Shimon Mayak

Effect of Wild-Type and Mutant Plant Growth-Promoting Rhizobacteria on the Rooting of Mung Bean Cuttings.

Abstract. Mung bean cuttings were dipped in solutions of wild type and mutant forms of the plant growth-promoting rhizobacterium Pseudomonas putida GR12-2 and then incubated for several days until roots formed. The bacteria P. putida GR12-2 and P. putida GR12-2/aux1 mutant do not produce detectable levels of the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase, whereas P. putida GR12-2/acd36 is an ACC deaminase minus mutant. All bacteria produce the phytohormone indole-3-acetic acid (IAA), and P. putida GR12-2/aux1 overproduces it. Treatment of cuttings with the above-mentioned bacteria affected the rates of ethylene production in the cuttings in a way that can be explained by the combined effects of the activity of ACC deaminase localized in the bacteria and bacterial produced IAA. P. putida GR12-2 and P. putida GR12-2/acd36-treated cuttings had a significantly higher number of roots compared with cuttings rooted in water. In addition, the wild type influenced the development of longer roots. P. putida GR12-2/aux1 stimulated the highest rates of ethylene production but did not influence the number of roots. These results are consistent with the notion that ethylene is involved in the initiation and elongation of adventitious roots in mung bean cuttings.

The mechanism involved in ethylene-enhanced ethylene synthesis in carnations

The plant hormone ethylene triggers and enhanced ethylene synthesis in certain ripening fruits and senescing flowers. Unlike most carnation (Dianthus caryophyllus L.) cultivars exhibiting climacteric rise in ethylene production at the onset of senescence, cv. Sandrosa does not show this phenomenon naturally. In order to understand the mechanism of autocatalytic ethylene production, we exposed carnation flowers cv. Sandrosa to ethylene which resulted in an enhanced capacity for ethylene synthesis in the petals. A short time response of one hour was measured for an increase in ACC oxidase activity, about five hours in advance of an increase in ACC synthase activity and ethylene production. The observed enhancement was dependent on the presence of exogeneous ethylene, and could be partially inhibited by prior treatment of the petals with α-amanitin or cycloheximide. The results of the present study suggest that in response to ethylene, activation of an existing enzyme is taking place first. This is followed by an increase in expression of ACC oxidase and ACC synthase mRNAs.

Expression of Ethylene Biosynthetic Pathway mRNAs is Spatially Regulated within Carnation Flower Petals

Summary The spatial regulation of ethylene biosynthesis within carnation (Dianthus caryophyllus L. cv. White Sim) flower petals was investigated. When detached petals separated into upper and basal portions were exposed to ethylene, autocatalytic ethylene production specifically in the basal portions resulted. Ethylene-induced ethylene production in the basal petal tissue was associated with the accumulation of mRNAs for 1-aminocyclopropane-1-carboxylate (ACC) synthase and ACC oxidase. In contrast, the upper petal portions did not accumulate ACC synthase mRNA nor exhibit an induction of ACC synthase activity in response to ethylene. Upper petal tissue exhibited a transient accumulation of ACC oxidase mRNA and increased ACC oxidase activity in response to ethylene, although the levels of both were significantly lower than that exhibited by basal tissue. Both upper and basal petal tissue responded to ethylene with the accumulation of senescence-related mRNAs represented by the cDNA clones pSR5 and pSR12, indicating that the lack of expression of ACC synthase and the limited accumulation of ACC oxidase mRNA were not a result of overall differences in ethylene responsiveness between upper and basal petal tissue. Upper portions isolated from intact senescing petals produced elevated levels of ethylene at approximately 25 % the rate of basal tissue and contained lower, but detectable levels of ACC synthase and ACC oxidase mRNAs as compared to basal petal tissue. Following dissection, the upper petal tissue exhibited a decrease in ethylene production, while the basal tissue continued to produce ethylene at elevated rates. These results indicate ethylene production in the upper tissue is largely the result of transport of ACC and ethylene from the basal tissue.

Cytokinins in cut carnation flowers. II: Relationship between endogenous ethylene and cytokinin levels in the petals

Tentative identification using HPLC and RIA techniques indicated the presence of zeatin-O-glucoside, zeatin, ribosylzeatin, dihydrozeatin, iso-pentenyladenine and iso-pentenyladenosine in the petals of carnation flowers. Dihydrozeatin is apparently responsible for most of the biological activity. Within the petals most activity was detected in the basal parts which also senesced much slower than the upper parts of the petals. Treatment with AOA extended petal longevity and reduced ethylene production. This was associated with higher cytokinin-like activity in the basal parts of the petals.These higher levels of cytokinins were not observed in the petals of ACC treated flowers or in the detached control flowers. It is suggested that cytokinin transport and/or metabolism may play an important role in regulating ethylene production in cut carnations.

Cold storage of rose flowers: Effects of cold storage and water loss on opening and vase life of ‘Mercedes’ roses

Abstract The effects of storing ‘Mercedes’ rose flowers ( Rosa hybrida L.) without water at 2°C and 95% RH on flower opening and on vase life were studied. Flowers were held without water (“dry”) or with their stem bases in deionised water (“wet”). Dry storage for 10 days did not significantly reduce the water content of the petals, but did reduce the subsequent vase life at 22°C compared with freshly cut flowers. Dry storage also reduced the maximum flower diameter and the number of reflexed petals after transfer to 22°C. Flowers stored wet had higher petal water content but shorter vase life than dry-stored flowers. The effects of water loss induced at 22°C were studied and compared with the effects of cold storage. Flowers were held at 22°C and 65% RH without water for 24 or 36 h and then placed in water. Only when petal fresh weight loss reached 19% was the flower vase life reduced. Water loss also caused a reduction in maximum flower diameter, petal area and the amount of petal reflexing. The effects of water loss on petal life could be nullified by detaching petals from the flowers and placing them in water. This indicated that in intact flowers, water loss induced an obstruction to subsequent water uptake and rehydration of the petals. In contrast, detachment of petals did not alleviate the effect of cold storage on vase life. It was concluded that water loss during dry cold storage is not the cause of the reduced vase life of cold-stored rose flowers.

Stimulation of the Growth of Tomato, Pepper and Mung Bean Plants by the Plant Growth- Promoting Bacterium Enterobacter cloacae CAL3

ABSTRACT The effect of a plant growth-promoting bacterium (PGPB), Enterobacter cloacae CAL3, on the growth of tomato, pepper and mung bean plants was evaluated. Seedlings were grown on vermiculite and supplied with Murashige and Skoog nutrient solutions. In parallel the plants were also inoculated with bacterial suspension. The present study highlights the potential for stimulating growth of plants by application of plant growth-promoting bacteria of the genus Enterobacter. It emphasizes that this bacterium can influence plant growth even in the presence of a nutrient solution. Mineral analysis of the bacterial suspension indicated it contained only trace amounts of minerals and thus rules out the possibility that minerals associated with the bacterium were the cause of the growth promotion effect. Tomato seedlings were more responsive to treatment with E. cloacae CAL3 than were mung bean plants. This was manifested in the shorter time it took to discern the promotion effect in tomato plants and in pepper than in mung bean plants. The promotion effect required the presence of a live bacterium, although a low level of growth promotion was also observed when plants were treated with autoclaved bacteria. These findings suggest that plants may be grown with lower amounts of applied fertilizers and implies (1) a reduction in the cost associated with growing plants and (2) a reduction in the pollution associated with agricultural practices.

Aminooxyacetic acid as an inhibitor of ethylenesynthesis and senescence in carnation flowers

Abstract α-Aminooxyacetic acid delayed ethylene (C2H4) production by cut carnation flowers at a concentration of 3 × 10−4 M. It also prevented the development of petal in-rolling (“sleepiness”) symptoms. The efficacy of inhibition is similar to that reported in apple tissue, but 10 times less efficient than in mung bean hypocotyls. The inhibitor had a slight delaying effect on the response of the flowers to exposure to C2H4. This apparent effect of the inhibitor on the action of C2H4 is discussed. The data are in agreement with the proposal that aminooxyacetic acid inhibits C2H4 biosynthesis.

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.

The effect of simulated shipping-conditions on subsequent bud opening of cut spray carnation flowers

Abstract A bud-opening technique was applied to pre-stressed spray carnation flowers. The stress imposed was influenced by the environmental conditions which prevailed during air shipment. The technique included placing tight bud cut flowers in a suitable solution until the flowers developed to a commercially acceptable stage of development. Pre-stressed flowers did not respond to the bud opening treatment as well as non-stressed flowers. Their longevity was shorter, and the continuation of flower development was inhibited. Lowering the temperature during simulated shipment improved the quality achieved following the bud-opening treatment. Apparently, the feasibility of using this technique as a post-shipment treatment depended on the extent to which stress during shipment was minimized. We conclude that stress induced during shipment is mediated primarily via abscisic acid, rendering the flower less capable of response to the bud-opening technique, and reducing quality. This conclusion is based on findings that: (a) the stress induced a rise in the content of abscisic acid, and (b) pre-treatment with abscisic acid reduced the response to the bud-opening technique.