Naringin Levels in Citrus Tissues

Abstract

ABSTRACIThe quantitative distribution of the flavanone-7-neohesperidoside, naringin, in seeds, seedlings, young plants, branches, flowers, and fruit of Citrusparadisi Macfad, cv 'Duncan' was analyzed by radioimmunoassay. High levels of naringin were associated with very young tissue and lower levels were found in older tissues. Seed coats of ungerminated seeds and young shoots had high naringin concentrations whereas cotyledons and roots had very low concentrations. Light-grown seedlings contained nearly twice as much naringin as etiolated seedlings and, in young plants and branches, the naringin content was highest in developing leaves and stem tissue. In flowers, the ovary had the highest levels of nari accounting for nearly 11% of the fresh weight. There was a net increase in the total naringin content of fruits during growth. However, due to the large increase in fruit size, there was a concomitant decrease in the narinn concentration as the fruit matured.The flavonoid pigments of plants have been intensively investigated over the past three decades and it is clear that this group of secondary metabolites is one of the largest and most diverse from both structural and functional standpoints (9) MATERIALS AND METHODS Plant Material. Fruits were obtained from grapefruit trees (var Duncan) grown at the Agricultural Experimental Station, Lake Alfred, FL. Seeds were removed from mature (November) fruit, placed on 1% agar, and were germinated under continuous illumination or in darkness. After 3 weeks, some seedlings were transferred to soil and were grown in a phytotron (25°C, 50% RH) under a 16-h light/8-h dark cycle. The 1-year-old plant used in this study was grown under the same conditions. Buds and flowers at various stages of development were collected from a single mature tree. Stages were defined according to the fresh weight and degree of development of the flowers.Extraction of Plant Tissues. For seeds, the outer seed coat, inner seed coat, and the cotyledons/embryo were separated before extraction. All tissues were cut into small pieces, placed in 5 ml methanol and boiled for 2 h. Tissues weighing more than 500 mg fresh weight were extracted in 10 ml methanol. After extraction, samples were filtered, brought to the original volume, diluted 50% with water, and stored at -20°C until assay. Fruits and fruit parts were extracted by maceration in a volume of 0.1 M Tris-HCI (pH 8.0) sufficient to prevent gelation ofendogenous pectins and the extracts stored at -20°C.Radioimmunoassay Procedure. The procedures for the naringin RIA have been described elsewhere (15; and part I of this series). Samples were diluted with water and assayed by the [3H] naringinol/oxime-hapten antiserum RIA described in part I.TLC and HPLC. Chromatographic analysis of the extracts were done using 5x concentrated samples after published procedures (6, 7). RESULTS AND DISCUSSIONThe genus Citrus is characterized by the accumulation of flavanone glycosides rather than the more common flavone, flavonol, or anthocyanin glycosides (I 1)...

Chiral HPLC separation and CD spectra of the C‐2 diastereomers of naringin in grapefruit during maturation

“…19 Naringin content is very high in very young grapefruit and then, due to the large increase in fruit size, there is a concomitant decrease in naringin concentration in mature fruit. 20 Analogously, in developing lemon the flavanone glycoside hesperidin builds up rapidly in the very small fruit (less than 2.5 cm diameter) and then tapers off as the fruit grows. 21 The naringin in immature fruits is essentially all (2S) and it is produced by enzymatic cyclization of its precursor.…”

Flavanone Glycoside Biosynthesis in Citrus

“…We chose young leaves and fruits because of their high flavanone-glycoside content (19). The cell-free extracts derived from young calamondin fruits contained relatively high levels of chalcone synthase activity (Table I).…”

Juvenile-Specific Localization and Accumulation of a Rhamnosyltransferase and Its Bitter Flavonoid in Foliage, Flowers, and Young Citrus Fruits

“…Indeed, naringin was shown previously not to accumulate in cotyledons of grapefruit (Jourdan et al, 1985). The appearance of 1-2-rhamnosyltransferase in etiolated and green seedlings begins with the initiation of true leaves, and the enzyme disappears as the leaves mature (data not shown), as described for older plants.…”

“…The accumulation and distribution of the major flavanoneglycoside products have been investigated during different stages of growth of grapefruit and sour orange without parallel studies of the enzymes involved. Flavanone-glycosides were found in almost a11 plant parts, but rapidly accumulated in young, developing Citrus leaves (Jourdan et al, 1985;Vandercook, 1989, 1991;Castillo et al, 1992). The specific parameters controlling synthesis and 10-calization of flavanone-glycosides in Citrus could not be studied until the terminal enzyme in the pathway itself was purified and an antibody was raised against it.…”