Plants water potential

Bozarth, C.S., Mullet, J.E. Boyer, J.S. (1987). Cell wall proteins at low water potentials. Plant Physiology, 85, 261-7. 

Johansson I, Larsson C, Ek B, Kjellbom P. 1996. The major integral proteins of spinach leaf plasma membranes are putative aquaporins and are phosphorylated in response to Ca2+ and apoplastic water potential. Plant Cell 8 1181-1191. 

Stress corrosion can arise in plain carbon and low-alloy steels if critical conditions of temperature, concentration and potential in hot alkali solutions are present (see Section 2.3.3). The critical potential range for stress corrosion is shown in Fig. 2-18. This potential range corresponds to the active/passive transition. Theoretically, anodic protection as well as cathodic protection would be possible (see Section 2.4) however, in the active condition, noticeable negligible dissolution of the steel occurs due to the formation of FeO ions. Therefore, the anodic protection method was chosen for protecting a water electrolysis plant operating with caustic potash solution against stress corrosion [30]. The protection current was provided by the electrolytic cells of the plant. 

The SAH water potential determines many aspects of their behavior in the soil. The processes of water redistribution in the soil, its transport to the plant roots, and assimilation follow the osmotic laws and are regulated by the thermodynamic potential. 

In many cases, where one is concerned with the effects of specific environmental factors it is appropriate to replace the general term stress by the appropriate quantitative measure (e.g. soil water content or water potential) together with an appropriate measure of the plant response (e.g. growth rate). 

Fig. 1. Rates of CO2 assimilation, A (/miol s ) leaf conductance, g (mol m s ) intercellular partial pressure of CO2, Pi (Pa) soil water potential and leaf water potential, xp (MPa) during gas-exchange measurements of a 30-day-old cotton plant, plotted against day after watering was withheld. Measurements were made with 2 mmol m sec" photon flux density, 30 °C leaf temperature, and 2.0 kPa vapour pressure difference between leaf and air (S.C. Wong, unpublished data).

This point was made clearly by Wong, Cowan Farquhar (1985). They imposed slow water stress on 30-day-old Zea mays plants grown in 45 1 plastic bins during early spring where glasshouse vapour pressure deficit was generally about 1.0-1.5 kPa. During the 14 day period the predawn leaf water potential declined from - 0.5 to - 0.8 MPa. Rate of assimilation. 

Boyer, J.S. (1970). Differing sensitivity of photosynthesis to low leaf water potential in corn and soybean. Plant Physiology, 46, 236-9. 

Potter, J.R. Boyer, J.S. (1973). Chloroplast response to low leaf water potentials. II. Role of osmotic potential. Plant Physiology, 51, 993-7. 

Sinclair, T.R. Ludlow, M.M. (1985). Who taught plants thermodynamics The unfulfilled potential of plant water potential. Australian Journal of Plant Physiology, 12, 213-17. 

Fig. 1. Elongation rate of stem intemode 12 (A), silks (A), leaf 8 ( ), and nodal roots (O) of maize at various water potentials. Elongation rates are the average per hour for 24 h of growth in a controlled environment chamber. Water potentials were measured in the growing region of each organ in the same plants. Samples were taken immediately after the growth period when the plants had been in the dark for the last 10 h. Each point is from a single plant. Modified from Westgate Boyer (1985a).

Seedlings were transplanted to the different water potentials 30 h after planting, and were grown in the dark at 29 °C and near saturation humidity. Elongation rates were constant when the measurements were made. Data of R.E. Sharp and G. Voetberg (unpublished). 

Fig. 9. Leaf water potential and turgor, abaxial stomatal conductance, and ABA content of abaxial epidermis of leaves of Commelina plants which were grown with their root systems divided between two pots. Water was either applied daily to both halves of the root system (A) or was withheld from one half of the root system after day 1 of the experimental period (A). Points for water relations and conductance are means s.e. Modified from Zhang, Schurr Davies (1987).

Fig. 10. Leaf water potential and abaxial stomatal conductance (upper figure), and water potential and turgor of secondary and tertiary root tips (lower figure) of maize plants growing in 1 m deep soil columns, watered daily (A) or not watered after day 0(A). The roots were sampled from the upper 20 cm of the soil column. Plants were 20 days old at the beginning of the experimental period. Points are means s.e. Modified from Zhang Davies (1989).

Boyer, J.S. (1968). Relationship of water potential to growth of leaves. Plant Physiology, 43, 1056-62. 

Jones, H.G. (1983). Estimation of an effective soil water potential at the root surface of transpiring plants. Plant, Cell and Environment, 6, 671-4. 

Sharp, R.E., Hsiao, T.C. Silk, W.K. (1988). Growth of the maize primary root at low water potentials. II. Spatial distribution of osmotic adjustment in the growing zone. Plant Physiology, (in press). 

So far this presentation has dealt exclusively with responses to water potential perturbations at the cellular level. In concluding we wish to consider one example of a response at the whole-plant level in the light of this analysis. This example is developed further by Yeo Flowers (Chapter 12) who also refer to further examples of the complexity of whole-plant responses. 

Matthews, M.A., Van Volkenburgh, E. Boyer, J.S. (1984). Acclimation of leaf growth to low water potential in sunflower. Plant Cell and Environment, 7, 199-206. 

Molz, F.S. Boyer, J.S. (1978). Growth induced water potentials in plant cells and tissues. Plant Physiology, 62, 423-9. 

Silk, W.K. Wagner, K.K. (1980). Growth sustaining water potential distributions in the primary corn root. Plant Physiology, 66, 859-63. 

Drought also has a profound effect on protein synthesis. In many plant tissues, a reduced water potential causes a reduction of total protein synthesis and a rapid dissociation of polyribosomes. The latter has been shown not to be the consequence of increase in ribonuclease activity (Hsiao, 1973 Dhindsa Bewley, 1976). For a specific protein, Jacobsen, Hanson Chandler (1986) have shown in barley leaves that water stress enhances the synthesis of one of the a-amylase isozymes. Using a cDNA probe they found that water-stressed leaves contained much more a-amylase mRNA than unstressed plants. 

Surprisingly, very little physiological work has been done to understand the nature and processes of plant recovery from extreme drought stress, especially in relation to plant production (Chapter 7). In order for the plant to recover properly from severe water stress, its various meristems must survive. The association between severe plant stress and the factors that affect meristem survival and function upon rehydration are unclear though osmoregulation may have a possible protective role and as a potential source of carbon for recovery. Active plant apices generally excel in osmoregulation and do not lose much water upon plant dehydration (Barlow, Munns Brady, 1980). 

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