Ribosomal Rna, Fraction I Protein Synthesis, and Ribulose Diphosphate Carboxylase Activity in Developing and Senescing Leaves of Cucumber

Abstract

SUMMARYThe synthesis of chloroplast ribosomes and Fraction I protein appear to be discrete events in the life of a leaf. Expanding cucumber leaves incorporated exogenous precursors of RNA and protein synthesis into chloroplastic rRNA and Fraction I respectively but, after full expansion, the synthesis of both of these components was greatly reduced while incorporation into cytoplasmic rRNA and other soluble proteins was still proceeding. It is suggested that the overall synthesis of whole molecules of Fraction I is controlled by the rate of synthesis, in the chloroplast of the large sub-unit of Fraction I and that this in part is related to the availability of 70S ribosomes.RuDPcarboxylase activity paralleled Fraction I protein content in developing leaves, but as the leaves senesced, the enzymatic activity declined at a faster rate than the loss of Fraction I protein.

Developmental and age-related processes that influence the longevity and senescence of photosynthetic tissues in arabidopsis.

“…Wittenbach referred to the photosynthetic decline as "functional senescence" to distinguish this process from the subsequent rapid loss of chlorophyll and macromolecular turnover associated with the senescence syndrome (Wittenbach, 1983). The physiological basis for functional senescence is not known, although a number of explanations have been suggested (Callow, 1974;Woolhouse, 1982;Nooden, 1988b). Perhaps, the simplest explanation for the observed functional decline in photosynthesis may be that maintenance and repair of the photosynthetic apparatus does not keep pace with the damaging effects of the free-radical byproducts of photosynthesis in the leaf (Bowler et al, 1992).…”

“…Analysis of photosynthetic processes revealed that carbon fixation rates declined progressively from the time of full leaf expansion (Figure 4). This age-related, progressive loss of photosynthetic function from the time of leaf maturity may be a general feature of annual plants because this phenomenon has been observed in cucumber (Callow, 1974), Perilla (Batt and Woolhouse, 1975), barley (Friedrich and Huffaker, 1980), wheat (Peoples et al, 1980), maize (Crafts-Brandner et al, 1984a), and soybean (Wittenbach, 1982;Ford and Shibles, 1988). Wittenbach referred to the photosynthetic decline as "functional senescence" to distinguish this process from the subsequent rapid loss of chlorophyll and macromolecular turnover associated with the senescence syndrome (Wittenbach, 1983).…”

The accumulation and storage of nitrogen by herbaceous plants

“…Furthermore, during senescence of Cucumis sativis leaves. Callow (1974) tneasured decreases in the synthesis of chloroplastic rRNA needed for the continued production of the large subunits of RUBISCO. Thus, both the high concentrations of RUBISCO in leaves (resulting particularly from a luxurious N supply) and the turnover characteristics of the protein are suitable attributes for a N storage compound, particularly in C3 plants.…”

Assimilate Source-Sink Relationships in Capsicum annuum L. II. Effects of Fruiting and Defloration on the Photosynthetic Capacity and Senescence of the Leaves

“…The relative rate of synthesis of fraction 1 protein was studied in order to assess the hypothesis that a high rate of turnover of the protein correlates with retention of photosynthetic capacity. The relative rate of turnover of fraction 1 protein proved to be lower than has been observed in newly expanded leaves of wheat (Tung and Brady 1972), cucumber (Callow 1974), Populus (Dickman and Gordon 1975), Vicia faba (Munns, unpublished data), and Vigna sinensis (Brady and Tung, unpublished data). There were slight increases in the relative rate of synthesis with leaf age (Fig.…”