CHROMOPLASTS OF TOMATO FRUITS. I. ULTRASTRUCTURE OF LOW‐PIGMENT AND HIGH‐BETA MUTANTS. CAROTENE ANALYSES

Abstract

Three pigment lines of the tomato cultivar ‘Pearson’ with isogenic backgrounds were studied to determine the relationship between certain carotenoids and the development of chromoplasts during fruit ripening. The lines were normal red ( r + /r + ), in which about 90% of the carotenoids in the ripe fruit is lycopene; high‐beta ( B/B ) mutant, in which beta‐carotene is the major pigment and the mature fruit color is deep orange ; and low‐pigment ( r/r ) mutant, in which carotenoids are drastically reduced and the mature fruit is pale yellow‐orange. This paper reports pigment analyses for the three lines and the ultrastructural changes in plastids of the two mutant lines. Very young, pale green fruits contain proplastids with limited lamellar structure. As the fruits reach the mature green stage, the plastids in all three lines develop into typical chloroplasts. Differences in pigment content and in ultrastructure among the lines are not apparent until ripening commences. In the low‐pigment mutant carotenoids are reduced as ripening progresses and no carotenoid crystalloids are formed. As chlorophyll decreases the fruits become pale yellow. The grana become disorganized and the thylakoids appear to separate at the partitions and tend to be arrayed in lines, some still with their ends overlapping. Globules increase slightly in number. In the high‐beta mutant the grana break down during ripening and globules increase greatly in size and number. Beta‐carotene, presumed to be largely in the globules, crystallizes into elongated or druse type forms which may distort the globules. The crystals may affect the shape of the chromoplasts; long crystals may extend the length of the plastid to over 15 μ. Thylakoid plexes with a regular lattice structure sometimes occur in the chromoplasts of the high‐beta mutant. Granules resembling aggregations of phytoferritin particles occur in the chromoplasts of both of these mutants.