The Effect of Light Intensity on Ultrastructure of Chloroplasts in Konjak (Amorphophallus konjac K. Koch)

[摘要] Konjak plants were given treatments of full sunlight, 50% and 70% shading immediately after leaflet expansion. Ultrastructure of the chloroplasts in leaflets at the top and base of blades was examined with an electron microscope at intervals of one or two weeks after treatment. 1. Leaf area increased at all light intensities for two weeks after leaflet expansion and the largest area was obtained from the plants grown at 70% shading. Green area of leaves grown at full sunlight began to decrease from 40 days after the leaflet expansion, but the leaves grown under the shade maintained the fully expanded area for three months (Fig. 1). 2. The chloroplasts just before the treatment had rudimentary grana, a small amount of plastoglobules and starch grains (Figs. 2 and 3), but two weeks after treatment the ultrastructural differences were noted in the chloroplasts developed at different light intensities. 3. The chloroplasts from plants grown at full sunlight had poorly organized grana consisting of 2-5 overlapping thylakoids, which began to separate from two weeks after leaflet expansion (Fig. 4). Most of the chloroplasts in adaxial side of palisade cells showed swelling and the grana had been destroyed at four weeks after leaflet expansion (Fig. 5), whereas those in abaxial side of palisade cells and in spongy parenchyma cells remained without conspicuous destruction (Figs. 7 and 8). In the chloroplasts from plants grown at full sunlight, the starch grains decreased but the plastoglobules continued to increase with aging (Figs. 4 and 5). 4. The chloroplasts from plants grown at both 50% and 70% shading contained well-developed grana having more than 10 overlapping thylakoids, which remained without remarkable separation for three months after leaflet expansion (Figs. 9-12). The difference was not clear in development of the inner membrane system between the chloroplasts from plants grown at 50% and 70% shading, but the chloroplasts from 50% shading contained larger amount of starch grains than those from 70% shading (Figs. 9-12). The change in chloroplast structure by shading was more distinct in leaflets at the top of blade than in those at the base (Figs. 4 and 13). According to the observation of the chloroplasts in konjak, which has been characterised as a shade plant, it is considered that the development of grana is accelerated under low light intensity and the senescence of chloroplast is delayed.

[学科分类] 农业科学（综合）