Effect of Previous Nitrate Deprivation on 15N-nitrate Absorption and Assimilation by Wheat Seedlings

Nitrate uptake and assimilation were examined in intact 18 days old wheat (Triticum aestivum, cv Capitole) seedlings either permanently grown on nitrate (high-N seedlings) or N-stressed by transfer to an 0 N-solution for the final 7 days (low-N seedlings). The N-stressed seedlings were characterized by a lower organic N content (2.5 mg instead of 4.9 mg per seedling) and an increased root dry weight.The seedlings received ¹⁵NO₃K for 7 h in the light. Nitrate uptake was 2.8 times higher in low-N than in high-N seedlings. The assimilation rate was 35 and 16 μmol NO₃^?·^h?1· g^?1 dry weight respectively. Partitioning of NO₃^? to reduction and assimilation was the very same in both kinds of seedlings. The results support the view that 50 % of the nitrate reduction in Triticum aestivum, cv Capitole could be achieved in the roots.The present observations are interpreted as evidence that factors closely associated with the seedling N-status may have a major role in regulating NO₃^? uptake and assimilation. In low-N seedlings, the high amount of carbohydrates in roots may add its stimulus to the specific inducing effect of nitrate whereas in high-N seedlings, excess of nitrate or amino-acids may set the pace by negative feedback control.     

Use of an Acylcyclohexanedione Growth Retardant, LAB 198 999, to Determine Whether Gibberellin A(20) Has Biological Activity per se in Dark-Grown Dwarf (le) Seedlings of Pisum sativum

Dwarf (le⁵⁸³⁹) seedlings of Pisum sativum respond to gibberellin A₂₀ (GA₂₀) in the dark, although the same dosage of GA₂₀ applied to light-grown le⁵⁸³⁹ seedlings elicits no growth response. The acylcyclohexanedione growth retardant, LAB 198 999, which is known to inhibit gibberellin oxidation and in particular 3β-hydroxylation such as the conversion of GA₂₀ to GA₁, also inhibits the growth response of dark-grown dwarf (le⁵⁸³⁹) seedlings to GA₂₀. Thus, the biological activity of GA₂₀ in the dark appears to be a consequence of its conversion to GA₁, even though it is known from studies with light-grown seedlings that the le mutation reduces the conversion of GA₂₀ to GA₁.     

Dark septate root endophytic fungi increase growth of Scots pine seedlings under elevated CO2 through enhanced nitrogen use efficiency

Although increasing concentrations of atmospheric CO₂ are predicted to have substantial impacts on plant growth and functioning of ecosystems, there is insufficient understanding of the responses of belowground processes to such increases. We investigated the effects of different dark septate root endophytic (DSE) fungi on growth and nutrient acquisition by Pinus sylvestris seedlings under conditions of N limitation and at ambient and elevated CO₂ (350 or 700 μ1 CO₂ l^?1). Each seedling was inoculated with one of the following species: Phialocephala fortinii (two strains), Cadophora finlandica, Chloridium paucisporum, Scytalidium vaccinii, Meliniomyces variabilis and M. vraolstadiae. The trial lasted 125 days. During the final 27 days, the seedlings were labeled with ¹⁴CO₂ and ¹⁵NH ₄ ⁺ . We measured extraradical hyphal length, internal colonization, plant biomass, ¹⁴C allocation, and plant N and ¹⁵N content. Under elevated CO₂, the biomass of seedlings inoculated with DSE fungi was on average 17% higher than in control seedlings. Simultaneously, below-ground respiration doubled or trebled, and as a consequence carbon use efficiency by the DSE fungi significantly decreased. Shoot N concentration decreased on average by 57% under elevated CO₂ and was lowest in seedlings inoculated with S. vaccinii. Carbon gain by the seedlings despite reduced shoot N concentration indicates that DSE fungi increase plant nutrient use efficiency and are therefore more beneficial to the plant under elevated CO₂.     

Growth and leaf gas exchange in Populus euphratica across soil water and salinity gradients

Soil water and salinity conditions of the riparian zones along the Tarim River, northwest China, have been undergoing alterations due to water use by human or climate change, which is expected to influence the riparian forest dominated by an old poplar, Populus euphratica. To evaluate the effects of such habitat alterations, we examined photosynthetic and growth performances of P. euphratica seedlings across experimental soil water and salinity gradients. Results indicated that seedlings were limited in their physiological performance, as evidenced by decreases in their height and biomass, and the maximal quantum yield of photosystem II (PSII) photochemistry (F_v/F_m), the effective quantum-use efficiency of PSII (F_v′/F_m′), and photochemical quenching (q_P) under mild (18% soil water content, SWC; 18.3 g kg^?1 soil salt content, SSC) and moderate (13% SWC, 22.5 g kg^?1 SSC) water or salinity stress. However, seedlings had higher root/shoot ratio (R/S), increased nonphotochemical quenching (NPQ), and water-use efficiency (WUE) relative to control under such conditions. Under severe (8% SWC, 27.9 g kg^?1 SSC) water or salinity stress, P. euphratica seedlings had only a fifth of biomass of those under control conditions. It was also associated with damaged PSII and decreases in WUE, the maximal net photosynthetic rate (P _Nmax), light-saturation point (LSP), and apparent quantum yield (_α). Our results suggested that the soil conditions, where P.euphratica seedlings could grow normally, were higher than ～ 13% for SWC, and lower than ～22.5 g kg^?1 for SSC, the values, within the seedlings could acclimate to water or salinity stress by adjusting their R/S ratio, improving WUE to limit water loss, and rising NPQ to dissipate excessive excitation energy. Once SWC was lower than 8% or SCC higher than ～28 g kg^?1, the seedlings suffered from the severe stress.     

Ethylene-Mediated Regulation of Gibberellin Content and Growth in Helianthus annuus L

Elongation of hypocotyls of sunflower can be promoted by gibberellins (GAs) and inhibited by ethylene. The role of these hormones in regulating elongation was investigated by measuring changes in both endogenous GAs and in the metabolism of exogenous [³H]- and [²H₂]GA₂₀ in the hypocotyis of sunflower (Helianthus annuus L. cv Delgren 131) seedlings exposed to ethylene. The major biologically active GAs identified by gas chromatography-mass spectrometry were GA₁, GA₁₉, GA₂₀, and GA₄₄. In hypocotyls of seedlings exposed to ethylene, the concentration of GA₁, known to be directly active in regulating shoot elongation in a number of species, was reduced. Ethylene treatment reduced the metabolism of [³H]GA₂₀ and less [²H₂]GA₁ was found in the hypocotyls of those seedlings exposed to the higher ethylene concentrations. However, it is not known if the effect of ethylene on GA₂₀ metabolism was direct or indirect. In seedlings treated with exogenous GA₁ or GA₃, the hypocotyls elongated faster than those of controls, but the GA treatment only partially overcame the inhibitory effect of ethylene on elongation. We conclude that GA content is a factor which may limit elongation in hypocotyls of sunflower, and that while exposure to ethylene results in reduced concentration of GA₁ this is not sufficient per se to account for the inhibition of elongation caused by ethylene.     

Photosynthetic acclimation in shade-developed leaves of Euterpe edulis Mart (Arecaceae) after long-term exposure to high light

To analyze acclimation of Euterpe edulis seedlings to changes in light availability, we transferred three-year-old seedlings cultivated for six months under natural shade understory [≈ 1.3 mol(photon) m^?2 d^?1] to a forest gap [≈ 25.0 mol(photon) m^?2 d^?1]. After the transfer, changes in chlorophyll fluorescence and leaf gas-exchange parameters, as well as in the light-response curves of photosynthesis and photosynthetic induction parameters, were analyzed during the following 110 days. Simultaneously measured photosynthetic characteristics in the shaded seedlings grown in understory served as the control. Despite the fact that the understory seedlings were under suboptimal conditions to achieve their light-saturated net photosynthetic rate (P _Nmax), light-response curves and photosynthetic induction parameters indicated that the species had the low respiration rate and a fast opening of stomata in response to the intermittent occurrence of sunflecks, which exerted a feed-forward stimulation on P _Nmax. Sudden exposure to high light induced photoinhibition during the first week after the transfer of seedlings to gap, as it was shown by the abrupt decline of the maximal quantum yield of PSII photochemistry (F_v/F_m). The photoinhibition showed the time-dependent dynamics, as the F_v/F_m of the seedlings transferred to the forest gap recovered completely after 110 days. Furthermore, the net photosynthetic rate increased 3.5-fold in relation to priorexposure values. In summary, these data indicated that more than 21 days was required for the shade-acclimated seedlings to recover from photoinhibition and to relax induction photosynthetic limitations following the sudden exposure to high light. Moreover, the species responded very quickly to light availability; it highlights the importance of sunflecks to understory seedlings.     

Stimulation of root acid phosphatase by phosphorus deficiency is regulated by ethylene in Medicago falcata

Plants have developed numerous strategies to cope with phosphorus (P) deficiency resulting from low availability in soils. Evolution of ethylene and up-regulation of root secreted acid phosphatase activity are common for plants in response to P deficiency. To determine the role of ethylene in response of plants to P deficiency, we investigated the effects of ethylene precursor (1-amino cyclopropane-1-carboxylic acid, ACC) and ethylene synthesis antagonists (aminoethoxyvinylglycine AVG, cobalt, Co²⁺) on P concentrations in roots and shoots of Medicago falcata seedlings grown in P-sufficient (500 μM H₂PO₄⁻) and P-deficient (5 μM H₂PO₄⁻) solution. After transferring M. falcata seedlings from P-sufficient to P-deficient solution for 2 days, root P concentration was significantly reduced. The reduction in root P concentration was reversed by AVG and Co²⁺, and a similar reduction in root P concentration of seedlings exposed to P-sufficient solution was observed by ACC. Expression of high-affinity phosphate transporters (MfPT1, MfPT5) was enhanced by P-deficiency and this process was reversed by AVG and Co²⁺. There was a marked increase in activity of root acid phosphatase (APase) and expression of gene encoding APase (MfPAP1) under P-deficient conditions, and the increase in APAse activity and expression of MfPAP1 was inhibited by AVG and Co²⁺. APase activity and expression of MfPAP1 expression in seedlings grown in P-sufficient solution were enhanced by ACC. Root and shoot P concentrations were increased when organic phosphorus was added to the P-deficient solution, and the increase in P concentration was significantly inhibited by AVG and Co²⁺. These results indicate that ethylene plays an important role in modulation of P acquisition by possibly mobilizing organic P via up-regulating root APase activity and high-affinity phosphate transporters.     

Bicarbonate blocks iron translocation from cotyledons inducing iron stress responses in Citrus roots

The effect of bicarbonate ion (HCO₃⁻) on the mobilization of iron (Fe) reserves from cotyledons to roots during early growth of citrus seedlings and its influence on the components of the iron acquisition system were studied. Monoembryonic seeds of Citrus limon (L.) were germinated “in vitro” on two iron-deprived media, supplemented or not with 10 mM HCO₃⁻ (−Fe+Bic and −Fe, respectively). After 21 d of culture, Fe concentration in seedling organs was measured, as well as gene expression and enzymatic activities. Finally, the effect of Fe resupply on the above responses was tested in the presence and absence of HCO₃⁻ (+Fe+Bic or +Fe, respectively). −Fe+Bic seedlings exhibited lower Fe concentration in shoots and roots than −Fe ones but higher in cotyledons, associated to a significative inhibition of NRAMP3 expression. HCO₃⁻ upregulated Strategy I related genes (FRO1, FRO2, HA1 and IRT1) and FC-R and H⁺-ATPase activities in roots of Fe-starved seedlings. PEPC1 expression and PEPCase activity were also increased. When −Fe+Bic pre-treated seedlings were transferred to Fe-containing media for 15 d, Fe content in shoots and roots increased, although to a lower extent in the +Fe+Bic medium. Consequently, the above-described root responses became markedly repressed, however, this effect was less pronounced in +Fe+Bic seedlings. In conclusion, it appears that HCO₃⁻ prevents Fe translocation from cotyledons to shoot and root, therefore reducing their Fe levels. This triggers Fe-stress responses in the root, enhancing the expression of genes related with Fe uptake and the corresponding enzymatic activities.     

Phosphorus deficiency-induced reduction in root hydraulic conductivity in Medicago falcata is associated with ethylene production

Plants grown in phosphorus-deficient solutions often exhibit disruption of water transport due to reduction in root hydraulic conductivity (Lpr) and enhanced ethylene production. To uncover the relationship between the reduction in Lpr and increase in ethylene production, we investigated effect of phosphorus (P) deficiency on ethylene production and Lpr in legume plants of Medicago falcata L. There was an increase in ethylene production and a reduction of Lpr of M. falcata roots when M. falcata seedlings grown in P sufficient solutions (0.5 mM H₂PO₄^2?) were transferred to P-deficient solutions (5 μM H₂PO₄^2?). Antagonists of ethylene biosynthesis, CoCl₂ and aminoethoxyvinylglycine (AVG), abolished the P deficiency-induced ethylene production. Root hydraulic conductivity of M. falcata seedlings grown in P-sufficient solutions was insensitive to CoCl₂ and AVG, while the two chemicals enhanced Lpr for those grown in P-deficient solutions, suggesting that P deficiency-induced decrease in Lpr can be reversed by inhibiting ethylene production. Ethylene precursor 1-amino cyclopropane-1-carboxylic acid (ACC) and ethylene donor ethephon had greater inhibitory effect on Lpr of P-sufficient seedlings than that of P-deficient seedlings. Root hydraulic conductivity of P-sufficient seedlings was more sensitive to HgCl₂ than that of P-deficient seedlings. Taken together, these findings suggest that ethylene induced by P deficiency may play an important role in modulation of root hydraulic conductivity by affecting aquaporins in plants.     

Light Intensity Alters the Extent of Arsenic Toxicity in Helianthus annuus L. Seedlings

The present study is aimed at assessing the extent of arsenic (As) toxicity under three different light intensities—optimum (400 μmole photon m^?2 s^?1), sub-optimum (225 μmole photon m^?2 s^?1), and low (75 μmole photon m^?2 s^?1)—exposed to Helianthus annuus L. var. DRSF-113 seedlings by examining various physiological and biochemical parameters. Irrespective of the light intensities under which H. annuus L. seedlings were grown, there was an As dose (low, i.e., 6 mg kg^?1 soil, As₁; and high, i.e., 12 mg kg^?1 soil, As₂)-dependent decrease in all the growth parameters, viz., fresh mass, shoot length, and root length. Optimum light-grown seedlings exhibited better growth performance than the sub-optimum and low light-grown seedlings; however, low light-grown plants had maximum root and shoot lengths. Accumulation of As in the plant tissues depended upon its concentration used, proximity of the plant tissue, and intensity of the light. Greater intensity of light allowed greater assimilation of photosynthates accompanied by more uptake of nutrients along with As from the medium. The levels of chlorophyll a, b, and carotenoids declined with increasing concentrations of As. Seedlings acquired maximum Chl a and b under optimum light which were more compatible to face As₁ and As₂ doses of As, also evident from the overall status of enzymatic (SOD, POD, CAT, and GST) and non-enzymatic antioxidant (Pro).     

Biosynthesis of sitosterol in barley seedlings

A method is described for the chemical synthesis of stigmasta-5,24-dien-3β-ol-[26-¹⁴C] and (24S)-24-ethylcholesta-5,25-dien-3β-ol-[26-¹⁴C] (clerosterol). 28-Isofucosterol-[7-³H₂] fed to developing barley seedlings (Hordeum vulgare) was incorporated into sitosterol and stigmasterol confirming the utilisation of a 24-ethylidene sterol intermediate in 24α-ethyl sterol production in this plant. Also, the use of mevalonic acid-[2-¹⁴C(4R)-4-³H₁] verified the loss of the C-25 hydrogen of 28-isofucosterol during its conversion into sitosterol and stigmasterol in agreement with the previously postulated isomerisation of the 24-ethylidene sterol to a Δ²⁴⁽²⁵⁾-sterol prior to reduction. However, feeding stigmasta-5,24-dien-3β-ol [26-¹⁴C] to barley seedlings gave very low incorporation into sitosterol. Attempts to trap radioactivity from mevalonic-[2-¹⁴C(4R)-4-³H₁] in stigmasta-5,24-dien-3β-ol when this unlabelled sterol was administered to barley seedlings gave only a very small incorporation although both 28-isofucosterol and sitosterol were labelled.     

Effects of Elevated [CO2] and Low Soil Moisture on the Physiological Responses of Mountain Maple (Acer spicatum L.) Seedlings to Light

Global climate change is expected to affect how plants respond to their physical and biological environments. In this study, we examined the effects of elevated CO₂ ([CO₂]) and low soil moisture on the physiological responses of mountain maple (Acer spicatum L.) seedlings to light availability. The seedlings were grown at ambient (392 µmol mol⁻¹) and elevated (784 µmol mol⁻¹) [CO₂], low and high soil moisture (M) regimes, at high light (100%) and low light (30%) in the greenhouse for one growing season. We measured net photosynthesis (A), stomatal conductance (g _s), instantaneous water use efficiency (IWUE), maximum rate of carboxylation (V _cmax), rate of photosynthetic electron transport (J), triose phosphate utilization (TPU)), leaf respiration (R _d), light compensation point (LCP) and mid-day shoot water potential (Ψ_x). A and g _s did not show significant responses to light treatment in seedlings grown at low soil moisture treatment, but the high light significantly decreased the C _i/C _a in those seedlings. IWUE was significantly higher in the elevated compared with the ambient [CO₂], and the effect was greater at high than the low light treatment. LCP did not respond to the soil moisture treatments when seedlings were grown in high light under both [CO₂]. The low soil moisture significantly reduced Ψ_x but had no significant effect on the responses of other physiological traits to light or [CO₂]. These results suggest that as the atmospheric [CO₂] rises, the physiological performance of mountain maple seedlings in high light environments may be enhanced, particularly when soil moisture conditions are favourable.     

Improving acclimatization through the photoautotrophic culture of coconut (Cocos nucifera) seedlings: an in vitro system for the efficient exchange of germplasm

An in vitro photoautotrophic step based on the supply of CO₂-enriched air (1,600 μmol mol^?1) during the light phase and ambient air (350 μmol mol^?1 CO₂) during the dark phase has been used to promote the ex vitro establishment of coconut (Cocos nucifera L.) seedlings. The introduction of this step into a previously developed in vitro protocol was found to improve the quality of the seedlings (as assessed by fresh weight increase, physical stature, leaf area and thickness, stomatal density, and chlorophyll a content, and primary and secondary root production), the proportion of seedlings successfully transferred to soil (improvement from 40% to 100%) and achieved in a shorter time (reduction from 10 to 6 mo). Best results using this photoautotrophic growth step were obtained when a low medium concentration of sucrose (43.8 mM or lower) was used, when it was applied to seedlings that had already reached 4 or 5 mo of age in the in vitro culture step, and when seedlings were cultured in the photoautotrophic system for 2 mo or more before transfer to soil. Our improved protocol is more efficient and it reduces the cost per plant for the international exchange of coconut germplasm.     

Interconversion of gibberellin A1 to gibberellin A8 in seedlings of dwarf Oryza sativa

[³H]Gibberellin A₁ ([³H]GA₁)applied to seedlings of dwarf rice (Oryza sativa L. cv. Tanginbozu) was metabolized to GA₈. Identification of GA₈, was made by gas-liquid radiochromatography using three liquid stationary phases.     

Purification and Properties of Oxalate Oxidase from NaCl Stressed Grain Sorghum Seedlings

The effect of NaCl stress on molecular and biochemical properties of oxalate oxidase (OXO) was studied in leaves of grain sorghum hybrid (var CSH-14) seedlings. There was no effect on molecular weight and number of subunits of the enzyme but it showed some important changes in its kinetic parameters such as K_m for oxalate and V_max. Optimum pH (5.8), activation energy (5.084 kcal mole^?1), time of incubation (6 min) and K_m for oxalate (1.21×10^t-4M) were increased, while V_max (0.182 mmole min^?1) decreased and no change in optimum temperature was observed. This showed that substrate affinity and maximum activity of the enzyme was adversely affected. The specific activity of oxalate oxidase was increased in seedlings grown in a NaCl containing medium compared to normal, which reveals the increased de novo synthesis of the enzyme to sustain oxalate degradation.     

De novo synthesis of d-alanine in germinating Pisum sativum seedlings

The amounts of d-alanine derivatives, γ-l-glutamyl-d-alanine and N-malonyl-d-alanine, increase rapidly during the early growth of pea seeds. Pyruvate-[1?¹⁴C], l-alanine-[U?¹⁴C], d-alanine-[U?¹⁴C], l-alanine-[¹⁵N] and ¹⁵NH₄Cl were therefore fed to the seedlings and the incorporation investigated. Labelling results revealed that pea seedlings can utilize these erogenous compounds to form d-alanine and that labelled l-alanine is effectively converted to the d-enantiomer with retention of ¹⁴C and, largely, ¹⁵N label. Enzyme analyses in vitro provided additional evidence that the extract of pea seedlings catalyzes the direct conversion of l-alanine to d-alanine. The data suggest that the de novo synthesis of d-alanine in pea seedlings occurs by a racemase reaction.     

The raz1 mutant of Arabidopsis thaliana lacks the activity of a high-affinity amino acid transporter

The raz1 mutant of Arabidopsis thaliana (L.) Heynh. has been selected as resistant to the toxic proline analogue, azetidine-2-carboxylic acid (2AZ). Seedlings of the mutant tolerated fivefold higher concentrations of 2AZ (ED₅₀ = 0.25 mM) than the wild-type seedlings (ED⁵⁰ = 0.05 mM). The mutant gene was found to be semi-dominant and the corresponding RAZ1 locus was mapped on chromosome 5 at 69.6±1.8 cM. The resistance to 2AZ could be fully and exclusively accounted for by the lower uptake rate of the proline analogue in the mutant. The influx of L-proline in roots of wild-type seedlings could be dissected into two components: (i) a component with a high affinity and a low capacity for l-proline (K _m≈20 gmM, V _max≈60 nmol·(g FW)^-1·h^-1) and also a high affinity for L-2AZ (K _i≈40 μM) and (ii) a low-affinity, high-capacity component (K _m≈5 mM: V _max = 1300 nmol·(g FW)^-1·h^-1). Clearly, the raz1 mutation affects the activity of a high-affinity transporter, because the high-affinity uptake of proline in the mutant was at least fivefold lower than in the wild-type, whereas the low-affinity uptake was unchanged.     

Genetic Regulation of Development in Sorghum bicolor: VI. The ma(3) Allele Results in Abnormal Phytochrome Physiology

Physiological processes controlled by phytochrome were examined in three near-isogenic genotypes of Sorghum bicolor, differing at the allele of the third maturity gene locus. Seedlings of 58M (ma₃^R ma₃^R) did not show phytochrome control of anthocyanin synthesis. In contrast, seedlings of 90M (ma₃ma₃) and 100M (Ma₃Ma₃) demonstrated reduced anthocyanin synthesis after treatment with far red and reversal of the far red effect by red. De-etiolation of 48-hour-old 90M and 100M dark-grown seedlings occurred with 48 hours of continuous red. Dark-grown 58M seedlings did not de-etiolate with continuous red treatment. Treatment of seedlings with gibberellic acid or tetcyclacis, a gibberellin synthesis inhibitor, did not alter anthocyanin synthesis. Levels of chlorophyll and anthocyanin were lower in light-grown 58M seedlings than in 90M and 100M. Etiolated seedlings of all three genotypes have similar amounts of photoreversible phytochrome. Crude protein extracts from etiolated seedlings were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and transferred to nitrocellulose. Phytochrome was visualized with Pea-25, a monoclonal antibody directed to phytochrome from etiolated peas. The samples from all three genotypes contained approximately equivalent amounts of a prominent, immunostaining band at 126 kD. However, the sample from 58M did not show a fainter, secondary band at 123 kD that was present in 90M and 100M. The identity and importance of this secondary band at 123 kD is unknown. We propose that 58M is a phytochrome-related mutant that contains normal amounts of photoreversible phytochrome and normal phytochrome protein when grown in the dark.     

Breaking-off tissue specific activity of the oil palm metallothionein-like gene promoter in T1 seedlings of tomato exposed to metal ions

Metallothioneins (MTs) are cysteine-rich metal-binding proteins that are involved in cell growth regulation, transportation of metal ions and detoxification of heavy metals. A mesocarp-specific metallothionein-like gene (MT3-A) promoter was isolated from the oil palm (Elaeis guineensis Jacq). A vector construct containing the MT3-A promoter fused to the β-glucuronidase (GUS) gene in the pCAMBIA 1304 vector was produced and used in Agrobacterium-mediated transformation of tomato. Histochemical GUS assay of different tissues of transgenic tomato showed that the MT3-A promoter only drove GUS expression in the reproductive tissues and organs, including the anther, fruit and seed coat. Competitive RT-PCR and GUS fluorometric assay showed changes in the level of GUS mRNA and enzyme activity in the transgenic tomato (T₀). No GUS mRNA was found in roots and leaves of transgenic tomato. In contrast, the leaves of transgenic tomato seedlings (T₁) produced the highest GUS activity when treated with 150 μM Cu²⁺ compared to the control (without Cu²⁺). However, Zn²⁺ and Fe²⁺ treatments did not show GUS expression in the leaves of the transgenic tomato seedlings. Interestingly, the results showed a breaking-off tissue-specific activity of the oil palm MT3-A promoter in T₁ seedlings of tomato when subjected to Cu²⁺ ions.