Influence des h m rop riodes tr s courtes sur la croissance de Lolium multiflorum, sa composition pigmentaire et l'ultrastructure chloroplastique

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Abstract
We have described some characteristics of Lolium multiflorum cultivated under very short photoperiods (2 hours and 1 hour). The estimations of leaf growth were based on dry weight, surface measurements, and chlorophyll content. The pigment analyses were carried out by column chromatography; chloroplast ultrastructure was observed after chemical fixation. These measurements have permitted us to note a sharp drop in the growth curve of plants grown under different day-lengths: the limiting photoperiod lies between 1 hour and 2 hours of daily illumination. Pigment analyses and chloroplast ultrastructure observations show that there is a greater difference between plants cultivated under 1 hour and 2 hours of daily illumination than between plants cultivated under 2 hours and 12 hours. A decrease in day-length causes a deficit in the chlorophyll b content as well as a poor development of the grana. We have attempted to correlate these structural anomalies with the abnormal chlorophyll a/chlorophyll b ratio.