Ethephon-Induced Ethylene Enhances Protein Degradation in Source Leaves, but Its High Endogenous Level Inhibits the Development of Regenerative Organs in Brassica napus

To investigate the regulatory role of ethylene in the source-sink relationship for nitrogen remobilization, short-term effects of treatment with different concentrations (0, 25, 50, and 75 ppm) of ethephon (2-chloroethylphosphonic acid, an ethylene inducing agent) for 10 days (EXP 1) and long-term effects at 20 days (Day 30) after treatment with 100 ppm for 10 days (EXP 2) on protein degradation and amino acid transport in foliar sprayed mature leaves of Brassica napus (cv. Mosa) were determined. In EXP 1, endogenous ethylene concentration gradually increased in response to the treated ethephon concentration, leading to the upregulation of senescence-associated gene 12 (SAG12) expression and downregulation of chlorophyll a/b-binding protein (CAB) expression. Further, the increase in ethylene concentration caused a reduction in protein, Rubisco, and amino acid contents in the mature leaves. However, the activity of protease and expression of amino acid transporter (AAP6), an amino acid transport gene, were not significantly affected or slightly suppressed between the treatments with 50 and 75 ppm. In EXP 2, the enhanced ethylene level reduced photosynthetic pigments, leading to an inhibition of flower development without any pod development. A significant increase in protease activity, confirmed using in-gel staining of protease, was also observed in the ethephon-treated mature leaves. Ethephon application enhanced the expression of four amino acid transporter genes (AAP1, AAP2, AAP4, and AAP6) and the phloem loading of amino acids. Significant correlations between ethylene level, induced by ethephon application, and the descriptive parameters of protein degradation and amino acid transport were revealed. These results indicated that an increase in ethylene upregulated nitrogen remobilization in the mature leaves (source), which was accompanied by an increase in proteolytic activity and amino acid transport, but had no benefit to pod (sink) development.

Supraoptimal Cytokinin Content Inhibits Rice Seminal Root Growth by Reducing Root Meristem Size and Cell Length via Increased Ethylene Content

Cytokinins (CKs), a class of phytohormone, regulate root growth in a dose-dependent manner. A certain threshold content of CK is required for rapid root growth, but supraoptimal CK content inhibits root growth, and the mechanism of this inhibition remains unclear in rice. In this study, treatments of lovastatin (an inhibitor of CK biosynthesis) and kinetin (KT; a synthetic CK) were found to inhibit rice seminal root growth in a dose-dependent manner, suggesting that endogenous CK content is optimal for rapid growth of the seminal root in rice. KT treatment strongly increased ethylene level by upregulating the transcription of ethylene biosynthesis genes. Ethylene produced in response to exogenous KT inhibited rice seminal root growth by reducing meristem size via upregulation of OsIAA3 transcription and reduced cell length by downregulating transcription of cell elongation-related genes. Moreover, the effects of KT treatment on rice seminal root growth, root meristem size and cell length were rescued by treatment with aminoethoxyvinylglycine (an inhibitor of ethylene biosynthesis), which restored ethylene level and transcription levels of OsIAA3 and cell elongation-related genes. Supraoptimal CK content increases ethylene level by promoting ethylene biosynthesis, which in turn inhibits rice seminal root growth by reducing root meristem size and cell length.

Tabebuia avellanedae Lor. ex Griseb. (Bignoniaceae) submitted at the flooding and the "Ethrel" and silver nitrate application

Three-month-old Tabebuia avellanedae Lor. ex Griseb. (Bignoniaceae) plants cultivated in the greenhouse were submitted to 56 days of flooding and to "Ethrel" and silver nitrate applications to find out it’s capacity for morphological and physiological modifications to survive under flooding conditions and at which degree such responses were correlated with alterations in the ethylene level. Flooding and the "Ethrel" application caused growth reduction and epinasty in T. avellanedae and the application of silver nitrate lessened some these symptoms. Certain symptoms shown during flooding by this species and its ability to develop structures which lessen hypoxia effects, such as stem fissures and hypertrophied lenticels in the roots, modifications which enable the species to adapt to short flooding periods, could be related to increases in the ethylene concentration in the plant tissues.

Effect of ozone on qualities of fruits and vegetables in cold storage

Ozone at the concentration of 0.04 mL L–1 appears to have potential for extending the storage life of broccoli and seedless cucumbers stored at 3°C. Response to ozone was minimal for mushrooms stored at 4°C and cucumbers stored at 10°C. Ozone generators producing 0.04 mL L–1 ozone reduced the ethylene level in vegetable storage rooms from 1.5–2 mL L–1 (as produced by apples placed in the room) to a non-detectable level. At concentrations of 0.4 mL L–1, ozone was effective in removing ethylene from the atmosphere in an apple and pear storage room. The ozonized and non-ozonized apples and pears showed no difference in fruit quality. This study explored a potential use of ozone application in wholesale storage rooms where ethylene-producing and ethylene-sensitive fruits and vegetables may be stored together. Key words: Ozone, ethylene, fruit, vegetable, apple, pear, broccoli, cucumber, mushroom, storage

Ripening of climacteric fruits initiated at low ethylene levels

Mature, unripe mango, peach, custard apple, kiwifruit and tomato were stored at 20˚C in air containing ethylene at <0.005, 0.01, 0.1 1.0 and 10 L/L. The time to ripen of all the climacteric fruits increased linearly with logarithmic decrease in ethylene concentration over the whole concentration range examined. Similar observations were also obtained with kiwifruit and custard apple held at 0 and 14˚C, respectively. However, the sensitivity of fruits to ethylene varied with banana and kiwifruit > custard apple and mango > tomato, avocado and peach. Since the ethylene level around horticultural produce during marketing is always >0.005 L/L, the time climacteric fruit can be held in an unripe condition is currently less than optimal but intervention to limit ethylene action would appear to be only warranted for the most sensitive fruits.

Ethylene levels associated with fruit and vegetables during marketing

Over 700 measures of the level of ethylene in the atmosphere of fruit and vegetable holding areas in wholesale markets, distribution centres, supermarket retail stores and domestic refrigerators were taken over a 3-year period. The lowest ethylene levels were found in supermarket stores with a mean level of 0.017–0.035 L/L in produce receival, storage and display areas. Levels in the ambient air of wholesale markets and distribution centres were higher at about 0.06 L/L. Domestic refrigerators were grouped into those that contained or did not contain apples with the ethylene level being much higher at 0.20 L/L where apples were present and 0.029 L/L where apples were absent. Using a rating scale, which was developed from published literature on non-climacteric produce, of ≤0.015 L/L ethylene as a low level where less than 10% of potential postharvest life is lost and ≥0.1 L/L as a high level where there is higher than 30% loss of postharvest life, suggests that most produce during marketing is held in an ethylene atmosphere where 10–30% of potential postharvest life is lost.