β-Glucosidase activity in almond seeds

Area of Science:

• Plant genetics
• Biochemistry
• Food science

Background:

• Almond bitterness is a key trait for breeding, with bitter seeds often discarded.
• Amygdalin hydrolysis by β-glucosidases, specifically prunasin hydrolases (PH), is central to bitterness.
• Previous studies suggest differences in PH location between sweet and bitter almonds.

Purpose of the Study:

• To isolate and characterize prunasin hydrolases (PHs) in sweet and bitter almonds.
• To investigate if genomic or protein sequence variations in PHs determine almond seed taste.
• To understand the genetic basis of almond bitterness.

Main Methods:

• RNA extraction from different almond tissues (tegument, nucellus, cotyledon) across ripening stages.
• RT-PCR and cloning to obtain nine PH sequences from sweet and bitter genotypes.
• Heterologous expression of PH clones in tobacco plants for activity assays.
• Enzymatic assays using Feigl-Anger and colorimetric methods to quantify PH activity and β-glucosidase activity.

Main Results:

• Nine PH sequences were successfully isolated from both sweet and bitter almond genotypes.
• Sequence analysis revealed single nucleotide polymorphisms (SNPs) between genotypes.
• Enzyme activity assays showed detectable differences, but no direct correlation with almond bitterness was established.

Conclusions:

• While sequence and activity differences in prunasin hydrolases exist between sweet and bitter almonds, they do not directly correlate with the bitter trait.
• The genetic control of almond bitterness may involve other factors or regulatory mechanisms beyond the characterized PH sequences and activities.
• Further research is needed to fully elucidate the genetic underpinnings of almond bitterness.