Distribution of Acid and Alkaline Zones on the Cell Surface of Chara corallina under Stationary and Local Illumination

Abstract

A scanning microprobe technique was used to study pH distribution near the cell surface of Chara corallina Klein ex Willd. under variations of light intensity, dark–light transitions, and local illumination of various cell parts. In darkness, the H+-transporting activity of plasmalemma was distributed homogeneously over the cell surface. However, after exposing the cell to weak light (irradiance 0.2–0.5 W/m2), individual alkaline peaks with ΔpH of 1–2 units were observed in the longitudinal pH profile. The peaks in the longitudinal pH profile became more numerous with the increase in light intensity. The plot of ΔpH as a function of light intensity included a steep transition from zero to its maximum amplitude. In strong light (100 W/m2), the pH bands alternated along the cell length with a periodic length of about 7 mm. It is shown that the light-induced formation of ring-shaped bands with H+-exporting and H+ sink activities is preceded by the appearance of irregularly located spots (patches). When small cell parts were illuminated and the light spot was suddenly shifted along the cell to another position, the alkaline bands reorganized in two ways. In some cases, this treatment was followed by a gradual shift in the band position (without attenuation in the peak height) toward the illuminated area. In other cases, the initial band disappeared after such treatment, and a new alkaline band emerged in the vicinity of the illuminated area. Despite the apparent similarity of regular bands in the longitudinal pH profiles, the properties of individual bands (variable sensitivity to light intensity changes, the ability of bands to move along the cell under external treatment) differ substantially. It is supposed that the light-induced formation of the pH profile is based on primary fluctuations of photosynthetic and transport activities in the chloroplast layer and the plasmalemma, as well as on further rearrangements of membrane domains that stabilize band locations.