Aerenchymaimprovesmaizedroughttolerance747

Root length (cm) per frame at 50cm deep soil by minirhizotron

200

12

WSWW

a

b

f

cd

e

g

gh

bc

Shoot dry weight (g)

96300

10

20

30

40

50

Root length (cm) 40–50 cm deep from soil coring

r² = 0.632 (P < 0.01)

150

b

cd

100

i

50

j

Root counts per frame at 50 cmdeep soil by minirhizotron

5040

ab

cd

a

90Yield (g)/plant

r² = 0.309 (P < 0.05)

30201000

20

40

WSWW

60

e

30

ef

g0

33

248

331

34

77

284

364

6080

Root number 40–50 cm deep from soil coring

g

g

Figure10.Correlationsbetweenmeasurementsmadeat50cm

deepsoilbyminirhizotrontechniqueand40–50cmdeepbysoilcoringtechniqueforrootlength(upperpanel)androotnumber(lowerpanel)inthe eld.

Low RCAHigh RCA

Recombinant inbred lines

Figure12.Shootdryweightat oweringstage(upperpanel)

underwaterstress(x)(Figs1&3).Thelinearregressionformulawasy1=-0.014x+0.148(r2=0.94,P<0.001).Asimilarcorrelationwasfoundforseminalrootrespirationperunitweight(y2)andpercentageofRCAunderwaterstress(x)(Figs1&3).Thelinearregressionformulawas

andgrainyield(lowerpanel)ofsevengenotypesinwell-watered(WW)andwater-stressed(WS)conditionsinthe eld.Data

shownaremeans SEofthemean(n=4).Meanswiththesamelettersarenotsigni cantlydifferent(P 0.05).

100%

ab

Relative water content

WWWS

ab

abbcd

ab

90%

cd

e

d

80%

e

e

70%

332483313477284364

Low RCAHigh RCA

Recombinant inbred lines

Figure11.Leafrelativewatercontentat56dafterplanting

(DAP)forsevengenotypesinwell-watered(WW)and

water-stressed(WS)conditionsinthe eld.Datashownare

means SEofthemean(n=4).Meanswiththesamelettersarenotsigni cantlydifferent(P 0.05).

y2=-30.4x+293(r2=0.77,P<0.05).Theseindicatethatabout6%RCAinseminalrootshalvesrootrespirationperunitlengthorweightunderwaterstress.Fanetal.(2003)reportedthat20%RCAcutsrootrespirationperunitvolumeinhalfatlowphosphorusavailabilityinasolutionculturestudy.

Inmaize,anadditionalbene ttoreducingrootcostsisthatyieldlossestodroughtarerelatedtocarbohydrateavailabilityduringreproductivegrowth(Boyer&Westgate2004).ReducedrootcarbondemandinhighRCAgeno-typesmaybebene cialbyincreasingcarbohydrateavail-abilityduringreproductivegrowth,sincereproductionandrootsarecompetingsinksforcurrentphotosynthate(Figs3,12&13).

WeobservedthatwaterstressinducedgreaterexpressionofRCAindrought-tolerantlinesinbothseminalrootsof5-week-oldplantsinmesocosmsandnodalrootsof8-week-oldplantsinthe eld,comparedwiththesensitivelines(Figs1,2,7,12&13),althoughtheabsolutevaluesofincreasedRCAdifferedinvariousroottypes.Seminalrootsof5-week-oldplantsandnodalrootsof8-week-oldplantsaremajorcomponentsofrootsystemarchitecture.Thisresponsetowaterstressallowsmorecarbonallocationfor

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