HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Das, S. B. Articles by McKersie, B. D. Search for Related Content PubMed Articles by Das, S. B. Articles by McKersie, B. D. Agricola Articles by Das, S. B. Articles by McKersie, B. D.

A High Leaf-Starch Mutant in Alfalfa Has Altered Invertase Activity

Agriculture and Agri-Food Canada, Saskatoon Res. Centre, 107 Science Place, Saskatoon, SK S7N OX2

Stephen R. Bowley and Bryan D. McKersie^*

Dep. of Crop Science, Univ. of Guelph, Guelph, ON, N1G 2W1, Canada

^* Corresponding author (mckersie{at}crop.uoguelph.ca).

A mutant phenotype isolated from alfalfa (Medicago sativa L) cv. Excalibur appeared to have dramatic changes in source-sink relations and the partitioning of carbohydrates. Leaves emerged normally, but starch accumulatedin the chloroplasts of the palisade mesophyll cells with maturity. Subsequently the cells of the palisade layer lost chlorophyll, exhibited ultrastructural symptoms of senescence, and necrotic spotting appeared on the adaxiai surface of fully expanded leaves. Segregation analysis of this phenotype, designated as hls (high-leaf starch), with F₁, BC₁, and F₂ progenies revealed that two independent dominant genes condition the trait. The hls phenotype had five-fold more starch in mature leaves and less in the taproot than in the normal leaf phenotypes, suggesting a blockage in transport of carbohydrate from the leaf to the root. In vitro activity assays and native polyacrylamide gel electrophoresis (PAGE) analysis revealed that most enzymes involved in carbohydrate metabolism were not altered in the hls phenotype. However, invertase activity of expanding leaves was significantly higher in plants with the hls phenotype than in those with a normal phenotype. The visual appearance of the mutation, high leaf starch content, and high invertase activity co-segregated in the progeny. Native PAGE revealed that a fast-moving invertase isozyme (F) was developmentally inactivated in normal phenotypes during leaf expansion but remained active in the hls phenotype. A biochemical model for the hls phenotype is proposed in which high invertase activity blocks phloem loading and reduces the availability of cytosolic inorganic orthophosphate for exchange with triose-phosphate across the chloroplast envelope, thereby promoting starch accumulation.

Received for publication July 8, 1996.