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Post-Harvest Alteration of In Vitro Translatable mRNA Population in Alfalfa (Medicago sativa L.)

Station de recherches sur les sols et les grandes cultures, Agriculture Canada, 2560 boul. Hochelaga, Ste-Foy (Québec), Canada G1V 2J3
Universite Laval, Fac. des Sciences de l'Agriculture et de l'Alimentation, Dép. de Phytologie, Cité Universitaire Ste-Foy (Québec), Canada G1K7P4

^* Corresponding author (jmferu{at}rsvs.ulaval.ca).

During harvest and post-harvest handling, alfalfa (Medicago sativa L.) forage undergoes metabolic changes that result in a rapid, significant loss of nutritional quality, especially in protein content. In the present work, the hypothesis was raised that these changes might be initiated by the onset of specific metabolic changes under the control of de novo gene expression. Changes in the population of translatable poly(A) + RNA from alfalfa leaves after harvest were monitored by in vitro translation followed by a two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) analysis of translation products. In a first experiment, which involved plants grown in a growth chamber, the disappearance of 34 of about 120 translation products present before harvest and the appearance of 37 new ones were observed. Comparison of harvest stress with heat shock, cold, and water deficit, revealed that 14 of the 37 translation products increased specifically after harvest, whereas most of the decreasing polypeptides were common to all treatments. In a second experiment, alfalfa was grown and harvested in open field conditions. Among the 40 polypeptides found to increase after harvest, 23 were common with those induced in the first experiment. These results suggest that harvest leads to both specific and non-specific stress responses within plant cells, that result not only in the disappearance of many mRNA species, but also in the de novo expression of several mRNAs. Further characterization of genes whose expression is specifically induced during post-harvest could provide tools for the study of post-harvest metabolism and its modification by genetic engineering.

Received for publication July 26, 1995.