Reversible form- und volumenänderungen des Mougeotia-Chlorophsten

Abstract

Summary 1. Besides the contraction in high intensity light, reported in the first paper of this series, i. e. above 10 kerg/cm2sec, contraction can be obtained also in low intensity light (50–500 erg/ cm2sec) and in darkness. In contrast, light of medium intensity forces the contracted chloroplast to regain its original shape and volume («dilatation»). 2. In low intensity contraction, only blue light is effective, as has been found for the high intensity contraction also. Thus, a flavin is suggested as the photoreceptor. In contrast, the dilatation proceeds in blue and red light as well (fig. 5) and is assumed, therefore, to make use of the photosynthetic pigments. 3. The low intensity contraction is much slower than the high intensity contraction, and the dark contraction proceeds still more slowly (cf. fig. 1 with 3). In all cases, increase of temperature accelerates the response and shortens the lag phase. Within the limits of the experiments of this paper, no final level of contraction has been reached (fig. 1 and 3). The dilatation, at the other hand, proceeds rather quickly without a measurable lag phase, and reaches its final level within a few hours (fig. 5). 4. The low intensity contraction has its optimum at about 100 erg/cm2sec. Neither this optimum intensity, nor the upper intensity limit of this response depends on the temperature (fig. 2). In the low intensity contraction and the dark contraction as well, increase of temperature always results in higher contraction values (fig. 1–3). 5. The range of intensities responsible for dilatation overlaps to some degree, in blue light, with the low intensity contraction region. Thus, in certain intensities, a low level of contraction can be reached by contraction or dilatation, depending on the start position (cf. fig. 5 with fig. 1). 6. It is suggested that light exerts two different effects: it provides energy for the contraction and dilatation mechanisms (probably ATP) and it triggers the way the ATP will be used. The triggering effect may be concerned with fastening or loosening of the chloroplast at the cortical cytoplasm. 7. The orientation movement of the chloroplast (turning in the cell) is possible, though more slowly, even if the chloroplast is contracted and does not touch the cortical cytoplasm. This is compatible with contractile fibrils as the mechanism of chloroplast movement. 8. It seems probable that the three different types of contraction are based upon different systems; these systems and the dilatation reaction system as well do not seem to be identical with the reaction systems of orientation movement though some relationship may exist.