The Hill reaction and oxygen uptake in isolated pine chloroplasts

The Hill reaction and oxygen uptake in chloroplasts prepared from pine leaves were studied. Pine chloroplasts active for the Hill reaction were isolated from mature leaves in the presence of 25% PEG in the isolation buffer. Time courses of the Hill reaction in chloroplasts isolated from leaves at different seasons differed. In chloroplasts isolated in the autumn, Hill activity decreased rapidly with illumination time. This rapid decrease of Hill activity was inferred to result from concomitant production of some inhibitory substance(s) during the Hill reaction. The protective effect of PEG on inactivation by aging of pine chloroplasts was found. In the presence of PEG, chloroplasts were stabilized and Hill activity was maintained even after storage for 26 hr; whereas, in the absence of PEG inactivation by aging proceeded rapidly and oxygen uptake occurred after 20 hr. Chloroplasts isolated without PEG had no ability of the Hill reaction; but, inversely showed pronounced oxygen uptake. Oxygen uptake was also observed in aged or DCMU-inhibited chloroplasts. The presence of benzoquinone strongly suppressed oxygen uptake.