In vivo stable isotope labeling and computer-assisted metabolic flux analysis were used to investigate the metabolic pathways in petunia (Petunia hybrida) cv Mitchell leading from Phe to benzenoid compounds, a process that requires the shortening of the side chain by a C2 unit. Deuterium-labeled Phe (2H5-Phe) was supplied to excised petunia petals. The intracellular pools of benzenoid/phenylpropanoid-related compounds (intermediates and end products) as well as volatile end products within the floral bouquet were analyzed for pool sizes and labeling kinetics by gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry. Modeling of the benzenoid network revealed that both the CoA-dependent, β-oxidative and CoA-independent, non-β-oxidative pathways contribute to the formation of benzenoid compounds in petunia flowers. The flux through the CoA-independent, non-β-oxidative pathway with benzaldehyde as a key intermediate was estimated to be about 2 times higher than the flux through the CoA-dependent, β-oxidative pathway. Modeling of 2H5-Phe labeling data predicted that in addition to benzaldehyde, benzylbenzoate is an intermediate between l-Phe and benzoic acid. Benzylbenzoate is the result of benzoylation of benzyl alcohol, for which activity was detected in petunia petals. A cDNA encoding a benzoyl-CoA:benzyl alcohol/phenylethanol benzoyltransferase was isolated from petunia cv Mitchell using a functional genomic approach. Biochemical characterization of a purified recombinant benzoyl-CoA:benzyl alcohol/phenylethanol benzoyltransferase protein showed that it can produce benzylbenzoate and phenylethyl benzoate, both present in petunia corollas, with similar catalytic efficiencies.

The molecular mechanisms responsible for postpollination changes in floral scent emission were investigated in snapdragon cv Maryland True Pink and petunia cv Mitchell flowers using a volatile ester, methylbenzoate, one of the major scent compounds emitted by these flowers, as an example. In both species, a 70 to 75% pollination-induced decrease in methylbenzoate emission begins only after pollen tubes reach the ovary, a process that takes between 35 and 40 h in snapdragon and ‫ف‬ 32 h in petunia. This postpollination decrease in emission is not triggered by pollen deposition on the stigma. Petunia and snapdragon both synthesize methylbenzoate from benzoic acid and S -adenosyl-L -methionine (SAM); however, they use different mechanisms to downregulate its production after pollination. In petunia, expression of the gene responsible for methylbenzoate synthesis is suppressed by ethylene. In snapdragon, the decrease in methylbenzoate emission is the result of a decrease in both S -adenosyl-L -methionine:benzoic acid carboxyl methyltransferase (BAMT) activity and the ratio of SAM to S -adenosyl-L -homocysteine ("methylation index") after pollination, although the BAMT gene also is sensitive to ethylene.

Changes in ethylene responsiveness of senescence-related (SR) genes in carnation (Dianthus caryophyllus cv. White Sim) petals were investigated during flower development. Dose-response and time-response analysis of SR gene expression indicate that SR genes can be divided into two groups according to their response to ethylene. The ethylene biosynthetic genes, ACC synthase and ACC oxidase represent one group. They show a marked delay of 6 and 9 h in mRNA accumulation in response to ethylene and their apparent dissociation constants of the response (K r ) at open flower stage of development are 17.20 and 1.76 ml l ª1 ,

The incorporation of a hydrophilic polymer into annual landscape beds was found to buffer temperature changes by as much as 3C (37F) during daylight hours. Under dry conditions, hydrophilic polymer incorporation increased the growth and flowering of petunias by as much as 64% and 75%, respectively. Vinca and marigold flowering did not increase with polymer incorporation. However, in the case of marigolds, the medium rate of polymer incorporation resulted in an average of 40% higher dry weights compared to control plants. Under nonlimiting water conditions, the advantage of using polymers were less pronounced than under dry conditions. In addition, plant growth and flowering were not affected. The findings suggest that drought-sensitive plants such as petunia may benefit from the addition of a hydrophilic polymer in areas receiving little or sporadic rainfall in addition to elevated temperatures.

A study was conducted to test the ability of hydrophilic polymers to retain moisture in annual bedding plant beds in addition to reducing NO3 and NH4 leaching. Petunia plants were transplanted into raised concrete benches containing a drainage pipe that allowed for excess leachate to be collected. Beds that were treated with 0 or 366 g·m–2 of hydrogel and 0 or 186 g of ai N. Watering of beds followed a strict irrigation schedule and soil moisture was monitored daily. At termination, plant dry weight was measured and analyses of plant tissue and leachate were conducted for NO3 and NH4 concentrations. Results from this study demonstrated that, under suboptimal conditions of minimal irrigation and fertilization, polymer incorporation had a significant effect on water, NH4, and NO3 retention in soils. Water leaching was decreased by 17%; NH4 retention was increased by 83%; and NO3 retention, where additional N was added, was increased by 64% due to polymer incorporation. In addition, a 47% reduction in NO3 concentration of water leachate was detected when polymer was incorporated under minimal fertilization. Growth or N levels of petunia were not significantly affected by polymer incorporation.

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Hydrogel (Hydrosource™, Western Polyacrylamide, Inc.) was incorporated into 102 cm × 122 cm landscape beds at 25, 50, 75, or 100 lbs per 1000 sq ft. Weed barrier and 2 cm of pine bark mulch were added to the top of each bed. Controls consisted of 1) no hydrogel with weed barrier and mulch and 2) no hydrogel with mulch but no weed barrier. Each treatment was replicated four times with ten plants of petunia, marigold, and vinca planted per bed, for a total of forty plants of each species per treatment. Flower number of vinca and petunia increased with hydrogel incorporation, 75 lbs of hydrogel having the greatest number of flowers. Petunia also had higher visual ratings with increased hydrogel rates. Soil temperatures directly under the mulch and 10 cm below the mulch, at 1400 hr, were 49C and 40C respectively for controls, compared to 42C and 36C for beds with hydrogel.

Two experiments were conducted in which a polyacrylamide gel (Hydrosource, Western Polyacrylamide) was incorporated into 56 × 38-cm, raised, concrete beds, 20 cm deep, with a drain pipe in the center of each bed. In Expt. 1, treatments included (in grams of i.a. N) 0, 186, 372, or 558 plus 0 or 366 g hydrogel/m2, for a total of eight treatments. Each treatment was replicated three times. Petunia plants were transplanted into each plot for a total of 30 plants per treatment. Plants were kept well watered. Polymer incorporation had no effect on soil water retention, soil NO3 or NH4 retention, or plant growth. Expt. 2 included treatments of 0 or 186 g of ai N and 0 or 366 g hydrogel/m2. Each treatment was replicated six times with 10 plants per replication, resulting in a total of 60 plants per treatment. Minimal irrigation was imposed on treatments. This study demonstrated that under suboptimal conditions of minimal irrigation and fertilization, polymer incorporation significantly increased soil moisture (17%), NH4 retention (83%), and NO3 retention where additional N was added (64%) compared to soils without polymer.