Floral Metabolism of Sugars and Amino Acids: Implications for Pollinators’ Preferences and Seed and Fruit Set

Abstract

Primary metabolism in flowers sustains a plenitude of physiological and ecological functions related to floral development and plant reproduction. Carbohydrates and amino acids provide energy and precursors for the reactions of floral secondary metabolism, such as the molecules for color and scent, and constitute an important resource of food for the pollinators. Recent discoveries have advanced our understanding of the cycles of carbohydrate hydrolysis and resynthesis that regulate pollen development, pollen tube growth, and pollination as well as the composition of nectar. Pathways of de novo amino acid biosynthesis have been described in flowers, and the proteins that regulate pollen tube guidance and ultimately control fertilization are being progressively characterized. Finally, a novel field of research is emerging that investigates the chemical modification of sugars and amino acids by colonizing microorganisms and how these affect the pollinators' preferences for flowers. In this Update article, we provide an overview of the new discoveries and future directions concerning the study of the primary metabolism of flowers.The chemistry of flowers is unique, as it sustains very diverse physiological functions such as flower development, the transition from flower to fruit, and the initial phases of seed set (O'Neill, 1997;Pélabon et al., 2015). In addition, floral metabolites fulfill relevant ecological roles, such as acting as signaling molecules in the chemical communication with animal pollinators (Borghi et al., 2017), providing protection against pests and colonizing microorganisms (Kessler and Baldwin, 2007;Nepi, 2014). Stunning displays of the metabolic resources of flowers are, for example, their colors and fragrance, which occur following the accumulation and emission of tinted and scented secondary metabolites, respectively (Grotewold, 2006;Tanaka et al., 2008;Khan and Giridhar, 2015). Perhaps less sensational, but equally as important, are the reactions of primary metabolism. Indeed, these sustain the physiology of flowers, provide the chemical precursors, and meet the energy demand of floral secondary metabolism (Muhlemann et al., 2014). Moreover, sugars and amino acids also serve as a nutritional reward for the pollinators that feed on nectar and pollen (Pacini et al., 2006;Heil, 2011;Roy et al., 2017). Therefore, knowing how primary metabolites are imported or de novo synthesized in flowers, and how they are secreted and catabolized, is at the heart of floral biology, being relevant to understand the physiology of plant reproduction and the role that flowers play in the ecosystem. In this article, we aim to provide an overview of floral central metabolism. How primary metabolism sustains flower development, and fruit and seed set, also will be addressed. Finally, given the considerable proportion of primary metabolites that are channeled into nectar, we will discuss the chemical composition of nectar, the modifications that arise from fermentation processes by colonizing yeasts and bacteria, an...

Alyssum (Lobularia maritima) selectively attracts and enhances the performance of Cotesia vestalis, a parasitoid of Plutella xylostella

“…The nutrients from flowers may support C. vestalis to mature more eggs for parasitism. Floral nectar provides not only sugars for parasitoids, but also proteins, amino acids and lipids [58][59][60] , which are vital for fecundity of parasitoids 61,62 . However, the fecundity of female C. vestalis was not improved by heronsbill.…”

The impact of yeast presence in nectar on bumble bee behavior and fitness

“…The presence of microbes in nectar often results in pronounced changes in nectar traits such as pH, sugar and amino acid composition, temperature, and floral scent (reviewed in Pozo et al. and Borghi and Fernie ). In our experiment, we added different yeast species to sucrose‐rich sugar water (sucrose, glucose, fructose) containing traces of peptone, yeast, and malt extract and administered this solution to the bees.…”

Cyanogenesis in Macadamia and Direct Analysis of Hydrogen Cyanide in Macadamia Flowers, Leaves, Husks, and Nuts Using Selected Ion Flow Tube–Mass Spectrometry

“…Previous reports have mentioned that cyanogenic compounds are highest in growing tissues of plants and that activation of metabolic processes coincide with cyanogenic glycoside production [6,44]. The flower is the main reproductive organ of a plant and has very active and complex morphological and physiological features, which support an abundance of ecological functions related to floral development and plant reproduction [45][46][47]. For instance, de novo synthesis of amino acids, enzymes, and structural proteins, which are precursors of N-containing secondary metabolites (such as cyanogenic glycosides) and signaling molecules, all occur in floral tissues [47].…”

“…The flower is the main reproductive organ of a plant and has very active and complex morphological and physiological features, which support an abundance of ecological functions related to floral development and plant reproduction [45][46][47]. For instance, de novo synthesis of amino acids, enzymes, and structural proteins, which are precursors of N-containing secondary metabolites (such as cyanogenic glycosides) and signaling molecules, all occur in floral tissues [47]. These complex metabolic processes during floral development and growth could be contributing to the increased biosynthesis of cyanogenic glycosides Foods 2020, 9, 174 9 of 15 resulting in the higher concentration of hydrogen cyanide generated in the flower than in the other parts of Macadamia.…”