Root exudates involvement in tomato plant response to low P levelsV. Santoro1, M. Schiavon2, A. Ertani2, S. Nardi2, M. Martin1, D. Said-Pullicino1, L. Celi1

1 DISAFA, Università Degli Studi Di Torino, Grugliasco (TO), Italia; 2 DAFNAE, Università Degli Studi Di Padova, Legnaro (PD), Italia

Carotenoid-derived compounds (Fig. 1) with effects on rootgrowth and architecture (Fig. 2) and exudates production andcomposition

STRIGOLACTONES (SLs)

AIM OF THE WORK and HYPOTHESIS

PLANTS AND EXUDATES CHARACTERIZATION

1. P deficiency can induce several variations in exudate composition;

2. WT and KO plants reacted differently to the stress regimen in terms of quantity and quality of exuded compounds.

Preliminary aeroponic experiment

P deficiency can induce several variations in exudate composition

WT and SL- plants reacted differently to the stress regimen in terms of quantity

and quality of exuded compounds

Evaluation of the effect of exudates on P release from other Fe-P

adsorbed/coprecipitated systems with different P forms and P/Fe (Fig. 5)

CONCLUSIONS

EXPERIMENTAL DESIGN

Does SLs exudation influence the quality and quantity

of root exudates?

Fig. 2: SLs effects on: a) internode outgrowth, b) leaf senescence,c) root hair and primary root, d) secondary growth, e) axillary budoutgrowth, f) adventitious roots and g) lateral roots (Al-Babili et al.,2015; Yoneyama et al., 2007).

ROOT EXUDATES and P DEFICIENCY

P is an essential nutrient but often a growth limiting factor

Plants strategies to cope with P deficiency include the

exudation of organic acids, polyphenols, enzymes

P deficiency has also a stimulatory effect on the production

and exudation of SLs by tomato plant roots

INT

RO

DU

CT

ION

Fig. 1: Chemical structure of SLs

QUESTION

Understanding the role of SLs and root exudates in

tomato plants response to P stress conditions

The enhanced exudation of SLs may modify the chemical

composition of tomato root exudates in order to

improve P release and uptake from soil

Hydroponic experiment

Wild-type (WT) tomato plants (M82) and plants with gene for SLs synthesis

(CCD7) silenced (SL-) were left in P deficiency conditions for 10 days in an

aeroponic growth system (Fig. 3). Exudates were collected in 10 L solutions

according to the reported scheme and analysed.

T4 analyses revealed too diluted exudates!

COLLECTION SCHEME

Day Mon Wed Fry Mon Wed

Samplename T0 T1 T2 T3 T4

Fig. 3: aeroponic growth system

Water Change

Water Change

Water Change

Water Change

WT and SL- plants were sewed and germinated in peat pots, moved into 100 mL

flasks (hydroponic growth system, Fig. 4) and left with full nutrient solution for 10

days. Then P stress condition started (10 days).

Fig. 4: hydroponic growth system

• Biomass parameters• Total P content• Carbon (C) and Nitrogen (N) content• Chlorophyll content (SPAD index)• Strigolactones• Organic Acids• Polyphenols• Hormonal activity• Inorganic and organic P content• Total P content• Dissolved Organic Carbon (DOC) and

Nitrogen (DON)

PL

AN

TS

EX

UD

AT

ES

WT + P WT - P SL- + P SL- - PPlanttype

Pi(μg)

Porg

(μg)

WT + P 3.18 45.95

WT - P 1.41 37.05

SL- + P 2.66 35.68

SL- - P 2.17 36.17

0

5

10

15

20

25

30

35

40

pp

m

Oxalic acid

WT + P WT - P KO + P KO - P

a

b

ab

b

Plants

TREATMENTS

WT+P(3 plants)

WT-P(3 plants)

SL- +P(3 plants)

SL- -P(3 plants)

Exudates

Marked decrease in both roots and shoots

biomass of WT plants, with an opposite

trend in the SL-. Total P and water contents

have the same trend as biomass, and WT

plants increase their PUE (phosphorus use

efficiency) under P deprivation. In general, a

stronger effect of P deprivation is observed

in WT plants

ORGANIC ACIDS

Greater production of oxalic acid

with P depletion in WT plants.

Succinic acid present in high

concentration (40-60 ppm) but not

influenced by P depletion. Citric,

malic, glycolic, lactic, acetic present

in concentrations <1 ppm

Gallic acid was quantified in an

intermediate sampling time in the

aeroponic system

Fig. 5: Fe-Pcoprecipitated system

PHOSPHORUS

POLYPHENOLS

BibliographyAl-Babili, S., Bouwmeester, H.J., 2015. Ann Rev Plant Biol, pp. 161-186. Santoro et al., 2019 (Geoderma, in press)Yoneyama, K., Xie, X., Kisugi, T., Nomura, T., Sekimoto, H., Yokota, T., 2011. Plant Growth Regul, 65(3), 495-504.

0

2

4

6

8

10

WT+P WT-P KO+P KO-P

FW

bio

mas

s(g

)/P

co

nte

nt

(mg

)

PUE

SL- +P SL- -P

-0,40

-0,20

0,00

0,20

0,40

0,60

0,80

1,00

WT+P WT-P KO+P KO-P

P (m

g/p

lan

t)

P content

Roots ShootsSL- +P SL- -P

EFFECT OF EXUDATES ON P AND Fe RELEASE

0,00

0,10

0,20

0,30

0,40

0,50

0,60

0,70

0,80

0,90

1,00

0 50 100 150 200 250 300 350

M/M

0

TIME (MIN)

Citric 10 mM Ascorbic 10 mM

Oxalic 10 mM Gallic 10 mM

Gallic 5 mM + Citric 5 mM

0,00

0,10

0,20

0,30

0,40

0,50

0,60

0,70

0,80

0,90

1,00

0 50 100 150 200 250 300 350

M/M

0

TIME (MIN)

Dissolution rate: oxalic > ascorbic > citric > citric + gallic > gallic

Some of the compounds characterized in the exudates(polyphenols and organic acids) were used to dissolve a Fe-Psystem obtained through oxidative precipitation of Fe(II) in thepresence of inorganic P (P/Fe ratio = 0.5) (Santoro et al., 2019),thanks to their reducing or chelating ability

P

Fe

FUTURE WORK

This research has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 727929 (A novel and integrated approach to increase multiple and combined stress tolerance in plants using tomato as a model - TOMRES)

SL- +P SL- -PWT+P WT-P