ALUMINUM TOXICITY IN TOMATO .2. LEAF GAS-EXCHANGE, CHLOROPHYLL CONTENT, AND INVERTASE ACTIVITY

The effect of aluminum (Al) toxicity on leaf gas exchange, leaf chloro phyll content, and sucrose metabolizing enzyme activity of two tomato cultivars (Lycopersicon esculentum Mill, 'Mountain Pride' and 'Florame rica') was studied to determine the mechanism of growth reduction obse rved in a related study (Simon et al., 1994, Part 1). Plants were grow n in diluted nutrient solution (pH 4.0) with 0, 10, 25, or 50 mu M 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 mo re sensitive to Al toxicity than 'Floramerica', agreeing with growth r esponses observed. Reductions in carbon dioxide (CO2) assimilation rat e appeared to be due to nonstomatal factors in 'Floramerica', but stom atal and non-stomatal limitations in 'Mountain Pride'. Chlorophyll con tent of leaves was not affected by Al. Acid invertase (AI) and neutral invertase (NI) activity of roots responded consistently to Al concent ration in both cultivars. Root AI and NI activity decreased to a great er extent for 'Mountain Pride' than for 'Floramerica'.