Fotoprotección en las hojas de avocado enrelación con el manejo del canopeo
Photoprotection in avocado leaves inrelation to canopy management
Barry Osmond 1,2 Britta Förster 2
and John Leonardi 3
1 University of Wollongong2 Australian National University
3 Avocados Australia
Abstract: avocado retains a deep canopy ofshade leaves with high photosynthetic efficiency.
They are doubly photoprotected by 2 pigmentsystems and do well in diffuse light and long sun-flecks, achieving 20-50% photosynthesis rates ofsun leaves at the same light intensity. Dependingon pruning style shade leaves suffer light stress
for >3 days, but re-invent the pigment systems ofsun leaves in ~10 days; simply amazing!!
Proceedings VII World Avocado Congress 2011 (Actas VII Congreso Mundial del Aguacate 2011). Cairns, Australia. 5 – 9 September 2011
One hundred-fold range in photosynthesis within aSouthern Hemisphere avocado canopy at noon
N
S
EW
0.19
114
0.79
ØPSII = efficiency of light use
ETR = capacity to fix carbon
DS = protection against excess light
0.68
52
0.28
0.76
21
0.13
0.43
134
0.56
0.83
1
0.06
Orchard at Goodwood Qld; at noon 23 July 2010
• why do avocados keep deeply shadedinner canopies with high efficiency, low
capacity leaves seemingly poorlyprotected against excess light?
• how do these leaves tolerate extremecanopy management regimes?
Differential effects of pruning strategy on shadeleaf photosynthesis
0
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0 200 400 600 800 1000
Light intensity; PFD, μmol m-2 s-1
Ca
pa
city
tofix
CO
2;
ET
R,
μm
olm
-2s
-1
shade (Fv/Fm 0.75±0.02)
sun 4.5 h (Fv/Fm 0.76±0.01)
sun 3 d (Fv/Fm 0.70±0.02)
dark 3 d (Fv/Fm 0.77±0.03)
sun (Fv/Fm 0.73±0.02)
Selectivebranchremoval
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0 200 400 600 800 1000
Light intensity; PFD, μmol m-2 s-1
Po
ten
tia
lC
O2 f
ixa
tio
n;
ET
R,
μm
ol m
-2s
-1
shade (Fv/Fm 0.82±0.01)
1 d sun (Fv/Fm 0.47±0.03)
3 d sun (Fv/Fm 0.43±0.01)
3 d dark (Fv/Fm 0.78±0.01)
sun (Fv/Fm 0.73±0.02)
"V" pruning
of upper
canopy
Lu
tein
ep
oxid
ec
ycle
Lx-c
ycle
Vio
laxan
thin
cycle
V-c
ycle
Two pigment cycles in avocado shade leaves:both may stabilize photoprotection (NPQ)
Rabinowitchet al (1975)
in greentomatoes
Yamamotoet al (1962)
in lettuceleaves
Reversal of Lx-cycle is 10-100 x slower than V-cycle in
avocado shade leaves
L
Lx
Z
A
V
Photoprotection 1: ΔL “locks-in” high NPQ for 72h in shade leaves
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10
20
30
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70
Lx L* V A Z
Pig
men
ts,
mm
olm
olC
hl
-1
cont (Fv/Fm=0.81; DS=0.01)
exp 1h (Fv/Fm=0.78, DS=0.33)
cont 24h (Fv/Fm=0.78, DS=0.02)
rec 24h (Fv/Fm=0.78, DS=0.09)
0
0.5
1
1.5
0 120 240
0
0.5
1
1.5
0 100 200 300 400 500
NP
Q,
a.u
.
0
5
10
15
20
25
0 100 200 300 400 500
ET
R,
µm
olm
-2s
-1
cont
exp 1h
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5
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20
25
0 100 200 300 400 500E
TR
,µ
mo
lm
-2s
-1 cont 24h
rec 24h
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0.5
1
1.5
0 100 200 300 400 500
PFD, µmol m-2
s-1
NP
Q,
a.u
.
0
0.5
1
1.5
0 120 240
Time, s
A
B C
D E
Lx VL
A Z
NPQΔL
NPQΔLAZ
NPQΔL
New science from avocado:shade leaves prove that
LUTEIN has one, possiblytwo, roles in photoprotection
AZcost
After just 1 h in 10 %sun Lx→ ∆L and ∆L
replaces A+Zovernight to sustain
high NPQ
Lutein first to decreaseon shade-sun transfer:photoxidative protection
(as in retina?)
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90
cont 0830 exp 0830 exp 1630
Pig
ments
,m
molm
ol
-1C
hl
Lx
L* (-100)
no∆L
cost
∆L
Photoprotection 2: huge new synthesis of ΔL and A+Z from carotenes
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120
1.0 1.3 2.0 10.0 10.3 11.0 19.0 19.3 20.0 39.0 39.3 40.0
Days after transfer to sun
Pig
me
nts
,m
mo
lm
ol
-1C
hl
Lx
ΔL
0
20
40
60
80
100
120
0.0 0.3 1.0 10.0 10.3 11.0 19.0 19.3 20.0 39.0 39.3 40.0
Days after transfer to sun
Pig
me
nts
,m
mo
lm
ol
-1C
hl
V
A+Z
Surprising science: oldavocado shade leaves are
able to reinvent themselvesas sun leaves in ~10 days
0
50
100
150
200
Lx L* (-100) V A+Z
Pig
me
nts
mm
olm
ol-1
Ch
l
inner
outer N
avocado pigments, Goodwood