Cytoplasmic alkalization and cytoplasmic streaming induced by light and histidine in leaf cells of egeria densa: In vivo ³¹P-NMR study

Rotational streaming of the cytoplasm including chloroplasts was induced by L-histidine, as well as by light, on the anticlinal face of leaf cells of Egeria densa. In the case of treatment with L-histidine some of the chloroplasts remained stationary on the periclinal face of cells after rotational cytoplasmic streaming was initiated. However, these chloroplasts were easily dislodged and translocated to the centrifugal end of the histidine-treated cells by application of a centrifugal force that barely affected the location of chloroplasts in cells incubated in the dark without L-histidine. This result indicates that the anchoring of chloroplasts was weakened by L-histidine. Thus only the release of chloroplasts from anchoring was not enough for initiation of their streaming.The cytoplasmic pH (pH_c) and vacuolar pH (pH_v) were noninvasively monitored by in vivo ³¹P-nuclear magnetic resonance (NMR) spectroscopy. Compared with the dark control value, both illumination and treatment with L-histidine increased the pH_c by 0.3 units. In contrast, pH_v changed only a little with both illumination and treatment with L-histidine. Release of chloroplasts from anchoring and initiation of cytoplasmic streaming are discussed in relation to the increase in pH_c induced by both light and L-histidine.