Whole‐Plant Physiological Responses to Water‐Deficit Stress

Abstract

Plants that receive insufficient water experience a stress called water deficit. Plant water deficits disrupt many cellular and whole‐plant functions, negatively affecting plant growth and reproduction. Plants respond to soil water deficits by avoiding the occurrence of leaf water deficits (drought avoidance) or tolerating low cellular water contents (drought tolerance). Plants avoid drought by closing the stomatal pores that regulate water loss from the leaves, restricting the transpiring area (by decreasing growth or shedding leaves) and/or maintaining root water uptake as the soil dries. Plants have evolved many different mechanisms to tolerate low tissue water contents including upregulation of antioxidant systems to decrease the impact of damaging reactive oxygen species. Availability of water is the most important environmental factor that reduces crop production, thus there have been considerable efforts by biotechnologists to enhance drought tolerance and irrigation managers to enhance crop water use efficiency.

Key Concepts

  • Low cellular water contents can constrain plant growth and decrease crop yield.
  • Plants can tolerate low cellular water contents or avoid them.
  • Sufficient water in plant cells allows them to exert a pressure (turgor) on the cell wall to allow growth.
  • Restricting the rate of water loss (by closing the stomata or growing more slowly) or acquiring more water via root proliferation allows plants to avoid drought.
  • Increasing antioxidant status allows plants to tolerate water deficits.
  • Lack of turgor impairs cellular metabolism and restricts growth, but stomata can close and growth can slow in the absence of changes in turgor.
  • Plant roots can sense drying soil and transmit chemical signals (such as the plant hormone ABA) to the shoot to regulate stomatal function and growth.
  • Sufficient ABA in the plant is essential for normal growth and stomatal function.
  • Increasing plant sensitivity to, or accumulation of, the plant hormone ABA can increase yield of water‐limited crops.
  • Changes in irrigation management can provide ‘more crop per drop’.

Keywords: water‐deficit stress; water relations; stomata; biotechnology; irrigation management

Figure 1. Resistance to water‐deficit stress can arise from mechanisms involving avoidance or tolerance of the water deficit.
Figure 2. Cellular and soil water potential control water uptake into the cell. Osmotic adjustment, a lowering of cellular osmotic potential caused by solute accumulation/synthesis, can permit water uptake and restore cellular turgor.
Figure 3. ABA biosynthesis beginning with a carotenoid and proceeding through the major pathway for catabolism. Both synthesis and breakdown contribute to the level of ABA in a particular organ of the plant in response to water deficit. The numbers in boxes represent enzymes that have been cloned in Arabidopsis. (1) 9‐cis‐epoxycarotenoids dioxygenase 3 (NCED3) catalyses the cleavage of cis‐xanthophylls during water‐deficit stress. (2) The product xanthoxin is converted into ABA aldehyde by a short‐chain alcohol dehydrogenase, ABA2. (3) Abscisic aldehyde oxidase AAO3, an enzyme that requires a sulfurylated form of MoCo (synthesised by (4) MoCo sulfurase (ABA3)), completes the final step of ABA biosynthesis. (5) The key step of ABA catabolism is the hydroxylation of the 8′ methyl group to yield 8′ hydroxy ABA by a cytochrome P450 monooxygenase CYP707A3. Phaseic acid is then formed spontaneously. Increased ABA concentrations initiate a signal transduction pathway, leading to the induction of specific genes.
Figure 4. Fold change in root system hydraulic conductance in response to nutrient solution‐supplied ABA in pea (Beaudette et al., – diamonds), bean (Markhart et al., – circles) and maize (Hose et al., – squares) plants. Re‐drawn from Dodd (2013) © New Phytologist Trust.
Figure 5. Crop yield ratio of PRD to DI at similar irrigation volumes (a ratio of 1 indicates that yield with both techniques is equivalent). The fraction of full irrigation is given as a thick line in each column. Columns are means ± SE of the number of experiments/seasons given in parentheses at the base of each column. Shaded columns denote pot experiments where the root system was confined. Significant (P < 0.05) differences between PRD and DI are indicated with an asterisk (*). For further details of the studies summarised, see Dodd, . Reproduced with permission from Dodd (2009) © Oxford University Press.
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Maggio A, Zhu J‐K, Hasegawa M, et al. (2006) Osmogenetics: aristotle to arabidopsis. Plant Cell 18: 1542–1557.

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Yamaguchi‐Shinozaki K and Shinozaki K (2006) Transcriptional regulatory networks in cellular responses and tolerance to dehydration and cold stresses. Annual Review of Plant Biology 57: 781–803.

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Dodd, Ian C, and Ryan, Annette C(Jan 2016) Whole‐Plant Physiological Responses to Water‐Deficit Stress. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0001298.pub3]