Studies In Mechanism Of Ammonium Toxicity In Tomato (Lycopersicon Esculentum Mill) Under Different Light Intensities

In this paper, the effects of ammonium and nitrate on toma.io(Lycopersicon Esculentum Mill) plant growth, nitrogen assimilation enzymes(GS and GDH), the content of free ammonium, photosynthesis, photorespiration, chlorophyll fluorescence(Fv/Fm and Fv/Fo), roots vigour, roots proton extrusion, roots plasmalemma- and tonoplast- H+-ATPase and Ca2+- ATPase, roots plasmalemma redox system under different light intensity were studied, in order to elucidate physiological mechanisms of ammonium toxicity in tomato plants.1. Under high light intensity, plant biomass and GS activity in roots and leaves were significantly decreased by ammonium nutrition, compared with nitrate-supplied plants. At the same time leaf plasmalemma permeability, GDH activitiy and free ammonium content in roots and leaves were significantly increased. However, under low light intensity, there are no significant differences in plant biomass and leaf GS activity between ammonium-supplied plants and nitrate-supplied plants, and root GS activity in ammonium-supplied plants increased. Leaf plasmalemma permeability , GDH activitiy and free ammonium content in root and leaves were also increased, but the increase extent was less than that under high light intensity.2. Under high light intensity, leaf GS activity in ammonium-supplied plants was significantly decreased, compared with nitrate-supplied plants. Photorespiration rate, photosynthetic rate, Fv/Fm and Fv/Fo were significantly decreased and O2-producing rate and H2O2 content in leaves were significantly increased. However, under low light intensity, there are no significant differences in all these parameters between ammonium-supplied plants and nitrate-supplied plants.3. Under high light intensity, root growth and root vigor of ammonium-supplied plants were significantly decreased, compared with nitrate-supplied plants. At the same time, root proton extrusion rate and plasmalemma permeability were significantly increased. However, under low light intensity, there are no significant differences in root biomass, root vigor and root plasmalemma permeability betweenammonium-supplied plants and nitrate-supplied plants. Root proton extrusion rate in ammonium-supplied plants increased, but the increase extent was less than that under high light intensity.Under high light intensity, activities of plasmalemma H+-ATPase and Ca2+-ATPase, tonoplast Ca2+-ATPase and plasmalemma redox system in roots of ammonium-supplied plants significantly increased, compared with nitrate-supplied plants. At the same time, activity of root tonoplast H+-ATPase in ammonium-supplied plants was significantly decreased. However, under low light intensity, activities of plasmalemma H+-ATPase, plasmalemma Ca2+-ATPase and plasmalemma redox system in roots of ammonium-supplied plants was also increased, but the increase extent was less than that under high light intensity. On the contrary, the increase extent in the tonoplast Ca2+-ATPase activity in the roots of ammonium-supplied plants was more than that under high light intensity. The decrease extent in the activity of root tonoplast H+-ATPase in ammonium-supplied plants under low light intensity was less than that under high light intensity.