Expression of -Amylase from Alfalfa Taproots¹

Joyce A. Gana, Newton E. Kalengamaliro, Suzanne M. Cunningham, and Jeffrey J. Volenec^*

Department of Agronomy, Purdue University, West Lafayette, Indiana 47907-1150

Alfalfa (Medicago sativa L.) roots contain large quantities of -amylase, but little is known about its role in vivo. We studied this by isolating a -amylase cDNA and by examining signals that affect its expression. The -amylase cDNA encoded a 55.95-kD polypeptide with a deduced amino acid sequence showing high similarity to other plant -amylases. Starch concentrations, -amylase activities, and -amylase mRNA levels were measured in roots of alfalfa after defoliation, in suspension-cultured cells incubated in sucrose-rich or -deprived media, and in roots of cold-acclimated germ plasms. Starch levels, -amylase activities, and -amylase transcripts were reduced significantly in roots of defoliated plants and in sucrose-deprived cell cultures. -Amylase transcript was high in roots of intact plants but could not be detected 2 to 8 d after defoliation. -Amylase transcript levels increased in roots between September and October and then declined 10-fold in November and December after shoots were killed by frost. Alfalfa roots contain greater -amylase transcript levels compared with roots of sweetclover (Melilotus officinalis L.), red clover (Trifolium pratense L.), and birdsfoot trefoil (Lotus corniculatus L.). Southern analysis indicated that -amylase is present as a multigene family in alfalfa. Our results show no clear association between -amylase activity or transcript abundance and starch hydrolysis in alfalfa roots. The great abundance of -amylase and its unexpected patterns of gene expression and protein accumulation support our current belief that this protein serves a storage function in roots of this perennial species.

Plant Physiol. (1998) 118: 1495-1506
Copyright Clearance Center:   0032-0889/98/118//12
© 1998 American Society of Plant Physiologists

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