Content and Aggregation of Ribosomes during Formation, Dormancy and Sprouting of Tubers of Helianthus tuberosus.

The ribosomes and their qualitative (monosomes-polysomes) and quantitative variations over a whole vegetative period of the tuber of Helianthus tuberosus L. (cv. OB 1) were examined. Tubers in different phases of growth, dormancy and sprouting or slices of dormant tubers activated with 2 × 10-6 M indol-3-acetic acid were used. The ribosomes were analyzed by a linear sucrose gradient. During flowering, polysomes of tuber disappeared almost completely and rRNA decreased in comparison with the level present at the beginning of tuber formation. After flowering, there was a new synthesis of monosomes and polysomes until the onset of dormancy; this last period was characterized by a marked increase in polysomes and a proportional increase in monosomes. The level remained almost constant till the break of dormancy. When the tubers sprouted, ribosomes, present almost exclusively as monosomes, decreased considerably; on the contrary the non-photosynthetic sprouts contained many monosomes and polysomes. The first phases of activation (3 h) of tuber slices were characterized by a RNA synthesis, which occurred during one hour, in the subunit region of the gradient. Successively (10 h of activation) the 32P incorporation was seen also in the polysome region and increased with time. Some possible interpretations of these last results are discussed. [ABSTRACT FROM AUTHOR]