Showing papers by "Rana Munns published in 1993"
TL;DR: It is argued that salts taken up by the plant do not directly control plant growth by affecting turgor, photosynthesis or the activity of any one enzyme, and rather, the build-up of salt in old leaves hasten their death, and the loss of these leaves affects the supply of assimilates or hormones to the growing regions and thereby affects growth.
Abstract: Recent progress in improving the salt tolerance of cultivated plants has been slow. Physiologists have been unable to define single genes or even specific metabolic processes that molecular biologists could target, or pinpoint the part of the plant in which such genes for salt tolerance might be expressed. While the physiological might be expressed. While the physiological processes are undoubtedly complex, faster progress on unraveling mechanisms of salt tolerance might be made if there were more effort to test hypotheses rather than to accumulate data, and to integrate cellular and whole plant responses. This article argues that salts taken up by the plant do not directly control plant growth by affecting turgor, photosynthesis or the activity of any one enzyme. Rather, the build-up of salt in old leaves hasten their death, and the loss of these leaves affects the supply of assimilates or hormones to the growing regions and thereby affects growth.
1,500 citations
TL;DR: In this paper, the role of ABA as a long-distance signal in controlling growth by root-to-shoot communication is unclear: the concentrations found in xylem sap can affect stomatal conductance, but seem too low to affect leaf expansion.
Abstract: Hormones appear to be important in controlling plant growth in soils of low water potential, particularly in changing the root:shoot ratio as the soil dries or becomes saline, and in communicating soil conditions to the leaves. This review has necessarily focused on abscisic acid (ABA), as there is little information about the role of other hormones in controlling growth in dry or saline soils. ABA is partly responsible for the differential response of root and shoot growth to dry soils. In dry soil it maintains root growth and inhibits shoot growth. However, when applied to well-watered plants, it usually inhibits root and shoot growth, showing that plants in dry soil respond quite differently from well-watered plants. ABA affects the rate of cell expansion in plants in dry soils: it maintains cell expansion in roots and inhibits that in leaves. It may also affect the rate of cell production, but little is known about this. The role of ABA as a long-distance signal in controlling growth by root-to-shoot communication is unclear: the concentrations found in xylem sap can affect stomatal conductance, but seem too low to affect leaf expansion. Yet drought and salinity generally affect leaf expansion before they affect leaf conductance. A possible solution to this puzzle is that ABA is transported in xylem sap in a complexed form, or that another compound in xylem sap stimulates the synthesis or activity of ABA in leaves, or affects leaf expansion independently of ABA.
191 citations
TL;DR: High CO2 increased growth by stimulating the development of tiller buds that would otherwise have been inhibited in wheat plants, indicating that salt uptake was largely independent of water uptake, and that high CO2 did not increase growth by reducing the salt load.
Abstract: Wheat plants (Triticum aestivum cv. Matong and T. durum cv. Modoc) were grown at ambient and elevated CO2 (350 cm3 m-3 above ambient) in soil with or without 150 mol m-3 NaCl for 6 weeks. The increase in dry matter, leaf area and tillering under high CO2 was relatively greater under saline than non-saline conditions for both cultivars. Tillering was the primary component of growth affected by both salinity and high CO2. Salinity greatly reduced tillering and high CO2 partly reversed the effects of salinity. High CO2 increased dry matter accumulation of the salt-sensitive Modoc to a greater extent (+104%) than that of the more salt-tolerant Matong (+73%) in the salt treatment. Transpiration rates were greatly reduced by salinity for both cultivars. Under high CO2, increased leaf areas compensated for reduced transpiration rates per unit leaf area (i.e. greater stomatal closure), and total transpiration was little affected by CO2 level within each treatment. The more salt-tolerant Matong showed greater stomatal closure and higher transpiration efficiencies than the salt-sensitive Modoc under salinity. High CO2 reduced transpiration rate (per unit dry weight) by 40 to 50%, but did not significantly change the rate of sodium accumulation (per unit dry weight), indicating that salt uptake was largely independent of water uptake, and that high CO2 did not increase growth by reducing the salt load. Our results suggest that high CO2 increased growth by stimulating the development of tiller buds that would otherwise have been inhibited.
102 citations
TL;DR: It is suggested that storage at -20°C causes the aggregation or polymerization of a small compound with low activity to form a large compound with high activity.
Abstract: Xylem sap was collected from wheat and barley growing in a drying soil, and the effect of the sap on transpiration was detected by a bioassay with detached wheat leaves. The inhibitory activity of fresh sap was small, and could be largely accounted for by the abscisic acid content (about 2×10-5mol m-3). When fresh sap was stored at -20°C for several days, the activity increased. Maximum activity developed after a week. This increase in activity was due to a compound that increased in size with storage at -20°C. When fresh sap was fractionated with filters of different molecular size exclusion characteristics, and the separated fractions stored at -20°C for a week, activity developed only in the fraction containing compounds smaller than 0·3 kDa. However, when sap already stored at -20°C was fractionated, activity was only in fractions containing compounds larger than 0·3 kDa. The increase in activity and in size did not occur with storage in liquid nitrogen (-196°C) or at -80°C. These results suggest that storage at -20°C causes the aggregation or polymerization of a small compound with low activity to form a large compound with high activity. This change is not catalysed by an enzyme because it can occur in a fraction from which molecules larger than 0·3 kDa are removed. It is probably promoted by high solute concentrations when ice crystals form. Sap collected from plants in soils of high water potential had little or no activity after storage at -20°C.
52 citations