Abscission in Horticulture Crops

7/28/2019 Abscission in Horticulture Crops

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FUNDAMENTALS OF

HORTICULTURE

ABSCISSION

S.ESWARA REDDY


2/20

AbscissionAbscission: the shedding of leaves,

flowers, & fruit from living plants,

separates senescent organs

Senescence: normal, energy-dependent

developmental process controlled by

genes (compare necrosis-death from physicaldamage)

-photoperiod, temperature, shading

from other leaves

-salvages resources in leaves-> back into plant through phloem*enzymes break down proteins,

carbohydrates, nucleic acids into

sugars, nucleosides, amino acids*minerals

http://homepage.ntlworld.com/tir

ain/galleries/autumn/vert.htm


3/20


4/20

AbscissionMore about ethylene:

-used commercially for fruit ripening, inducing abscission for

fruit thinning or drop in cotton, cherry, & walnut-induces cucumber femaleness, also maple trees

-prevent self pollination, increase yield, inhibit terminal growth &

increases lateral growth

-store fruits at low & low temperature to inhibit ethylenebiosynthesis, CO2 also prevents ethylene action in ripening

-Transgenic tomato: insert antisense

of ethylene precursor = delayed

softening, can delaytomato & petunia wilt &

senescence for weeks

www.hylineorchards.com/cherryharvest.html www.gardeners.com


5/20

Abscission

Ethylene regulates abscission, auxin suppresses ethylene effect(large amounts of auxin can cause ethylene production, resulting in abscission,

auxin analogs in Agent Orange)

Effects of auxin & ethylene:

-target cells in abscission zone protected by auxin from being

sensitized by ethylene

-auxin produced in the leaf travels down through petiole

-if auxin is removed by cutting off leaf blade, the petiole soon

falls off, too

-if auxin is put in place of the leaf blade, petiole abscission &

ethylene-induced accumulation of cellulase mRNA & protein areinhibited

-if auxin is put on the tree side of cut petiole, abscission

speeds up

Therefore, auxin gradient determines ethylene sensitivity (more on

tree side increases it, more on blade side decreases it)


6/20

AbscissionWhat triggers sensitivity, & what

happens when target cells become

sensitive?Leaf senescence reduces auxin

transport from leaf blade, so target

cells lose the auxin protection &

become sensitive; producesethylene

Low concentrations of ethylene cause target cells to synthesize &

secrete cellulase & other cell-wall degrading enzymes, & mature

parenchyma cells begin dividing into cells with weaker cell walls

-when cell walls break down, protoplasts are freed-form stable spherical shapes, increase in volume, & push leaf apart

Cells in abscission layer produce suberin which begins to block water

& raw material flow to leaf

-chlorophyll cannot form -> fading leaves-further decrease of auxin flow


7/20

Abscission

Auxin Auxin

Ethylene

Separation layer

digested

Yellowing


8/20

AbscissionOriginal plan:

Find & compare abscission cellulases in

different tree species, especially

comparing those with different leaf drop

times

However..no Quercus AND abscission AND cellulase

results on NCBI

search for abscission AND cellulase-BLASTp with result forSambucus nigra, European elder

-chose 15 proteins; 10 had E-values of 0.0; 5 had E-values

between -139 & -131

-to increase variety of species


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10/20

AbscissionLooked at paper: The gene promoter for a bean

abscission cellulase is ethylene-induced in transgenic

tomato & shows high sequence conservation with asoybean abscission cellulase by Susan Koehler, et al. 1996.

-abscission related to de novo accumulation of cellulase (endo-

1,4-B-D-glucanase)-so unless the samples used for obtaining protein sequences

in NCBI were collected during abscission, probably shouldnt

be able to find them--some must have been collected then

-de novo based on radioimmunoassays & fact that afterethylene exposure, there is a 12-18 hour lag period then rapid

decrease in break strength to pull petioles off stem

-break strength decrease occurs with 40-fold increase of

cellulase activity


11/20

Abscission

Determined that block must be transcriptional, so there

must be some cis-acting intron somewhere(-auxin inhibits abscission & blocks accumulation of

cellulase mRNA & protein (find mRNA if translational)

-ethylene increases RNA synthesis in abscission layer

-RNA synthesis inhibitor blocks synthesis & cellulase

mRNA & protein-polysome-associated BAC mRNA occurred with

increased BAC activity in ethylene-induced

abscission zones

-ethylene required for sustaining accumulation of thismRNA)

Now interested in promoters


12/20

Abscission

An ethylene responsive element (ERE) for pathogenesis-

related (PR) proteins & carnation are known. Koehleret al.did not find either sequence in bean or soybean abscission cellulase.

-not all of my proteins started with M (ATG), so I searched for these

patterns in them

PR ERE: TAAGAGCCGCC

carnation ERE: ATTTCAAA

-I translated the ERE sequences & searched my proteins with them

-> 27 finds for PR ERE (0 for carnation ERE), but those 27 were

located at least 100 aa in, & target sequence only 2 aa long

-I backtranslated my proteins & searched for ERE in them-> nomatches for either until 7 mismatches, & target sequences only 11 &

8 bp long -> with 7 mismatch PR ERE = 1664, carnation ERE = 90

Expected, since Koehleret al. did not find any either, & my

sequences probably do not include promoter regions


13/20

AbscissionI used pileup & pretty to get a consensusI also obtained a consensus from clustalw, & I looked at JalView:


14/20

Abscission

I did doublegap to see the % identity

-some were very high

-comparisons between abscission

cellulases in the same species were

98-100%-comparison between red pepper & tomato was 89%

identity

-comparison between white poplar & sweet orange was

83% identity-most were between mid-50s

to mid-60s % identities


15/20

Abscission

I used clustalw &

treeview to prepare this

phylogenetic tree:

-tomato is interesting, only

54% identity between 2tomatoes from doublegap-maybe one for leaf, one forfruit-79% identity for bottomtomato & white poplar-56% for white poplar & toptomato-60% identity for Montereypine & strawberry-57% for strawberry & sweet

orange

European elder

European elder

Tomato

Red pepper

Red pepper

Bean

Bean

Bean

Arabidopsis

Arabidopsis

Tomato

White poplar

Sweet orange

Monterey Pine

Strawberry


16/20

Abscission

I used PSORT to see where the

sequence forSambucus nigra is

located (this was my target sequence

for BLASTp)

PSORT results showed localization was most likely in

the microbody, but plasma membrane had a value only

0.005 lower


17/20

Conclusion-Auxin protects target cells in the abscission zone from being

sensitive to ethylene

-When auxin is reduced or removed--such as by senescence,

target cells become sensitive to ethylene

-This causes them to produce cellulase & other cell wall

degrading enzymes, & newly produced cells have weakwalls

-Released protoplasts round out & help push the layer apart

-My sequences did not contain the published EREs

-My proteins were quite conserved-Some of my proteins may have been for fruit abscission

-My first protein--used to get all the rest--is most likely

localized in the microbody or plasma membrane

-This makes sense--close to the cell wall


18/20

Works Cited

Koehler, Susan M.; Gali L. Matters; Pravendra Nath; Elizabeth C.

Kemmerer; and Mark L. Tucker. 1996. The gene promoter for a bean

abscission cellulase is ethylene-induced in transgenic tomato and shows

high sequence conservation with a soybean abscission cellulase. Plant

Molecular Biology 31: 595-606.

Nikon Microscopy. Confocal Microscopy Image Gallery: Abscission Layer.

http://www.microscopyu.com/galleries/confocal/abscission.html

Taiz, Lincoln; and Eduardo Zeiger. Plant Physiology, Third EditionSinnauer Associates, Inc.: Sunderland, MA. 2002: 370-531.


19/20

Works CitedPictures

Red maple, paper birch, sugar maple, red oakChemical of the week. The chemistry of autumn colorshttp://scifun.chem.wisc.edu/chemweek/fallcolr/fallcolr.html

yellow maple leaveshttp://homepage.ntlworld.com/tirain/galleries/autumn/vert.htm

cherry shaker

http://www.hylineorchards.com/cherryharvest.html

tomatohttp://www.gardeners.com/department.asp?CMP=IL8892&DeptPGID=16979&lstCategory=17065&SC=CNB883

Phaseolus vulgaris, common bean, string and bush beanhttp://www.mpiz-koeln.mpg.de/~pr/garten/schau/PhaseolusvulgarisL/Common_bean.html

strawberryhttp://www.noursefarms.com/catalog/strawberries.html

white poplarhttp://www.nps.gov/plants/alien/fact/poal1.htm

fallen leaveshttp://www.digitalphotography.tv/mff2001_01/2.htmlcopyright 2001-2002, digitalphotography.tv/Charlie Morey


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Thank you!

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Abscission in Horticulture Crops