En-rich enzymes and nitrogencontaining precursors are involved in the production of

En-rich enzymes and nitrogencontaining precursors are involved in the production of what are termed C-based defenses [20?3], however, so this classification of defenses as C- or N-based may be an oversimplification and confound interpretation of responses to resources in the framework of the CNBH or GDBH. There has, in fact, been much debate as to the utility of the CNBH [24,25], and it has also been erroneously applied [26]. Nonetheless, the empirical support for this hypothesis shows predicted patterns of phenotypic changes in defenses for temperate woody [27,28], herbaceous [29], and tropical [30?3] species. The GDBH is more detailed than the CNBH and predicts a negative correlation between growth and defense under conditions of moderate to high MedChemExpress 298690-60-5 resource availability [11]. The GDBH is difficult to test because: 1) a broad range of resource availability must be included in studies, 2) most variables assessed are merely correlates of the plastic physiological processes that are part of the hypothesis (e.g., biomass is often a proxy for resource allocation to growth, but it can include tissues and compounds important in defense and storage as well), and 3) it is difficult to ensure the maintenance of experimental resource conditions throughout a plant’s growth [34]. Despite these challenges, valuable insights on trade-offs and priorities in plant resource allocation can be gained from studies addressing aspects of the GDBH [35?7]. A key postulate of the CNBH and the GDBH is that defenses will increase under conditions of limited growth when photosynthesis continues to function at normal levels. This mechanistic aspect of the hypotheses is difficult to test, yet some studies have measured photosynthesis, growth, and defense simultaneously. Results from these studies show a variety of patterns. Light can increase photosynthesis and N-based defenses but decrease Cbased defenses [38]; available nitrogen can increase photosynthesis and monoterpene production (except during the leaf expansion stage) [39], and high nitrogen can have inverse effects on photosynthesis (positive) and phenolic defenses (negative) [40,41]. In addition, the down-regulation of genes important to photosynthesis has been shown to accompany herbivore induced 76932-56-4 manufacturer upregulation of defenses in Nicotiana attenuata (Solanaceae) [42,43], although resource conditions mediate changes in transcription such that they do not always correspond to equivalent changes in the products encoded for [43]. Nevertheless, the paradigm persists that growth is more sensitive to a plant’s resource environment than is photosynthesis, and decreased growth with concomitant increases in defenses has been documented many times [11,33,44?47]. The sensitivity of photosynthesis to environmental conditions and the connection between photosynthesis and growth and defense production merit more empirical study. Here we present experimental results quantifying saponin (terpenoid) and flavan (phenolic) production in a neotropical tree, Pentaclethra macroloba Kuntze (Fabaceae: Mimosoideae), a shadetolerant species with nitrogen-fixing root nodules [48] that produces high levels of saponins which function as an antiherbivore defense [49,50] as well as flavonoids. Saponins are a class of glycosylated triterpenoid, steroid, or steroidal alkaloid C-based compounds produced primarily via the mevalonic acid pathway [51], and flavans are flavonoids known to serve as plant defenses in a related genus, Inga [52,53]. Most s.En-rich enzymes and nitrogencontaining precursors are involved in the production of what are termed C-based defenses [20?3], however, so this classification of defenses as C- or N-based may be an oversimplification and confound interpretation of responses to resources in the framework of the CNBH or GDBH. There has, in fact, been much debate as to the utility of the CNBH [24,25], and it has also been erroneously applied [26]. Nonetheless, the empirical support for this hypothesis shows predicted patterns of phenotypic changes in defenses for temperate woody [27,28], herbaceous [29], and tropical [30?3] species. The GDBH is more detailed than the CNBH and predicts a negative correlation between growth and defense under conditions of moderate to high resource availability [11]. The GDBH is difficult to test because: 1) a broad range of resource availability must be included in studies, 2) most variables assessed are merely correlates of the plastic physiological processes that are part of the hypothesis (e.g., biomass is often a proxy for resource allocation to growth, but it can include tissues and compounds important in defense and storage as well), and 3) it is difficult to ensure the maintenance of experimental resource conditions throughout a plant’s growth [34]. Despite these challenges, valuable insights on trade-offs and priorities in plant resource allocation can be gained from studies addressing aspects of the GDBH [35?7]. A key postulate of the CNBH and the GDBH is that defenses will increase under conditions of limited growth when photosynthesis continues to function at normal levels. This mechanistic aspect of the hypotheses is difficult to test, yet some studies have measured photosynthesis, growth, and defense simultaneously. Results from these studies show a variety of patterns. Light can increase photosynthesis and N-based defenses but decrease Cbased defenses [38]; available nitrogen can increase photosynthesis and monoterpene production (except during the leaf expansion stage) [39], and high nitrogen can have inverse effects on photosynthesis (positive) and phenolic defenses (negative) [40,41]. In addition, the down-regulation of genes important to photosynthesis has been shown to accompany herbivore induced upregulation of defenses in Nicotiana attenuata (Solanaceae) [42,43], although resource conditions mediate changes in transcription such that they do not always correspond to equivalent changes in the products encoded for [43]. Nevertheless, the paradigm persists that growth is more sensitive to a plant’s resource environment than is photosynthesis, and decreased growth with concomitant increases in defenses has been documented many times [11,33,44?47]. The sensitivity of photosynthesis to environmental conditions and the connection between photosynthesis and growth and defense production merit more empirical study. Here we present experimental results quantifying saponin (terpenoid) and flavan (phenolic) production in a neotropical tree, Pentaclethra macroloba Kuntze (Fabaceae: Mimosoideae), a shadetolerant species with nitrogen-fixing root nodules [48] that produces high levels of saponins which function as an antiherbivore defense [49,50] as well as flavonoids. Saponins are a class of glycosylated triterpenoid, steroid, or steroidal alkaloid C-based compounds produced primarily via the mevalonic acid pathway [51], and flavans are flavonoids known to serve as plant defenses in a related genus, Inga [52,53]. Most s.