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- Mechanisms underlying plant resilience to water deficits: prospects for water-saving agriculture




Table 1. Effect of controlled irrigation on physiological responses of field-grown grapevines





Full irrigation (FI)


Deficit irrigation (DI)


Partial root-zone drying (PRD)


Non-irrigated (NI)

Afield (µmol m–2 s–1) 16.3–10.0 13.3–11.3 14.6–8.3 12.5–3.3
gs field (mol m–2 s–1) 0.30–0.28 0.23–0.19 0.19–0.15 0.13–0.07
Acontrolled (µmol m–2 s–1) 13.3±0.5 12.0±1.1 11.5±0.9 9.5±0.9
gs controlled (mol m–2 s–1) 0.35±0.04 0.33±0.05 0.25±0.05 0.14±0.01
{Psi}pd (MPa) –0.10 to –0.18 –0.14 to –0.44 –0.14 to –0.30 –0.22 to –0.64
Sap flow (g h–1 m–2) 402–356 275–196 145–130 109–101
Berries {delta}13 C ({per thousand}) –26.3±0.17 –25.9±0.28 –23.7±0.07 –22.4±0.69
Leaf area (m2 per vine) 6.3±0.26 4.9±0.15 4.3±0.21 3.6±0.18
Exposed clusters (%)

9.8±2.8

12.9±3.2

16.8±3.5

22.8±3.8

Maximum and minimum values of leaf net photosynthetic rates (Afield) and stomatal conductance (gs field) measured at midday, from mid-June to mid-September 2000, in the grapevine cultivar Moscatel, under different irrigation treatments, FI, DI, PRD, and NI. Acontrolled and gs controlled measured under controlled conditions of light (1200 µmol m–2 s–1) and temperature (25 °C) at the end of August (mean values ± SE). Maximum and minimum values of leaf predawn water potential ({Psi}pd) for the same period as above and for sap flow measurements done during August. Discrimination of 13C in the berries, measured at harvest, in September (mean values ± SE). Leaf area per vine measured at harvest and percentage of sun-exposed cluster at maturation (mean values ± SE). (Data from Souza et al., 2003; Santos et al., 2003).

 

 


Table 2. Recent achievements in improving drought tolerance in crops through genetic engineering


Gene/enzyme


Organism of origin


Target plant


Effect


Author

Functional proteins        
Superoxide dismutase (MnSOD) Nicotiana plumbaginifolia Alfalfa Better performance in the field under drought McKersie et al. (1996)
HVA1 (group 3 Lea gene) Barley Rice Constitutive expression leads to protein accumulation in leaves and roots and improved recovery after drought and salt stress Xu et al. (1996)
Myo-inositol O-methyltransferase (IMT1) Mesembryanthemum crystallinum Tobacco Enhanced photosynthesis protection and increased recovery under drought, through the accumulation of D-ononitol. Sheveleva et al. (1997)
Trehalose-6-P synthase, Trehalose-6-P phosphatase Bacteria Tobacco Better photosynthetic efficiency and higher dry weight under drought stress Pilon-Smiths et al. (1998)
HVA1 (group 3 Lea gene) Barley Wheat Constitutive expression (ubiP) improved biomass productivity and water use efficiency under water-stress Sivamani et al. (2000)
Aldose/aldehyde reductase (MsALR) Alfalfa Tobacco Detoxification effect (reduced amounts of reactive aldehydes derived from lipid peroxidation) leading to tolerance to multiple stresses, including drought Oberschall et al. (2000)
NADP-malic enzyme Maize Tobacco Drought avoidance phenotype through decreased stomatal conductance and increased fresh weight per unit water consumed. Growth and rate of development similar to wild type Laporte et al. (2002)
Fusion gene with Trehalose-6-P synthase and Trehalose-6-P phosphatase (TPSP) regulated by ABA inducible promoter or small subunit rbcS promoter E. coli Rice Sustained plant growth and reduced photo-oxidative damage under drought and other abiotic stresses. Improved photosynthetic activity also under non-stress conditions. Garg et al. (2002)
Mannitol-1-phosphate dehydrogenase (mtlD) E. coli Wheat Improved drought tolerance with mannitol accumulation at a concentration insufficient for osmotic adjustment Abebe et al. (2003)
Aquaporin NtAQP1 Tobacco Tobacco Over-expression of NtAQP increased membrane permeability for CO2 and water, and increased leaf growth Uehlein et al. (2003)
Regulatory proteins        
Calcium dependent protein kinase (OsCDPK7) Rice Rice Over-expression of OsCDPK7 led to induced expression of a glycine rich protein (salT) and LEA proteins (rab16A, wsi18) under stress. Increased salt and drought-tolerance. Saijo et al. (2000)
CBF1 (DREB1B) (driven by P35SCaMV)

Arabidopsis

Tomato

Increased resistance to water-stress, but dwarf phenotype. Higher levels of proline than controls, and faster closure of stomata under water stress. Higher catalase activity and lower (McAinsh et al., 1996), with or without stress

Hsieh et al. (2002)

The genes used were originated from plants or bacteria and accounted for various cellular responses ending up in increased drought tolerance.



 


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