Chloroplasts of many species of hornworts (Anthocerotae) have a structure that resembles the pyrenoid of green algae but whether these two structures are homologous has not been determined. We utilized immunogold labelling on thin sections to determine the distribution of ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO), the major protein of algal pyrenoids, in sixteen hornwort species with and without pyrenoids. Several species (Phaeoceros laevis, Anthoceros punctatus, A. formosae, A. laminiferus, Folioceros fuciformis, Folioceros sp., Dendroceros tubercularis, D. japonicus, D. validus, Notothylas orbicularis, N. temperata, and Spaerosporoceros adscendens) have uniplastidic (or primarily uniplastidic) cells with large prominent multiple pyrenoids. In all of these species, the labelling is found exclusively in the pyrenoid and, with the exception of the Folioceros, Dendroceros, and Notothylas species, the labelling is randomly distributed throughout the pyrenoid. In the exceptional species, the pyrenoids have prominent pyrenoglobuli or other inclusions that are unlabelled. In Megaceros flagellaris and M. longispirus, the cells are multiplastidic (with the exception of the apical cell and some epidermal cells) and the chloroplasts lack pyrenoids. Anthoceros fusiformis and Phaeoceros coriaceus have primarily uniplastidic cells but the chloroplasts lack pyrenoids; only an area of stroma in the center of the plastid devoid of starch, reminiscent of a pyrenoid, is found. In all of the species lacking pyrenoids, RuBisCo is found throughout the stroma, including the stromal spaces made by the so-called channel thylakoids. No preferential accumulation of RuBisCo is found in the pyrenoid-like region in A. fusiformis and P. coriaceus. These data indicate that 1) the hornwort pyrenoid is homologous to algal pyrenoids in the presence of RuBisCo; 2) that at least some of the RuBisCo in the pyrenoid must represent an active form of the enzyme; and 3) that, in the absence of pyrenoids, the RuBisCo is distributed throughout the stroma, as in higher plants.

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京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19188号 / 工博第4065号 / 新制||工||1627(附属図書館) / 32180 / 京都大学大学院工学研究科合成・生物化学専攻 / (主査)教授 跡見 晴幸, 教授 森 泰生, 教授 濵地 格 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

In this diploma work changes of initial and total activities and content of Rubisco in beech and Norway spruce were studied. The plants were cultivated in conditions with ambient CO2 concentration (350 mol·mol–1) and elevated CO2 concentration (700 mol·mol–1). Three series of samples (at the beginning, in the middle and at the end of growing season) were taken. Initial and total Rubisco activities were measured spectrophotometrically and activation state was calculated. Rubisco content was determined by SDS–PAGE method. Rubisco activity in beech cultivated in elevated CO2 concentration decreased during the whole growing season while in beech growing in ambient CO2 concentration Rubisco activity decreased up to middle of growing season and then increased. Rubisco content in beech in ambient CO2 concentration slightly increased and in beech in elevated CO2 concentration decreased up to middle of growing season and then increased. Rubisco activities in Norway spruce both in ambient and elevated CO2 concentration decreased. Rubisco content in Norway spruce in ambient CO2 concentration decreased but in Norway spruce in elevated CO2 concentration first decreased and then increased.