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  • Author or Editor: Mike A. Nagao x
  • Journal of the American Society for Horticultural Science x
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Abstract

The abscission of young Macadamia integrifolia Maiden & Betche fruit was investigated in vitro with explants consisting of a single fruit attached at the distal end of a segment of the peduncle. A 30% reduction in fruit removal force (FRF) of explants incubated in distilled water was evident within 48 hr after excision and was correlated with increased ethylene production. Pretreatment of explants with 5 and 10 mm ethephon accelerated FRF reduction. Pretreatment with increasing concentrations of silver nitrate (AgNO3) to 1.47 mm or AOA to 0.05 mm, inhibited the reduction in FRF. FRF reduction also was inhibited by 1000 μm NAA and 100 pM 2,4-D. GA3 and BA had no effect. Chemical names used: (2-chloroethyl)phosphonic acid (ethephon); 1-naphthaleneacetic acid (NAA); (2,4-dichloro- phenoxy)acetic acid (2,4-D); gibberellic acid (GA3); N-(phenylmethyl)-H-purin-6-amine (BA); (aminooxy)acetic acid (AOA).

Open Access

Abstract

Two types of raphides and 2 types of raphid idioblasts were observed in Dieffenbachia maculata (Lodd.) G. Don cv. Rudolph Roehrs. Small raphides, about 25 μm long and 0.4 μm wide, with barbs and grooves were found in idioblast cells similar in shape to adjacent ground parenchyma cells. Larger raphides, about 120 μm long and 4 μm wide, with wide grooves were found in spindle shaped, obtuse ended idioblasts, about 165 μm long and 40 μm in diameter.

Open Access

The effects of water stress and GA, on breaking dormancy of flower buds of coffee (Coffea arabica L.) were investigated. In the first experiment, water was withheld until the trees reached leaf water potentials (WP) of -1.20, - 1.75, -2.65, or -3.50 MPa. Water potential, ethylene production, and ion leakage of flower buds and leaf disks were examined from release from water stress until anthesis. Trees that had experienced leaf WP of less than - 2.65 MPa, and flower bud WP of about - 4.0 MPa flowered within 9 days after irrigation. In flower buds where dormancy had been broken with water stress, ethylene production was low compared to dormant buds and flowers at anthesis. In the second experiment, O, 50, 100, or 200 mg GA3/liter was painted on branches of nonstressed trees. In experiment three, water was withheld until plants reached leaf WP of -0.6, -1.3, - 2.1, or - 3.0 MPa, then two branches per tree were painted with O, 50, and 100 mg GA3/liter. Gibberellic acid partially compensated for insufficient water stress to initiate flower opening. Ethylene evolution of flower buds was affected by water stress but not by GA3 treatment. Severe water stress treatments and GA, treatment (200 mg·liter-1) increased ethylene evolution of leaf disks. Ion leakage of flower buds and leaf disks was increased by severe water stress. Ion leakage of flower buds was highest at anthesis. After water stress, dormant and nondormant flower buds at the 4-mm stage could be distinguished based on their ethylene evolution. Chemical name used: gibberellic acid (GA3).

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