Season vs. Nutrition-Dependent Fruit Loading: Effects on Pigment Dynamics of Tomato Leaves

ABSTRACT

The effect of season on fruit load is drastic when tomato (Lycopersicum esculentum, cv. Dombito) plants are grown hydroponically during winter or summer. In this paper, we report the effect of high (HT) vs. low (LT) temperatures on chlorophyll a and b, pheophytin a and b, carotene a and b, and zeaxanthin, lutein, antheraxanthin, neoxanthin, lutein-5,6-epoxide, and violaxanthin dynamics of tomato leaves. Furthermore, based on the assumption that season may prevail over nutrition, we report the effect of normal vs. quarter-normal Hoagland nutrient solution on these pigments' profiles. Chlorophyll concentration was three to four times higher during HT. Chlorophyll loss during LT was more intense for chlorophyll b (chl-b) than for chlorophyll a (chl-a), and the chl-a/chl-b ratio was higher during LT. Chlorophyll concentration was less affected by nutrition and more by season. Nutrition affected chlorophyll concentration more at HT. Pheophytin a (pheo-a) increased intensely with increase of temperature and total solar radiation (SR), while the opposite was observed for pheophytin b (pheo-b). Especially during LT, pheo-b presented an impressive increase opposite to that of chl-a, chl-b and pheo-a. Carotenoid concentration was less affected by nutrition and more by season. Nutrition affected the concentration of carotenes more than that of the other carotenoids, especially at HT. Carotenes a (car-a) and b (car-a) were significantly higher during HT, and the same was true for the concentrations of epoxide-free xanthophylls, zeaxanthin (Z), and lutein. Epoxide-free xanthophylls, car-a, car-b, and pheo-a presented the same pattern of changes during both seasons, and all these pigments were affected positively by the increase of SR and temperature. Concentrations of the mono-epoxides antheraxanthin (A), neoxanthin, and lutein-5,6-epoxide, and of the di-epoxide violaxanthin (V) presented a second group with the same pattern of changes. As opposed to epoxide-free xanthophylls, they were negatively affected by the increase of temperature and SR. In winter, the xanthophyll ratio A+Z/V (i.e, xanthophylls involved in the violaxanthin cycle, as a photoprotective mechanism) showed an impressive increase at the last five weeks (when temperature and SR were increased), when they were two times higher than during the remainder of the period (when temperature and SR were low). In summer, A+Z/V was high during the period of particularly high temperature and SR (weeks 7–11, with an average temperature of 33°C–35°C and SR of 29–32 MJ m⁻²) and lower at the last five weeks, when temperature and SR decreased (< 28°C and SR 27 MJ m⁻² respectively).

Keywords:

• tomato
• carotenoids
• chlorophyll
• pheophytin
• effects of seasonal changes
• nutrition on pigments

ACKNOWLEDGMENTS

This work is dedicated to the memory of our teacher, Professor C.A. Niavis.