Julian C. Crane

Dormancy Regulation in Peach Seeds

An inhibitor of seed germination was isolated from the integuments of Lovell peach seeds. Evidence from chromatographic analysis, from studies of its absorption of ultraviolet light and from assays on its effects on plant growth, indicate that the inhibitor is, if not identical with, dormin. Termination of rest in peach seeds is correlated with the disappearance of the inhibitor. The effects of the inhibitor are antagonistic to those of gibberellic acid on sections of wheat coleoptiles.

Gibberellin-Induced Inhibition of Bud Development in Some Species of Prunus.

Development of both floral and vegetative buds was inhibited by application of gibberellin to branches of Prunus species. The development of the lateral meristem was blocked, in general, through inhibition of mitosis, while, concurrently, the growth of certain other plant organs was stimulated in some cases. That higher dosages were required to block vegetattive than floral bud growth suggests that gibberellin also exerts the more specific effect of inhibiting floral initiation.

2,4,5-trichlorophenoxyacetic Acid: effect on ethylene production by fruits and leaves of fig tree.

Production of ethylene by fruits and leaves of the fig tree was stimulated by the application of 2,4,5 trichlorophenoxyacetic acid (20 parts per million) to levels that apparently were responsible for hastened matura tion of fruit, epinasty, and senescence of leaves.

Kinin-Induced Parthenocarpy in the Fig, Ficus carica L.

Parthenocarpic Calimyrna fig fruits induced with a kinin were identical morphologically to those previously produced parthenocarpically with auxin or gibberellin. Thus, the three types of endogenous hormones thought to originate in the seeds and to stimulate directly fruit growth can be supplied by plant parts other than seeds.

Auxins in Parthenocarpic and Non-Parthenocarpic Figs

Studies of the auxin content of developing fig fruits revealed a sudden 30-fold increase in auxin concentration in the variety Calimyrna at the time of formation of the endosperm tissue. A similar and even larger rise in the parthenocarpic Mission variety was associated with the development of a parthenogenetic endosperm. By chromatographic analysis this auxin was shown to be different from those present at earlier and later stages of growth and to be chemically distinct from indoleacetic acid. Its function is thought to be the prevention of fruit drop. No evidence was found that the rate of fruit enlargement was in any way dependent on the auxin concentration.

Some Histological Effects of 2,4,5-Trichlorophenoxyacetic Acid Applied to Mature Apricot Leaves

Apricot trees were sprayed with 2,4,5-trichlorophenoxyacetic acid at concentrations of 50, 100, and 200 ppm on May 22, 1965, when spur leaves were fully expanded. Some effects of 2, 4,5-T were studied in leaves collected up to October 2. Increase in petiole diameter resulted from enlargement of cells of the ground tissue and from greatly stimulated development of secondary xylem and phloem. Increase in leaf blade thickness was caused primarily by increased depth of palisade tissue and bundle sheaths and their extensions, but evidence of limited induced cell division in both mesophyll tissues contributed in some leaves; in a few leaves from the 50-ppm treatment, much cell division without cell enlargement in mesophyll tissues accounted for all the increase in leaf thickness between vascular bundles. In the mesophyll of leaves treated with the higher concentrations, many cells and nuclei were larger than in controls. Distributions of frequencies of cell widths and of nuclear diameters in palisade cell populations indicated that the general degree of endopolyploidy increased following 2,4,5-T treatment and that some of the comparable cells in controls were also polyploid. The number of stomata per unit length of the lower epidermis was almost one-half less in leaves given the highest 2,4,5-T concentration than in the controls. The immediate causes were (a) a great increase in treated plants in the cell size in bundle sheath extensions and correspondingly of some epidermal cells, and (b) stretching, or (c) a few cell divisions of other epidermal cells. Tyloses in control petioles and midveins were not numerous until October, but in petioles of treated leaves many developed early. It is suggested that the actions of 2,4,5-T in stretching cell walls and in stimulating endopolyploidy combined to cause tylosis formation, the stretched pit membranes of the vessels not having been able to withstand the pressure of enlarging polyploid xylem parenchyma. Aside from exceptional instances of limited cell proliferation in phloem ray cells, no abnormalities were induced. The general effects of 2,4,5-T as applied here were concluded to have been acceleration or stimulation of processes occurring normally in untreated leaves.

Cell Division and Enlargement in Mesocarp Parenchyma of Gibberellin-Induced Parthenocarpic Peaches

1. Gibberellin at concentrations of 50, 250, and 500 mg/l sprayed on branches bearing emasculated blossoms at the time of full bloom induced parthenocarpy in the Fay Elberta peach. 2. Eleven weeks after bloom no statistically significant difference occurred among the mean numbers of parenchyma cells along the mesocarp radii in pollinated fruits and in parthenocarpic ones induced by the different GA concentrations. This indicates that the GA concentration was not critical in stimulating cell division to the normal extent in unfertilized peach ovaries, at least within the range of concentrations used here. 3. Significant differences in mean cell volumes of mesocarp parenchyma occurred between parthenocarpic fruits induced with 50- and 250-mg/l concentrations and the mean cell size in pollinated fruits. The mean cell volume in fruits induced with the 500-mg/l concentration was not significantly different, however, from the mean in pollinated fruits. The degree of cell enlargement was thus related to the GA concentration applied. 4. The only microscopic differences found in the mesocarp of parthenocarpic as contrasted with pollinated fruits were evidences of increased cell-wall plasticity in fruits induced with 250- and 500-mg/l concentrations and the much larger amounts of starch stored in cells of fruits produced with 50 mg/l. 5. Thus one application of GA at a concentration of 500 mg/l almost exactly reproduced in the parthenocarpic fruits the effects, as concerns mesocarp growth and development, that follow fertilization in pollinated fruits.