ISSN:
1432-2048
Keywords:
Ammonia
;
Cytosol (pH)
;
C3 and C4 plants
;
Dye (pH-indicating)
;
Vacuole (pH)
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract Atmospheric ammonia (NH3) from various anthropogenic sources has become a serious problem for natural vegetation. Ammonia not only causes changes in plant nitrogen metabolism, but also affects the acid-base balance of plants. Using the pH-sensitive fluorescent dyes pyranine and esculin, cytosolic and vacuolar pH changes were measured in leaves of C3 and C4 plants exposed for brief periods to concentrations of NH3 in air ranging from 1.33 to 8.29 μmol NH3 · mol-1 gas (0.94–5.86 mg · m-3). After a lag phase, uptake of NH3 from air at a rate of 200 nmol NH3 · m - 2 leaf area · s- 1 into leaves of Zea mays L. increased pyranine fluorescence indicating cytosolic alkalinisation. The increase was much larger in the dark than in the light. In illuminated leaves of the C3 plant Pelargonium zonale L. and the C4 plants Z. mays and Amaranthus caudatus L., NH3-dependent cytosolic alkalinisation was particularly pronounced when CO2 was supplied at very low levels (16 or 20 μmol CO2 · mol- 1 gas, containing 210 mmol O2 · mol- 1 gas). An increase in esculin fluorescence, which was smaller than that of pyranine, was indicative of trapping of some of the NH3 in the vacuoles of leaves of Spinacia oleracea L. and Z. mays. Photosynthesis and transpiration remained unchanged during exposure of illuminated leaves to NH3, yielding an influx of 200 nmol NH3 · m-2 leaf area · s-1 for up to 30 min, the longest exposure time used. Both CO2 and O2 influenced the extent of cytosolic alkalinisation. At 500 μmol CO2 · mol-1 gas the cytosolic alkalinisation was suppressed more than at 16 or 20 μmol CO2 · mol-1 gas. The suppressing effect of CO2 on the NH3induced alkalinisation was larger in illuminated leaves of the C4 plants Z. mays and A. caudatus than in leaves of the C3 plant P. zonale. A reduction of the O2 concentration from 210 to 10 mmol O2 · mol -1 gas, which inhibits photorespiration, increased the NH3induced cytosolic alkalinisation in C3 plants. Suppression by CO2 or O2 of the alkaline pH shift caused by the dissolution and protonation of NH3 in queous leaf compartments, and possibly by the production of organic compounds synthesised from atmospheric NH3, indicates that NH3 which enters leaves is rapidly assimilated if photosynthesis or photorespiration provide nitrogen acceptor molecules.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00231393
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