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- Author or Editor: J. T. Watkins x
- Journal of the American Society for Horticultural Science x
Abstract
The involvement of naphthaleneacetic acid (NAA), a synthetic auxin, and methyl-2-chloro-9-hydroxy-fluorene-9-carboxylate (chlorflurenol), an auxin transport inhibitor, in fruit set in cucumber (Cucumis sativus L.) was investigated. In the greenhouse, exogenously applied NAA and chlorflurenol enhanced fruit set depending on the position of application. In the growth chamber, when NAA was applied directly on the stigma, a small quantity moved into the ovary after 24 hours. However, when auxin was applied on the ovary, significant quantities of 14C NAA were detected in the ovary and other plant pieces. When NAA was placed on the peduncle, more accumulated in peduncle and stem sections than when NAA was placed on the stigma or ovary. Chlorflurenol applications to the peduncle inhibited movement of NAA out of the ovary and resulted in accumulation of auxin in that tissue. NAA movement in the intact plant was similar to that of excised sections: chlorflurenol applied to the peduncle reduced NAA movement out of the ovary. Thus, the regulation of fruit set by chlorflurenol may be through the restriction of auxin movement from the ovary. The increased auxin accumulation in the ovary may trigger fruit set and subsequent growth.
Abstract
Concentrations of O2 greater than 21% stimulated germination rate of Capsicum annuum L. (sweet pepper) at 25°C but inhibited germination rate at 15°. At a 10% O2 concentration, germination rates were reduced at both temperatures. Gibberellins A4A7 (GA4+7) increased germination rates at 15° and 25° in air. At 25° in 100% O2, germination rates of GA-treated and nontreated seeds were the same. At 15° and 100% O2, germination rates were increased slightly by GA4+7 application; however, the rates were slower than in air. Total respiratory activity at 25° was higher in 100% O2 than in air. High O2 concentrations did not affect the proportion of respiration which was in the cyanide-sensitive and -resistant pathways. Cyanide-resistant respiration comprised only a small percentage of total respiratory activity. At 15°, total respiration and the cyanide-sensitive and -resistant components were similar regardless of O2 treatment. The addition of GA increased respiratory activity only after radicle emergence occurred. Thus, germination rate of pepper seed can be increased by increasing temperature, higher O2 concentrations at the higher temperature, and GA4+7 at normal and low temperatures. GA appears to affect germination through metabolic events which occur before radicle emergence and which do not include alteration of respiratory activity.
Abstract
Capsicum annuum (‘Early Calwonder’) seeds germinated (radicle protrusion) in 8 days at 15°C and 4 days at 25°. The seeds have an endosperm 7 to 9 cells in thickness which lies directly in front of the radicle. The external appearance of the endosperm did not change until one day before radicle emergence, when the endosperm in front of the radicle enlarged and protruded outward. This change was accompanied by breakdown and loss of endosperm cellular integrity and reduction in endosperm thickness directly in front of the radicle, but not in other regions of the endosperm. Gibberellic acid (GA4+7) decreased the time for appearance of the protruding endosperm and radicle protrusion through the seed coat by one day. Cell wall degrading activity was detectable during the early stages of germination and became extremely high after radicle emergence. Seeds treated with 100 ppm GA4+7 showed slightly increased enzyme activity during early germination and differences became more pronounced as germination progressed. Cellulase activity was not found in the extracts, but seed enzyme preparations degraded a galactomannan substrate. The enzyme exhibited only endohydrolytic activity, indicating an enzyme which may participate in the weakening of cell wall. It was postulated that an endomannanase is needed for endosperm breakdown in front of the radicle in order for rapid germination of pepper to occur. A reduction in germination temperature from 25° to 15° reduced the rate of radicle movement through the seed coat by one half.