Perception and signalling of soil and atmospheric drought. Bill Davies Lancaster Environment Centre, UK

Transcription

1 Perception and signalling of soil and atmospheric drought Bill Davies Lancaster Environment Centre, UK

2 Summary An introduction to long distance signalling ACC and ethylene signalling and the control of shoot growth and the control of g s and shoot water status Interacting stress effects in protecting leaf metabolism APX expression in response to climatic and edaphic influences Exploitation of signalling in agriculture

3 Can we sustain growth in dry environments (under deficit irrigation)? Control of shoot water status as a result of chemical control of g s Root signals

4 Can we sustain growth in dry environments (under deficit irrigation)? Growth promotion Control of shoot water status as a result of chemical control of g s Root signals

5 Can we sustain growth in dry environments (under deficit irrigation)? Growth promotion Control of shoot water status as a result of chemical control of g s Inhibition Other specific root signals Root signals

6 Can we sustain growth in dry environments (under deficit irrigation)? Growth promotion Control of shoot water status as a result of chemical control of g s Inhibition Other specific root signals Need to overcome chemical inhibition if growth of shoots is to be sustained? Root signals

7 Copyright restrictions may apply. Sharp, R. E. et al. J. Exp. Bot : ; doi: /jexbot/

8 Chemical restriction of shoot growth Ethylene signalling in the plant 1. Evidence that stress ethylene can restrict leaf growth 2. Low ethylene transgenic much less sensitive to soil drying Entire leaflet (mm day -1 ) Terminal leaflet (mm day -1 ) Days Days ( y ) ACO1 WT Volumetric soil water content (g cm -3 ) b c Sobeih et al 2004

9 Genetic solutions but also management possibilities NH 3 + α-ketobutyric acid ACC Deaminase ACC bacterium ACC rhizosphere ACC root ACC Oxidase Ethylene signalling internal and external cues. Impact of rhizobacteria Ethylene (re-drawn from Glick et al J. Theoretical Biology 190, 63-68)

10 Experimental Design Pisum sativum cv Sparkle grown in 0.43 L pots in a growth cabinet at LEC, Lancaster John Innes #2 - nodulation not observed 2 Watering regimes: (well-watered and controlled soil drying) from 7 to 26 days after germination Evapotranspiration replenished daily 3 Treatments: Tap water (control) 10 µm AVG (inhibits ethylene production) 5 x 10 6 cells/ g soil Variovorax paradoxus 5C2 (contains ACC deaminase)

11 Significant stimulation of root biomass by AVG / bacteria under WW / drying soil BUT shoot / total biomass increased by bacteria only in dry soil Percentage increase caused by AVG or PGPR treatment (compiled for both genotypes) Total Leaf Area WW AVG 5C2 Drying Shoot biomass Root biomass Total biomass A, B and C show significant differences against controls at P < 0.05, P < 0.01 and P < respectively (Fisher's LSD Test) Belimov et al A B C A B A WW Drying WW Drying WW Drying

12 Transposome mutagenesis of Variovorax paradoxus 5C2 Transform electrocompetent bacteria with commercially available transposome that provides resistance to trimethoprim (selection marker) Replica plate onto minimal-plates containing only ACC as a nitrogen source Bacteria plated onto appropriate selection marker (trimethoprim) Isolate clone and grow in presence of selective agent to confirm (reproduce) sensitivity to selective agent Hypothesis: Transposome has inserted itself into part of genome that is important for growth with ACC as the only nitrogen source. This important gene could be ACC deaminase. Hontzeas, 2005

13 Significant stimulation of leaf area & biomass by WT bacteria ONLY slightly greater effect in drying soil Percentage increase caused by mutant or WT bacterial inoculation Total Leaf Area WW mutant WT Drying Shoot biomass Root biomass Total biomass A, B and C show significant differences against controls at P < 0.05, P < 0.01 and P < respectively (Fisher's LSD Test) A B B B C C B C WW Drying WW Drying WW Drying Belimov et al 2005

14 Bacteria increase biomass of all plant parts under soil drying 60 WW plants soil drying % increase caused by bacteria Root Straw Seed Total Belimov et al. 2005

15 Bacteria increase specific root nodulation (per unit root DW) Nodule number per unit root dry weight 140 WW plants Soil drying P = P = Number of Nodules per unit dry root dry weight Control V. paradoxus 5C2 0 Belimov et al. 2005

16 Can we sustain growth in dry environments (under deficit irrigation)? Growth promotion Control of shoot water status as a result of chemical control of g s Inhibition Other specific root signals In plant improvement programmes we need to overcome chemical inhibition of growth of shoots and sustain shoot water status to drive cell expansion and protect developing reproductive structures Root signals

17 Can we sustain growth in dry environments (under deficit irrigation)? Growth promotion Control of shoot water status as a result of chemical control of g s Inhibition Other specific root signals In plant improvement programmes we need to overcome chemical inhibition of growth of shoots and sustain shoot water status to drive cell expansion and protect developing reproductive structures Root signals A combination of plant improvement and crop management?

18 Integrating the impacts of soil drought and atmospheric stress - protection of shoot functioning Reduced g s Soil drying

19 Integrating the impacts of soil drought and atmospheric stress - protection of shoot functioning High radiant load Oxidative stress Reduced g s Soil drying

20 Integrating the impacts of soil drought and atmospheric stress - protection of shoot functioning High radiant load Up-regulation Oxidative stress Reduced g s Protection via antioxidants Soil drying

21 Integrating the impacts of soil drought and atmospheric stress - protection of shoot functioning High radiant load Up-regulation Oxidative stress Reduced g s Protection via antioxidants Soil drying Root signals?

22 Imaging of APX2 gene expression using a luciferase reporter gene Arabidopsis grown at PPFD of 200 µmol m -2 s -1 and exposed to photo-oxidative stress of 1000 µmol m -2 s -1 for 1 hour Increasing counts Fryer et al. Plant J, 2003, 33:

23 Threshold for petiolar APX2-LUC osmotic expression Ψπ (MPa) Control (ddw) 0.15M 0.30M 0.60 M Mannitol Sorbitol PEG Ψπ (MPa) APX2 expression can also be induced in excised petioles by osmotic stress at normal light Fryer et al. 2003

24 What is the cause of the osmotic stress and leaf drying effects? Leaves sprayed with 10 and 100 µm ABA at PPFD of 200 µmol m -2 s -1 Luciferase activity (RLU x 10 4 gm fwt -1 ) ABA 10-5 M ABA 10-4 M Time (h) Applied ABA induces APX2 expression even at growth light Baker et al. 2005

25 APX2 expression is a function of a combination of stresses Jia and Davies, 2005

26 APX2 expression is a function of a combination of stresses ,2,3 Jia and Davies, 2005

27 Integrating the impacts of soil drought and atmospheric stress - protection of shoot functioning High radiant load Up-regulation Oxidative stress 1 and 3 Reduced gs Protection of leaf metabolism as a function of soil and atmospheric stress Soil drying Root signals? 2

28 Critical need to reduce water use in agriculture Most water applied is wasted 90% of water taken up is wasted Micro-irrigation systems apply vastly reduced quantities of water BUT how do we tell when and what to apply?

29 Opportunities to apply less water, increase water use efficiency but also manipulate plant growth Deficit irrigation to restrict leaf growth in favour of reproductive development Use less water but keep the leaves growing

30 Deficit irrigation does not just save water Novel ways to control growth - reducing the need for pruning Improved crop uniformity - reducing labour costs Reduced crop wastage Reduced chemical use Increased crop quality WW PRD WW RDI

31 Increasing water use efficiency in agriculture a classical example grape vines in the Murray Darling catchment Annual diversion (GL/Year) average natural flow to the sea SA Vic NSW Qld Total

32 Exploiting chemical signals moving from the roots by crop managemnt Partial rootzone drying a particular form of deficit irrigation to limit leaf growth Control Treated % Difference Significance Irrigation (ML/ha) Fruit wt. (kg/vine) Pruning wt (kg/vine) Leaf area (m 2 /vine) gs (mmol/m 2.s) Bunch exposure ns < < < <0.01

33 WUE, t/ml Yield t/ha Premium reds 18 Low value whites 35 Premium whites 27 PRD control 32 PRD 29 0 Water use efficiency of commercial and experimental grapevines subjected to Deficit Irrigation Redrawn from Skewes and Meisner, 1997

34 Brian Loveys and Peter Dry (Adelaide) PERFORMANCE OF VARIOUS IRRIGATION METHODS IN A COMMERCIAL SHIRAZ VINEYARD Control PRD PRD RDI surface drip surface drip sub-surface drip surface drip Water, ML/ha Yield, t/ha WUE, t/ml Berry wt, g Juice o Be Juice ph Wine (1=best) 3,3 1,1 n/a 2,2 Reduced water use, high yield and good quality wine!