PHLOEM DEVELOPMENT IN SWEET ORANGE Pedicels

Phloem development in the pedicel determines the contribution of assimilated to the fruit, limiting its growth, nevertheless the related histological information is incomplete. Consequently, the differentiation of phloem in samples of pedicels of Citrus sinensis L. var “Valencia” and “Salustiana” was studied. During Phases I and II of fruit growth a histological study at the light microscope and scanning electron microscope was made. As a result, during the anthesis the vascular bundle presented a small portion of protophloem and agreeing with Phase I of growth metaphloem was developed, formed by sieve-tube members of simple sieve plate and these with numerous pores surrounded by callose. At the end of Phase I, the primary phloem was increased considerably and showed external fibers and obliterated protophloem. During Phase II of growth differentiation of vascular cambium was observed and the phloem presented sieve-tube elements in long radial series, fibers ring development towards the interior of the phloem (beginning by metaphloem) and widened rays of parenchyma. At the end of the study, the secondary phloem with clear capacity of conduction was limiting the ring of cells immediate to the vascular cambium, forming a ring of little thickness but of increased perimeter that adjusted to the growth in circumference of pedicel during the secondary growth. The two varieties studied have similar histological development of phloem, with small chronological variations.