Studies on a barley mutant lacking chlorophyl b. I. Photochemical activity of isolated chloroplasts

• 1.

  1. Chloroplasts were isolated from the leaves of a barley mutant which lacked chlorophyll b and compared with the chloroplasts from the normal strain which had the normal content of chlorophyll a and chlorophyll b.

• 2.

  2. Hill-reaction measurements were made with either 2,3′,6-trichlorophenol-indophenol, ferricyanide or NADP⁺ as oxidant. At a light intensity of 40 000 lux, the mutant chloroplasts were more active per mg of total chlorophyll than the normal chloroplasts, but only slightly more active per mg of chlorophyll a. Normal chloroplasts were saturated at a light intensity of about 30 000 lux whereas the mutant chloroplasts required an intensity of nearly 60 000 lux for saturation. At low light intensities (< 15 000 lux) the mutant chloroplasts were less active than the normal chloroplasts. The mutant chloroplasts were inactivated at a greater rate if allowed to stand at 0° and they were more susceptible to inhibition by 1-(p-chlorophenyl)-3,3′-dimethylurea.

• 3.

  3. Microscopic examination under phase contrast showed no significant differences in the appearance of isolated chloroplasts from the normal and mutant plants.

  The lack of chlorophyll b in the mutant was confirmed by absorption and spectrofluorimetric measurements at the temperature of liquid nitrogen. The spectrofluorimetric method was capable of detecting one molecule of chlorophyll b in the presence of 1000 molecules of chlorophyll a.

• 4.

  4. The results are discussed in relation to the function of chlorophyll b in photosynthesis.