Effect of Prolonged Geo-stimulation and Presence of 32P on the Elongation of Lateral Shoots of Decapitated Pea Seedlings

The effects of prolonged geo-stimulation and presence of ³²P on 3-leaf decapitated pea (Pisum sativum L. cv. Alaska) seedlings were studied with regard to lateral bud elongation as well as accumulation and recovery of isotope. Prolonged geo-stimulation favoured the dominance of basally located, upwardly directed buds and suppressed the elongation of subapical bud — a gravimorphic response similar to the one shown by intact geo-stimulated branches of woody plants. Basal bud 2 was an exception as it dominated both in the above- and below-axis position. Accumulation of ³²P in buds was the result of their own growth, whereas in the other parts of the seedlings accumulation of isotope was not necessarily related to growth. Geo-stimulation affected ³²P recovery in redistribution experiments, whereas it had no effect in distribution experiments. In the former, the decrease in the isotope level in the seedling suggests a loss of ³²P. Prolonged presence of ³²P in the seedlings had a deleterious effect on bud elongation.     

Maintenance of 32P uptake and transport in Pinus serotina seedlings under hypoxic growth conditions

In the present study, we examined the effects of long- and short-term hypoxia on net uptake and transport of phosphorus to shoots of pond pine (Pinus serotina Michx.), a moderately flood-tolerant southern pine, and the influence aerenchyma formation might have in maintenance of P uptake and transport. Seedlings were grown under aerobic (250 μM O₂) or hypoxic (≤50 μM O₂) solution conditions for 5.3 weeks in continuously flowing solution culture containing 100 μM P. Intact seedlings were then labeled with ³²P for up to 24 h to determine how short- and long-term hypoxic solution conditions affected rates of unidirectional influx and the accumulation of ³²P in roots and shoots. Seedlings in the long-term hypoxic treatment were grown for 5.3 weeks in hypoxic solution and also labeled in hypoxic uptake solution. The short-term hypoxic treatments included a 24-h hypoxic pretreatment followed by time in labeled hypoxic uptake solution for seedlings grown under aerobic or hypoxic conditions; in the latter case, diffusion of atmospheric O₂ entry into stem and root collar lenticels was blocked, thus removing any influence that aerenchyma formation might have had on enhancing O₂ concentrations of root tissue. Although unidirectional influx rates of ³²P in roots of seedlings grown under long-term hypoxic conditions were 1.4 times those of aerobically grown seedlings, accumulation of ³²P in roots was similar after 24 h in labeled uptake solution. These results suggest that ³²P efflux was also higher under hypoxic conditions. Higher shoot/root fresh weight ratios and lower shoot P concentrations in seedlings grown under hypoxic solution conditions suggest that the “shoot P demand” per unit root should be high. Yet accumulation of ³²P in shoots was reduced by 50% after 24 h in hypoxic uptake solution. Both short-term hypoxic treatments decreased accumulation of ³²P in roots by more than 50%. Short-term hypoxia decreased shoot accumulation in seedlings grown under aerobic and hypoxic conditions by 84 and 50%. respectively. Short- and long-term hypoxic conditions increased the percentage of root ³²P in the nucleic acid and chelated-P pools, resulting in a significantly smaller percentage of ³²P in the soluble inorganic phosphate (p_i) pool, the pool available for transport to the shoot. However, a reduction in pool size or in labeling of the pool available for transport cannot fully account for the large reduction in accumulation of ³²P in shoots, particularly in the short-term hypoxic treatment of aerobically grown seedlings. Our results suggest that both influx and transport of ³²P to shoots of pond pine seedlings are O₂-dependent processes, and that the transport of ³²P to shoots may be more sensitive to hypoxic solution conditions than influx at the cortical and epidermal plasmalemma, with aerenchyma formation supporting a substantial amount of both ³²P uptake and transport.     

Phosphorus nutrition of barley, buckwheat and rape seedlings. I. Influence of seed-borne P and external P levels on growth, P content and 32P/31P-fractionation in shoots and roots

Schjørring, J. K. and Jensén, P. 1984. Phosphorus nutrition of barley, buckwheat and rape seedlings. I. Influence of seed-borne P and external P levels on growth, P content and ³²P/³¹P-fractionation in shoots and roots. Seedlings of barly (Hordeum vulgare L. cvs Salka and Zita), buckwheat (Fagopyrum esculentum Moench) and rape (Brassica napus L. ssp. napus ev. Line) were grown at 8 or 10 different external P levels in the range 0-2000 μM. Apart from P, the nutrient solutions were complete. In some experiments with barley and rape, ³²P-labelled phosphate was used. Root fresh weights of buckwheat and rape decreased when the external P supply exceeded the level required for maximal root development. In all three species, the roots constituted a decreasing proportion of the total plant fresh weight as the external P level increased. The shoot/root fresh weight ratio increased linearly with the P concentration of the roots. The ratio between the P concentration in shoots and roots increased with the P status of the seedlings grown at low to intermediate external P levels, but decreased at higher P levels. The proportion of total seedling-P held in roots consequently reached a minimum value and thereafter increased as the P status of the seedlings increased. This indicates that some control mechanism counteracted the accumulation of harmful P levels in the shoots. ³²P-Phosphate uptake by seedlings of barley and rape grown in solutions with 2 μM P overestimated the actual net phosphorus uptake by a factor of 6 to 7, indicating a marked fractionation of ³²P and ³¹P. For seedlings grown in solutions with 25 μM P (barley) or 50 μM (rape) no fractionation occurred. The relative excess of ³²P in high P seedlings accumulated in the roots. It is suggested that the fracionation was caused by efflux of low specific activity phosphorus and by diffusion of free phosphate ions across the plasmalemma of the root cells in response to a difference in the concentration gradient between the two P isotopes.     

Seed source variation in 32P uptake in inus taeda L. seedlings: A possible regulation by efflux

Short-term ³²P uptake experiments were conducted with intact seedlings of loblolly pine (Pinus taeda L.) to examine possible seed source variation in net accumulation of ³²P in roots and shoots, and in rates of unidirectional influx. Seed source had a highly significant effect on biomass and P concentrations of shoots and roots. Seedlings from two seed sources representing fast-growing populations (a broadly-adapted and wet-site seed source) accumulated over 60% more total seedling P than smaller seedlings from a drought-hardy seed source, reflecting higher biomass and root P concentrations. Rates of unidirectional ³²P influx in seedlings from the drought-hardy seed source were more than twice the rates of the seedlings from the broadly-adapted seed source. However, after 24 h in labeled uptake solution, net accumulation of ³²P was similar, suggesting that rates of unidirectional efflux from roots of the drought-hardy seed source were also high. Although there were no significant differences in biomass and tissue P concentrations between the two fast-growing seed sources, rates of unidirectional influx in seedlings from the broadly-adapted seed source were 42% lower than rates in seedlings from the wet-site source. Yet, after 24 h in labeled uptake solution, net accumulation of ³²P in seedlings from the broadly-adapted seed source was 50% higher. Unidirectional efflux out of the root may regulate net uptake of P as much, if not more, than influx in loblolly pine seedlings-at least under high-P growth conditions. The results in this study do not support previous studies with herbaceous plants suggesting that fast-growing species typically exhibit higher rates of nutrient uptake than slow-growing species.     

32P uptake and transport to shoots in Pinuus serotina seedlings under aerobic and hypoxic growth conditions

We examined the effects o long-term hypoxic growth conditions on net uptake and transport of P to shoots of pond Pine (Pinus serotina Michx.), a moderately flood-tolerant southern pine. Seedlings were grown under aerobic orhypoxic solution conditions for 4–5 weeks in continuously flowing solution culture containing 100 μM P. Short – and long-term ³²P. experiments were then concluded with intact seedlings to determine rates of ³²P influx, efflux and net transport to the shoot. Shoot fresh weight/root fresh weight ratios were significantly higher under hypoxic gorwth conditions, reflecting the larger reduction in root growth than shoot growth, despite extensive aerechyma formation in roots. Estimates for the unidirectional influx of ³²P in aerobic and hypoxic seedlings were 1.43 and 3.20 μmol P (g_FW root)_?1 h_?1, respectively. However, ³²P accumulation between the two treatments became similar within 8 h, suggesting that efflux was also higer in seedlings from the hypoxic treatment. Indeed in a separate experiment, hypoxic growth conditions increased efflux by over 60%. Transport of ³²P to shoots was significantly reduced under hypoxic growth conditions, despite higher root P concentrations and lower shoot P concentrations. After 48 h, ³²P accumulation in roots was similar between the two treatments. Yet total accumulation of seedling ³²P decrcased by 31% under the hypoxic treatment, largely because of reduced transport of ³²p to the shoot. The lower accumulation of ³² by shoots of seedlings in the hypoxic treatment may be the result of a direct inhibition on the transport process in O²-defident tissues, but could also reflect a slower turnover or labeling of the ool available for transport. Indeed, the percentage of total ³²P in. roots present in the soluble P. (or transportable form of P) was about 33% lower in seedlings from the hypoxic treatment, probably reflecting increased assimilation into organic compounds as well as chelation with iron. Our results suggest that P transport to the shoots of acclimated seedlings may be more sensitive to hypoxic solution conditions than influx at the root Plasmalemma.     

Accumulation of 32P and [14C]sucrose in decapitated and intact shoots of the fern Davallia trichomanoides blume

The transport and accumulation of ³²P and [¹⁴C] sucrose in decapitated and intact shoot segments of the fern Davallia were studied. The apical buds of intact shoots and the expanding buds of shoots decapitated 4 weeks before application are major sinks for these nutrients. Decapitation results in a shift of ¹⁴C accumulation from the apex to the lateral buds within 36 h. This shift can be reversed in shoots decapitated for 12 h by replacing the apex. Increased ¹⁴C accumulation into the stump region occurs when decapitated shoot segments are treated with indole-3-acetic acid, and decreased label accumulation into the apical region results when intact shoots are treated with 2,3,5-triiodobenzoic acid.     

Tissue partitioning of cadmium in transgenic tobacco seedlings and field grown plants expressing the mouse metallothionein I gene

Since agricultural crops contribute >70% of human cadmium (Cd) intake, modification of crops to reduce accumulation of this pollutant metal during plant growth is desirable. Here we describe Cd accumulation characteristics of seedlings and field grown tobacco plants expressing the Cd-chelating protein, mouse metallothionein I. The objective of the transformation is to entrap Cd in roots as Cd-metallothionein and thereby reduce its accumulation in the shoot. Transformed and control seedlings were exposed for 15 days in liquid culture at a field soil-solution-like Cd concentration of 0.02 μm. Transformed seedlings ofNicotiana tabacum cultivar KY 14 contained about 24% lower Cd concentration in shoots and about 5% higher Cd concentration in roots than control seedlings. Dry weights of transformed and control tissues did not differ significantly. In the field in 1990, mature transformedN. tabacum cv. KY 14 plants exposed only to endogenous soil Cd contained about 14% lower leaf lamina Cd concentration than did controls. Differences were significant at thep≤0.1 level in 13 of 16 leaf positions. Leaf dry weight did not differ significantly but transformed field plants had 12% fewer leaves and were 9% shorter than the controls. Copper (Cu) concentration was significantly higher (ca10%) in the bottom nine leaf positions of transformed plants suggesting that reduced leaf number and plant height may be due to Cu deficiency or toxicity. Alternatively, somaclonal variation or gene position effects may be involved. No differences were found in zinc levels. WithN. tabacum cv. Petit Havana, transformed seedlings contained no less Cd in shoots but 48% higher Cd concentration in roots. However, dry weights of shoots and roots of transformed seedlings were 25% and 26%, respectively, greater than in controls. In the field, transformed and control plants of this cultivar showed little significant differences in leaf Cd content, plant height or leaf number. Although comparison of additional metallothionein-expressing tobaccos and other plants is needed, results obtained with cultivar KY 14 support the hypothesis that sequestration of Cd in roots as Cd-metallothionein may have potential for reducing Cd content of above root tissues of certain plants.     

Effect of auxin on the elongation of lateral buds and32P accumulation in 2-leaf decapitated pea seedlings

The effect of short and long term auxin treatments on the elongation of axillary buds and³²P accumulation were studied in 2-leaf decapitated Alaska pea sailings. It was found that (1) auxin delayed the elongation of the lateral buds, (2) none of the auxin concentration applied completely inhibited the elongation of axillary buds, (3) auxin had no retarding effect on the growing buds, (4) strong polarization of 32P occurred in the parts above the treated leaf, when auxin was applied for a short period just after decapitation, (5) long term auxin treatments did not induce any such polarization of 32P to the parts above the treated leaf, (6) the root acted as an alternate accumulating organ for 32P when the apex was removed and the buds were inhibited, and (7) in decapitated plants the growing buds polarized 32P.     

Influence of external zinc and phosphorus supply on Cd uptake by rice (Oryza sativa L.) seedlings with root surface iron plaque

Rice seedlings were grown in hydroponic culture to determine the effects of external Zn and P supply on plant uptake of Cd in the presence or absence of iron plaque on the root surfaces. Iron plaque was induced by supplying 50 mg l⁻¹ Fe²⁺ in the nutrient solution for 2 day. Then 43-day-old seedlings were exposed to 10 μmol l⁻¹ Cd together with 10 μmol l⁻¹ Zn or without Zn (Zn–Cd experiment), or to 10 μmol l⁻¹ Cd with 1.0 mmol l⁻¹ P or without P (P–Cd experiment) for another 2 day. The seedlings were then harvested and the concentrations of Fe, Zn, P and Cd in dithionite–citrate–bicarbonate (DCB) extracts and in roots and shoots were determined. The dry weights of roots and shoots of seedlings treated with 50 mg l⁻¹ Fe were significantly lower than when no Fe was supplied. Adsorption of Cd, Zn and P on the iron plaque increased when Fe was supplied but Cd concentrations in DCB extracts were unaffected by external Zn or P supply levels. Cd concentrations in shoots and roots were lower when Fe was supplied. Zn additions decreased Cd concentrations in roots but increased Cd concentrations in shoots, whereas P additions significantly increased shoot and root Cd concentrations and this effect diminished when Fe was supplied. The percentage of Cd in DCB extracts was significantly lower than in roots or shoots, accounting for up to 1.8–3.8% of the plant total Cd, while root and shoot Cd were within the ranges 57–76% and 21–40% respectively in the two experiments. Thus, the main barrier to Cd uptake seemed to be the root tissue and the contribution of iron plaque on root surfaces to plant Cd uptake was minor. The changes in plant Cd uptake were not due to Zn or P additions altering Cd adsorption on iron plaque, but more likely because Zn or P interfered with Cd uptake by the roots and translocation to the shoots.     

The phytoprotective effects of arbuscular mycorrhizal fungi on Enterolobium contorstisiliquum (Vell.) Morong in soil containing coal-mine tailings

The purpose of this study was to evaluate the effects of arbuscular mycorrhizal fungi (AMF) on pacara earpod tree (Enterolobium contorstisiliquum) growth and phytoprotection in soil containing coal-mining waste. A greenhouse experiment was carried out with three inoculation treatment groups (non-inoculated, inoculated with Rhizophagus clarus, and inoculated with Acaulospora colombiana) in two substrates (0 or 30% tailings). After 90 days the seedlings were collected to quantify growth parameters, quality, mycorrhizal root colonization rate, and leaf content of chlorophylls and carotenoids. Macronutrients were quantified in the shoots; Cu, Zn, and Mn levels were measured in the shoots and roots; and glomalin content was measured in the rhizosphere. Colonization by A. colombiana (40%) promoted phytoprotection and better growth in seedlings planted in partial tailing substrate, due to the lower Cu (1.04 mg kg^?1) and Zn (13.4 mg kg^?1) levels in shoot dry mass and reduced translocation of these elements to the shoots. A. colombiana increased soil glomalin concentrations (2.98 mg kg^?1) and the accumulation of nutrients necessary for synthesizing chlorophylls and carotenoids in the leaves. Colonization by R. clarus (81%) produced no phytoprotective effects.     

Plant regeneration from different explants of neem

When different seedling explants, i.e. hypocotyl, epicotyl, cotyledonary node, root-shoot zone, cotyledon, leaves and roots from 7-day-old seedlings of neem were cultured on Murashige and Skoog's medium supplemented with 2 mg l⁻¹ benzyladenine and 0.1 mg l⁻¹indole-3-acetic acid, shoot buds were initiated from all the explants tested, with leaf explants producing the highest average number of shoots/explant. The regenerated shoots were further subcultured and later could be rooted on a medium supplemented with indole butyric acid (1 mg l⁻¹) and complete plants could be obtained. This revised version was published online in June 2006 with corrections to the Cover Date.     

Mechanisms for tolerance of very high tissue phosphorus concentrations in Ptilotus polystachyus

Study of plants with unusual phosphorus (P) physiology may assist development of more P‐efficient crops. Ptilotus polystachyus grows well at high P supply, when shoot P concentrations ( [P] ) may exceed 40 mg P g^?1 dry matter (DM). We explored the P physiology of P. polystachyus seedlings grown in nutrient solution with 0–5 mM P. In addition, young leaves and roots of soil‐grown plants were used for cryo‐scanning electron microscopy and X‐ray microanalysis. No P‐toxicity symptoms were observed, even at 5 mM P in solution. Shoot DM was similar at 0.1 and 1.0 mM P in solution, but was ～14% lower at 2 and 5 mM P. At 1 mM P, [P] was 36, 18, 14 and 11 mg P g^?1 DM in mature leaves, young leaves, stems and roots, respectively. Leaf potassium, calcium and magnesium concentrations increased with increasing P supply. Leaf epidermal and palisade mesophyll cells had similar [P]. The root epidermis and most cortical cells had senesced, even in young roots. We conclude that preferential accumulation of P in mature leaves, accumulation of balancing cations and uniform distribution of P across leaf cell types allow P. polystachyus to tolerate very high leaf [P].     

Phosphorus export from roots to shoots of barley, buckwheat and rape seedlings with different P status

Seedlings of barley (Hordeum vulgare L. cvs Salka and Zita), buckwheat (Fagopyrum esculentum Moench) and rape (Brassica napus L. ssp. napus cv. Line) were grown in complete nutrient solutions with 8 or 10 different P concentrations in the range of 0–2 mM. Phosphate export from roots to shoots was determined from the amount of ³²P (or ³³P) absorbed and exported to shoots in 1 h from a nutrient solution containing 0.1 mM radiolabelled phosphate. P export was also determined in the presence of a metabolic uncoupler (DNP, 2.4-dinitrophenol) and a protein synthesis inhibitor (CH, cycloheximide). Phosphorus export from roots to shoots reached a maximum at a certain optimum level of phosphorus in shoots and roots, and decreased at both higher and lower P levels. Maxinmm P export was 1.7 ± 0.2 and 4.5 ± 0.5 (mean ±se of the three species) times higher than the P export at the lowest and highest [P]_root, respectively. Hill plots as well as plots of the untransformed decreasing P export vs root or shoot P concentrations above the optimum were linear and had high correlation coefficients. The Hill coefficient (n_H) based on [P]_root, was —7.7 for barley cv. Salka and varied between -3.8 and -4.5 for the other species. Based on [P]_shootot n_H was—16.1 for barley cv. Salka, -3.7 for barley cv. Zita and -6.4 for the two dicotyledonous species. Relative to the amount of P simultaneously absorbed by the root system, the import of P per unit shoot weight decreased linearly over the whole range of shoot P concentrations in the dicotyledonous species. In contrast, the relative import of P per unit shoot weight of the two barley cultivars increased at low levels of [P]_shoot and decreased at higher levels. DNP and CH almost eliminated P export from roots to shoots of seedlings with low or high P status. In seedlings with medium P status only 60 to 75% of the P export was affected.     

Cysteine, gamma-Glutamylcysteine, and Glutathione Levels in Maize Seedlings : Distribution and Translocation in Normal and Cadmium-Exposed Plants

The levels of cysteine (Cys), γ-glutamylcysteine (γEC), and glutathione (GSH) were measured in the endosperms, scutella, roots, and shoots of maize (Zea mays L.) seedlings. GSH was the major thiol in roots, shoots, and scutella, Cys predominated in endosperms. The endosperm, scutellum, and functional phloem translocation were required for maintenance of GSH pools in roots and shoots of 6-day-old seedlings. Exposure of roots to 3 micromolar Cd, besides causing a decline in GSH, caused an accumulation of γEC, as if the activity of GSH synthetase was reduced in vivo. [³⁵S]Cys injected into endosperms of seedlings was partly metabolized to [³⁵S]sulfate. The scutella absorbed both [³⁵S]sulfate and [³⁵S]Cys and transformed 68 to 87% of the radioactivity into [³⁵S]GSH. [³⁵S]GSH was translocated to roots and shoots in proportion to the tissue fresh weight. Taken together, the data supported the hypothesis that Cys from the endosperm is absorbed by the scutellum and used to synthesize GSH for transfer through the phloem to the root and shoot. The estimated flux of GSH to the roots was 35 to 60 nanomoles per gram per hour, which totally accounted for the small gain in GSH in roots between days 6 and 7. For Cd-treated roots the GSH influx was similar, yet the GSH pool did not recover to control levels within 24 hours. The estimated flux of GSH to the entire shoot was like that to the roots; however, it was low (11-13 nanomoles per gram per hour) to the first leaf and high (76-135 nanomoles per gram per hour) to the second and younger leaves.     

Effect of calcium chloride on heavy metal induced alteration in growth and nitrate assimilation of Sesamum indicum seedlings

In the early growth phase of Sesamum indicum cv. PB-1, the decrease in fresh and dry mass was higher with 1.0 mM Cd²⁺ than with the same level of Pb²⁺ and Cu²⁺. Recovery from the metal stress was considerable in the root fresh weight and almost completely in the root dry weight when 10.0 mM (1.9 EC), calcium chloride was supplied to the growing seedlings along with the metal salts in various combinations. Accumulation of Pb²⁺, Cd²⁺ and Cu²⁺ was differential to the metals and the plant parts when supplied without or with 10.0 mM calcium chloride. The order of endogenous metal accumulation was Cu²⁺Cd²⁺Pb²⁺ and roots accumulated more metal than the leaves in the absence, as well as in the presence, of calcium chloride. Calcium chloride could recover loss of in vivo NRA in roots caused by either of the metal combinations, whereas the salt could recover the loss in leaf NRA caused only by Pb²⁺Cd²⁺ (1.0 mM each). Response of root and leaf NRA was on the other hand, different when the enzyme was assayed directly using an in vitro assay method, and the salt accelerated the loss in enzyme activity drastically. The organic-N content of root and leaf was, however, increased significantly (p < 0.001) with calcium chloride alone and with the metals supplied in various combinations. Our data indicate that instead of a high endogenous accumulation of Cu²⁺, Cd²⁺ and Pb²⁺ in roots and leaves the metal toxicity is recovered to a great extent in the presence of 10.0 mM calcium chloride in the root environment regarding growth and nitrate reduction of the roots and leaves of young sesame seedlings.     

Influence of aluminium on biomass, nutrients, soluble carbohydrates and phenols in beech (Fagus sylvatica)

The effects of aluminium on biomass, nutrients and soluble carbohydrates and phenols were studied in beech ( Fagus sylvatica L.) seedlings. After germination, seedlings with cotyledons and the buds of the first leaf-pair developed, were preconditioned for two weeks and then grown for 31 days in nutrient solutions containing 0.1, 0.5, 1.0 or 2.0 m M A1C1₃. Aluminium did not affect the dry weights of roots but at Al concentrations ≥ 1.0 m M the development of the terminal shoot above the first leaf pair, was reduced by 80% or more. The concentrations of most nutrients (P, Ca, Mg, Zn, Cu) in the plant tissues decreased strongly even at the lowest Al levels, but K increased in the shoots. The tissue concentration of N was not affected of Al. but the distribution between the organs was changed to a higher content of N in the roots. At ≥1.0 m M Al the concentrations of starch in both the shoots and the roots were significantly increased, and at ≥ 0.5 m M the roots contained more of total phenols than untreated seedlings. The elevated concentrations and contents of starch and phenols in the seedlings may partly be related to the reduced shoot growth. The observed effects of Al were marked already at Al levels found in soil waters from beech forests in southern Sweden.     

Inhibition of glutathione synthesis reduces chilling tolerance in maize

 The role of glutathione (GSH) in protecting plants from chilling injury was analyzed in seedlings of a chilling-tolerant maize (Zea mays L.) genotype using buthionine sulfoximine (BSO), a specific inhibitor of γ-glutamylcysteine (γEC) synthetase, the first enzyme of GSH synthesis. At 25 °C, 1 mM BSO significantly increased cysteine and reduced GSH content and GSH reductase (GR: EC 1.6.4.2) activity, but interestingly affected neither fresh weight nor dry weight nor relative injury. Application of BSO up to 1 mM during chilling at 5 °C reduced the fresh and dry weights of shoots and roots and increased relative injury from 10 to almost 40%. Buthionine sulfoximine also induced a decrease in GR activity of 90 and 40% in roots and shoots, respectively. Addition of GSH or γEC together with BSO to the nutrient solution protected the seedlings from the BSO effect by increasing the levels of GSH and GR activity in roots and shoots. During chilling, the level of abscisic acid increased both in controls and BSO-treated seedlings and decreased after chilling in roots and shoots of the controls and in the roots of BSO-treated seedlings, but increased in their shoots. Taken together, our results show that BSO did not reduce chilling tolerance of the maize genotype analyzed by inhibiting abscisic acid accumulation but by establishing a low level of GSH, which also induced a decrease in GR activity. Received: 9 November 1999 / Accepted: 17 February 2000     

An investigation of morphogenesis within the genus Trifolium

Morphogenic responses within the genus Trifolium were investigated by culturing various explants from seedlings of 72 species. Seedlings from 32 species produced callus alone, 40 produced adventitious shoots and/or roots, of which 25 species produced only shoots and 7 species formed only roots. Seedlings within each species also varied in their response to culture. The section of these seedlings most likely to produce adventitious shoots was the original shoot with the remnants of the surrounding hypocotyl and cotyledons, followed by the excised cotyledons themselves.Inter- and intra-varietal variation was observed in T. repens. Genotypes that produced adventitious buds were selected and crossed. An improvement in the proportion of the population capable of morphogenesis was observed in one cultivar.     

Influence of Salt Stress on Growth, Ion Accumulation and Seed Oil Content in Sweet Fennel

A greenhouse experiment was conducted to assess the effect of 25, 50, 75, and 100 mM NaCl on growth, ion accumulation, seed yield, and seed oil content in 67-d-old plants of Foeniculum vulgare Mill. Increasing NaCl concentration caused a significant reduction in fresh and dry masses of both shoots and roots as well as seed yield. Na⁺ and Cl^– in both shoots and roots increased, whereas K⁺ and Ca²⁺ decreased consistently with the increase in NaCl concentration. Plants maintained markedly higher Ca²⁺/Na⁺ ratios in the shoots than those in the roots, whereas that of K⁺ /Na⁺ ratios remained almost uniform in both shoots and roots. Proline content in the shoots increased markedly at the highest NaCl concentration. Oil content in the seed decreased progressively with increase in salinity.