Effects of Ammonium Nutrition on Water Stress, Water Uptake, and Root Pressure in Lycopersicon esculentum Mill

Abstract

Wilmington, Del. 19898. During the experiment th pH was checked daily and found to range from 6.5 to 7.5 with NO,--N and 6.5 to 5.0 with NH,'-N.The rate of water uptake by intact plants was determined by measuring the decrease in solution weight over a 24-hr lightdark period. Water uptake by excised tops was determined by decapitating the plant under water approximately 5 cm above the root system and immersing the stem in a 250-ml flask of deionized water. The amount of water lost was measured from the flask over a 3-hr light period at mid-day.The volume of exudate per plant was measured at mid-day over a 3-hr period with the root system exposed to the solution in which the plant grew. The aerial portion of the plant was decapitated 5 cm above the root system, and a 10-ml pipette was attached directly to the stump with Tygon tubing.Leaf water potential was measured by the dye method described by Knipling (2). Samples consisting of 10 leaf discs 2 cm in diameter were collected at mid-day and immersed for a period of 2 hr in test tubes containing 10 ml of a series of sucrose solutions.All experiments were conducted in a controlled environment growthroom (1800 ft-c 16-hr photoperiod; 70% relative humidity; 24 C day, 18 C night). RESULTSThe rate of water uptake (ml/gram fresh weight of plant) by tomato plants decreases as they develop. The rate at which uptake changes with increasing plant size or age varies with nitrogen source (Fig. 1). Transferring plants from a NO-to an NH4* solution brings about a more rapid decline in water uptake. However, if after 5 days the plants are again returned to a solution containing only NO.--N, water uptake is rapidly restored to a rate equal to or greater than that for continuous NO--N. Recovery was much slower for plants exposed to NH4-N for 10 days.This inhibition of water uptake by NH4' was further characterized by measuring the changes in leaf water potential, root pressure, and water uptake by excised tops. Leaf water potential gradually decreased with increasing age for plants grown continuously on NO.--N (Fig. 2). Transferring the plants to a solution containing NH,+-N greatly decreases water potential, and after 10 days on NH,+ the water potential is twice as low as that of NO3-plants. Returning the plants to NO.--N increases the leaf water potential of plants previously exposed to NH+ for either 5 or 10 days.Exudation volume per gram fresh weight of root declines with age, and there is less exudate from plant roots exposed to the NH4+ solutions (Fig. 3). The recovery of plants exposed to NH4, for 5 days is immediate and after only 1 day on NO,-

Photocontrol of Anthocyanin Synthesis

“…Ethanol inhibits Chl synthesis (Fig. 4) (43), and for its inhibition of H20 uptake (33). Levulinic acid is an inhibitor of porphyrin biosynthesis, and inhibits the synthesis of Chl and respiratory pigments.…”

Ammonium nutrition increases water absorption in rice seedlings (Oryza sativa L.) under water stress

“…This is suggested to be responsible for the frequently observed smaller leaf area and lower root volume of plants supplied with NH 4 + than those given NO 3 − (Ali et al 1994(Ali et al , 1998Chance et al 1999;Pill and Lambeth 1977;Quebedeaux and Ozbun 1973;Wilcox et al 1977).…”

“…Water uptake of excised shoots: Shoots were cut under water 2 cm above the intersection between the roots and shoots; the excised shoots were subsequently immersed in deionized water in a 150-mL conical flask and then fixed and sealed by a sponge, according to Quebedeaux and Ozbun (1973). Shoot transpiration was determined by weighing the depletion of deionized water in the flask from 09:30 to 14:00 under light.…”

EFFECTS OF AMMONIUM AND NITRATE NUTRITION ON THE OSTRICH FERN (Matteuccia struthiopteris)

“…A measurable amount of free ammonium in a plant tissue can signify the onset of ammonium toxicity (Reisenauer 1978;Ikeda andOsawa 1979, 1980 (Quebedaux and Osbun 19'73;Plll andLambeth 1977, 1980). This effect has been attributed to a direct effect of ammonium on membrane permeability in the root (Quebedaux andOsbun 1973:P1ll andLambeth 1917). Pafi of the ammonium toxicity could also have occurred in the leaves because it has been reported that ammonium ions may restrict photosynthetic phosphorylation (Gibbs and Calo 1959), inhibit respiration (Haynes and Goh 1978), accelerate respiratory breakdown of carbohydrate (Barker et al 1965) and disrupt chloroplast membranes (Puritch and Barker 1967 (Haynes and Goh 1978 …”

“…obs.). Prange (1980) Quebedaux and Osbun (1973) and Pill and Lambeth (19'7'7). and not ammonia gas as suggested by Stuart and Haddock (1968).…”