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W.F. Whitehead and B.P. Singh

Two studies were conducted to assess the effects of leaf aging on gas exchange in okra [Abelmoschus esculentus (L.) Moench] leaves. Gas exchange was measured at 6- to 10-day intervals starting 15 days after leaf emergence (DFE) and continuing until senescence at 50 DFE. Rates of transpiration (E), stomatal conductance (gs) and CO2 exchange (CER) increased as leaves matured up to ≈25 DFE, about full leaf expansion. Transpiration rate, gs, and CER declined after 25 DFE and as leaves aged further. Internal leaf CO2 concentration (Ci) was higher in old than young leaves. This study suggests that the most efficient okra canopy would maximize exposure of 25-day-old leaves to sunlight.

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Michael V. Mickelbart

determined from 20 leaves from each of four positions for both early- and late-season leaves. The ratio was different between leaf ages, but not among positions, so the pooled data were used to generate a standard curve for each leaf age estimating leaf dry

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M. Elena Garcia, C.R. Rom and J.B. Murphy

Two experiments were conducted to determine the effects of leaf age and shading on the phenolic content and composition of apple foliage. In the first study, it was determined that the phenolic content of `Liberty', at increasing leaf developmental stages, was leaf age—dependent. Early during leaf development, there was an increase in the phloridzin (the primary glycoside identified) and in total phenolics, reaching a maximum when the leaf is 6 days from 20-mm blade length. After this stage, the phenolic content decreased with increasing leaf age. In the second study, the leaves of two cultivars, `Liberty' and `Starkspur Law Rome', were tagged weekly when the leaf was two-thirds unfolded. Three weeks after budbreak, the trees were placed under three shade cloth treatments (0%, 60%, and 90% shade). After 4 weeks under the shade treatments, the tagged leaves were collected to determine their phenolic content. Shade significantly affected the foliar phenolic content. Leaves in 0% shade had the highest phenolic content, whereas the lowest content was found in leaves exposed to 90% shade. There was a significant leaf age × shade interaction. The phenolic content decreased with increasing leaf age except for those leaves whose development occurred before the experiment was started. The results indicate that light and leaf developmental stage are important factors in determining the phenolic content of apple leaves, but shading appears to have a stronger influence than leaf developmental stage. E-mail mgarcia@zoo.uvm.edu; phone (802) 656-2824.

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M.E. Garcia, C.R. Rom and J.B. Murphy

The effects of shading and leaf age on the production of foliar phenolics of two apple (Malus domestica Borkh.) cultivars, `Liberty' and `Red Rome Beauty', were studied. Potted trees were grown outdoors and their leaves tagged weekly when they reached 20 mm in length. This process continued for the duration of the experiment. At 3 weeks from budbreak, the trees were placed in three shade treatments: 0% shade (control), 60% shade, and 90% shade. After 5 weeks, the leaves were collected for phenolic assay. Specific leaf weight (SLW) was determined from the leaf below the tagged leaf. Shade significantly affected the total phenolic content. Leaves in 0% shade had the highest levels of total phenolics. The phenolic content decreased with increasing shade, with trees in 90% shade having a 72% reduction in total phenolics. There was a significant shade by leaf age interaction. There was a decrease in total phenolic content with increasing leaf age except for those leaves whose development occurred before the experiment was started. The 1-week-old leaf had the highest phenolic content, while 4-week-old leaf had the lowest amount. The 5- and 6-week-old leaves that had been tagged prior to the onset of the shade treatments has similar phenolic content in all treatment. SLW significantly decreased with increasing shade and increased with leaf age. Results of this study indicate that light and leaf developmental stage are important factors in the total foliar phenolic content, but, once phenolics are synthesized, shading does not affect their content.

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Vladimir Orbović, Diann Achor, Peter Petracek and James P. Syvertsen

Effects of air temperature, relative humidity (RH), and leaf age on penetration of urea through isolated leaf cuticles of `Marsh' grapefruit (Citrus×paradisi Macfad.) trees on `Carrizo' citrange (C. sinensis L. Osbeck × Poncirus trifoliata (L.) Raf. rootstock were examined. Intact cuticles were obtained from adaxial surfaces of `Marsh' grapefruit leaves of various ages. A finite dose diffusion system was used to follow movement of 14C-labeled urea from urea solution droplets across cuticles throughout a 4-day period. Within the first 4 to 6 hours after urea application, the rate of urea penetration increased as temperature increased from 19 to 28 °C, but there was no further increase at 38 °C. Increasing relative humidity increased urea penetration at 28 °C and 38 °C. Cuticle thickness, cuticle weight per area, and the contact angle of urea solution droplets increased as leaves aged. Cuticular permeability to urea decreased as leaf age increased from 3 to 7 weeks, but permeability increased in cuticles from leaves older than 9 weeks. Contact angles decreased with increased urea solution concentration on leaf surfaces that were 6 to 7 weeks old, but solution concentration had no effect on contact angle on cuticles from younger and older leaves. Changing urea solution pH from 8.0 to 4.0 could have an effect on the amount of urea penetrating the cuticle through the loss of urea from breakdown possibly due to hydrolysis. Results from this study define leaf age, environmental conditions, and formulation for maximum uptake of foliar-applied urea.

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Malkeet S. Padda and D.H. Picha

tissues ( Huang et al., 2004 ; Islam et al., 2002 , 2003b ; Walter et al., 1979 ). However, these previous studies provided no information regarding the effect of root size and leaf age on phenolic composition and antioxidant properties of sweetpotato

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J.H. Lieth and C.C. Pasian

A mathematical description for the relationship between the rate of rose (Rosa hybrida L.) leaf net photosynthesis and photosynthetically active radiation, leaf temperature, and leaf age is developed. The model provides a tool for the prediction of these rates for leaves growing in a rose crop canopy.

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Vladimir Orbovic, Diann Achor, Peter Petracek and James P. Syvertsen

We examined the effects of air temperature, relative humidity (RH), leaf age, and solution pH on penetration of urea through isolated cuticles of citrus leaves. Intact cuticles were obtained from adaxial surfaces of different aged grapefruit leaves. A finite dose diffusion system was used to follow movement of 14C-labeled-urea from solution droplets across cuticles throughout a 4-day period. The rate of urea penetration increased as temperature increased from 19 °C to 28 °C, but penetration was not further increased at 38 °C. Increasing RH increased droplet drying time and urea penetration at both 28 °C and 38 °C. Cuticle thickness, weight per area, and the contact angle of urea solution droplets increased as leaves aged. Cuticular permeability to urea decreased as leaf age increased from 3 weeks to 7 weeks, but permeability increased in cuticles from leaves older than 9 weeks. Contact angles decreased with increased urea solution concentration on six 7-week-old leaf surfaces, but solution concentration had no effect on contact angle on cuticles from younger and older leaves. Reducing pH of urea solution from pH 8 to pH 4 accelerated the loss of urea from breakdown, possibly due to hydrolysis.

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Mark W. Farnham, Ellis J. Caniglia and Claude E. Thomas

Broccoli (Brassica oleracea L. Italica group) breeders routinely use anther or microspore culture to produce dihaploid (diploid), homozygous lines. During the culture process, polyploidization occurs and diploid regenerants can result. However, polyploidization may not occur at all, or it may involve a tripling or quadrupling of the chromosome complement. Thus, regenerated populations must be screened to identify the diploids that are the regenerants most likely to set seed and serve as inbred lines. DNA flow cytometry has proven a useful procedure for determining ploidy of anther derived regenerants. This study was undertaken to evaluate the effect of leaf age and sampling procedures on ploidy determination via flow cytometry. Anther-derived plants were analyzed at a four- to five-leaf stage (transplant stage) and at time of heading (mature plant stage). In addition, leaves were sampled on a given date and stability of the flow cytometry preparations was evaluated over 7 days. Lastly, the stability of ploidy readings of leaves stored at 4°C was examined over a 7-day period. In only one case out of 123 comparative assays did leaf age affect ploidy determination. For that exception, a haploid at transplant stage was a diploid at the mature plant stage. Flow cytometry preparations and also leaves stored at 4°C gave consistent ploidy determinations up to four days after preparations were made or tissue was refrigerated, respectively. These results indicate that broccoli breeders can make flow cytometry preparations on site and send them offsite for flow cytometry analysis. Alternatively, leaves could be refrigerated, sent offsite, and then prepared and analyzed at another location.

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B.R. Bondada, J.P. Syvertsen and L.G. Albrigo

Foliar-applied urea nitrogen (N) has potential to become an important component in fertilizer programs for citrus in Florida and other citrus growing areas as it can reduce nitrate leaching into ground water. We evaluated seasonal absorption characteristics of three urea formulations, Triazone-urea, liquid urea, and spray grade urea by citrus leaves that were from 2 weeks to 6 months old. The effect of leaf age on 15N absorption by N-deficient and N-sufficient leaves, together with urea absorption over an eight-week period were studied using greenhouse-grown and field-grown plants. All foliar N applications were based on a recommended rate of 34 kg N/ha in 469 L of water. In the field studies, leaf N was increased similarly by the three urea formulations one week after three weekly applications. Young leaves (0.25 month and 1 month old) absorbed a greater percentage of N than the older leaves (3 month and 6 month old). Epicuticular wax concentration increased and 15N absorption declined with leaf age. Nitrogen deficient leaves (1.80% N) had greater wax concentration and lower N absorption than N sufficient leaves (2.60% N). Four to 8 weeks after urea applications, Triazone-urea sprayed leaves had significantly greater leaf N concentration than leaves sprayed with liquid urea or nonsprayed control leaves. The greenhouse studies revealed that the 15N absorption was greater through abaxial leaf surfaces than through adaxial surfaces regardless of leaf N level and application time. Applying foliar 15N-urea during night (2000 hr to 2200 hr) resulted in greater absorption of 15N than in the morning (0800 hr to 1000 hr) or afternoon (1200 hr to 1400 hr). It is clear that maximum N absorption from foliar urea sprays occurred at night through the abaxial surfaces of young leaves with sufficient N. Triazone-urea acted as a slow-release N source that could be exploited in supplying N over an extended period of time.