Ribosomes germination

The phenylamide fungicides affect especially hyphal growth and the formation of haustoria and spores in oomycetes [22]. Since spores contain many ribosomes to support early growth stages, RNA synthesis is fully operational only after spore germination therefore, later development stages are most sensitive [19]. As a consequence of RNA inhibition, the precursors of RNA synthesis (i.e., nucleoside triphosphates) are accumulated. They activate j8-l,3-glucan synthetases, which are involved in cell wall formation [19] with the result that metalaxyl-treated hyphae often produce thicker cell walls than untreated ones. 

The lipolytic process in germinating oil seeds is still unclear. How seed oils, present in oil bodies, are converted to products which can then be handled by the fatty acid oxidation system of glyoxysomes, is not clear. It appears that membrane-bound lipases are involved in the process. A further area for clarification is the intracellular transport of insoluble triacylglycerols from oil bodies to the site of complete (or partial) hydrolysis and thence to the glyoxysomal enzymes of gluconeogenesis. Recent electron microscope studies with several oil seeds have provided evidence for a close association of ribosome-containing membranes with spherosomes these may be lipolytic membranes involved in triacylglycerol breakdown (Wanner and Theimer, 1978). 

Good evidence that germinating seeds can utilize ribosomes formed during the maturation phase has come from studies on P. vulgaris embryonic axes [190]. Here, embryo development requires 35 days for completion, and RNA synthesis can be observed up to day 24. After this time protein synthesis continues for several days, but there is no new RNA synthesis while the pool size of some RNA precursors is reduced, the RNA content of the embryo remains constant throughout and subsequent to maturation. Most of this RNA is stored as ribosomes which become involved in protein synthesis during germination, prior to any new RNA synthesis. 

The situation in peas appears to be somewhat similar to that in Phaseolus in that the RNA synthesized early in maturation is stable and is maintained (mainly in ribosomes as ribosomal RNA) during seed desiccation [143]. Many dried seeds contain active ribosomes (see Chapter 5 for a more complete consideration of protein and RNA synthesis during germination). 

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