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Abstract
Reducing the atmospheric pressure in the refrigerated storage chamber at 6°C markedly retards avocado fruit ripening. This effect is more pronounced when the pressure is reduced below 100 mm Hg. Fruit stored at 760 and 200 mm Hg ripened after 35 and 50 days, respectively, while fruit stored at pressures below 100 mm Hg remained unripe for 70 days in storage. The best storage pressure tested for avocado fruits was found to be 60 mm Hg. The inhibition of ripening under these conditions is explained by the lower oxygen partial pressure which retards respiration and ethylene production, and by the acceleration of the outward diffusion of ethylene from the tissue which lowers its internal level.
Abstract
The influence of reduced atmospheric pressure on the green peach aphid, Myzus persicae, in lettuce (Lactuca sativa L.) heads was determined. Exposing lettuce heads to a pressure of 2.66 kPa for 52 hr resulted n 100% aphid mortality, whereas the lettuce marketing quality was not affected. In view of the marked requirement for aphid-free lettuce heads, commercial use of the nonchemical reduced pressure method is suggested.
A study was conducted to elucidate the effects of chloride in the irrigation water on growth and development of two citrus rootstocks. `Cleopatra' mandarin (Citrus reshni Hort. ex Tan) is salt tolerant and `Troyer' citrange (Poncirus Citrus sinensis) is salt sensitive. Increasing chloride from 2 to 48 mm in the irrigation water resulted in increased leaf chloride levels, more severe damage of the leaves, and reduced branch growth. High chloride in the irrigation water also caused increased putrescine (PUT) and decreased spermine (SPM) contents of the leaves. These effects were slight in `Cleopatra' but highly apparent in `Troyer'. The symptoms caused by high chloride were associated with high PUT and low SPM levels in the leaves. PUT may be involved in the development of chloride toxic symptoms, and SPM may protect or have no effect on chloride plant injury. The leaf polyamine profiles of `Troyer' and `Cleopatra' under nonstress chloride conditions were different. In `Troyer' leaves, PUT level was 9-fold higher than in `Cleopatra'; in `Cleopatra' leaves, SPM level was 25-fold higher than in `Troyer'. Nitrate supplement to saline water reduced chloride accumulation in the leaves and reduced the increase in PUT. The possible connection between ethylene production and PUT and SPM levels in the leaves of stressed plants is discussed.
Abstract
Tomato plants (Lycopersicon esculentum) infected with root-knot nematodes, Meloidogyne javanica, contain 2.2 to 2.6-times higher levels of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) in the roots and leaves compared with uninfected plants. The nematode-induced increase in the ACC coincides with increased ethylene production in the infected plants. Foliar spray with aminoethoxyvivyl-glycine (AVG), which inhibits ethylene production or with silver thiosulfate (STS) which inhibited ethylene action, partially or completely eliminated the pathogenic symptoms displayed by a nematode-infected plant, indicating that the ethylene induced by the nematode infection plays a major role in the pathogenic symptoms infliced by the nematode. Foliar spray with 3 mM STS 4 to 8 days after the nematode inoculation was found to be the most effective treatment for reversing the nematode infection symptoms.
Abstract
The main evidence for a single mechanism of ethylene action is the observation that nearly all responses to the gas have the same dose response curve (8), suggesting a single type of receptor molecule. If so, the case is similar to that of phytochrome where one biochemical change produces a multitude of secondary changes resulting in a variety of physiological responses depending upon the tissue involved. We have chosen to use the etiolated pea seedling to investigate the primary and secondary actions of the gas because all parts of this plant have been extensively studied and are highly responsive to ethylene. When this seedling is exposed to ethylene stem growth slows, the hook tightens, the subapex swells and nutates horizontally, root growth slows and the zone of elongation swells, root hairs form, lateral root formation is inhibited, and the root tip bends plageotropically. The causes of these changes are to be found in the effects of ethylene on cell division, cell expansion, and auxin transport.