Occurrence of a High Temperature Sensitivity of Chloroplast Ribosome Formation in Several Higher Plants

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Abstract
A specific high temperature-induced deficiency of chloroplast ribosome formation, as indicated by the absence of chloroplast rRNA, was observed in the leaves of light- or dark-grown seedlings of Avena sativa L., Hordeum vulgare L. and Triticum aestivum L. at certain temperatures between 28-34.degree. C. While the growth of the leaves (size, morphology, total amino N content) was little affected by the elevated temperature, chlorophyll accumulation was strongly inhibited, amounting to only 2-20% of its content in 22.degree. C-grown leaves which were used as a reference for normal development. The carotenoid contents were lower but still reached at least 15-20% of the corresponding measurements at 22.degree. C. Ribulose-1,5-bisphosphate carboxylase was absent at the higher temperature while NADP-glyceraldehydephosphate dehydrogenase reached high activities. For the peroxisomal marker enzyme hydroxypyruvate reductase, 30-70% of the activity present in 22.degree. C-grown leaves was found in extracts from high temperature-grown leaves. Fumarase reached 1.5- to 4-fold higher activities at the elevated growth temperature than at 22.degree. C. Leaves of Pisum sativum L. were completely chlorotic and deficient of 70S ribosomes at 33.degree. C but simultaneously suffered from a severe general inhibition of their growth. In Zea mays L., a formation of chlorotic leaves was not observed at elevated temperatures.