PubMed · 891376
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H A Nieper. 1977-07-15. [Counter-statement].. https://pubmed.ncbi.nlm.nih.gov/891376/
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Amygdalin, the phytochemical responsible for the characteristic bitterness of apricot (Prunus armeniaca L.) kernels, also exhibits significant bioactive properties and therapeutic potential. Genetic regulation of amygdalin content is therefore a key objective in apricot breeding programs aimed at quality improvement. In this study, we conducted quantitative trait loci (QTL) mapping to uncover the genetic basis of sweet-bitter differentiation in apricot kernels. We identified a 15-bp insertion/deletion (indel) polymorphism strongly related to kernel bitterness, with marker validation achieving 100% concordance across 601 apricot germplasm accessions. Notably, this polymorphic site is located within the helix-loop-helix (HLH) domain of the basic HLH (bHLH) transcription factor PabHLH2. Protein interaction analyses revealed that the 15-bp deletion variant impaired dimerization capacity, reducing transcriptional activation of downstream targets. Using yeast one-hybrid screening and dual-luciferase reporter assays, we identified PaCYP71AN24 and PaCYP79D16 as direct transcriptional targets of PabHLH2. Functional characterization further indicated that the PabHLH2a variant (harboring the 15-bp insertion) significantly enhanced the promoter activity of these cytochrome P450 genes compared with the deletion variant. Transient overexpression and silencing experiments in apricot kernels further confirmed that the 15-bp insertion positively regulates both PaCYP71AN24/PaCYP79D16 expression and prunasin accumulation, the immediate biosynthetic precursor of amygdalin. Overall, these findings provide mechanistic insights into the allelic variation underlying kernel bitterness and delineate the molecular cascade of amygdalin biosynthesis. The identified molecular markers and functional characterization establish a basis for marker-assisted breeding of low-amygdalin apricot cultivars, supporting the dual-purpose utilization of kernels in food and pharmaceutical industries.
We demonstrate that although the guinea pig liver cytosolic beta-glucosidase does not catalyze the hydrolysis of gentiobiose, it does hydrolyze, disaccharide-containing glycosides such as p-nitrophenyl-beta-D-gentiobioside (Glc beta 1----6Glc beta-pNP) and mandelonitrile-beta-D-gentiobioside (amygdalin). Furthermore, we establish that the enzyme attacks disaccharide glycosides exolytically; specifically, we document the exolytic deglucosylation of amygdalin and the generation of the intermediate monosaccharide glycoside mandelonitrile-beta-D-glucoside prior to the formation of the aglycone (mandelonitrile). We also show that the cytosolic beta-glucosidase catalyzes the hydrolysis of various phenolic (e.g. arbutin and salicin) and cyanogenic plant glucosides (e.g. prunasin). Using the everted gut-sack technique, we demonstrate that the plant glucosides, amygdalin, prunasin, and vicine, are transported across the small intestine of the guinea pig efficiently and without being hydrolyzed. Based on these data we speculate that the cytosolic beta-glucosidase may participate in biotransformation of toxic plant glucosides.