Distinct Peculiarities of In Planta Synthesis of Isoprenoid and Aromatic Cytokinins

Abstract

The biosynthesis of aromatic cytokinins in planta, unlike isoprenoid cytokinins, is still unknown. To compare the final steps of biosynthesis pathways of aromatic and isoprenoid cytokinins, we synthesized a series of nucleoside derivatives of natural cytokinins starting from acyl-protected ribofuranosyl-, 2′-deoxyribofuranosyl- and 5′-deoxyribofuranosyladenine derivatives using stereoselective alkylation with further deblocking. Their cytokinin activity was determined in two bioassays based on model plants Arabidopsis thaliana and Amaranthus caudatus. Unlike active cytokinins-bases, cytokinin nucleosides lack the hormonal activity until the ribose moiety is removed. According to our experiments, ribo-, 2′-deoxyribo- and 5′-deoxyribo-derivatives of isoprenoid cytokinin N6-isopentenyladenine turned in planta into active cytokinins with clear hormonal activity. As for aromatic cytokinins, both 2′-deoxyribo- and 5′-deoxyribo-derivatives did not exhibit analogous activity in Arabidopsis. The 5′-deoxyribo-derivatives cannot be phosphorylated enzymatically in vivo; therefore, they cannot be “activated” by the direct LOG-mediated cleavage, largely occurring with cytokinin ribonucleotides in plant cells. The contrasting effects exerted by deoxyribonucleosides of isoprenoid (true hormonal activity) and aromatic (almost no activity) cytokinins indicates a significant difference in the biosynthesis of these compounds.

In Planta, In Vitro and In Silico Studies of Chiral N6-Benzyladenine Derivatives: Discovery of Receptor-Specific S-Enantiomers with Cytokinin or Anticytokinin Activities

“…This is consistent with the notion that only cytokinin bases have real biological activity, whereas their ribosides are mostly the inactive transport forms of these hormones and either cannot bind to cytokinin receptors or, even when binding, are unable to activate them [ 44 ]. Although ribonucleoside 12a demonstrated some GUS activity, mainly with the AHK3 Arabidopsis receptor, and the activity of cytokinin ribosides in biotests has been previously described [ 45 ], this residual activity was presumably due to their enzymatic conversion to free bases in vivo (see also the discussion below).…”

“…The structure of the heterocyclic ribonucleoside base undoubtedly affects the efficiency of ribose cleavage [ 45 ]. In this work, we also observed that the presence of some substituents at C 2 apparently made it difficult to detach the ribofuranose residue, which blocked the cytokinin activity of riboside compound.…”

Modulatory Effects of Phytochemicals on Gut–Brain Axis: Therapeutic Implication

“…These compounds have been shown to interact with the gut microbiota, immune system, and neurotransmitter systems, thereby influencing brain function. Phytochemicals such as polyphenols, carotenoids, flavonoids, and terpenoids have been identified as having potential therapeutic implications for various neurological disorders [ 19 ].

FIGURE 1 Modulatory effects of phytochemicals on the gut–brain axis.

…”

“…It has been demonstrated that GBA is essential for the onset and course of a number of neurological conditions, such as PD, MS, depression, anxiety, and ASD [ 1 ]. The gut microbiota, composed of the gastrointestinal tract’s resident bacteria, is a crucial element of the GBA that may impact behavior and brain function through diverse pathways [ 19 ]. An imbalance in the makeup of the gut microbiota, or dysbiosis, has been linked to a number of neurological conditions, suggesting that modulating the gut microbiota may have potential therapeutic implications for these conditions [ 23 ].…”