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  • Author or Editor: Bernard B. Bible x
  • Journal of the American Society for Horticultural Science x
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Purslane (Portulaca oleracea L.) is an excellent source of the essential fatty acid α-linolenic acid (LNA) but little is known of the effects of cultural conditions on LNA concentration. Purslane seedlings were grown under an instantaneous photosynthetic photon flux [PPF (400 to 700 nm)] of 299 or 455 μmol·m-2·s-1 for a daily duration of either 8, 12, 16, or 20 hours. Thus, plants were exposed to a daily PPF of 8.6, 12.9, 17.2, or 21.5 mol·m-2·d-1 in the low PPF treatment (299 μmol.m-2.s-1) and 13.1, 19.7, 26.2, or 32.8 mol·m-2·d-1 in the high PPF treatment (455 μmol·m-2·s-1). Plants in all treatments received a 20-hour photoperiod by providing ≈5 μmol·m-2·s-1 from incandescent lamps starting at the end of the photosynthetic light period. At low PPF, purslane grown under a 16 hour PPF duration produced the highest concentrations of total fatty acids (TFA) and LNA per unit leaf dry weight (DW), but at high PPF, concentrations of these compounds were highest under 8 and 12 hour PPF duration. Trend analysis indicated that maximum TFA and LNA concentrations occurred with a daily PPF of 14.1 and 17.2 mol·m-2·d-1, respectively; and in the thylakoids, protein, chlorophyll, and LNA concentrations peaked at a PPF of 21.8, 19.9, and 16.1 mol·m-2·d-1, respectively. LNA as a percentage of TFA was unaffected by treatment. Shoot DW increased with PPF up to the highest PPF exposure of 32.8 mol·m-2·d-1.

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The early onset of bract necrosis in poinsettia (Euphorbia pulcherrima Willd. ex. Klotzch) is characterized by small dark-stained spots that precede the development of enlarged necrotic lesions. Electron micrographs of adaxial epidermal and subepidermal tissues with early symptoms of necrosis revealed large, electron-dense deposits in cell vacuoles. These spherical bodies resembled condensed tannins observed in the epidermal tissues of peach and apple fruit. Chemical analysis of bract tissues confirmed the presence of condensed tannins. Furthermore, there were higher concentrations of condensed tannin in bract samples with 2-mm-diameter lesions than in samples with lesions <0.5 mm (equivalent to catechin concentrations of 59 and 13 mg·g-1 fresh mass, respectively). No tannin bodies were observed in parallel samples of healthy-appearing bracts in which only trace concentrations of condensed tannins were measured (0.2 mg·g-1 fresh mass). The evidence suggests an association between condensed tannin accumulation in localized areas of the bract and the early appearance of bract necrosis symptoms.

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Purslane (Portulaca oleracea L.) has been identified as an exceptionally rich source of α-linolenic acid (LNA), an essential fatty acid that is beneficial in reducing the incidence of coronary heart disease and certain cancers. In general, about two thirds of the LNA in terrestrial plants is associated with chloroplasts. A green-leafed unnamed cultivar of purslane and a golden-leafed cultivar `Goldberg' were grown hydroponically in a complete nutrient solution with 14.3 mm nitrogen provided as nitrate (NO3 -) and ammonium (NH4 +) forms to yield NO3 --N: NH4 +-N ratios of 1:0, 0.75:0.25, 0.5:0.5, and 0.25:0.75. Young leaves, harvested 18 days after treatment initiation, were analyzed to determine the fatty acid composition and concentrations, and thylakoid protein and chlorophyll concentrations. Although the leaves of plants grown with a NO3 --N: NH4 +-N ratio of 0.5:0.5 contained 239% and 114% more LNA than plants grown with ratios 1:0 and 0.75:0.25, respectively, they contained only 41% and 26% more chlorophyll. The green-leafed cultivar had higher (39%) chlorophyll concentrations than `Goldberg', but both cultivars had similar LNA concentrations [per g dry weight (DW)]. These results suggest that the LNA concentration in the fatty acid-rich species P. oleracea may not be as closely associated with chlorophyll concentration as reported earlier for other plants. Leaves of plants grown in solutions with 0.25:0.75 NO3 --N: NH4 +-N ratio contained 35% less LNA per g leaf DW than the leaves of plants grown in nutrient solutions with a 0.5:0.5 ratio. Although total DW production was not affected by the NO3 --N: NH 4 +-N ratios in the nutrient solutions, the green-leafed cultivar produced higher fresh weight, leaf area, total DW, and number of shoots than `Goldberg'.

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Abstract

Tissue analysis of 14 cultivars of cabbage (Brassica oleracea L. Capitata group) in both 1974 and 1975 indicated that late maturing cultivars generally were higher in thiocyanate ion (SCN) content than early maturing cultivars. In both years, there was a significant positive correlation between SCN content of cultivars and days to maturity. While SCN content of late-planted (June 18, 1975) unirrigated ‘Badger Market’ and ‘Storage Green’ cabbages were more than twice as high as corresponding late-planted cabbages irrigated 5 times per week, the SCN content of early-planted (May 6) cabbages of both cultivars was not significantly influenced by irrigation treatment. In contrast, the marketable head fresh weight of both cultivars was lowest in late-planted, unirrigated plots. Head SCN content was negatively correlated with marketable head fresh weight and with total top weight of both cabbage cultivars.

Open Access

Abstract

The thiocyanate ion (SCN) content in leaves and stems of 2 cauliflower (Brassica oleracea L. Botrytis group) and 2 broccoli (B. oleracea L. Italica group) cultivars was highest in 15-day seedlings at the cotyledon stage of development, then decreased rapidly and showed little change in 72-day and older plants. The highest quantities of SCN in cauliflower curds and broccoli heads generally occurred at the premature stage of development, after which it decreased rapidly. Except for ‘Jet Snow’ cauliflower, relatively high quantities of SCN were found in edible curds of 9 other cauliflower cultivars and heads of 6 broccoli cultivars at the optimum mature stage.

Open Access

Abstract

Under greenhouse conditions, butanedioic acid mono-(2, 2-dimethylhydrazide) (daminozide) at concentrations of 100, 500, or 1000 mg/liter applied to ‘Burpee white’ radish (Raphanus sativus L.) and 500 or 100 mg/liter applied to ‘Snow Ball’ turnip (Brassica rapa L.), significantly increased root thiocyanate content. Concentrations of 1000 mg/liter gibberellic acid (GA), 500 mg/liter 6-benzylamino purine (BA), and 10 mg/liter 2,4-dichlorophenoxyacetic acid (2,4-D) also increased root thiocyanate content of both species. Under field conditions, applications of 1000 mg/liter daminozide, 1000 mg/liter GA, and 500 mg/liter BA increased root thiocyanate in ‘Burpee White’ radish, ‘Tokyo Cross’ turnip, and ‘Snow Ball’ turnip grown on both loam and organic soil. While there was no effect of these growth regulators on thiocyanate content in roots of ‘White Icicle’ radish, heads of ‘Early Green Ball’ cabbage (B. oleracea L., Capitata group), or ‘Green Mountain’ broccoli (B. oleracea L., Italica group), results for head thiocyanate content of ‘Waltham 29’ broccoli were inconsistent. Five of the seven crops grown on organic soil had thiocyanate contents that were higher than those grown on loam soil.

Open Access

Abstract

Glucosinolates extracted from seeds of 2 rutabaga (Brassica napus L. Napobrassica group) and 2 turnip (B. rapa L. Rapifera group) cultivars, and also from roots sampled at 2-week intervals during growth and development on 2 soil types, were hydrolyzed and the individual volatile products identified by gas chromatography and mass spectrometry. Four isothiocyanates (3-butenyl-, 4-pentenyl-, 4-methylthiobutyl-, and 2-phenylethyl-isothiocyanates), and 2 nitriles (1-cyano-4-methylthiobutane and 2-phenylethylnitrile), were identified. Yields of each constituent varied considerably between cultivars, and also seasonally in root tissue, but generally were quantitatively similar in trend within cultivar grown on loam and organic soils; 2-phenylethyl-isothiocyanate was predominant in roots.

Open Access