EFFECT OF LOW ROOT TEMPERATURE ON RIBONUCLEIC-ACID CONCENTRATIONS IN FIGLEAF GOURD AND CUCUMBER ROOTS DIFFERING IN TOLERANCE TO CHILLING TEMPERATURE

To clarify the involvement of RNA metabolism in chill-tolerant figleaf gourd (Cucurbita ficifolia Bouche) and chill-intolerant cucumber (Cuc umis sativus L), the effects of root temperatures ranging from 12 degr ees to 26 degrees C on root RNA concentrations and root growth were st udied. RNA concentrations in figleaf gourd roots were affected by root temperature, being lowest at 23 degrees to 26 degrees C, increasing w ith lower temperatures and peaking at 14 degrees C; concentrations the n decreased at 12 degrees C. The concentration at 14 degrees C was 2.5 times higher than it was at 23 degrees to 26 degrees C. A similar tre nd was observed in cucumber roots, but much less dramatic. The marked increase of RNA concentration in figleaf gourd roots was due to increa ses of such RNA species as rRNA, mRNA, tRNA, and RNA precursors. The e xtent of increases was most prominent in tRNA. Six days after exposure to 14 degrees C, the roots were transferred to 23 degrees C. The move caused a rapid drop of RNA concentration within 2 days to a pre-chill level in figleaf gourd roots but no change in cucumber roots. The mar ked increase of RNA concentration in figleaf gourd roots exposed to 14 degrees C may be caused by the low temperature-induced net accumulati on of RNAs. Root growth of figleaf gourd paralleled that of RNA concen tration/temperature curve; that of cucumber was nearly linear from 12 degrees C to 26 degrees C. The marked increase in RNA concentration in figleaf gourd roots exposed to 14 degrees C is discussed in relation to chilling tolerance.