Abscisic acid increases carotenoid and chlorophyll in leaves and fruit of two tomato genotypes
Barickman, T. C., D. A. Kopsell, and C. E. Sams.  2014.  Journal of the American Society for Horticultural Science, 139(3):261-266.

One important regulator that coordinates response to environmental stress is the hormone abscisic acid (ABA), which is synthesized from xanthophyll pigments. In spite of the fact that there is strong evidence of increases in ABA concentrations under various environmental stresses, information concerning the effects of exogenous ABA applications on leaf pigments and fruit carotenoids in tomato (Solanum lycopersicum) is lacking. This study investigated the impacts of root tissue ABA applications on tomato leaf and fruit pigmentation concentrations of ‘MicroTina’ and ‘MicroGold’ tomato plants. Tomato plants were treated with increasing concentrations of ABA in the nutrient solution. Therefore, the purpose of this study was to determine dose-response effects of ABA treatment in solution culture for maximum leaf pigmentation and fruit carotenoids in two distinct genotypes of dwarf tomatoes. Since application of ABA to plants has resulted in increases in chlorophylls and carotenoids, we hypothesized that ABA would have a positive impact on leaf chlorophylls and carotenoids, thus increasing fruit carotenoids. The results indicated that ‘MicroTina’ plants treated with ABA (0.5, 5.0, and 10.0 mg•L-1) had a significant increase in β-carotene (BC; P ≤ 0.001), lutein (LUT; P ≤ 0.001), zeaxanthin (ZEA; P ≤ 0.05), and neoxanthin (NEO; P ≤ 0.001) in the leaf tissue. In ‘MicroGold’ tomato plants carotenoids responded similarly. For example, there were significant increases in BC (P ≤ 0.05), lutein (P ≤ 0.001), and NEO (P ≤ 0.001). In ‘MicroTina’ tomato leaves there were significant increases in chlorophyll a (Chl a; P ≤ 0.05) and chlorophyll b (Chl b; P ≤ 0.01) concentrations. Furthermore, there were significant increases in Chl a (P ≤ 0.05) and Chl b (P ≤ 0.01) in ‘MicroGold’ leaf tissue. In ‘MicroTina’ tomato fruit tissue, the concentration increased significantly for lycopene (LYCO; P ≤ 0.05). However, in ‘MicroGold’ there was no significant changes in carotenoid concentrations. Therefore, ABA has been shown to positively change tomato leaf and fruit tissue pigment concentrations.