Characteristics of light fragments from different thylakoid regions of maize mesophyll

Two fractions of light particles enriched in photosystem I, which sedimente d at 70000 and 100000 g, respectively, were isolated after digitonin solubi lization of isolated chloroplasts from maize (Zea mays L.) mesophyll. In te rms of particle-diameter distribution on electron micrographs, the 100000 g fraction particles were similar to those obtained from pea intergranal thy lakoids, In addition to the above particles, the 70000 g fraction contained larger particles (125-200 nm), the average size of which was close to that of particles from the marginal regions of granal thylakoids from spinach. Measurement of chlorophyll fluorescence induction demonstrated that the two types of thylakoid fragments differed in the relative content of Q(B)-redu cing and Q(B)-nonreducing PS II complexes. They also differed in the charac teristics of their low-temperature fluorescence spectra. Analysis of pigmen t and protein compositions revealed a different proportion of major pigment -protein complexes in particles obtained from different thylakoid regions a nd their distinction from analogous particles obtained from pea thylakoids, One of the light fractions was shown to contain mainly fragments of interg ranal thylakoids, whereas the other fraction also contained fragments of ma rginal regions of granal thylakoids, Differences in the characteristics of light fragments obtained from maize mesophyll thylakoids from those obtaine d from pea thylakoids might be related to differences in the structure of t he two types of thylakoids.