 97 0 , 1 97 3 ; Smi th and Wareing, 1 97 1 , 1972a, b ; Eriksen and Mohammed , 1 974 , Mohammed and Eriksen , 1 97 4 ; Greenwood � 1 974 ; Ryugo and Breen , 1 974 ; Mohammed , 1975). Furthermore, a continuous IAA supply during the ini tial primordial devel opment was essenti al for root ini t i ation ( Haiss ig, 1 97 0 ; Greenwood e t 1 974 , Mohammed and Eriksen, 1 974 ) . Resul ts in Section III suggested that root ini tiation in MM 1 06 and

EM XII was controlled primarily by endogenous IAA levels. No evi dence that IAA acted by forming c omplexes wi th cofac tor-l ike compounds as sugge sted by He s s ( 1 96 5 ) and Fadl and Hartmann ( 1 967 a , b ) , was found . Total removal and res toration o f the rooting s timulus in MM 1 06 were directly relate d t o

1 50.

leve l s of free IAA wi thin the cuttings. Whi l e root ini tiation in EM XII

c ould no t be promo ted by IAA alone , different levels of applied IAA , in c ombinati on with a standard IBA treatment, increased the promotion o f roo t ing cons i derably. Because EM XII had a very low free IAA l evel in a rapid and vi gorous IAA-inactivation sys tem may operate whi ch inactivates exogenous ly-applied IAA when admini stered alone , thus preventing the in­ duc t i on of ro o t primordia. This could al s o explain why a spring peak o f roo ting of EM XI I seen i n Section I was only evi dent after an IBA pre­ treatment. :MM 1 06 could have a less vigorous IAA-inac tivati on sys tem in

enabl ing high l evels of endogenous IAA to be re tained by the ro o t­ s tock.

There was no evi dence that IBA ac ted on the same root -promo ting processes as IAA in ei ther roo t s tock. Thi s casts doubt on the interpretati on of re­ sul ts by equat ing exogenously-applied synthe tic auxins wi th endogenous IAA ;

in terms of a total auxin pool reaching optimum requirements. IBA c oul d only promo te rooting in cuttings containing near-optimum levels o f I AA . Therefore IBA must have promoted root ini tiat ion by some supporting reac tion t o that of IAA . Ryugo and Breen ( 1 974 ) found that IBA inhibited IAA-oxidas e ac t ivity as measured by the rate of 1 4co2 evoluti on, in plum cut tings .

Inhibi tion o f the IAA-inac tivation sys tems i n appl e roots tocks could account for the observed promo ti ons of root ini t i at i on in

MM

1 06 and EM XI I. In roots tocks wi th a hi�n endogenous !AA level

(MM

1 06 ) , any inhibi t i on of IAA inac tivation would al l ow optimum levels of IAA to accumulate more rapidly

in the cutting base , fac i l i tating greater induc tion of root primordia , the auxin sensi tive phase of root ini tiation ( Hai s s ig, 1 97 0 ; Greenwood � al . ,

1 97 4 ; Mohammed and Eriksen , 1 974 ). Thi s would be reflected in a p romotion o f root ini t iation, both in numbers roo ted and average number o f roots per cut ting. In roo t s tocks wi th a l ow IAA s tatus ( EM XII ) application o f IBA may not promo te roo ting, s ince insufficient IAA may have been synthe sised even though IAA inac tivation systems were inhibi ted. I f IBA was applied

and the endogenous IAA l evel increased ( e.g. by spring bud-burst or by

exogenous IAA-lanolin appl i cation ) simul tane ously , the IAA woul d be pro tected from inactivation and coul d then induce root initiat ionq It is proposed that this mode o f ac t i on coul d occur in EM XI I cut tings s ince : -

( i ) an increas e in endogenous IAA re sul ti ng in improved rooting in early spri ng \-las ei ther protected by or the resu l t of an IBA pre treatment pri or to plant ing the cuttings.

( i i ) the only treatment t o ini ti ate ro o t s on EM XII cuttings was the IAA/IBA combination.

( i i i ) by increasing the IAA level to 1 % IAA in lanol in, a 5o% promo t i on in roo t initiation was achi eved on EM XII

cu ttings rece iving the combined IAA/IBA treatment, compared wi th a 0.1 % IAA-lano lin appli cation.

In document TítuloEvolución del nivel de endeudamiento de las empresas en España (página 36-40)