Tsipora Tirosh

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.

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.

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.

The fate of ribulose-1,5-bisphosphate carboxylase subunits during development of carnation petals

Abstract The fate of ribulose-1,5-bisphosphate carboxylase was studied during development of carnation ( Dianthus cryophyllus L. cv. White Sim) petals. The petals of various developmental stages were dissected into upper wide and basal narrow parts, and analyzed separately. Rubisco activity was assessed in aqueous extracts of the petal parts in parallel with measurements of CO 2 fixation by intact petals. During development, CO 2 fixation declined markedly, Rubisco activity per corolla declined slightly and Rubisco activity per g dry weight increased. Analysis of the steady state level of the large and small subunits (LSu, SSu) of Rubisco by western blotting, demonstrated a decline in the amounts of both. The reduction in the level of SSu appeared prior to the decrease in the amount of LSu. An analysis of the spatial distribution of the Rubisco subunits revealed that the upper part of the petal was devoid of SSu in both young and old flowers. The data suggest that two different mechanisms are involved in the regulation of the decline in the amount of LSu. The first is at the transcriptional level and operates primarily in the basal part of the petal. The second mechanism operates in the upper part of the petal and may involve post-transcriptional processes.

Interrelated effects of short-term treatment with nutritive solution and shipment conditions on the quality of iris flowers

Abstract Short-term treatment (12 h) with nutritive solution containing 2% w/v sucrose and citric acid 2 g l−1 (“pulsing”), improved the quality of cut iris flowers cultivar ‘Prof. Blaauw’ held in water after pulsing. The improvement achieved was not observed when the flowers were exposed to simulated air-shipment conditions (48 or 72 h at 20° C) immediately after pulsing. Apparently, the temperature factor during shipment was mainly responsible for reducing the beneficial effect of pulsing. Holding the flowers for the same period at 4°C preserved the beneficial of the treatment. The relevance of the findings to experimental studies and commercial practice is discussed.