Studies on foliar abscission

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Authors Sullivan, William James, 1926-

Publisher The University of Arizona.

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STUDIES 01 FOLIAR ABSCISSION

This thesis has been submitted in partial fulfillment of requirements for an advanced degree at the University of Arizona and is deposited in the Library to be made available to borrowers under rules of the Library. Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the dean of the Graduate College when in their judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author*

SIGNED:

ACKN0WLED-GE1EHTS

This work, was made possible wider a fellowship from the Department ©f Botanyj, University of Arisonao I wish; to express my siaeer® appreciation t© Dr0 Bo B» Kurts, Dr® Mo 'So Phillipss, and Dr* Rs M0 Harris9 University of Arizona •for their valuable . suggestions throughout the problem*

TABLE OF GOMTEMTS:

LMTHODUGTIOM s o » . » * 0 o o * « «, . oREVIEW AID PROPOSED MEGHAIISM OF ABSGISSIOIMETHODS AMD RESULTS 0 «> e' 6 » . 0 „ -y. o o »BISGUSSIOl AlD GOieLUSIOMS V » • * » » o '.

o e o o 0 , 0 o o o o o a o o 6 o o

LITERATURE CITED O o O o - o O O o O ^ Q G O

LIST OF FIGURES.

Pagesection ©£' .very young petiole ,

sission area o '.

LISt OF TABLES

■I,

■II,

imr@ % q far-#> o % JKWLp 0 AM V o X £ , 4*^20e».53 t #

O 0 O O O vO O t> O O O O 0 O © 0 0 © o O

total lei eated with si

8g 10

1

IITROBUGTJOI

in the. gross aspect is concerned with si ditig of harkg. opening of seed e@ntain.ersg , frmit 'drop,

a shedding of leaves^ and:many other.similar The present study is" limited to foliar©ms @f

abscission® • It the foe,

that ences foliar afoseisgietio Beoata.se ©f the lew>©raS$ir©s during the winter9 an, infra red heat lamp

plants. of the same a heat lamp did

ageleaves* Barini were gs

am influence "on the. rate of f©l&» This .preliminary observation ini# the effect of white and•infra red

Lght on

REVIEW AMD PROPOSED MEGHAIISM OF ABSCISSION

tot 13,i. aiiatomieal stMies* but ia' that

ed theas Fr@m 1917 t@ 1933was ±ateasifi@i&: It was

leubt. {51 noted abscission by &tl@m along thi

in.gated e

JSep-sual transition from long days of summer te short days of m

88 [211 dim#the' ®i

the, but that.this is ©

.G&lgt©a and Hand |S) fomnd that ^Whem terminal s@®ti©ms ©f @ti@lat@d pea epieetyl are ®3£©i®@d and grem in aqiae©ms medlag the grewtk is dependent. ©a auxin eomeentratioias -Hew^ ewrs at any giwn amxin levels ishite light decreases the amount ©f growth pr©dm©edo This deerease- is not .due to dlf# ferenoes- in -amein ©ontent between- darkened and Illuminated tissm®s3 but rather t© a light®iadmeed differential response t© auxin®, Very brief exposures t© light b@f®re9 during9 ©r after auxin treatment are to earnse .marked reduetions im

luxineindueed. elongation ©f etiolated pea epie@tyls was

.that moraslly x-jould not respemd t® IAA-®- ..BdrShyiek et ale (2) .shetied that gemmiaatloa ®f Imbibed

Laetaea matlva seeds is- iBflneneed by ©xp®smre to,..r®d:..aad iafra red., mdiatieaso If the last -ezposmr© gif ea the. seeds was" red' light 0 germiaatioB was at. .least 9$ per eent $, but if

fa) Pigmemt -H EX - & Pigment X-h E6900 i Maxo 7300 1. Maxo

. Sermamt ; §emiaatiag -

eemplex ESg and IS ean then initiate the auxin response» In

6

This series of equations is combined into the cyclic form as follows. Auxin

responsesES\ Dark

Infra Red \ (slow) light \(fast) \S +E

edlight

In addition to the effects of light on abscission and light on auxin many studies have been made of the effect of auxin on abscission.

In Coleus deblading of leaves stops the elongation of petioles, but the application of IAA to the debladed petiole increases the elongation until the normal length is reached.It was also found that the addition of auxin to the leaf blade delays the formation of the abscission layer, Myers(26).

Rossetter and Jacobs (26) not only confirmed the inhibitory effect of IAA on the abscission of debladed petioles, but found that this effect is influenced by the proximity of whole leaves.

Gardner and Cooper (9) tested 1$6 compounds to determine their effectiveness in delaying the abscission of Coleus petioles. They found that spray applications were relatively ineffective. The best means of application of these compounds

fer delaying abseission was 0o05 per ©ent im lanolin paste# Howeverg IAA was most effective at a .eoneentration of three per ©ent in' lamella paste*

Shoji ^,§1* (5©)s in a study of the' absolute amxin ©one tent of the leaf blade and stalk of beam plants9 found that the auxin content drops rapidly just before abscission® They conclude that abscission is controlled by the auxin gradient rather than the'absolute auxin content©

Im summaryg it has been shown, that light has certain efw feets on foliar abscission, that auxin activity is influenced by various components of light, particularly in the red«far red range of the spectrum# and that foliar abscission is in*, flueneed by auxin* Therefore8 it is proposed that the r@d= far red'range of the spectrum might effect foliar abscission through control of the auxin balance in the plant 0 The pre& sent study has attempted to substantiate this proposed meeha^ aism of leaf abscission« . . -

METHODS AID RESULTS

s were msec

o Bush i>@aE8 mung bean ̂ and sunflower seeds were obtained from Dangers8 Floral Shop9 song Arisonao Castor bean seeds.were grown locallyo Cotton seed was Aeala 44 variety9 Arisona certified seedo

was made to determine at what stage of cotton leaf maturity the abscission son© ©an first be detected micro* sedpie&llyv Various ages of leaves were examined® The mater* ial was fixed in formalin=*aeet©»al@ohol8 embedded in paraffin^

> The earliest noted at a time when stage cell division

leaf blade was very rapid9

Experiment lo® 1 ?e light apparently influences- the' rate of foliar a W

of foliar abseission was stmdiedo Large dark chambers were constructed for this purpose (Figure 2}» These chambers were 5 feet high and feet squareThey were made of one^ineh

ired with corrugated

9

Figure la. Longitudinal section of very young petiole showing abscission area.

Figure lb. Enlarged section of figure la showing cell division.

3 CM. a I FOOT

Figure 2. - D A R K C H A M B E R

plants 12 weeks old were exposed to a oomblmatlem of sunlight and white light from a tungsten 30O«watt Mlhs line plants were used in eaeh groupo These mine plants were ditided into groups of three plants per p@t@ Although - growth was aeeeler# ated by longer photoperiod^ there was a© abseisslen'(Table I)

the quality of the light caused the'abseissloa observed when plants were exposed t© infra red light and sunlight0 Three groups.of twenty plants per group were set upG Gottorn plants 6 weeks © M were used* These and all the plants used in the following experiments were grown in wrrieulite in plastie containers.and supplied with Hoagland$ s complete nutrient

12

Average

Table 10

̂lomrs of phot.operi.od

Height in cm* from ground level to apical bud®

31 Ad 56 65 75, , gy

30 50 60 68 77 9530 58 57 69 76 - ; 77

dead ' 55' 59 66 ; 78 9732 56 58' 73 74 '' 85

31 5:2 60 68 ' 78̂ .1 6932 • 49 59 69 83 1 ; 8931 ' 51 57 62 76 90: t i ; '. A l ZZ ' m

31 52 58 67 78 89

Height .©f cotton plants after exposmr® t@ varioms photoperiods® . ’ ClXp® H©» 1,

53 to 6t=:,12»#53) *•..

Figure 3. Progressive effects of settling sad necrosis* Upper row, left to right; aorssl. slightly settled, fairly settled, eery settled* Bettes row. left to rights very slightly necrotic, slightly secretle, fairly necrotic, very necrotic*

Forty days after the beginning ©f treatment the first leaf fell in the group treated with infra red light (Table Il3"s Sinee abscission is preceded by the above mentioned symptoms% when the experiment was concluded the leaves remaining on the plants were inspected for these symptoms (Table 111)® Based on external appearance9 most of the leaves ©n the plants treated with the infra red light were well toward abscission®

Experiment Ho® 3 Because red and far red light effect auxin content and

auxin influences abscission8 this experiment was to determine if red and far red light ..control abscission*. The chambers ■were 12 x 12 x 18 inches with built in light filters® Two chambers had filters made ©f two layers ©f red and two layers of blue cellulose, acetate designed t@ transmit far red radi«= ation; two chambers with filters-of four layers of.red eelluw loss acetate to transmit red and infra red radiation; and two chambers had filters of four layers of clear cellules® a@@° tab®* . light was supplied from JOCMmtt tungsten bulbs which

15

Days ef .Treatment

Number of' leave#

4243444546

50515253

00000001139

1315

0

6

121315IS.1921

Sunlight : 0

0 0 0 0

000.0000

Table II.® Daily total leaf abseission ©f eotton plants.. . , treated .with sunlight and radiation from bung* -

. sten filament bulb or infra.red lamp* (Ezp, loa Z9 10=1S#53 to 12-9- '

Condition,of leaves remaining on plant

Number of..leaves

white light Sanlightslightly mottled ;: ' 1 0 0moderately mottled 11 0 0very mottled -i . . as a

Total mottled 21 25 0

slightly necrotic 5 : Smoderately meerotic . ? . . 13 - .0very neerotic - i- : : •■In; " &

Total necrotic . 20 42 : ; ' 0

Total . M - 6% ' - ■ 0

Table III® Mottling and necrotic effect on cotton after exposmre t© sanlight plus radiation from tungsten filament bulb or infra red lamp0 (Exp, No® 2a 10»lSe53- to 12-9-53 „

The planS s wer© rgmoved and inspe-eSed after treatment for 4if©@kSe . - ■ •

There was a© abseisslen (Table 1W}» Plants grew under far red averaged 15 em» in height and all the leaves were ■ very-ehleroti@a while plants grown rnider red plus.far red radiation averaged 29 ©fflo The leaves exposed to red light

: isere' as. green as the cheek plants grown with light filtered through ®1ear eellulose-aeetat©0 . The check plants averaged 15 sm5. in height# All..plants had four fElly expanded leaves# Leaf areas from eaeh treatment were-" meaparedg but there was ,n©; signifleant variation^.- Although no. abscission ©equrr.ed in any ©f the groupsp light quality did effect the.plants singe . far red radiation inhibited.stem, elongation#

Bmrafeioa (fergo) 6 12 1#2424 22252426 2?

: : 21 26 2225

M S i %

23 2625 28 25-26 2624 2625 27

2222242126232829212623

242525282225242526 20 24 24

24 24

6 12. 18 24 6 12 18 2i14 ' 16 , ■ 13 15 26 29 29 ■ 2716 12 15 14 30 27. 28 2912 : 14 ' 17 15 30 28 • 29 3214 17; : 17 14 26. 2? ' 30 2?16 13 15 ■14 28 29 25 3318 , 15 ■ .16 - 17 29 29 2? 3015 16 16 17 .28 ■ 29 32.' 3©13 11 16 15 31 30 ■ 27 3115 16 • 15 18 28 29 32 3014 16 13 17 ' 25 26 30 3016 15 17 ■..13 30 31 29 28

18 27 30 29 2615 ■ 15 16 " 15' ■ 28 29 29 . .. 29

Average height .of each series 25 15Table I¥0 Height of bush bean plants measured in. em«' from soil level to shoot

V apex0 (Exp = So6 3» 8#12«53 bo 9 « 8 « 5 3 .

V I S I B L E i I N F R A R E Dud H(n

m H) S3

H* to

400 . 1200 1600 2000 2 4 0 0 2 8 0 0 3 0 0 0

WAVELENGTH. IN MILLIMICRONS

period of IS hours6 Siz week ©Id bush beams were divided im# to two sets $ ©me of the sets was illuminated with a 300-̂ watt tungsten bmlbg the ether set was illuminated with a 3$0mwatt infra red lamp© The intensity was §5® foot ©andles at the level of the filter© Beth light sources were suspended ele** ven inches above the filters©

After four weeks of treatment the plant s were removed and inspectedo There was no diseernabl® difference between the groups grown with the tungsten light source and. the infra red light source CTable f)e All plants had five secondary leaves per plant» The plants with clear filters (checks)9 and red filters had normal color© The plants exposed .to far red radiation were very ehlorotie» Comparisons, were made of the sise of the leaves ®f the same &g&9 but there was no variation in any of the groups^ The results of this experiment show that there was little variation due to the light source^

Experiment lo© 5 In this experiment 6 week ©Id cotton plants were used to

determine if the results found with bush beans would fee the

filament bulb Gheek Far.red Bed

Infra red

23 1522 1626 1425 1526 :1626 ,1424 . ,1623 . 1625 , ' 1326 : 13■27 : 1426 : v : ==?= • - > ': ■ m24.9 , 14

In mo, of-''bean ,h@mr

2926

27

2.9*3from sell level t© s3

used, in all treatment s®

Check Far.red Be<30 17 2626 14 3024 ■15 3023 . 17 2925 15 2?25 16 2927 13 2625 13 252? ■ 15 252i 13 2?24 15 • 2922 m M. 26.0. ' 14.7 27

H

same $ The filters were the same as in the previous expert- ment except for the addition of a copper stalfate solution (10 go/lo and 3 enu depth) to the red filter to take, out the hulk of the infra red radiation (36)® Photoperiods of 12 and 6 hours were used®

Treatment

12 hours of far red radiation 6 hours of far red radiation 1245

Light was supplied by 250-watt infra red lamps® One suspended eleven inches,above each filter and a few of the plants appeared necrotic after 21 days ©f treatment® After 49 days all the plants in both phot©periads exposed to far red radiation appeared burned® The plants treated with red ■ light were normal and their color9 siae*• number of leavess ' and general appearance were the same as those- grown, with sunlight (Figure 5)o There was no effect of photoperiod© The results varied from those obtained in Experiment Ho* 3®

xnexcessive temperature in the chambers, the |

Figure 5a. Cotton plants treated with red radiation.

Figure 5b. Cotton plants treated withfar red radiation.

of the heat woeM fee dis= aad woiald fee detectable at the smrface of the leaf<

of the lea're© (25Jo The did met exceed. 280gs 9 ©a©

degree less than the maxlmam air tem^erathre^ Siae© femraiag of leaves was the same as im Experiment lo® 5 (Figar® 5)» this

tifeilitj of cotton to defoliation suggested the use of sua= light as a supplement t© far red radiation in order to in*® crease the rate of foliar abscission in cotton® The light sources were 250«watt infra red lamps0 The radiation was filtered through two layers of red and two layers ©f blue @@1»> lulose acetate® In an attempt to determine the ph©t@p@ri@d of supplementary light necessary t© cause abscission9 photo =» periods of 6 and 12 hours were established»,- Eight week old cotton plants were exposed t© sunlight plus far red radiation^

Treatment1 Sunlighi

1:days after treatment began§ the first leaf

fell in the group receiving 12 hours of far red radiationabscissed in the group treated with 6

Figure 6a. Cotton plants treated with red radiation.

Figure 6b. Cotton plants treated withfar red radiation.

Bays of" 3fomb®g of leaves abseisssdtreatmemt '

. Far red radiation plas suhIIght Sunlight,6 homrs 12 hoars •

0#)6 0 0 037 O' 3 03# 0 3 . ©39 © - 4 04© . 0 4 041 0 5 - O42 . © 6 043 0 1 O44 0 10 645 0 12 ' : ; ©46 \ • ' 0 1? 047 O 20 ’ • 04S 1. . 25 / : 049 3 2& „ O50 5 ' 3.2 ■ 0-

Tafele Fl0 Baily total leaf abseissiom ©f ebtten plants.. ... treated with far re

Meurs ©f far red radiatioa only after fort#y

■ i©o

e>

' ©

■ l© o

©

29

the different light qualities.® Growth in length of the plants

in the dark® It was on the growth rat Btiolated plants

that light quality has no @£* the rat® of abscission of any of

the varia ion ofthe previous experimentss abscission of cotton was studied in

.vitro f23)o This technique consists of the culture of small excised pieces (explants) of plant® Each explant includes an abscission area0 Aseptic conditions were maintained by dis= infecting the explants by 4aSinute immersion in 0©0G6 per cent Eocealg and all solutions and glassware were antedated® The Eeceal was supplied by Sterwin Gh@mieals9 laco# New York®

Experiment No© 9 The first ijj vitro experiment was designed to determine

at which nod® the most uniform abscission rate of the petioles ©sours© Gottorn plants 6 weeks old were used for this purposes The cotyledons were still functional and two leaves above the cotyledons were fully expanded© The eotyledonary node was designated the first n©d@9 and the nodes above this the se@«= and node and third node© Three per cent sterile agar was poured into shallow petri plates t© a depth of l/8 inch© A 1 em@ strip of agar was removed along a diameter- of the dish such that anchor strips were left at the ends of the w®lls The explants had a stem length of 1®5 cm® and the petiole was 1 cm© long® Explants from the first8 second^ and third nodes

30

©m agar plates with a portion hanging into the well® the emXtmres were them plaeed .in, the dark and examined dailyc The rate- ©f abs@ission was mnifom at any one -nodep hut the variation between nodes was marked o Petioles at the first mode . ®©mple-t@ly abscissed in eight dayss and petioles at.the seeond and third modes ahseissed in fourteen amd twenty

In order to eliminate the need of opening the dish and .applying, pressure t©; determine if abscission has been aeeom=- plished, and im order to eliminate the effect of .geotrepism*, Pyrex tubing was welded upright on the side of the maim bar of holders similar t© those used-by. Addicott (11 (Figure.7)e Due t© the.sise of the explants8 deep well petri dishes werev used*

" Experiment 1©0 10This experiment was t.©. determine if , the petiole is the -

receptor for the light response® The experiment would also - show the induction period necessary to cause a variation in rate of abseission.0 Explants from, the second node of 6 week ©Id cotton plants- were used® The chambers and filters, des^ eribed previously were used® Sixteen petri dishes equipped with the special holders, were.- used with ten" explants per dish. Two dishes were placed and maintained in continuous darkness', as a check® The remaining fourteen dishes were divided into two groups$ ©me to be treated with reds and one to be treated with.far red® The phot©period was 12 hours* One dish from

-4- 1

I CM.

Figure 7. - E X P L A N T H O L D E R

eadh. treatmeat was. remewd aad placed in e^ezy ether day9 This gave a variation of Induction periods of Gp: ,.2g 4» 69 ,8, 10j 12g and 14 days0 The explants were -in- speeted on days alternate with the removal from the light chamber's The rate of abscission ef the explants treated with either light source was hot as uniform as:those.kept in the dark 9 but there was no correlation with photoperiod or light

H © e 1 1

. ■ Because .©f results obtained in the previous experiment^ it was thought that heat might be a factor causing some of the irregularity in the rate ; of absei ssion 0 1 ventilatingsystem was installed in the chambers so that a large volume of air movement ©ecurmd without entrance ©f light (Figure S)» The experiment was repeated$ and a temperature check takeno The air temperature, in each chamber was 30oGs One and one-= half per cent agar.was substituted for the three per cent agar previously used* All other conditions were the same as before< Again the quality of light had me effect ©n the 'rate of abseis= si on*

Due to the results obtained in experiment M©* llg, the possibility'that the leaf blade. may be the receptor for the light response was investigated e, Am in vitro study with the whale leaf blade remaining on the. explant was made o Because

4 CM = I F O O TF I L T E R

F igu re 3. - V E N T I L A T E D E X P O S U R E C H A M B E R WI TH B U I L T IN F I L T E R

34

leaves.w©r@ msede Dae te the sise of the plants ea@h holder.was now limited to three explants three holders were placed in a held in pla©® with 1'J per cent s dishes were msed® '

Gmlttire dish Ho® 1 ».Gontinuous .darkness ■ (cheek)2*3 days r@d; lights 13 -days dark dish I©# 3 e* ,21 -days red light

ays far r®d? 18 days dark Chaltiar® dish M©« 5 ̂21 days far red

The experiment was concluded .at 21 days when Ehiiopms eontsuinated the ©alture*-- ill the, explants held their leaves forthe whole: periods There was no variation.between any of thtreatments or the eheek as to eolora-Seventyetw© per eent of. the. explantsat the end of the experiment# There

Lght.s, .

rootsin

DISCUSSION AND CONCLUSIONS

area rea@h@s a ee:

smparable to (28). The

.eal- stmiy it was demoastr mot appear in the petiole

rtain si8e8 msmally 1 @m«> nuaber ene leaf, positi ssiom'aene d@

there is little inerease. in the rate of @ell divi

the leaf broads This size n described by ©mg with the d®« sslon ,pr@eess$.

si on in

Par red radiation by itself was shown to reduee the gabion ©f bmsh bean.plants whi@h is known to be auxin

©©mtrolled^ even though there was no.inerease in the rate absei-ssioa» When eettoa plants were exposed to the same

$5 the results were burning and,;rapid death of the .

■Exposure ©f eott'on plants to- a eombinatioa ©f ;sunlight 12 hours of supplementary far red radiation: eamsed an in i© in the rate ©f. foliar abseission.̂ Sunlight plus 6

36

edttea ¥y Hallabsels„slQa.0

The results

hmt it apparently is met associated

from the in witr© studies

i@ results using/whole

The results of k et ale {2%

that the auxin

.of sunlight9 res: and inactive auxin Is

g. age. ©f the leaf i@ . I1

|22)> ■ It ap* ah sei ssion. is© omstamtly the red.and far red■

ahseissimgjfall"in those

of the ia# . amxlrn is insmf^ En turn* this: _

exceed the amount

red "bmlh. used in ■ thi.ae S)e- During the

to

after a time* absei ssi

auxin a M t theof inactive auxitts. and^

©©our*. TheI© IB'

it tends t© hold leaves that would absciss on the plante If we consider liverman and : irv s

BS as the siabstanee. neeessary to maintain a leaf on a cotton,'. plantp it can be seen'how'exposure t@ far red-radiation,would eamse abscission 'of' - the leaf by the break down of BS . to Ep

Si„ and red .would tend to -prevent•abscissionby stimulating formation ©fa high ©oncentration of ESa.

True abscission involves break down of the middle lamel# . la#, . Decomposition .of the calcium poet ate ©f the middle lamel# la.is inhibited by auxin (32)o Therefore9 if the auxin is decreased o r -inactivated by natural| @he®i©alp or light ef# . ■ festSp true abscission of the ..leaf will ©eeur.' if the abscis^. si ©a area has been developed#. - ■ ..

; Leaves"of numerous deciduous plants are- shed with the advent of winter0 The first frost.in the fall will -usually ,resmlt. in:abs@issi@h in many plantse . lot-ratil the„first experiments of LaBu® (21) was auxin suspected ©f being the controlling mechanism of foliar -abscission^ Numerous workers ; have .repeated the--., original work and many types, of experiments'" have .been performed along this.general linea It, is -a©s? be#.. lieved that the auxin production'declines'with the increased age ©f the . leaf & At a certain -p©inta the auxin concentration.'-; ©f the'l@af:falls bel©w a threshold level and the leaf ab% selsses (13g'. 14)s -If early'.frosts are not severe and there , ;v is not excessive tissue damage8 the.leaf will.absciss in the normal manner e-L. - However p -if there,- is a sudden, free me a leaf \tissue is killed and.the leaf will remain on- the plant in a

Eventually by mechanical movement--the leaves

equivalent to sadden senescence9 it.becomes apparent that the auxin theory may be applied t© natural leaf fall© The. action of some defoliants can also be explained on this same basis#, Some defoliants act as anti^auxias by competitively inhibiting the auxinq The apparent auxin eoneentration then drops belen? the threshold and abscission occurs» If excessive ceaceatra# tions ©f defoliants are applied 9 normal abscission does not occur| instead the tissue throughout the plant is killed and the leaves dry in place ©n the plants#

If the plants have m© sunlight and are exposed intermit=3 tantly to far red radiation^ the result is similar to plants treated with a toh©t” defoliant 0 : They appear burned and the plants eventually di@o This burning may possibly be explained on a non^auxin basisq Hall (12) found that the higher the ■ starch content of the leaf8 the.loner the rate of abscission# Since Withrow ©t rio (36) has shown that very little chlor©-*

39

SXJMMRTlo Hist©]

i ©a© la eottem is© is

® a#g@igsi#aat a very early age ©f She leaf<

M

beds abseissien- was met

the

of

3«. By meaas ©f selective- filters^ it was determined red light does a©t stiimlate absei-ssiea in eottoa amc

plant Si Far red. radiati©n8. applied without s lightjj has a burning effeet on cotton plants 9 but

net burn bush bean plants and. deereases elengatien of bean stems

40

or inhibits the atixin that normally prevents leaf absoission in C9ttons thereby causing .-early-abscission'^ Red radiation prewnts-abssissi©n3 presamably by inereasing the active aux« im content, ' .

60 In vitro stmdies indicate that the mechanism controls ling abscission in- cotton is mot located entirely im the'leaf0

41

LITERATURE CITED

Is Addicottj, F0 To9 Lymeh9 Bo S0s Liiringstoag Go A* and Hmmterg J® K®. A methed for. the stmdy of foliar i . soission in. vitroo Plant Physiolo 24% 537e=,539o 1949© ■.....

g Ho A©9 Hendri@ksa So Be9 Parkerg K0 Wsg Toole9 1 s H o and' Toole g VQ lCti A.reversible photoreaetion eontrolling seed germinations Frees Hat® Acad® S.eio 3#: 662=6663 1952®

3e Borthmekj H0 A®s HendrickSo B0 and Parker9 Mo W

2 ih 5> Oo^abseission layersw- Imer* 950o . .

aad. their, ehemibal defoliation as affeeted by ©i' ?7«=*6S60 19§i»O A, W o

13e Hall

14«

d Wo Go .Stmdies" on the origin of ethylene fro; " ' '' Bote Gag. 113s 55-65* 1951oWe Go^thesis ©f foliar abscission® Boto Gaso 113« 310^ 22* 1952aWo Go and Lan@s Ho. G» itional and physios

the eheffiioal defoli o 27% 754-IBS Lighting Handbook® Published.by the Illuadaating Engineering Society^

Mew York#, 1947® ■Kents Mq and Gertner9 if* A® Effect of pr@&illemiaati©nof split

,® tiaio 112sIS# Laibaeho Fg &"& m&u jL&u&mx&u

'pollinien.e, Ber® Bentseh Bot* Ges® 51s 336=-340o

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