Photocontrol of the Germination of Onoclea Spores

Abstract

The changes in levels of metabolites during photoinduced germination of Onoclea sensibilis L. spores are described.Proteins and lipids, which constitute 25 and 20%, respectively, of the unimbibed spores on a dry weight basis, are hydrolyzed at the time of differentiation and elongation of the germling cells and may be utilized for these processes.Sucrose degradation, starch synthesis, and active respiration occur during dark imbibition, but these processes are accelerated by red or far red irradiation. Endogenous sucrose is the probable source of the carbon skeleton for starch synthesis.An imbibed fern spore given the proper inductive stimulus is able to germinate in the absence of exogenous nutrients (10 (1.1 X 10' ergs cm-2 sec-1; 50% transmittance at 720 nm) and then placed back in the dark for varying periods of time. The spores were then collected and lyophilized as described previously (27). Controls were incubated in the dark throughout the experimental period. Germination was scored by either the acetocarmine procedure or the protrusion method (25). Experiments were repeated at least twice with essentially the same results.The broad band red and far red filters and the dim green safelight were identical to those described previously (25).Extraction Procedure for Soluble Carbohydrates, Proteins, Amino Acids, and ATP. Fifty milligrams oflyophilized spores were extracted by grinding with sand alone and then with 1.5 ml of ice-cold 5% (v/v) perchloric acid for 10 min in a mortar with a pestle, and the brei was centrifuged at 20,000g for 10 min. The pellet was re-extracted with 1 ml of 5 % PCA2 and centrifuged as above. This re-extraction procedure was necessary to extract fully the metabolites. The pellet from the second centrifugation was used for protein determination. The perchlorate was precipitated from the combined supernatants by the addition of sufficient 1 M K2CO4 to raise the pH to 2 to 3. Aliquots of the supernatant were then used for determination of total soluble carbohydrates, amino acids, and ATP. The concentration of the metabolites was calculated on the basis of 1 mg of lyophilized spores.Protein Determination. The PCA-insoluble pellet was solubilized by heating at 75 C for 4 hr with 0

Biochemistry of Fern Spore Germination

“…Measurements of photosynthetic activity were not performed but data are available indicating that the spores are photosynthetically competent (23). Starch grains were observed in many of the chloroplasts (Fig.…”

“…Unlike non-green spores, these contain relatively large amounts of H20 and are known to be metabolically active, short-lived, and capable of germinating readily in contact with the proper medium (17). Spores of Onoclea sensibilis L. are representative of this group and they have been used previously in physiological studies of spore germination (5,19,23). The lack of an obvious dormant period and the presence of functional chloro-plasts indicate that the spores are metabolically distinct from seeds and non-green spores.…”

Spore Germination and Rhizoid Differentiation in Onoclea sensibilis

“…Some advantages of this system for biochemical and molecular studies of differentiation are its simplicity and the ability to isolate rhizoid protoplasts and separate them from protonemal cells (12 Previous studies of protein metabolism during fern spore germination were done without separation ofcell types, but they form an important background for the present study. The protein content of germinating spores of Onoclea (26) and Pteridium aquilinum (20) generally decreases during the initial stages of spore germination and rhizoid differentiation. Since light and electron microscopic studies of fern spore germination commonly show the progressive degradation of protein storage granules (e.g.…”

Characterization of a protease that acts specifically on the 22‐kDa protein in thylakoid membranes from green spores of the fern Osmunda japonica

“…During germination of fern spores, many proteins are degraded and synthesized. The degradation of total proteins or cytoplasmic reserve proteins in the spores of several ferns has been reported ( Towill and Ikuma 1975bRaghavan 1977Raghavan 1991DeMaggio and Stetler 1980Minamikawa et al 1984Paless et al 1984). Although some studies have been published on protein synthesis in chloroplasts isolated from gametophytes ( Raghavan and DeMaggio 1971) and on DNA synthesis in chloroplasts during germination ( Raghavan 1993), very few studies have focused on protein degradation in the chloroplasts of green spores during germination.…”