Hormonal and other chemical effects on plant growth and functioning Bill Davies Lancaster Environment Centre, UK
Integrating the impacts of soil drought and atmospheric stress High radiant load Reduced water availability Increasing soil strength Increased ionic stress High T High vpd Tendency to focus on individual factors but we need a mechanistic understanding of the operation of the whole plant if we are to take profit from new genetic opportunities and new management techniques
Summary Introduction - the sensitivity of plant growth and functioning to reduction in water availability Perception and effects of soil drying. Long distance chemical signalling ph and ABA signalling and the control of g s and shoot water status Some effects of ABA at the molecular level Conclusions
Impacts of soil drought and atmospheric stress on shoot functioning - Hydraulic effects High radiant load High vpd Soil drying
Impacts of soil drought and atmospheric stress on shoot functioning - Hydraulic effects High radiant load High vpd Reduced water uptake Soil drying
Impacts of soil drought and atmospheric stress on shoot functioning - Hydraulic effects High radiant load High vpd High Transpiration Reduced water uptake Soil drying
Impacts of soil drought and atmospheric stress on shoot functioning - Hydraulic effects High radiant load High vpd High Transpiration Reduced water uptake Shoot water deficit restricted growth, development and functioning Soil drying
However: growth and stomatal behaviour can be very sensitive to soil drying even when shoot water status is unaffected How can this occur? (Henson et al. 1989)
Impacts of soil drought and atmospheric stress on shoot functioning - Chemical effects Root signal generated
Impacts of soil drought and atmospheric stress on shoot functioning - Chemical effects Increased xylem ph Root signal generated
Impacts of soil drought and atmospheric stress on shoot functioning - Chemical effects Increased apoplastic ph Increased xylem ph Root signal generated
Impacts of soil drought and atmospheric stress on shoot functioning - Chemical effects High radiant load Increased apoplastic ph Increased xylem ph Root signal generated
Impacts of soil drought and atmospheric stress on shoot functioning - Chemical effects Reduced g s High radiant load Increased apoplastic ph Increased xylem ph Root signal generated
Impacts of soil drought and atmospheric stress on shoot functioning - Chemical effects Reduced g s High radiant load Increased apoplastic ph Control of shoot water status Regulation of development Increased xylem ph Root signal generated
Impacts of soil drought and atmospheric stress on shoot functioning - Chemical effects Reduced water flux Reduced g s High radiant load Increased apoplastic ph Control of shoot water status Regulation of development Increased xylem ph Root signal generated
theta (mv) g s (mmol m -2 s -1 ) [ ABA ] (nm) 900 800 700 600 500 400 300 550 500 450 400 350 300 250 200-1 -2-3 -4-5 -6-7 psi (bar) xylem ph 6.2 6.0 5.8 5.6 5.4 5.2 5.0 400 350 300 250 200 150 100 50 0 0 DAY 12 NIGHT 24 DAY 36 NIGHT Time (hours) Xylem ph controls g s? note ABA and Ψ are not affected Sobeih et al 2004
ph signalling 1.1 leaf extension rate (mm/48h) 1.0 0.9 0.8 0.7 0.6 0.5 0.4 H 2 O ph5.3 ph5.8 ph6.7 Wilkinson and Davies, 2002 0.3 2 3 4 5 6 7 8 9 days from start
Leaf apoplastic ph as affected by root sap ph value (a well watered, b droughted), transpiration rate (c high, d low) and ions (e nitrate, f ammonium) Jia and Davies, 2005
1 2 3 Leaf apoplastic ph as affected by root sap ph value (a well watered, b droughted), transpiration rate (c high, d low) and ions (e nitrate, f ammonium) Jia and Davies, 2005
Integrating the impacts of soil drought and atmospheric stress Reduced water flux Reduced g s 2 High radiant load Increased apoplastic ph 4 Control of shoot water status Regulation of development Increased xylem ph Root signal generated 1 and 3
Stomatal conductance (mmol m -2 s -1 ) 1600 1400 1200 1000 800 600 400 200 0 2 FIRST EXPERIMENT r 2 = 0.69 r 2 =0.88 300 400 500 600 700 800 9001000 High radiant load above a threshold closes stomata by raising the ph in the apoplast High pressure xylem sap ph 7.2 7.0 6.8 6.6 6.4 6.2 6.0 5.8 5.6 5.4 5.2 5.0 PPFD (umol m -2 s -1 ) Well-watered (r 2 =0.77) 0 200 400 600 800 1000 1200 Wilkinson and Davies, 2002
ABA - xylem phloem HABA How does ph control g s? ph and ABA distribution 1 drought ph 7.2 normal conditions ph 6.3 Wilkinson et al. 1997
ABA signalling 8 meristem (salt) drying soil ph salt compaction ABA soil ABA root ABA soil ABA root irrigated soil ph salt compaction 1 Zhang and Davies, 1989
Functional categories of the genes induced in multiple water-deficit experiments of Arabidopsis Bray, E. A. J. Exp. Bot. 2004 55:2331-2341; doi:10.1093/jxb/erh270 Copyright restrictions may apply.
Elongation rates of the primary root (solid circles) and shoot (open triangles) of seedlings of four species at various water potentials Sharp, R. E. et al. J. Exp. Bot. 2004 55:2343-2351; doi:10.1093/jxb/erh276 Copyright restrictions may apply.
Primary root elongation rate as a function of root tip (apical 10 mm) ABA content for various maize genotypes growing under well-watered (water potential of -0.03 MPa, open symbols) or water-stressed (water potential of -1.6 MPa, closed symbols) conditions (grown as described in Fig Sharp, R. E. et al. J. Exp. Bot. 2004 55:2343-2351; doi:10.1093/jxb/erh276 Copyright restrictions may apply.
The ABA biosynthetic pathway Taylor, I. B. et al. J. Exp. Bot. 2000 51:1563-1574; doi:10.1093/jexbot/51.350.156 Copyright restrictions may apply.
Relative elongation rate as a function of distance from the apex of the primary root of maize (cv Sharp, R. E. et al. J. Exp. Bot. 2004 55:2343-2351; doi:10.1093/jxb/erh276 Copyright restrictions may apply.
Time-course for expression of five expansin genes (northern blot analysis) in the primary root tip of maize (cv Sharp, R. E. et al. J. Exp. Bot. 2004 55:2343-2351; doi:10.1093/jxb/erh276 Copyright restrictions may apply.
Hypothesized role of ABA accumulation in promoting the antioxidant system in the growth zone of water-stressed roots, and thereby preventing high levels of reactive oxygen species (ROS), excess ethylene production and growth inhibition Sharp, R. E. et al. J. Exp. Bot. 2004 55:2343-2351; doi:10.1093/jxb/erh276 Copyright restrictions may apply.
Similarities in EST profiles among different regions of the primary root of maize (cv Sharp, R. E. et al. J. Exp. Bot. 2004 55:2343-2351; doi:10.1093/jxb/erh276 Copyright restrictions may apply.