Persistence of the effect of frugivore identity on post‐dispersal seed fate: consequences for the assessment of functional redundancy

Large frugivores play an important role as seed dispersers and their extinction may affect plant regeneration. The consequences of such extinctions depend on the likelihood of other species being functionally redundant and on how post‐dispersal events are affected. We assess the functional redundancy of two seed dispersers of the Atlantic Forest, the muriqui (Brachyteles arachnoides) and the tapir (Tapirus terrestris) through the comparison of their seed dispersal quality, taking into account post‐dispersal events. We compare tapirs and muriquis for: (1) the dung beetle community associated with their feces; (2) the seed burial probability and burial depth by dung beetles; and (3) the seed mortality due to predators or other causes according to burial depth. We determine how seed burial affects seed dispersal effectiveness (SDE) and compare the dispersal quality of four plant species dispersed by these frugivores. Muriqui feces attract 16‐fold more dung beetles per gram of fecal matter and seeds experience 10.5‐fold more burial than seeds in tapir feces. In both feces types, seed mortality due to predation decreases with burial depth but seed mortality due to other causes increases. Total seed mortality differ within plant species according to the primary disperser. Therefore, the effect of seed burial on SDE varies according to the plant species, burial depth, and primary disperser. As tapirs and muriquis differently affect the seed fate, they are not functionally redundant. Since the effect of the primary disperser persists into the post‐dispersal events, we should consider the cascading effects of these processes when assessing functional redundancy.     

Improving the nutritional content of tomatoes through reprogramming their flavonoid biosynthetic pathway

Flavonoids are a diverse group of phenolic secondary metabolites that occur naturally in plants and therefore form an integral component of the human diet. Many of the compounds belonging to this group are potent antioxidants in vitro and epidemiological studies suggest a direct correlation between high flavonoid intake and decreased risk of cardiovascular disease, cancer and other age-related diseases. Modifying flavonoid biosynthesis in chosen crops may provide new raw materials that have the potential to be used in foods designed for specific benefits to human health. We report that flavonoid biosynthesis in tomato fruit is subject to tissue specific and developmental regulation. Using transgenic modification, we have investigated the role of several of the enzymatic steps of tomato flavonol biosynthesis. Furthermore, we have generated several tomato lines with significantly altered flavonoid content. Most notably achieving an up to 78-fold increase in total fruit flavonols through ectopic expression of the biosynthetic enzyme, chalcone isomerase. This increase results principally from the accumulation of quercetin-glycosides in peel tissue. In addition, we report that chalcone synthase and flavonol synthase transgenes act synergistically to significantly up-regulate flavonol biosynthesis in tomato flesh tissues. A review of this work is presented in this paper.     

Increasing antioxidant levels in tomatoes through modification of the flavonoid biosynthetic pathway

Flavonoids are a diverse group of phenolic secondary metabolites that occur naturally in plants and therefore form an integral component of the human diet. Many of the compounds belonging to this group are potent antioxidants in vitro and epidemiological studies suggest a direct correlation between high flavonoid intake and decreased risk of cardiovascular disease, cancer and other age-related diseases. Enhancing flavonoid biosynthesis in chosen crops may provide new raw materials that have the potential to be used in foods designed for specific benefits to human health. Using genetic modification, it was possible to generate several tomato lines with significantly altered flavonoid content and to probe the role and importance of several key enzymatic steps in the tomato flavonoid biosynthetic pathway. Most notably an up to 78-fold increase in total fruit flavonols was achieved through ectopic expression of a single biosynthetic enzyme, chalcone isomerase. In addition, chalcone synthase and flavonol synthase transgenes were found to act synergistically to up-regulate flavonol biosynthesis significantly in tomato flesh tissues.     

Virus-induced gene silencing in detached tomatoes and biochemical effects of phytoene desaturase gene silencing

Virus-induced gene silencing (VIGS) is a technology that has rapidly emerged for gene function studies in plants. Many advances have been made in applying this technique in an increasing number of crops. Recently, VIGS has been successfully used to silence genes in tomato fruit through agroinfiltration of fruit attached to the plant. The phytoene desaturase (Pds) gene has been widely used as a reporter gene in VIGS experiments, although little is known about the changes that occur due to its silencing in plants. In this paper, we describe the efficient silencing of the Pds gene through the VIGS approach in detached tomato fruits, which makes the VIGS procedure even more versatile and applicable. After 16 days of agroinfiltration, approximately 75% of the tomatoes showed Pds silencing symptoms, although the distribution of silenced areas was variable among fruits. To study the potential effects caused by Pds silencing in detached tomatoes, carotenoids and other semi-polar secondary metabolites were analyzed using Liquid Chromatography-Mass Spectrometry. In addition, potential differences in primary metabolites were analyzed using Gas Chromatography-Mass Spectrometry. The results indicated that the yellow phenotype observed in Pds-silenced fruit was mainly due to the lack of the red-colored lycopene and therefore to a more pronounced contribution of the yellow-orange carotenoids (lutein, violaxanthin, and zeaxanthin) to the final color of the fruits. Furthermore, the biochemical changes observed in Pds-silenced detached tomatoes suggested that carotenoid and other pathways, e.g. leading to alkaloids and flavonoids, might be affected by the silencing of this reporter gene, and this should be taken into consideration for future experimental designs.