Mechanism of 2-acetyl-1-pyrroline biosynthesis in Bassia latifolia Roxb. flowers

Abstract

The flowers of Bassia latifolia are known to contain 2-acetyl-1-pyrroline (2AP), the compound responsible for pleasant aroma in basmati and other scented rice. Four growth stages of Bassia flowers were identified and 2AP contents were analysed in each stage. It was found that 2AP (3.30 ppm) gets synthesized only in fleshy corolla of mature flowers (fourth stage). The activity of γ-aminobutyraldehyde dehydrogenase (AADH); an enzyme responsible for synthesis of γ-aminobutyricacid (GABA) from γ-aminobutyraldehyde (GABald) was assessed in these four stages. The AADH activity was absent in the fourth stage. It was concluded that ceased activity of AADH in fourth stage flowers leads to the accumulation of γ-aminobutyraldehyde which is cyclised spontaneously to Δ(1)-pyrroline, the key precursor of 2AP. Δ(1)-pyrroline further reacts unenzymatically with methylglyoxal to form 2AP.

Keywords: 2 acetyl-1-pyrroline; Bassia latifolia; Biosynthesis; SPME; γ-aminobutyraldehyde dehydrogenase.

Fig. 1

Flower developmental stages in Bassia latifoliaa Inflorescence representing different stages of flower development, b Detached fleshy corollas, c Growth stages of flower

Fig. 2

2AP Peak area abundance in accordance to varied time and temperature conditions in Bassia latifolia flowers

Fig. 3

HS-SPME/GC-FID chromatogram of 2AP from four stages of Bassia latifolia flowers. Note the 2AP peak abundance in 4th stage. (1–4 represents flower stages). Superscript ‘a’ at stage 4 represents that 2AP values at stage 4 are statistically different from other stages at P = 0.01 level

Fig. 4

Proposed pathway for 2AP biosynthesis in mature Bassia latifolia flowers (a) against in other parts (b)