Bitterness in Almonds

Abstract

Bitterness in almond (Prunus dulcis) is determined by the content of the cyanogenic diglucoside amygdalin. The ability to synthesize and degrade prunasin and amygdalin in the almond kernel was studied throughout the growth season using four different genotypes for bitterness. Liquid chromatography-mass spectrometry analyses showed a specific developmentally dependent accumulation of prunasin in the tegument of the bitter genotype. The prunasin level decreased concomitant with the initiation of amygdalin accumulation in the cotyledons of the bitter genotype. By administration of radiolabeled phenylalanine, the tegument was identified as a specific site of synthesis of prunasin in all four genotypes. A major difference between sweet and bitter genotypes was observed upon staining of thin sections of teguments and cotyledons for b-glucosidase activity using Fast Blue BB salt. In the sweet genotype, the inner epidermis in the tegument facing the nucellus was rich in cytoplasmic and vacuolar localized b-glucosidase activity, whereas in the bitter cultivar, the b-glucosidase activity in this cell layer was low. These combined data show that in the bitter genotype, prunasin synthesized in the tegument is transported into the cotyledon via the transfer cells and converted into amygdalin in the developing almond seed, whereas in the sweet genotype, amygdalin formation is prevented because the prunasin is degraded upon passage of the b-glucosidaserich cell layer in the inner epidermis of the tegument. The prunasin turnover may offer a buffer supply of ammonia, aspartic acid, and asparagine enabling the plants to balance the supply of nitrogen to the developing cotyledons.

Molecular markers for kernel bitterness in almond

“…cellular localisations of the enzymes involved in the degradation pathway, possibly involving a seed coat prunasin hydrolase, have also been suggested to be related to bitterness in almond (Sánchez-Pérez et al 2008). However, the gene(s) determining bitterness in almond and in other Prunus species remains to be identified.…”

“…Werner and Creller (1997) hypothesised that the sk allele might code for a defective cyanoglycoside catabolic enzyme, resulting in a seed that is acyanogenic (sweet). Recently, Sánchez-Pérez et al (2008) also proposed that a prunasin hydrolase could be involved in bitterness in almonds, since a different localisation (apoplastic or symplastic) of this enzyme was found in the tegument (derived from sporophytic tissue in almond) of the sweet and bitter accessions. In this study, none of the CGs involved in the catabolism of amygdalin were located in G5.…”

β-Glucosidases

“…The bitterness in almonds is caused by the presence of cyanogenic glucosides [98]. Cassava is highly consumed in parts of Asia, Africa, and South America, and contains the cyanogenic b-glucoside linamarin and its b-glucosidase linamarase.…”

Characterization of a New (R)-Hydroxynitrile Lyase from the Japanese ApricotPrunus mumeand cDNA Cloning and Secretory Expression of One of the Isozymes inPichia pastoris

“…dulcis, it was named amygdalin, and has subsequently been found to be widespread in seeds of y To whom correspondence should be addressed. Tel: +81-766-56-7500 ext 530; Fax: +81-766-56-2498; E-mail: asano@pu-toyama.ac.jp Abbreviations: HNL, hydroxynitrile lyase; PmHNL, hydroxynitrile lyase from Prunus mume other members of Rosaceae, 26) apples (Malus sp. ), peaches (Pr.…”