Characterization of rice alpha-amylase isozymes expressed by Saccharomyces cerevisiae

Selection for low dormancy in annual ryegrass (Lolium rigidum) seeds results in high constitutive expression of a glucose-responsive α-amylase isoform

BACKGROUND AND AIMS

α-Amylase in grass caryopses (seeds) is usually expressed upon commencement of germination and is rarely seen in dry, mature seeds. A heat-stable α-amylase activity was unexpectedly selected for expression in dry annual ryegrass (Lolium rigidum) seeds during targeted selection for low primary dormancy. The aim of this study was to characterize this constitutive activity biochemically and determine if its presence conferred insensitivity to the germination inhibitors abscisic acid and benzoxazolinone.

METHODS

α-Amylase activity in developing, mature and germinating seeds from the selected (low-dormancy) and a field-collected (dormant) population was characterized by native activity PAGE. The response of seed germination and α-amylase activity to abscisic acid and benzoxazolinone was assessed. Using an alginate affinity matrix, α-amylase was purified from dry and germinating seeds for analysis of its enzymatic properties.

KEY RESULTS

The constitutive α-amylase activity appeared late during seed development and was mainly localized in the aleurone; in germinating seeds, this activity was responsive to both glucose and gibberellin. It migrated differently on native PAGE compared with the major activities in germinating seeds of the dormant population, but the enzymatic properties of α-amylase purified from the low-dormancy and dormant seeds were largely indistinguishable. Seed imbibition on benzoxazolinone had little effect on the low-dormancy seeds but greatly inhibited germination and α-amylase activity in the dormant population.

CONCLUSIONS

The constitutive α-amylase activity in annual ryegrass seeds selected for low dormancy is electrophoretically different from that in germinating seeds and its presence confers insensitivity to benzoxazolinone. The concurrent selection of low dormancy and constitutive α-amylase activity may help to enhance seedling establishment under competitive conditions.

Related dipeptide and characteristic dipeptide of optimal pH in alpha-amylase

Alpha-amylase is an enzyme of great significance to industry, but most alpha-amylases are unstable at lower pH. In this paper, we have studied the related dipeptide and characteristic dipeptide of optimal pH in alpha-amylase. On analysis, it gives the explicit results as follows: (1) Ten dipeptides are associated with alpha-amylase's optimal pH. AH, DV, EH, HR, and YV are of positive correlation, AM, IC, NG, NL, and PS are of negative correlation. (2) GE, RE, GS, and KS are higher pH alpha-amylase characteristic dipeptides; AS, GS, DY, and GI are high pH alpha-amylase characteristic dipeptides; TE, VR, DS, and ET are middle pH alpha-amylase characteristic dipeptides; DK, NT, PT, and RV are low pH alpha-amylase characteristic dipeptides; AT, DS, GR, and SR are lower pH alpha-amylase characteristic dipeptides.