Journal of the American Society for Horticultural Science 

About: Journal of the American Society for Horticultural Science is an academic journal published by American Society for Horticultural Science. The journal publishes majorly in the area(s): Shoot & Population. It has an ISSN identifier of 0003-1062. Over the lifetime, 5432 publications have been published receiving 158355 citations. The journal is also known as: ASHS journal.

Activity of phenylalanine ammonia-lyase (PAL) and concentrations of anthocyanins and phenolics in developing strawberry fruit

Abstract: Studies on regulation of production of phenolics in strawberry (Fragaria X ananassa Duch,) fruit were initiated by monitoring phenylalanine ammonia-lyase (PAL) activity and levels of anthocyanins, flavonoids, tannins, and other soluble phenols throughout fruit ontogeny in 'Tillikum'. PAL catalyzes the first step in the biosynthesis of phenylpropanoids, which are further modified into a wide variety of phenolic compounds. Peak in PAL activity (1 mol· s -l = 1 kat) of 90 pkat· mg -l protein was detected at 5 and 27 days after anthesis (DAA), when fruit was green and nearly ripe, respectively. PAL activity was only 10% of peak values in the white berry stage, when. fruit growth was most rapid. The second peak in PAL activity was followed by a rapid drop, to nearly zero in red-ripe fruit at 30 DAA. Total soluble phenols reached a maximum level soon after anthesis, just before the first peak in PAL activity, then declined to a low constant value well in advance of fruit ripening. Similar changes were observed in levels of tannins and flavonoids that, at anthesis, accounted for 44% and 51% of the soluble phenols, respectively. The concentration of anthocyanin was very low throughout most of fruit development, but beginning at 23 DAA it increased from 0.53 mg·g -l fresh weight in 3 days. This accumulation paralleled the second rise in PAL activity. Accordingly, strawberry fruit have a developmental- dependent expression of PAL activity and accumulation of phe- nolic substances derived from the phenylpropanoid pathway. Many distinctive developmental features of fleshy fruits, such as loss of astringency and appearance of characteristi c color at ripening, are related to changes in the synthesis and accumu- lation of phenolic compounds. For example, astringency is a tannin effect and the color of ripe fruit often results from ac- cumulated anthocyanins. Besides anthocyanins and condensed tannins (proanthocyanins), fruit also contain other flavonoids, as well as simple phenols such as phenolic acids and cinnamic acid derivatives (see review by Macheix et al., 1990). The type and amount of phenolic compounds in plant tissues depend on genotype and developmental stage (Hahlbrock and Griseback, 1-979). Tissues of fleshy fruits commonly have high levels of cinnamic acid derivatives, flavonoids, and tannins during early development, but accumulate anthocyanins only near maturity (Billet et al., 1978; Hyodo, 1971; Kataoka et al., 1983). In- formation on metabolism of phenolics is important not only because they influence the quality of fruit and related processed products, but also because of their roles in developmental phys- iology and defense mechanisms. Understanding phenolic metabolism in plant cells and tissues requires knowledge of the biosynthetic reactions and their reg- ulation. The majority of monophenolic compounds, most of which are phenolic acids and phenylpropanoids, are interme- diates and derivatives of the shikimate and phenylpropanoid pathways. Flavonoids, including anthocyanins and condensed tannins, are derived from p-coumaric acid of the phenylpropa- noid pathway. Another group of tannins, the hydrolyzable tan- nins, are ester derivatives of gallic acid that maybe synthesized via the shikimate or phenylpropanoid pathways (Ishikura et al., 1984). Conversion of L-phenylalanine to trans -cinnamic acid is the initial step of the phenylpropanoid pathway. This ammonia elimination reaction is catalyzed by L-phenylalanine ammonia- lyase (PAL) (EC 4.3.1.5), a key regulatory enzyme in the bio-

Stem-water Potential as a Sensitive Indicator of Water Stress in Prune Trees (Prunus domestica L. cv. French)

Abstract: Additional index words. evapotranspiration, leaf-water potential, soil water, stomatal conductance Abstract. The relative sensitivity of plant- and soil-based measures of water availability were compared for prune trees subjected to a range of irrigation regimes under field conditions. Over the growing season, leaf- and stem-water potentials (ψ) measured at midday exhibited clear differences between frequently irrigated trees and unirrigated trees that were growing on stored soil moisture. Stem ψ was less variable than leaf ψ, ψ, and the daily variability in stem ψ ψ was closely related to daily variability in evaporative demands, as measured by vapor pressure deficit (VPD). As a result of lower variability, stem ψ reflected the small stress effect of a moderate, 50% soil moisture depletion irrigation interval, whereas leaf ψ did not. The relation between soil water content and estimated orchard evapo- transpiration (ET) was influenced by local differences in soil texture within the experimental plot. The relation between stem ψ and ET, however, was not influenced by soil texture and, in addition, was very similar to the relation between stem ψ and leaf stomatal conductance. Both relationships indicated that a 50% reduction in leaf and canopy level water loss characteristics was associated with relatively small reductions (0.5 to 0.6 MPa) in stem ψ. ψ. Stem ψ appears to be a sensitive and reliable plant-based measure of water stress in prune and maybe a useful tool for experimental work and irrigation scheduling. Plant water stress under dry soil conditions is associated with various physiological responses, such as growth reductions and stomatal closure, which can reduce plant water use and can also limit overall plant productivity (Bradford and Hsiao, 1982). Ir- rigation to avoid plant water stress is a common practice, and the need for irrigation is often based on a soil-water balance approach, using estimates of environmental water demand (e.g., reference crop evapotranspiration (ET 0), Burman. 1980) and/or measures of soil-water status (Campbell and Campbell, 1982). The value of both of these measures, however, is limited, be- cause they are not directly related to the occurrence of plant water stress and hence may not be directly related to the symp- toms that ultimately reduce plant productivity. For instance, Denmead and Shaw (1962) found that under high ET0 conditions (6 to 7 mm·day -1 ), a relatively wet soil (soil matric potential greater than - 0.03 MPa) was required to support maximum plant transpiration. Under lower ET0 conditions, however (1.4

Growth and photomorphogenesis of pepper plants under red light-emitting diodes with supplemental blue or far-red lighting.

Abstract: Light-emitting diodes (LEDs) are a potential irradiation source for intensive plant culture systems and photobiological research. They have small size, low mass, a long functional life, and narrow spectral output. In this study, we measured the growth and dry matter partitioning of 'Hungarian Wax' pepper (Capsicum annuum L.) plants grown under red LEDs compared with similar plants grown under red LEDs with supplemental blue or far-red radiation or under broad spectrum metal halide (MH) lamps. Additionally, we describe the thermal and spectral characteristics of these sources. The LEDs used in this study had a narrow bandwidth at half peak height (25 nm) and a focused maximum spectral output at 660 nm for the red and 735 nm for the far-red. Near infrared radiation (800 to 3000 nm) was below detection and thermal infrared radiation (3000 to 50,000 nm) was lower in the LEDs compared to the MH source. Although the red to far-red ratio varied considerably, the calculated phytochrome photostationary state (phi) was only slightly different between the radiation sources. Plant biomass was reduced when peppers were grown under red LEDs in the absence of blue wavelengths compared to plants grown under supplemental blue fluorescent lamps or MH lamps. The addition of far-red radiation resulted in taller plants with greater stem mass than red LEDs alone. There were fewer leaves under red or red plus far-red radiation than with lamps producing blue wavelengths. These results indicate that red LEDs may be suitable, in proper combination with other wavelengths of light, for the culture of plants in tightly controlled environments such as space-based plant culture systems.