Andre Laroche

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


The effect of growth at low temperature on polysome metabolism in winter rye (Secale cereale cv Puma) has been investigated. A method for isolation of highly polymerized polysomes from mature leaf tissues has been developed. The degree of intactness of isolated polysomes was monitored by two independent but complementary methods: size class distribution on sucrose gradients and in vitro translation. The composition of the optimal polysome isolation buffer for mature rye leaves is similar for leaves grown at low (5{dollar}\sp\circ{dollar}) or high (20{dollar}\sp\circ{dollar}) temperature but different from that reported for young tobacco and pea leaves. The quantity of polysomes (per unit DNA) increases by a factor of 2.7 at low temperature. These polysomes are larger and their melting point is decreased by 3.7{dollar}\sp\circ.{dollar} Analysis of ribosome composition by one- and two-dimensional electrophoresis revealed that only a few peripheral ribosomal proteins (and possibly a subunit of initiation factor 3) are modified. No significant change in the rRNA could be detected. Polysomes isolated from leaves grown at low temperature incorporate twice as much label as polysomes isolated from control plants, regardless of the temperature of translation. Polysomes from low temperature plants require higher magnesium levels for optimal translation and were more sensitive to detergent. Electrophoretic analysis of translation products revealed that some transcripts are newly expressed (16 kD to 170 kD), some are repressed (35 kD to 105 kD) and others increase or decrease in quantity. It is suggested that growth of rye at low temperature leads to alterations in both the ribosome conformation and peripheral proteins which in turn provides for a more efficient translation system. Enhanced translational activity does not appear to be due to the mRNA, although transcription does appear to be altered at low temperature. These changes are considered significant in the adaptation and growth of rye at low temperature.



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