William M. Randle

Onion germplasm interacts with sulfur fertility for plant sulfur utilization and bulb pungency

SummarySixty-two onion (Allium cepa L.) entries grown under high (4.0 mequiv.liter-1) and low (0.1 mequiv.liter−1) S fertility were evaluated for foliar and bulb S utilization, and pungency. Significant differences were detected among entries at both S fertility levels for foliar and bulb %S, and enzymatically developed pyruvate (pungency) in bulb tissue. Correlations between foliar %S and enzymatically developed pyruvate and between bulb %S and enzymatically developed pyruvate were poor suggesting that S is differentially partitioned into flavor and non-flavor compounds in the bulbs of onion germplasm. Significant S by entry interactions were found for all variables tested indicating that selection for S utilization and bulb pungency in onions be conducted at S fertility levels indicative of targeted production areas.

Total sulfur and sulfate accumulation in onion is affected by sulfur fertility

Abstract Because sulfate (SO4 ‐2) accumulation patterns were unknown in onion, a study was conducted to determine how three onion varieties accumulated total bulb‐sulfur (S) and bulb‐SO4 ‐2 in response to increasing S‐fertility. Plants were greenhouse grown in pots containing washed river sand and fertilized with five different nutrient solutions possessing SO4 ‐2 concentrations of 5, 25, 50, 75, or 150 mg liter1 until the plants were mature. Bulbs were harvested and analyzed for total‐S, SO4 ‐2, and pungency, as measured by enzymatically developed pyruvic acid (EPY). Bulbs accumulated significant levels of SO4 ‐2 and S. The amount of bulb‐SO4 ‐2 and bulb‐S increased linearly as S‐fertility increased. The three varieties differed in total bulb‐S, bulb‐SO4 ‐2, the percent of total bulb‐S accumulated as SO4 ‐2, and EPY. Bulb‐SO4 ‐2 ranged from 0.047 to 0.318 % dry mass in response to S‐fertility level and variety, while total bulb‐S ranged from 0.154 to 0.535% dry mass. Diverse S and SO4 ‐2 accumulation and...

Selenium Accumulation in a Rapid-cycling Brassica Oleracea Population Responds to Increasing Sodium Seienate Concentrations

Abstract Because of their short life cycle, rapid‐cycling base populations (RCBP) of Brassica can act as model systems for investigating selenium (Se) metabolism in high sulfur (S) accumulating plants. To establish treatment responses for a B. oleracea RCBP, plants were grown in nutrient solutions containing 0, 3, 6, and 9 mg sodium seienate (Na2SeO4) L‐1. Depletion of Se from nutrient solutions increased linearly with in‐creasing Na2SeO4 concentrations. Selenium accumulation ranged from 551 to 1,916 μg Se g‐1 dry weight for leaf tissue, 267 to 1,165 μg Se g‐1 dry weight for stem tissue, and 338 to 1,636 μg Se g‐1 dry weight for root tissue. Selenium additions also resulted in linear increases in S accumulation in leaves and stems. Selenium supplementation has been shown to improve the health of individuals with low Se status. Because Brassica species are important vegetable and forage crops, their enrichment with Se maybe a good delivery system for mammalian diets.

Differential hydrolysis of alk(en)yl cysteine sulphoxides by alliinase in onion macerates : Flavour implications

Intact cells of Allium spp have no odour, but when cells are disrupted, the enzyme alliinase (EC 4.4.1.4) hydrolyses the S-alk(en)yl sulphoxides (ACSOs) to produce pyruvate, ammonia and the many volatile sulphur compounds associated with flavour and odour. In onions, there are three main sulphoxides: methyl, propyl and 1-propenyl, which gives rise to onions tear-producing effect. The relative proportions of these are a factor in determining the subsequent flavour. γ-Glutamyl peptides, which are biosynthetic intermediates to ACSOs, are also present in significant amounts, but their contribution to flavour is not known. There is little work on the reaction of alliinase in vivo. The hydrolysis of ACSOs by alliinase was studied in rapidly macerated bulbs at intervals between 5 s and 2 h. ACSO and γ-glutamyl peptide levels were measured by HPLC, and pyruvate levels were measured spectrophotometrically. Although the hydrolysis of propenyl cysteine sulphoxide (PrenCSO) was immediate and almost 100% between 5 and 20 s after bulb maceration, the hydrolysis of propyl cysteine sulphoxide (PCSO) and methyl cysteine sulphoxide (MCSO) was incomplete. After 5 s maceration, about 50% PCSO and MCSO remained and thereafter no further hydrolysis occurred. The levels of ACSOs and the extent to which they were hydrolysed were dependent on the cultivar and sulphur environment in which it was grown. The addition of pyridoxal phosphate cofactor enhanced the extent of MCSO and PCSO hydrolysis. Additional purified alliinase per se had no effect. Substantial hydrolysis of γ-glutamyl peptides also occurred after maceration, and this was unexpected. Levels of pyruvate product were between 15 and 25% of the expected amount from ACSO hydrolysis assuming a stoichiometric relationship. The incomplete hydrolysis of MCSO and PCSO, enhancement of activity by additional pyridoxal phosphate and non-stoichiometric production of pyruvate are evidenced that reaction inhibition of alliinase may be occurring in onion macerates.

Short-day onion cultivars differ in bulb selenium and sulfur accumulation which can affect bulb pungency

The close chemical similarity of S and Se allow for antagonistic behavior between the two elements. To determine variation for Se accumulation within onions, sixteen short-day cultivars were grown under high level (2.0 mg Na2SeO4 per litre) and no Se treatments. Selenium accumulation in bulb tissues was cultivar dependent, ranging from 60 to 113 µg Se per g dry wt. High Se fertility enhanced bulb S accumulation. Pungency was reduced in some cultivars grown under Se fertility when compared to the no Se treatment indicating that although S uptake was enhanced, S metabolism in the flavour precursor biosynthetic pathway was affected. The existing variability in onion Se uptake and accumulation have important implications for Se intake in mammalian diets.

Nitrogen and sulfur influence nutrient usage and accumulation in onion

Abstract To study the effects of nitrogen (N) and sulfur (S) fertility on onion (Allium cepa L.) bulb pungency, bulb fresh and dry weight, nutrient uptake and accumulation in the bulb, “Granex 33” onions were greenhouse grown using nutrient solution culture. A factorial arrangement of solutions containing 1.7, 15.0, and 41.7 mg L−1 S and 10, 50, 90, and 130 mg L−1 N were used. Bulb pungency and bulb fresh and dry weight were affected by both S and N treatments. Depletion patterns for most of the macronutrients from the nutrient solutions during plant growth were affected by N and S levels, and differed depending on the N and S combination. In certain N and S combinations, magnesium (Mg) and calcium (Ca) usage were unaffected over time. Bulb N levels increased with N fertility and decreased slightly with S availability, while bulb phosphorous levels responded linearly to N fertility. Overall changes in bulb Ca and Mg levels were minor, but were influenced by N and S fertility. Bulb S content was affected by low S and N fertility, decreasing with each. Boron levels in onion bulbs decreased with increasing N and S fertility, while bulb manganese, iron, and zinc concentrations tended to increase with increasing N availability and decrease with increasing S. Potassium, copper, and molybdenum bulb concentrations were unaffected by N or S fertility. These results have the potential of being used as a reference in developing nutritional programs designed for optimal onion performance having specific flavor intensities.

Nutrient Accumulation in Leaf Tissue of Rapid-cycling Brassuca Oleracea Responds to Increasing Sodium Selenate Concentrations

Abstract Brassica oleracea L. are important economic vegetables, and are capable of selenium (Se) enrichment to enhance human nutrition and health. Because Se enrichment may influence the nutrient balance of this crop, a study was done to test the effects of selenate‐Se on plant nutrients. Plants of a rapid‐cycling B. oleracea population were grown in nutrient solutions amended with Na2SeO4at 0.0, 3.0, 6.0, and 9.0 mg L‐1. Leaf tissue was then analyzed for nutrient content. Boron (B) (P=0.01), iron (Fe) (P=0.01), and phosphorus (P) (P=0.01) content decreased, while Se (P=0.01), sulfur (S) (P=0.01), and potassium (K) content (P=0.01) increased with increasing selenate‐Se treatments. Significant quadratic responses were found for magnesium (P=0.01) and molybdenum (P=0.01). No significant differences in leaf fresh or dry weight were detected. Changes in plant nutrient content can be expected when Brassicas are enhanced for delivery of beneficial organic Se.

Zinc Concentration in Hydroponic Solution Culture Influences Zinc and Sulfur Accumulation in Brassica rapa L

Abstract A rapid cycling population of Brassica rapa L. was grown hydroponically and subjected to solution zinc (Zn) concentrations ranging from 0.05 to 200 mg L−1. The objectives of the study were to determine how available Zn affected plant growth, and the accumulation of Zn, total sulfur (S), sulfate (SO4 2−) in B. rapa shoots. Plants exposed to Zn levels above 5 mg L−1 exhibited mild visual toxicity symptoms as well as stunted root and shoot growth. Plants exposed to Zn levels ≥50 mg L−1 had chronic toxicity symptoms after several days of exposure and did not measurably grow. Mineral analysis showed that Zn accumulated linearly in plant shoots in response to increasing Zn, despite the expression of varying levels of Zn toxicity symptoms. Total shoot S and SO4 2− accumulated at amounts greater than the control when exposed to Zn levels ≥25 mg L−1 Zn; even though solution S did not vary among treatments. At the higher Zn concentrations, shoot S did not differ from the control. Additionally, SO4 2− was responsible for the nearly all the S measured regardless of Zn exposure. This suggests that Zn uptake and accumulation differs from S when exposed to increasing Zn availability.

Sodium chloride timing and length of exposure affect onion growth and flavor

ABSTRACT This study investigated how sequentially exposing plants to sodium chloride (NaCl) would affect growth and the flavor quality of onion (Allium cepaL.) bulbs at harvest. In a greenhouse experiment beginning 74 d before harvest, 100 mM concentrations of NaCl were applied at biweekly intervals to onions growing in nutrient solutions. At harvest, fresh weights (FW) were measured and the bulbs were analyzed for soluble solids content (SSC), bulb pungency as measured by total pyruvate (TPY), bulb sulfur (S) and sulfate (SO4 −2) accumulation, flavor precursors, and their biosynthetic intermediates. Bulb and leaf FW decreased linearly the earlier NaCl was added during plant growth and development. While total bulb S was significantly affected by sequential addition of NaCl, bulb SO4 −2 was unaffected. Bulb pungency was significantly reduced by NaCl, especially when NaCl was introduced during early bulb development. NaCl generally reduced flavor precursor accumulation in a quadratic response, with the greatest depression occurring when plants were exposed to NaCl beginning in the early stages of bulbing. Significant reductions in plant growth and changes in the S-compounds associated with flavor suggested that the duration and timing of NaCl exposure are important in onion.

Growth and nutrition of pansy as influenced by N‐form ratio and temperature

Abstract Pansy (Viola xwittrockiana Gams.) producers often observe nutrient disorders among plants grown during warm periods (>18°C) of the growing season. These disorders typically are not seen when production temperatures are optimal (≥18°C) even though fertility regimes may remain the same. Our objectives were to assess the effects of temperature and nitrogen (N) fertility on growth and nutrition of pansy. Pansies cultivar ‘Crown White’ were grown until lateral branches had open flowers. Treatments consisted of two temperatures (12 and 22°C) and three NO3 −:NH4 + molar % ratios (100:0, 62:38, and 25:75) with a total concentration of 100 mg N L−1. A modified Hoaglands solution was used with NO3 −‐N supplied as Ca(NO3)2 and KNO3 and with NH4 +‐N as (NH4)2SO4. Cumulative nutrient absorption and foliar nutrient content were determined when plant lateral branches flowered. Root and shoot growth were limited when NH4 + was present in solutions at high ambient air temperature (22°C), but not at low temperatu...