Spinach Shoot Research Articles

The effect of pumice on reduction of cadmium uptake by spinach irrigated with wastewater

Increasing demand for irrigation water and scarcity of fresh water has caused significant increase in the reuse of urban and industrial wastewater throughout the world. Heavy metals in wastewaters are the main factors in the contamination of water and soil. The objective of this study was to evaluate the effect of application of pumice as soil amendment on the uptake of Cd by spinach (Spinach oleracea L.) under irrigation with wastewater (containing 10mg/L Cd). The experiment was conducted as a completely randomized design in a greenhouse with 3 replications in the research station of Isfahan University of Technology. Different levels of pumice (0, 4% and 8% w/w soil) were added to the soil. Results indicated that the addition of 4% and 8% of pumice in soil, decreased 30.19% and 46.17% Cd uptake in plants, respectively. The transfer factor into roots and shoots of spinach were significantly reduced (p<0.05) in pumice treatments compared to the control. The percentage of DTPA extractable Cd in soils amended with pumice significantly decreased (p<0.05) and this resulted in lower Cd accumulation in plants. Irrigation with wastewater containing Cd decreased the yield in comparison to irrigation with freshwater. So, it seems that pumice, as a cost-effective adsorbent, poses potential for immobilization and reduction of phytoavailability of Cd in polluted soils.

Molecular cloning and functional analysis of spinach SoSMT2 in response to excess nitrate stress

Plant sterols are important multifunctional lipids, which are involved in determining membrane properties. Sterol C24 methyltransferase2 (SMT2) governs the pattern of phytosterols synthesized in higher plants. In this study, the spinach sterol C24 methyltransferase2 (SoSMT2) cDNA was cloned by RT-PCR and RACE-PCR. The full length of SoSMT2 consists of 1614bp, including a 278bp 5′-untranslated region (UTR), a 1086bp open reading frame (ORF), and a 250bp 3′-UTR. The SoSMT2 gene encodes a polypeptide of 361 amino acid residues with a predicted molecular mass of 40.47kDa. RT-PCR analysis indicated that the expression of SoSMT2 was induced by excess nitrate in the root and shoot of spinach. The transcript level of SoSMT2 was decreased by NaCl treatment. In contrast, dehydration, and H2O2 treatment increased the transcript levels of SoSMT2. To examine the biological roles of SoSMT2 in stress responses, transgenic Arabidopsis plants that constitutively overexpress SoSMT2 under the control of cauliflower mosaic virus 35S promoter were generated. The germination rate of transgenic seeds was higher than wild type (WT) in MS medium supplemented with 160mM nitrate. When seedlings were transferred to MS liquid medium with 160mM nitrate for 0, 8, 24 and 48h, the transgenic plants showed lower levels of MDA and H2O2 contents, compared with WT plants. Additionally, transgenic plants had relatively higher SOD, CAT and POD activities and soluble sugar contents than WT plants under nitrate stress with the increasing of treatment time. These data suggest that SoSMT2 is involved in nitrate tolerance in spinach.

Effects of sepiolite on stabilization remediation of heavy metal-contaminated soil and its ecological evaluation

Stabilization in the remediation of heavy metal contaminated soils has been gaining prominence because of its cost-effectiveness and rapid implementation. In this study, microbial properties such as microbial community and enzyme activities, chemical properties such as soil pH and metal fraction, and heavy metal accumulation in spinach (Spinacia oleracea) were considered in assessing stabilization remediation effectiveness using sepiolite. Results showed that soil pH values increased with rising sepiolite concentration. Sequential extraction results indicated that the addition of sepiolite converted significant amounts of exchangeable fraction of Cd and Pb into residual form. Treatments of sepiolite were observed to reduce Cd and Pb translocation from the soil to the roots and shoots of spinach. Concentrations of Cd and Pb exhibited 12.6%–51.0% and 11.5%–46.0% reduction for the roots, respectively, and 0.9%–46.2% and 43.0%–65.8% reduction for the shoots, respectively, compared with the control group. Increase in fungi and actinomycete counts, as well as in catalase activities, indicated that soil metabolic recovery occurred after sepiolite treatments.

RETRACTED ARTICLE: Effect of lead pollution on soil microbiological index under spinach (Spinacia oleracea L.) cultivation

Lead (Pb) pollution is appearing as an alarming threat nowadays in both developed and developing countries. Excessive Pb concentrations in agricultural soils result in minimizing the microbiological activities which leads to the decrease in crop production. A pot experiment was conducted with the purpose to examine the deleterious effect of Pb on microbiological index under spinach cultivation. Pb was added to 5 kg soil in each pot (with 6 seeds/pot) using Pb(NO3)2 at the rate of 0, 150, 300, 450, and 600 mg kg−1 with three replications in completely randomized design. All soil microbial, enzymatic, and chemical properties and plant growth parameters and nutrient uptake were measured by standard methods. Both soil and plant measured parameters decreased after the addition of Pb (150, 300, 450, and 600 mg Pb kg−1 soil) treatments with the passage of time (from 15 to 60 days) compared with control (CK). However, high Pb levels had more suppressive effect, therefore, highest Pb level (600 mg Pb kg−1 soil) significantly (P < 0.05) decreased the microbial biomass carbon (5.59-fold); microbial biomass nitrogen (N; 11.71-fold); microbial biomass phosphorus (P; 25.1-fold); dehydrogenase (4.02-fold); phosphatase (9.40-fold); urease (9.26-fold); pH (1.40-fold); spinach shoot (2.17-fold) and root (2.54-fold) length; shoot (2.36-fold) and root (2.69-fold) fresh weight; shoot (3.90-fold) and root (3.50-fold) dry weight; chlorophyll content (5.60-fold); carotenoid content (4.29-fold); plant macronutrients uptake, i.e., N (4.38- and 2.97-fold), P (3.88- and 6.58-fold), K (3.88- and 4.6-fold), Ca (6.60- and 6.70-fold), and Mg (5.57- and 4.45-fold); and plant micronutrient uptake, i.e., Zn (2.39- and 3.05-fold), Cu (3.70- and 2.62-fold), Fe (4.13- and 3.23-fold), and Mn (4.17- and 4.09-fold) in spinach shoot and root, respectively. Conversely, highest Pb level, i.e., 600 mg Pb kg−1 soil significantly (P < 0.05) increased the biomass carbon (C)/nitrogen (N) (4.69-fold) and C/P (6.01-fold) ratios, soil extractable Pb (5.87-fold), and Pb uptake in spinach shoot (3.58-fold) and root (4.38-fold), respectively, at the end of the experiment, i.e., day 60. Pb contamination significantly decreased the soil microbial and enzymatic activities, pH, spinach plant growth, and nutrients uptake in all the samples spiked with Pb. The degree of the influence increased with the increased Pb concentrations and incubation time, showing that Pb threshold is strongly associated with the extent of Pb concentration and time to accumulate. The soil microbial biomass, enzymatic activities, pH, and spinach physiological indices, could be used as a sensitive indicators to reflect environmental stress in soil ecosystems.

Effects of Graded Levels of Cadmium on Spinach and Cabbage Grown in an Inceptisol

Cadmium (Cd) contamination of the soil and its concentrations in spinach and cabbage were studied in a pot culture experiment. Eight levels of Cd (0–100 mg kg−1 soil) were applied singly. Application of Cd of up to 10 and 15 mg kg−1 resulted in safe Cd concentrations (1.56 and 1.38 mg kg−1) in the shoots of spinach and cabbage, respectively, at the consumable stage. The total chlorophyll content gradually decreased with the addition of Cd, and the maximum decreases were 31.7 and 32% in spinach and cabbage, respectively, at 60 days of crop growth in the treatment Cd100 over the control. The greatest diethylene triamine penta-acetic acid (DTPA)–extractable Cd contents in the postharvest soil of spinach and cabbage were 22.09 and 24.22 mg kg−1, respectively, in the treatment Cd100. The DTPA Cd was significantly negatively correlated with leaf area and total chlorophyll content while positively correlated with root and shoot Cd concentrations of spinach and cabbage.

Assessment of sepiolite for immobilization of cadmium-contaminated soils

The current study investigated the remediation effects of sepiolite on soils artificially polluted with cadmium (Cd) using a set of variables (soil pH, available Cd content, plant Cd concentration, soil enzyme activities, and microorganisms). Results showed that increasing pH after the application of sepiolite favored the stabilization of Cd as well as displayed a significant negative correlation between soil pH and extractable Cd concentration (P<0.05). Sepiolite addition (0.5%–5%) significantly inhibited Cd absorption in spinach shoots, resulting in from 28.0% to 63.7%, from 29.4% to 67.8%, and from 17.2% to 72.1% reductions, respectively, when compared with unamended soil. At 1.25mgkg−1 Cd contamination, the concentrations of Cd in the edible portions of spinach at 1% sepiolite amendment were lower than 0.2mgkg−1 fresh weight, the maximum permissible concentration (MPC) for Cd in vegetables. MPC was met at higher concentrations of Cd (2.5 and 5mgkg−1) when the treatment of sepiolite was up to 5%. The changes in soil enzymatic activities and microbial numbers proved that certain metabolic recovery occurred after the application of sepiolite. Sepiolite-assisted remediation was shown to reduce successfully, on a field scale, Cd entry into the food chain.

In situ stabilization remediation of cadmium contaminated soils of wastewater irrigation region using sepiolite

The effects of immobilization remediation of Cd-contaminated soils using sepiolite on soil pH, enzyme activities and microbial communities, TCLP-Cd (toxicity characteristic leaching procedure-Cd) concentration, and spinach (Spinacia oleracea) growth and Cd uptake and accumulation were investigated. Results showed that the addition of sepiolite could increase soil pH, while the TCLP-Cd concentration in soil was decreased with increasing sepiolite. The changes of soil enzyme activities and bacteria number indicated that a certain metabolic recovery occurred after the sepiolite treatments, and spinach shoot biomass increased by 58.5%–65.5% in comparison with the control group when the concentration of sepiolite was ⩽ 10 g/kg. However, the Cd concentrations in the shoots and roots of spinach decreased with an increase in the rate of sepiolite, experiencing 38.4%–59.1% and 12.6%–43.6% reduction, respectively, in contrast to the control. The results indicated that sepiolite has the potential for success on a field scale in reducing Cd entry into the food chain.

Water use efficiency and accumulation of trace elements in spinach (Spinacia oleracea L.) irrigated with municipal wastewater

The use of wastewater for irrigation is on the rise in developing countries like Pakistan, because of scarcity of good-quality irrigation water. Wastewaters contain plant nutrients that favor crop growth but leave a burden of heavy metals, which can enter the food chain, causing great concern. The present study was undertaken to investigate the effects of surface and subsurface wastewater irrigations on water use efficiency (WUE) and accumulation of trace elements (TE) in the shoots of spinach (Spinacia oleracea L.) grown on a soil column. Wastewater was applied at two levels based on daily pan evaporation (PE) (that is, 50 and 100%). Subsurface wastewater irrigation increased plant growth and WUE better than surface irrigation. Irrigation at 100% PE apparently reduced the WUE. However, WUE was enhanced by subsurface irrigation. Higher concentrations of TE were found in plants irrigated with 100% PE whether under surface or subsurface irrigation. Surface irrigation accumulated more TE in plants than subsurface irrigation. Slightly enhanced accumulation of TE was observed in the 2nd layer (30 to 60 cm) of the soil column under 100% surface irrigation. Subsurface irrigation gave higher concentrations of TE in the lower zone of the soil. Lower moisture was found in the top soil under both irrigation systems, but the middle soil layer had the highest electrical conductivity (EC). Irrigation with 100% PE increased EC more than 50% PE irrigation water. Surface irrigation with wastewater produced slightly greater pH than subsurface irrigation. Key words: Surface irrigation, subsurface irrigation, wastewater, spinach growth, trace elements.

Influence of nutrient level on methylmercury content in water spinach

Widely consumed vegetables are often cultivated in sewage waters with high nutrient levels. They can contain high levels of methylmercury (MeHg), because they can form MeHg from inorganic Hg in their young shoots. We determined whether the MeHg uptake and the MeHg formation in the shoots of water spinach (Ipomoea aquatica) were affected by the presence of a high nutrient level in the growth medium. Water spinach shoots were rooted and pretreated in growth medium containing 7% (low) or 70% (high) Hoagland nutrient solution; thereafter, the plants were treated with either 0.02 microM MeHg or 0.2 microM HgCl2 for 3 d. Half the plants were then analyzed for total Hg and MeHg. The remaining plants were transferred to mercury-free medium with low or high nutrient levels and posttreated for 3 days before analysis of total Hg and MeHg in order to measure MeHg formation in the absence of external Hg. The results indicate that nutrient level did not influence MeHg uptake, but that a high nutrient level reduced the distribution of MeHg to the shoots 2.7-fold versus low nutrient level. After treatment with HgCl2, MeHg was found in roots and new shoots but not in old shoots. The MeHg:total-Hg ratio was higher in new shoots than in roots, being 13 times higher at high versus low nutrient levels. Thus, MeHg formation was the same in new shoots independent of inorganic Hg concentration, since the total Hg level decreased at a high nutrient level.

Cadmium, Nickel, Chromium, and Lead Levels in Soils and Vegetables under Long‐Term Irrigation with Industrial Wastewater

: The industrial activity areas, rivers, and water sources in neighboring areas are influenced by wastewater of manufacturers. Utilizing water influenced by wastewater increased heavy metals in soils and plants. In 2004, to investigate the effects of wastewater on cadmium (Cd), nickel (Ni), chromium (Cr), and lead (Pb) content in soil and plants, wastewaters of three manufactures (chrome chemical, wood and paper, and textiles) were examined. At harvest time roots, whole shoots (rice, spinach, clover, grass), and rice grain in industrial wastewater–influenced areas and uninfluenced areas were sampled. Soil samples were also taken (0–15, 15–30 cm). Results indicated that when wastewater was discharged into the river water, the concentrations of Cd, Ni, Cr, and Pb increased in river water. Application of river water influenced by industrial wastewater for irrigation of rice and another plants enhanced, the amounts of available Cd, Ni, Cr and Pb in soil. In subsurface horizons (15–30 cm), the concentrations of heavy metals were more than in the surface horizon (0–15 cm). With increasing cation exchange capacity in the soil, the amount of available Cr increased. When the calcium carbonate content in soils was raised, the available Cd and Pb increased in the soil, but Ni and Cr decreased. Meanwhile, organic matter enhanced the concentrations of heavy metals in soil. Accumulations of heavy metals were higher in the roots of rice (control and treatment) than in shoot and rice grain. Cadmium accumulation in rice root was three times that in whole shoot, and grain was two times more than control. The concentrations of Ni, Cr, and Pb in root, whole shoot, and grain of rice were two times higher in industrial wastewater–treated areas. The concentrations of heavy metals in root and whole shoot of spinach, clover, and grass in industrial wastewater area increased about 100%, but not to a toxic level. Cadmium translocated more than other heavy metals from soil to root, whole shoot, and grain of rice, and whole shoot of spinach, clover, and grass.

Effects of Long‐Term Irrigation using Industrial Wastewater on Soil Properties and Elemental Contents of Rice, Spinach, Clover, and Grass

Application of industrial wastewater on agricultural lands increased the amounts of elements in soil and plants. To investigate the effects of wastewater on soil properties and element content in soil and plants, wastewaters of three industries (chrome chemical, wood and paper, and textiles) were examined in 2005. At harvest time, the soil samples were taken from depths of 0–15 and 15–30 cm, and the roots and shoots of rice, spinach, clover, and grass and grain of rice in an industrial wastewater–treated area and untreated area were sampled. Results indicated that the concentrations of zinc (Zn), copper (Cu), manganese (Mn), and iron (Fe) increased in river water when wastewater was discharged into it. Use of the river water, influenced by industrial wastewater, for irrigation of rice and other plants increased the amounts of organic matter and available Zn, Cu, Mn, and Fe in soil. Cation exchange capacity was correlated with available Cu and Fe in soil (+0.431** and +0.499**, respectively). Soil organic matter was correlated with available Zn, Cu, Mn, and Fe in soil. However, the clay content in soil did not correlate with these elements. Meanwhile, in roots, shoots, and grains of rice and roots and shoots of spinach, clover, and grasses of agricultural land influenced by industrial wastewater, the amounts of Zn, Cu, Mn, and Fe increased. Therefore, by increasing the amount of Mn in the soil, the concentration of Zn in rice grain decreased and the concentration of Cu and Mn increased. Transferred Zn concentrations to rice grain and shoots of spinach, clover, and grass were more than Cu and Mn and increased in rice grain.

Influence of phosphorus application on growth and cadmium uptake of spinach in two cadmium‐contaminated soils

AbstractA pot experiment was conducted to investigate the influence of phosphate (P) application on diethylene triamine pentaacetic acid (DTPA)–extractable cadmium (Cd) in soil and on growth and uptake of Cd by spinach (Spinacia oleracea L.). Two soils varying in texture were contaminated by application of five levels of Cd (NO3)2 (0, 20, 30, 40, and 60 mg Cd kg–1). Three levels of KH2PO4 (0, 12, and 24 mg P kg–1) were applied to determine immobilization of Cd by P. Spinach was grown for 60 d after seeding. Progressive contamination of soils through application of Cd affected dry‐matter yield (DMY) of spinach shoot differently in the two soils, with 67% reduction of DMY in the sandy soil and 34% in the silty‐loam soil. The application of P increased DMY of spinach from 4.53 to 6.06 g pot–1 (34%) in silty‐loam soil and from 3.54 to 5.12 g pot–1 (45%) in sandy soil. The contamination of soils increased Cd concentration in spinach shoots by 34 times in the sandy soil and 18 times in the silty‐loam soil. The application of P decreased Cd concentration in shoot. The decrease of Cd concentration was higher in the sandy soil in comparison to the silty‐loam soil. Phosphorus application enhanced DMY of spinach by decreasing Cd concentration in soil as well as in plants. The results indicate that Cd toxicity in soil can be alleviated by P application.

The influence of plant growth–promoting rhizobacteria on growth and enzyme activities in wheat and spinach plants

AbstractA pot experiment in a greenhouse was conducted in order to investigate the effect of different N2‐fixing, phytohormone‐producing, and P‐solubilizing bacterial species on wheat and spinach growth and enzyme activities. Growth parameters and the activities of four enzymes, glucose‐6‐phosphate dehydrogenase (G6PD; EC 1.1.1.49), 6‐phosphogluconate dehydrogenase (6PGD; EC 1.1.1.44), glutathione reductase (GR; EC 1.8.1.7), and glutathione S‐transferase (GST; EC 2.5.1.18) were determined in the leaves of wheat (Triticum aestivum L., Konya) and spinach (Spinacia oleracea L.), noninoculated and inoculated with nine plant growth–promoting rhizobacteria (PGPR: Bacillus cereus RC18, Bacillus licheniformis RC08, Bacillus megaterium RC07, Bacillus subtilis RC11, Bacillus OSU‐142, Bacillus M‐13, Pseudomonas putida RC06, Paenibacillus polymyxa RC05 and RC14). Among the strains used in the present study, six PGPR exhibited nitrogenase activity and four were efficient in phosphate solubilization; all bacterial strains were efficient in indole acetic acid (IAA) production and significantly increased growth of wheat and spinach. Inoculation with PGPR increased wheat shoot fresh weight by 16.2%–53.8% and spinach shoot fresh weight by 2.2%–53.4% over control. PGPR inoculation gave leaf area increases by 6.0%–47.0% in wheat and 5.3%–49.3% in spinach. Inoculation increased plant height by 2.2%–24.6% and 1.9%–36.8% in wheat and spinach, respectively. A close relationship between plant growth and enzyme activities such as G6PD, 6PGD, GR, and GST was demonstrated. Plant‐growth response was variable and dependent on the inoculant strain, enzyme activity, plant species, and growth parameter evaluated. In particular, the N2‐fixing bacterial strains RC05, RC06, RC14, and OSU‐142 and the P‐solubilizing strains RC07 and RC08 have great potential in being formulated and used as biofertilizers.

Regulation of gibberellin 20-oxidase1 expression in spinach by photoperiod

The multifunctional gibberellin (GA) 20-oxidase [GA(53), 2-oxoglutarate:oxygen oxidoreductase (20-oxidizing), EC 1.14.11] has been extensively investigated in various species at the genetic and molecular levels, but not at the protein level. Here, we report on expression of GA20ox1 protein in spinach (Spinacia oleracea L.) in response to photoperiod. Polyclonal antibodies were raised against recombinant SoGA20ox1 in a chicken. These antibodies immuno-inhibited the enzymatic activity of the recombinant SoGA20ox1 and immuno-precipitated SoGA20ox1 (43 kDa) isolated from spinach shoot tips. Northern and western analyses showed that the levels of SoGA20ox1 transcript and protein increased in the blades, petioles, young leaves, and tips in response to long-day (LD) conditions. The transcript and protein levels of the SoGA20ox1 gene were up-regulated in the petioles and tips in a time-dependent manner. The estimated number of SoGA20ox1 protein molecules per cell was approximately 13-fold higher in tips grown in LD than in short-day (SD) conditions. The levels of SoGA20ox1 protein gradually decreased in tips when spinach plants grown in LD were transferred to SD conditions. SoGA20ox1 transcripts were detected by in situ hybridization in rapidly growing tissues--such as the shoot apical meristem, leaf and flower primordia, leaflets, and vascular tissues--but not in the expanding subapical region. In petioles, expression of SoGA20ox1 was detected in the companion cells.

In Vitro Flowering in Regenerated Shoots of Spinach.

In Vitro Flowering in Regenerated Shoots of Spinach.

Continuous shoot growth monitoring in hydroponics

A weighing apparatus for automatic recording of fresh weight of shoots of spinach plants (Spinacia oleracea L., cv. Subito) growing in nutrient solution is described. The system was tested for 17 days in a controlled environment and enabled the determination of the relative growth rate (RGR) of the shoot fresh weight. Results from three consecutive growth experiments demonstrated diurnal fluctuations in the relative growth rate of the shoot fresh weight. In general, relative growth rates were between 0.32 and 0.36 day−1 16 days after sowing and decreased to between 0.11 and 0.18 day−1 during the 12 following days. The variance between three replicate growth curves was compared with the variance of a growth function fitted through destructively obtained spinach shoot weight data.

Daily changes in uptake, reduction and storage of nitrate in spinach grown at low light intensity

Under poor light conditions, as normally used during winter production of greenhouse vegetables, the nitrate concentration in the shoot of spinach (Spinacia oleraceaL. cv. Vroeg Reuzenblad) showed a diurnal rhythm. This rhythm was mainly caused by a decrease during the day, followed by an increase during the night in the leaf blade nitrate concentration. Nitrate was mainly located in the vacuoles of the leaf blades. A strong correlation was found between net uptake of nitrate by the roots and the nitrate concentration in the leaf blade vacuoles. The nitrate concentration in the leaf blades increased during the initial hours of the night. This increase was caused by a marked increase in the net uptake rate of nitrate by the roots during the first hours of the dark period. During the second part of the night both net uptake rate of nitrate by the roots and the vacuolar nitrate concentration in the leaf blades remained constant.We conclude that nitrate is taken up for osmotic purposes when light conditions are poor because of a lack of organic solutes. During the night, nitrate influx into the vacuole is needed for replacement of organic solutes, which are metabolized during the night, and possibly also for leaf elongation growth. During the day, vacuolar nitrate may be exchanged for newly synthesized organic solutes and be metabolized in the cytoplasm. A strong diurnal rhythm in nitrate reductase (NR; EC 1.6.6.1.) activity was absent, due to the poor light conditions, and in vitro NR activity was not correlated with nitrate flux from the roots. In vivo NR activity also lacked a strong diurnal rhythm, but it was calculated that in situ nitrate reduction was much lower during the night, so that the major nitrate assimilation took place during the day.

The effect of short‐term H2S fumigation on water‐soluble sulphydryl and glutathione levels in spinach

Abstract. Short‐term fumigation of Spinacia oleracea with 380 μg m−3 H2S (250 ppb) resulted in a rapid accumulation of water‐soluble SH‐compounds in the shoots. After 1 h exposure a substantial increase in the SH‐content was already detectable and maximal accumulation, three‐ to four‐fold that in control plants, was observed after 24 h of exposure. Irradiation during H2S exposure only slightly affected the rate and level of SH‐accumulation. H2S fumigation did not affect the water‐soluble SH‐content of the roots. Glutathione was the sole water‐soluble SH‐compound accumulating upon exposure to H2S. It was calculated that during the first hour of exposure to 380 μg m−3 H2S 39% of the possible absorbed H2S was converted into glutathione. The SH‐content of the water‐soluble proteins of the shoots was not affected by H2S exposure. When fumigation was stopped, a rapid decrease in glutathione content was observed and after 48 h the content was comparable to that of the control plants. Contrary to H2S, SO2 fumigation did not result in a rapid accumulation of glutathione in spinach shoots. The possible role of glutathione accumulation during H2S fumigation is discussed.

Photoperiodic Control of Gibberellin Metabolism in Spinach

[(3)H]GA(20) applied to spinach plants (Spinacia oleracea L.) was metabolized to several products. Two of these were identified by combined gasliquid chromatography-radio counting as [(3)H]GA(29) and [(3)H]3-epi-GA(1). Inasmuch as both GA(20) and GA(29) are endogenous gibberellins in spinach (Metzger, Zeevaart 1980 Plant Physiol 65: 623-626), it was concluded that the conversion of GA(20) to GA(29) is a natural process. However, 3-epi-GA(1) was not detected in extracts of spinach shoots analyzed by combined gas chromatography-mass spectrometry. This indicates that the conversion of exogenous [(3)H]GA(20) to [(3)H]3-epi-GA(1) may be an artifact.Long-day pretreatment of spinach shoots caused a 2-fold increase in the rate of [(3)H]GA(20) metabolism over the rate of metabolism in plants maintained under short-day conditions. Furthermore, [(3)H]GA(29) accumulated more rapidly under long than under short days, whereas photoperiodic treatment had no effect on the accumulation of [(3)H]3-epi-GA(1). Thus, the long-day-induced increase in the level of endogenous GA(29) in spinach shoots (Metzger, Zeevaart 1980 Plant Physiol 66: 844-846) appears to be the result of an increased capability to convert GA(20) to GA(29).

Comparison of the Levels of Six Endogenous Gibberellins in Roots and Shoots of Spinach in Relation to Photoperiod

This communication describes the distribution of gibberellins (GAs) in roots and shoots of spinach in relation to photoperiod. From previous work (Metzger, Zeevaart 1980 Plant Physiol 65: 623-626) shoots were known to contain GA(53), GA(44), GA(19), GA(17), GA(20), and GA(29). We now show by combined gas chromatography-mass spectrometry that roots contain GA(44), GA(19), and GA(29). Trace amounts of GA(53) were detected by combined gas chromatography-selected ion current monitoring. Neither GA(17) nor GA(20) were detected in root extracts. Analysis by the d-5 corn bioassay also showed no effect of photoperiodic treatment on the levels of GA-like substances in root extracts. Both phloem and xylem exudates had patterns of GA-like activity similar to those found in shoots and roots, respectively. Moreover, foliar application of [(3)H]GA(20) resulted in the transport of label from the shoot to the roots. Over half of the label in the roots represented unmetabolized [(3)H]GA(20), indicating that part of the GA(20) in the phloem is transported to the roots. Consequently, if GA(20) is made in, or transported to the roots, it is rapidly metabolized in that organ. This is a clear indication that regulation of GA metabolism is greatly different in roots and shoots.