Effects of Water Stress on the Activities of Three Enzymes in Maize Seedlings

Abstract

Changes in the activities of three enzymes (nitrate reductase, L-phenylalanine ammonia-lyase, and a dehydronicotinamide adenine dinucleotide-oxidase complex) were measured during development of water stress in young maize (Zea mays) plants.L-Phenylalanine ammonia-lyase and nitrate reductase activities decreased markedly with water deficits of 10 to 20%. 'Abbreviation: PAL, L-phenylalanine ammonia-lyase. MATERIALS AND METHODSThe dominant tall form of the d1 dwarf maize (Zea mays) was grown in vermiculite in the greenhouse. Nutrient requirements were provided with a modified Hoagland's solution 1 (9). Moisture stress was initiated by withholding water for varying periods beginning approximately 10 days after germination. In early experiments, the plants remained in the greenhouse until sampled for assay, but in later experiments they were transferred to a growth chamber when water stress was initiated. The chamber environment was 27 C, 30 to 50% relative humidity, and had a light period of 12 hr/day of 1000 ft-c. The plants were sampled at the middle of the light period. In the rehydration experiments, the vermiculite base was saturated with water 24 hr prior to sampling.Water deficit was estimated by the method of Weatherly (21). Duplicate or triplicate 5-cm sections were taken from the midportion of the third leaf of two or three plants. The original weight was determined immediately after harvest, and the tissue was floated in deionized water for 4 hr. At that time, the saturated weight was taken and the tissue was dried at 95 C for 24 hr for dry weight determination. The water deficit was expressed as the ratio of water taken up divided by the final water content, multiplied by 100.The midportion of the leaf blades from four to six seedlings was used as the source of tissue for nitrate reductase and NADH oxidase. PAL was prepared from the leaf sheaths of the same or comparable seedlings. Nitrate reductase activity was determined by the method of Hageman and Flesher (6), except that the tissue was ground in a chilled mortar with pestle and sand. PAL was prepared and assayed as described by Reid and Marsh (15). NADH oxidase activity was determined in the same extract used for nitrate reductase. The reaction mixture for the oxidase assay contained 200 ymoles of tris buffer, pH 8.2; 20 ,tmoles of (NH4)2SO4; 0.66 umole of NADH; plus enzyme in a final volume of 3 ml. The reaction was run at 30 C and was initiated by the addition of NADH. Changes in absorbancy at 340 nm were followed spectrophotometrically for 5 min.One unit of activity for all three enzymes was defined as the amount of enzyme which catalyzed the formation of 1 ,tmole of product in 1 min under standard conditions. Protein was determined by standard biuret or Lowry methods (12) with bovine serum albumin as a standard. RESULTSThe results of water deficit measurements (Fig. 1)

Mixed rhizobia and Herbaspirillum seropedicae inoculations with humic acid-like substances improve water-stress recovery in common beans

“…The PAL activity was higher in co-inoculation treatments in the first experiment during the stress and recovery periods, while in the second experiment, the PAL activity was higher in the co-inoculation treatment only during the recovery period. The second experiment corroborates a previous study in which the level of PAL decreased with mild to moderate water stress and recovered readily after re-watering [36].…”

Nitrate Reductase Activity in Maize (Zea mays L.) Leaves

“…Experiments were conducted to determine whether the nitrate flux to the leaves or the nitrate content of the leaves regulated the nitrate reductase activity (NRA) Nitrate reductase activity is sensitive to changes in the water status of plants and is inhibited when the water potential of plants declines (1,9,14). Morilla et al (14) (4), in the same tissue used for determination of NRA and nitrate content.…”

“…Nitrate reductase activity is sensitive to changes in the water status of plants and is inhibited when the water potential of plants declines (1,9,14). Morilla et al.…”

Nitrate Reductase Activity and Polyribosomal Content of Corn (Zea mays L.) Having Low Leaf Water Potentials

“…Among the activity of certain enzymes (1,12,7,22). One of the most severely affected is nitrate reductase which has been shown to decline to 42% of the controls in barley leaves having a T"' of about -11 bars (12) and to 50% of the controls in corn seedlings having a water deficit of 10% (1).…”

“…Among the activity of certain enzymes (1,12,7,22). One of the most severely affected is nitrate reductase which has been shown to decline to 42% of the controls in barley leaves having a T"' of about -11 bars (12) and to 50% of the controls in corn seedlings having a water deficit of 10% (1). This large effect of desiccation on NR is not surprising, since the enzyme is very labile (13,17) and is affected by many environmental factors (3,8,15,26).…”