Aluminum toxicity in tomato. Part 2.Leaf gas exchange, chlorophyll content, and invertase activity
The effect of aluminum (Al) toxicity on leaf gas exchange, leaf chlorophyll content, and sucrose metabolizing enzyme activity of two tomato cultivars (Lycopersicon esculentum Mill. 'Mountain Pride' and 'Floramerica') was studied to determine the mechanism of growth reduction observed in a related study (Simon et al., 1994, Part 1).Plants were grown in diluted nutrient solution (pH 4.0) with 0, 10, 25, or 50 lM Al for 16 days. Leaf gas exchange was reduced 2-3 fold in both cultivars as Al concentration increased. Gas exchange of 'Mountain Pride' was more sensitive to Al toxicity thanFloramerica', agreeing with growth responses observed. Reductions in carbon dioxide (CO2) assimilation rate appeared to be due to nonstomatal factors in 'Floramerica', but stomatal and non-stomatal limitations in Mountain Pride'.Chlorophyll content of leaves was not affected by Al. Acid invertase (AI) and neutral invertase (NI) activity of roots responded consistently to Al concentration in both cultivars.Root AI and NI activity decreased to a greated extent for 'Mountain Pride' than for 'Floramerica'.