Amihud Borochov

1-Methylcyclopropene inhibits ethylene action in cut phlox flowers

Abstract Phlox (Phlox paniculata cv. Rembrandt) flowers were found to be very sensitive to ethylene. Exposure to ethylene enhanced flower abscission in a concentration-dependent manner, with 50% abscission attained after treatment with 1 μl l−1 ethylene for 12 h. As a result, ethylene also reduced the number of open flowers on the stems throughout their vase life. A 6-h pre-treatment with a volatile inhibitor of ethylene action, 1-methylcyclopropene (1-MCP), completely inhibited the ethylene-induced flower abscission and hence the reduction in the number of open flowers on the stems. 1-MCP was maximally effective in inhibiting the ethylene response at a low concentration (25 nl l−1) and had no visible toxic effects, even at 500 nl l−1. The effects of 1-MCP on flower abscission were comparable to that of a pulse treatment with silver thiosulfate (STS). We therefore suggest that it may serve as an alternative to the commercial treatment of phlox flowers with STS, the latter being an environmental hazard.

Sugar-Dependent Gibberellin-Induced Chalcone Synthase Gene Expression in Petunia Corollas.

The induction of anthocyanin synthesis and anthocyanin biosynthetic gene expression in detached petunia (Petunia hybrida) corollas by gibberellic acid (GA3) requires sucrose. Neither sucrose nor GA3 alone can induce these processes. We found that GA3 enhances sucrose uptake by 20 to 30%, and we tested whether this is the mechanism by which the hormone induces gene expression. Changing the intracellular level of sucrose with the inhibitors p-chloromercuribenzenesulfonic acid and vanadate did not inhibit the induction of chalcone synthase gene (chs) expression by GA3. Growing detached corollas in various sucrose concentrations did not affect the induction of the gene but did affect its level of expression and the level of anthocyanin accumulated. Only metabolic sugars promoted GA3-induced anthocyanin accumulation. Mannitol and sorbitol had no effect and 3-O-methylglucose only slightly promoted chs expression and anthocyanin accumulation. Our results do not support the suggestion that sugars act as specific signals in the activation of anthocyanin biosynthetic gene expression during petunia corolla development. We suggest that sugars are essential as general sources of carbohydrates for carbon metabolism, upon which the induction of pigmentation is dependent.

Enhancement of petunia and dendrobium flower senescence by jasmonic acid methyl ester is via the promotion of ethylene production

Methyl jasmonate (JA-Me), applied to dendrobium and petunia flowers either as an aqueous solution through the cut stem or stigma, or as a gas, accelerated senescence. The rate of appearance of wilting symptoms was directly related to the amount of JA-Me applied to the flowers. JA-Me increased ethylene production by the flowers, irrespective of application method, and this effect was also proportional to the dose of the compound. In both dendrobium and petunia flowers, the JA-Me induced increases in ethylene production and 1-aminocyclopropane-1-carboxylic acid content followed similar patterns. Aminooxyacetic acid, an inhibitor of ACC-synthase, and silver-thiosulfate, an inhibitor of ethylene action, completely inhibited the effects of JA-Me. It is concluded that JA-Me enhances petunia and dendrobium flower senescence via the promotion of ACC and ethylene production.

Effects of heat treatment on plasma membrane of apple fruit

Abstract Apple fruits (Golden Delicious) were held at 20 or 38 °C for four days prior to storage at 0 °C for five months. Plasma membrane composition and function were examined before and after storage. While fruits were held at 38 °C, membrane microviscosity and sterol content increased, phospholipid fatty acids became more saturated and there was increased electrolyte leakage from apple fruit discs. ATPase activity increased during the first day of heating and decreased thereafter. After five months of storage at 0 °C, microviscosity and leakage were lower in heated fruit, and increased more slowly during ripening at 20 °C than in control apples. ATPase activity was similar in both treatments. Phospholipid content was higher in membranes from heated apples than in those from control fruit. Although fatty acid content in apples from both treatments was similar after storage, the loss of unsaturated fatty acids during ripening occurred more rapidly in control apples. Heated apples recovered rapidly from stress and acclimated more successfully to 0 °C than did control apples.

Increase in membrane fluidity in liposomes and plant protoplasts upon osmotic swelling.

Osmotic gradient across the membrane of nonsonicated liposomes and rose petal protoplasts are shown to induce swelling. Concomitantly, the lipid fluidity as measured by fluorescence depolarization is increased, probably due to increase in molar free volume. It is suggested that osmotic swelling can affect cell physiology via changes in membrane fluidity.

Pollination-induced senescence of Phalaenopsis petals

The longevity of cut Phalaenopsis (Phalaenopsis hybrid, cv. Herbet Hager) flowers is normally 2 to 3 weeks. After pollination however, there was a rapid acceleration of the wilting process, beginning after only 24 h. Enhancement of senescence in several Phalaenopsis cultivars as well as in Doritaenopsis, Dendrobium and Cymbidium, was induced by successful pollination and only slightly or not at all by emasculation. Wilting of the flowers was accompanied by a loss of water from cells of the upper layer of the petals, leading to their upward folding. Following pollination there was an increase in ethylene production and sensitivity to ethylene. The increase in ethylene production began about 10 h after pollination and reached its peak after 30 h. An obvious increase in sensitivity to ethylene could already be detected 4 h after pollination and reached its peak 10 h after pollination. The increase en ethylene sensitivity following pollination was not dependent on endogenous ethylene production as it occurred also in flowers treated with (aminooxy)acetic acid, an inhibitor of ethylene biosynthesis.

Response of Melon Plants to Salt: 1. Growth, Morphology and Root Membrane Properties

Summary An excess of NaCl in the growth medium of melon ( Cucumis melo L.) seedlings affected growth rate, morphology, and contents of dry weight, chlorophyll, potassium, sodium and chloride in the root and leaf tissues. In roots of seedlings grown in NaCl the electrolyte leakage to iso-osmotic medium was more rapid. Fluorescence polarization measurements revealed that root membranes isolated from these seedlings were significantly less fluid. Chemical analysis disclosed a lower lipid to protein weight ratio in these membranes. The relative contents of phospholipids and free sterols were only slightly affected by excess NaCl. Accordingly, the fluidity of liposomes prepared from lipid extracts of membranes isolated from control and from salt-grown seedlings was similar. The extent of partitioning of the root microsomal membranes between the two phases of aqueous polymer mixtures revealed differences in the surface properties of the root plasma membrane of control and salt-grown seedlings. Possible relationships between the changes in membrane properties and the response to excess salt are discussed.

Quantitative and Qualitative Changes in Membrane Proteins during Petal Senescence

Summary Senescence of cut flower petals was previously shown to be accompanied by both the decrease of protein content and the reduction of lipid fluidity of the membranes. In carnation (Dianthus caryophyllus) and rose (Rosa hyb.) petals, qualitative changes in the composition of membrane proteins were observed. Also, modifications in the polypeptide population of the membranes have been revealed by SDS-PAGE. They were associated with changes in the apparent hydrophobicity of several polypeptides as well as a gradual decrease in the relative accessibility of thiol groups, as measured by the fluorescence of membranes treated with DA. However, no significant changes in the hydrophobicity of the immediate microenvironment of the labelled thiol groups were detected. Modulation of the rate of senescence by ethylene or by its potent inhibitor, STS, respectively, was accompanied by an acceleration or slowing down in the reduction of labelled thiol groups. It is concluded that the reported decline in membrane enzyme activity with age is a result not only of alterations in membrane lipid fluidity and quantitative changes in the membrane proteins, but also of qualitative changes in these proteins.

Transient water stress and phospholipid turnover in carnation flowers

Summary Transient water stress, followed by a recovery period, resulted in a decline in the longevity of cut carnation ( Dianthus caryophyllus L., cv. White Sim) flowers. This was accompanied by a sharp decrease in the phospholipid content of the petal membranes. The content of 1,2-diacylglycerol in a plasma membrane enriched fraction, expressed as a fraction of total phospholipids, increased with water stress and decreased during recovery, as did the concentration of inositol 1,4,5-trisphosphate in the tissue water. These results suggest that water stress in carnation flowers causes the release of both of these putative secondary messengers. This may in turn lead to the induction of processes associated with accelerated senescence.

Temperature effects on growth, pigmentation and post-harvest longevity of petunia flowers

Abstract Petunia ( Petunia hybrida , cv. ‘VR’) flowers produced at 32/27°C (day/night) developed from Stage 1, when the corolla is barely visible, to full anthesis within 4 days, as compared with 9 days for flowers produced at 17/12°C (day/night). However, the flowers produced at high temperatures were approximately half the size of the latter at anthesis, owing to differences in both fresh and dry weights. Corolla pigmentation was enhanced at the lower growth temperatures, owing to higher anthocyanin content. Northern analyses revealed that both growth and pigmentation are regulated by temperature at the molecular level. In contrast to its beneficial effect on size and pigmentation, growth at lower temperatures resulted in a shorter vase life for the cut flowers, which was associated with enhanced ethylene production. Cut petunia flowers were treated with aminooxyacetic acid, silver thiosulfate or 1-aminocyclopropane carboxylic acid. The results supported our contention that ethylene is indeed involved in the regulation of the growth—temperature effects on petunia flower vase life. In this study, petunia did not behave according to the common conception that lower growth temperatures lead to better quality cut flowers.