Growth Promoting Substances in The Developing Fruit of Peach (Prunus PersicaL.)

Growth substances extracted from the ovules of developing fruits of July Queen, Halehaven and Fall Late peaches–respectively early, midseason and late-maturing cultivars–were studied. Whole and fractionated extracts were bioassayed, and the growth of the fruit and the development of the seed were examined.Determination of “total” growth-promoting substances during the development of the fruits resulted in concentration curves that were generally similar from year to year. The seeds of each cultivar, regardless of its season of maturation, produced a first flush of growth substances that seemed to be correlated with either nucellus or endosperm development. The second and major growth substance peak came at the time of rapid embryo growth and maximum endosperm development. At this time fruits of July Queen ripened and abscissed. A third flush of growth substance was detected at the same time in Halehaven and Fall Late seeds, at which time the embryo was essentially complete. The mature fruits of Halehaven then abscissed, but Fall Late fruits remained on the tree for another three or four weeks before maturation and abscission. It was concluded that the concentration of seed growth substances as measured here was not related to the final-flush of growth of peach fruits, or to the abscission of mature fruits.In dissected ovules of Halehaven peaches the endosperm was the most concentrated source of total growth substances on a dry weight basis but, because of its small size, it contributed less of them on a per-seed basis than did the the integuments at first, and later the embryo. The nucellus was a minor source of growth substances, both on a concentration and on a per-ovule basis. Apparently, the total growth substances that constituted the second and major auxin peak in Halehaven peach ovules came mostly from the integuments, endosperm and embryo, whereas the third peak could be attributed almost entirely to substances from the embryo. These studies of individual ovule tissues were made after that period of development during which the first growth substance peak made its appearance.Studies of growth substances in the flesh of developing peach fruits revealed only trace amounts with no consistent pattern, although there is some evidence that a true picture may not have been obtained because of interference by inhibitors.Silica gel partition column chromatography showed the presence of several growth-promoting substances which changed qualitatively and quantitatively during the growing season. One of these was probably indole-3- acetic acid, its identification being based primarily on studies by gas chromatography and spectrophotofluorometry.