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Farida Safadi and Harrison Hughes

Detached and intact leaves (first fully expanded leaf from the top) of tobacco (Nicotiana tabaccum L.) plantlets hardened in vitro with 2.0% polyethylene glycol (PEG) showed increased diffusive resistance (r) over those of nonhardened plantlets as measured by a steady state porometer. The leaves of the PEG hardened plants maintained a higher resistance throughout the one hour dessication period in approximately 30% relative humidity although both treatments showed an increase in diffusive resistance after 30 minutes. This indicates that the stomates are functioning in the in vitro tobacco plantlets. The higher (r) in the PEG treated plants may be due to more complete closure of stomates, higher cuticle wax content or a combination of both.

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C.P. Sharma and Sandhya Singh

When grown in refined sand with one-twentieth normal K supply, cauliflower (Brassica oleracea L. var. botrytis L. cv. Pusi) had lower dry matter and tissue concentration of K than the controls and developed visible symptoms characteristic of K deficiency. In K-deficient plants, the specific leaf weight, diffusive resistance, and proline concentration in leaves were significantly higher and relative water content (RWC), leaf water otential (ψ), stomatal aperture, stomatal density, and transpiration rate were significantly lower than in control plants. When K-deficient plants were supplied additional Na to the extent K was deficient, Na concentration in the plants increased and the plants recovered from the K deficiency effect on free proline concentration, RWC, leaf water potential, stomatal aperture, stomatal density, specific leaf weight, diffusive resistance, and transpiration.

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Susan S. Han

Leaf yellowing of excised Easter lily leaves was significantly delayed by application of gibberellic acids ≥250 mg·liter-1 or benzyladenine ≥50 mg·liter-1. Rapid development of foliar chlorosis following cold storage was delayed significantly by applying 500 mg·liter-1 of GA3 or BA before storage. Poststorage treatments were less effective. Development of chlorosis was associated with rapid loss of fresh weight and was not related to the aperture of the stomates (diffusive resistance). Respiration rates of leaves treated with growth regulators were significantly lower than those of the controls.'

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Alan R. Biggs

The proportion of spurs blooming on `McIntosh' apples (Malus domestica Borkh.) was reduced significantly in 1986 and 1988, but not in 1987, following seasonal programs of six bitertanol or flusilazole treatments applied at two and three rates, respectively. The fungicides were not associated with any visible phytotoxic effect nor was shoot length reduced by any fungicide treatment. In two of three experiments conducted in May and June 1986, transpiration was reduced by the low rate of flusilazole and the high rate of bitertanol relative to both the captan and nonsprayed trees. In all three experiments, flusilazole at 1.4 g a.i./100 liter was associated with transiently reduced transpiration rates, lasting a minimum of 48 hours, relative to the nonsprayed control. Fungicides affected the diffusive resistance of apple leaves in all three experiments; however, there were no consistent treatment effects on diffusive resistance among the three experiments.

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Chana Phromtong, Floyd M. Woods, James O. Garner Jr., and Juan L. Silva

Sixteen sweet potato (Ipomoea batatas L.) genotypes were chilled for 36 hours at 5C with 85% RH and a 12 hour photoperiod. Transpiration, leaf diffusive resistance and visual scores for plant quality were taken before chilling and 2 days after the chilling treatment. Differences between the before and after readings were used to indicate the extent of chilling injury or tolerance. Visual score gave a better separation of the genotype for tolerance, however, the difference in transpiration was the most critical of the two objective measurements.

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Virginia I. Lohr and Caroline H. Pearson-Mires

Cut flowers of eight cultivars of Rosa hybrida L. were held in preservative solutions containing up to 4 mg F-/liter. Leaf diffusive resistance was increased by holding flowers in F-solutions. In most cultivars, fresh weight gain was decreased, the degree of flower opening was affected, and visual symptoms of injury were noted in the presence of. F- in the holding solution. Damage at 2 mg F-/liter was almost as severe as at 4 mg/liter. Number of days to petal abscission or bent-neck was shortened by F- for `Samantha' and `Bridal Pink'.

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James Q. Garner Jr. and Thammasak Thongket

Proline content, leaf water potential (LWP), and leaf diffusive resistance (LDR) were determined for eight sweetpotato genotypes underwater stress conditions. Changes in fatty acid compositions of leaf polar lipids were determined in two sweetpotato genotypes during declining soil moisture. Proline did not accumulate and LWP did not decrease until soil moisture dropped below 10%, but LDR increased as soil moisture decreased. Genotypic differences in proline accumulation and LWP were found. Changes in fatty acid compositions occurred more in glycolipids than in phospholipids. Fatty acid changes were more pronouned in genotype MS20-2 than in “Vardaman”

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Michael Knee

A method was devised for measuring the resistance to gaseous diffusion of bulky plant organs, such as apple (Malus domestica Borkh.) fruits, in which the skin is the major barrier to diffusion. An individual fruit was incubated in a sealed container in the presence of a measured concentration of ethane for a certain time (usually 20 min). The fruit was then transferred to another, similar container. The ethane concentration that diffused into the new container was measured after an equal time (usually 20 min). An expression relating resistance to the measured ethane concentrations was derived from Fick's First Law of diffusion. An estimate of the internal volume of the fruit, accessible to ethane, was also necessary. The method was tested on several fruits of various apple cultivars. Longer incubation periods are necessary for apples with high diffusive resistance.

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Khin San Wai and S.E. Newman

The response of Antirrhinum majus (snapdragon) cultivars (`Tampicoi' and `Rainier White') to night air temperatures (10C and 20C) and elevated root-zone temperature (26C and ambient) was studied. Height of plants grown with a heated root-zone were greater, compared to unheated at both night temperatures for both cultivars. Shoot dry weight of `Tampico' plants was reduced by heated root-zone temperature at 20C night air temperature. Raceme length was greater with heated root-zone temperature compared to unheated at 10C night air temperature. Days to flower were shorter with heated compared to unheated root-zone at both night air temperatures for both cultivars. Stomatal diffusive resistance was greater on plants with unheated compared to heated root-zone temperature at 10C night air temperature for `Rainier White'.

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L.G. Sanabria and S.E. Newman

Various uniconazole (Sumagic™) rates were either sprayed or drenched alone or in combination with 6-BA and GA4+7 (Promalin™) or dikegulac-sodium (Atrinal™) on Hibiscus rosa-sinensis `Brilliant'. The rates of uniconazole were 0, 5, 10, and 15 mg a.i./L; 6-BA and GA4+7, 25 mg a.i./L each; and dikegulac-sodium 1000 mg a.i./L.

Plant height was reduced by uniconazole when drenched at rates as low as 5 mg/L and 15 mg/L when sprayed. Dikegulac-sodium slightly counteracted the effects of uniconazole. Uniconazole activity was increased when either sprayed or drenched with application of 6-BA and GA4+7 resulting in greater height reduction.

Transpiration and stomatal diffusive resistance of plants drenched with uniconazole alone was erratic; however, when uniconazole was sprayed or drenched and mixed with 6–BA and GA4+7 or dikegulac-sodium transpiration increased.