CHROMOPLAST ULTRASTRUCTURE AS AFFECTED BY GENES CONTROLLING GRANA RETENTION AND CAROTENOIDS IN FRUITS OF CAPSICUM ANNUUM

Plastids in the fruits of isogenic lines of pepper (Capsicum annuum) were examined by electron microscopy with reference to four genotypes determining the carotenoid composition and the colors red, yellow, brown, and green of the ripe fruit. One gene pair (y+/y) influences carotenoid content and the other pair (cl+/cl) controls the chlorophyll. The retention of the grana and chlorophyll in the ripe fruits of the brown and green phenotypes is correlated with the cl cl genotype. The y+ gene increases the total carotenoids and promotes the formation of red pigments. Giant grana were found in the yellow and green phenotypes, but during ripening these disappeared in the yellow. Unusual dichotomous and concentric grana were observed in the green. Globule-associated carotenoids forming fibrillar crystalloids were present in all color types, although to a lesser degree in the yellow fruit. Membrane-associated carotenoids occurred only in the yellow and green phenotypes. FREY-WYSSLING AND Kreutzer (195 8a), the first to study the chromoplasts of pepper (Capsicum annuum L.) at the ultrastructural level, suggested that the origin of the submicroscopic filaments in which much of the pigment is centered is connected with the disintegration of the grana. Kirk and Juniper (1967) investigated four cultivars of pepper differing in fruit color (red, orange, yellow, and white) and found that only red fruit had fibers with globular swellings; they suggested that the carotenoids are in some way responsible for this difference. Spurr and Harris (1968) studied chromoplast ultrastructure in pepper, primarily thylakoid membrane changes. They demonstrated, however, that the formation of osmiophilic globules is not directly related to the loss of grana, and they regarded the fibrillar crystalloids as extensions of crystalloids in the globules. Harris and Spurr (1969a, b) have shown, with essentially isogenic lines of tomato, that differences in carotenoids are associated with marked differences in ultrastructure of the chromoplasts. Some of the contrasting views in the literature on the chromoplasts of pepper may be due to the use of materials with markedly different genetic backgrounds. The isogenic material used in this study, with genes differing only for fruit color and carotenoid composition, permits a more controlled examination of chromoplasts. 1 Received for publication 13 October 1972. 2Present address: Departamento de Hortalizas, Instituto Nacional de Investigaciones Agricolas, Apartado 112, Celaya, Gto., Mexico. The authors express appreciation to Professor Paul G. Smith for his interest and helpful suggestions on this study. In peppers, the cl+/cl gene pair relate to the retention and loss of chlorophyll and grana during fruit ripening. The recessive gene cl prevents decomposition of chlorophyll and the lysis of the grana while cl+ has the converse expression. A second gene pair y+/y is involved with the formation of red pigments in the fruit. The dominant y+ gene promotes red pigment formation, while the recessive condition results in yellow fruits. When combined, these two independent genes give ripe fruits of four different color phenotypes-red, brown, yellow, and green (Smith, 1950). In the context of this work, reference to the ripe fruit colors red, brown, yellow, and green applies exclusively to the following genotypes (Lippert, Smith, and Bergh, 1966). y+y+ cl+cl+ red y+y+ cl cl brown y y c1+cl+ yellow