Water stress resistance

Abscisic acid (44) is involved in a number of hormonal roles in plants (Fig. 26.16) (Milborrow, 1983). This plant growth-regulating compound, probably found in all higher plants, acts as a growth inhibitor and is involved in bud and seed dormancy. (+ )-(5)-Abscisic acid is a potent effector of stomatal closure. Abscisic acid also is linked to water stress resistance in plants. To date, the presence of abscisic acid has not been confirmed in bryophytes (Milborrow and Netting, 1991). 

Ben-Hayyim, G. (1987). Relationship between salt tolerance and resistance to polyethylene glycol-induced water stress in cultured citrus cells. Plant Physiology, 85, 430-4. 

Therefore drought resistance (in terms of plant production) is positively associated with T or Ea, m or WUE and HI under drought stress. A simple simulation using (1) would indicate that a given increase in Tor m is most effective towards plant production when water stress is not severe. 

Blum, A. (1983). Breeding programs for improving crop resistance to water stress. In Crop Reactions to Water and Temperature Stresses in Humid, Temperate Climates, ed. C.D. Raper Jr and P.J. Kramer, pp. 263-76. Boulder, Colorado Westview Press. 

Hanson, A.D., Nelson, C.E., Pedersen, A.R. Everson, E.M. (1979). Capacity for proline accumulation during water stress in barley and its implications for breeding for drought resistance. Crop Science, 19, 489-93. 

The reported (14) mechanisms of action of allelochemlcals Include effects on root ultrastructure and subsequent Inhibition of Ion absorption and water uptake, effects on hormone-induced growth, alteration of membrane permeability, changes In lipid and organic acid metabolism, inhibition of protein synthesis and alteration of enzyme activity, and effects on stomatal opening and on photosynthesis. Reduced leaf water potential Is one result of treatment with ferulic and p-coumaric acids (15). Colton and Einhellig (16) found that aqueous extracts of velvetleaf (Abutllon theophrastl Medic.) Increased diffusive resistance In soybean fGlycine max. (L.) Merr.] leaves, probably as a result of stomatal closure. In addition, there was evidence of water stress and reduced quantities of chlorophyll In Inhibited plants. 

Stomatal closure was associated with a genetic factor in onion wherein the stomata of sensitive plants did not close. The effect of ozone and PAN on stomatal opening depends on many interacting factors those representing water stress appear to be the most important. Dean related stomatal density to the difference in sensitivity between two tobacco cultivars. Evans and Ting found that maximal sensitivity of bean primary leaves was not associated with changes in stomatal number or leaf resistance. Ozone exposure caused a decrease in relative water content, but no change in resistance. Bean leaf sensitivity seemed more a function of internal activities. 

In this paper we summarize our work on the role of indole alkaloids and hydroxamic acids on the resistance of cereals to aphids. In addition, we describe the effects of water stress on susceptibility of barley to aphids. 

The water stress Incurred by trees growing on the south site Is hypothesized to have modified foliage quality such that trees became highly susceptible to the budworm. This appears to have been primarily due to the decrease In the resistance factors beta-plnene and bornyl acetate accompanied by an Increase In alpha-plnene. If alpha-plnene consistently Increases In stressed Douglas-flr trees. It Is then possible that budworm may use It as an attractant or cue In locating suitable hosts. 

All of the many biological transfer processes combine to determine a net surface resistance to transfer. Empirical relationships can be used to infer stomatal resistance from data on photosynthetically active radiation, water stress, temperature, atmospheric humidity and carbon dioxide levels. The resulting net surface resistance has been coupled with mathematical descriptions of aerodynamic and boundary-layer resistances in a "big leaf" model derived on the basis of agricultural and forest meteorology literature (4). At present, the big-leaf model is relatively coarse, permitting application only to areas dominated by maize, soybeans, grass, deciduous trees, and conifers. 

Properties White powder. A unique ceramic material. D 3.016, mp 2570C. Hardness (Mohs) 9. Soluble in acids and alkalies insoluble in water. High electrical resistivity and thermal conductivity transparent to microwave radiation undamaged by nuclear radiation. High heat-stress resistance. Can be fabricated into finished shapes. 

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