Physiological Characterization of Two Nicotiana tabacum Lines Differing in Seed Productivity

Tobacco is a plant with a wet stigma, which produces reactive oxygen species (ROS) and abscisic acid (ABA) which is important for in vivo pollen germination. Furthermore, ROS can be linked to growth processes, stimulating or inhibiting them. However, to what extent do differences in the redox environment and ABA level on the stigma and in pistil tissues correlate with flower growth, pollination success and resulting fruit parameters? We investigated redox homeostasis and ABA concentrations in stigma exudates of two tobacco lines ("Samsun" and "Fortune") with different floral organ size and seed production. Fortune has longer flowers, larger fruits, and more seeds than Samsun. We report here that Samsun has a higher total oxidative capacity in stigma exudate, and possibly also higher NO level, than Fortune, as estimated by electron paramagnetic resonance spectroscopy. Fortune has a higher ascorbate peroxidase (APX) content in stigma tissues, as determined by Western blot analysis, and a higher ABA concentration in stigma exudate. Analyzing ROS levels and enzyme activity during the elongation stage in buds, we found that shorter Samsun styles had higher ROS levels, but they also had higher superoxide dismutase (SOD) and APX activity. The results of this study may help in developing approaches to a targeted increase in flower size and seed productivity.