Application of Bacillus megaterium MCR-8 improved phytoextraction and stress alleviation of nickel in Vinca rosea

The current research was performed to evaluate the effect of Bacillus megaterium MCR-8 on mitigation of nickel (Ni) stress in Vinca rosea grown on Ni-contaminated soil (50, 100, and 200 mg Ni kg^?1 soil). The treated plants exhibited reduced growth, biomass, gas exchange capacity, and chlorophyll (Chl) content under Ni stress. The inoculated plants growing in Ni-contaminated media exhibited relatively higher growth, total soluble protein, and proline contents. Similarly, bacterial inoculation improved the activity of antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) under Ni stress. The Ni stress alleviation in inoculated plants was attributed to the reduced level of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂), enhanced synthesis of protein, proline, phenols, and flavonides in conjunction with improved activity of antioxidant enzymes. The growth-promoting characteristics of microbe such as 1-aminocyclopropane-1-carboxylate deaminase (ACCD) and phosphate solubilization activity, siderophore, and auxin production capability also improved the growth and stress mitigation in inoculated plants. Furthermore, the inoculated plants exhibited higher value for bioconcentration factor (BCF), translocation factor (TF), and resulted in higher loss of Ni content from soil. The current results exhibited the beneficial role of B. megaterium MCR-8 regarding stress alleviation and Ni phytoextraction by V. rosea.     

Cadmium effects on mineral nutrition and stress in <Emphasis Type="Italic">Potamogeton crispus</Emphasis>

The mechanisms of plant tolerance to cadmium stress were studied by short-term exposure of Potamogeton crispus L. to various concentrations of Cd ranging from 0 to 0.09 mM. The accumulation of Cd and its influence on nutrient elements, chlorophyll pigments, ultrastructure, proline and MDA contents, and free radical production, as well as the activities of superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), and glutathione reductase (GR) were investigated. The higher Cd concentration in the medium resulted in a significant enhancement of Cd accumulation. Photosynthetic pigment content decreased and ultrastructural damage to the leaf cells was aggravated with the increase in the Cd concentrations. Disruption of chloroplasts and mitochondria was observed even at the lowest concentration of Cd. Meantime, the rate of O₂^*− generation and the contents of H₂O₂ and MDA significantly increased under Cd stress, suggesting that Cd caused oxidative stress. In addition, the antioxidant system was clearly activated following Cd exposure. SOD and POD activities increased initially and then decreased, while APX and GR activities markedly increased. Simultaneously, mineral nutrition was disturbed. While K, P, Ca, and Cu contents decreased, Na, Fe, and Mn contents increased. Induction of antioxidant enzyme activities in leaves exposed to elevated Cd concentrations may be involved in Cd tolerance of P. crispus.     

Physiological responses of four herbaceous plants to aluminum stress in South China

Different plants have physiological responses under Al stress, but there is no systematic study to examine physiological responses of herbaceous plants under Al stress. The aim of this study is to investigate the effect of Al on physiological characteristics of four herbaceous plants, which distributed in red soil area in South China, and to analyze the differences in physiological responses to Al stress between the four herbaceous plants. Four herbaceous plants (Pharbitis nil, Cassia occidentlis, Echinochloa colonum and Aeschynomene indica) were used, and the seed germination percentage, the contents of chlorophyll, proline, and malondialdehyde (MDA), membrane permeability (MP), soluble sugar, and activities of peroxides (POD) and catalase (CAT) in leaves under five Al³⁺ treatments (0, 80, 400, 2 000, and 10 000 mg/L) were assayed with the sand culture method. The results showed remarkable effects of Al³⁺ on physiological characteristics of these four herbaceous plants. The seeds of all the four species could not germinate at 10 000 mg/L, and the growth of all plants were retarded under the 2 000 mg/L Al³⁺ treatment. Compared with the control, 2 000 mg/L Al³⁺ significantly (P < 0.05) reduced the contents of chlorophyll a and chlorophyll a + b, and increased the contents of MDA and MP. The content of proline increased very significantly (P < 0.01) and activities of POD and CAT were depressed. The contents of MDA and MP in leaves of P. nil and A. indica decreased, and the activities of POD and CAT in leaves of the two plants increased under 80 mg/L and 400 mg/L. However, the changes in C. occidentlis leaves were opposite to those of the above two plants. The changes in leaves of E. colonum were similar to those of P. nil and A. indica at 80 mg/L, but were opposite to those at 400 mg/L Al³⁺. It is suggested that plants with higher activities of POD and CAT, more contents of chlorophyll and proline, and lower contents of MDA and MP consequently improve the tolerance to Al stress under low and middle Al treatments. __________ Translated from Acta Phytoecologica Sinica, 2005, 29(4): 644–651 [译自: 植物生态学报, 2005, 29(4): 644–651]     

Microalgae Improve the Photosynthetic Performance of Rice Seedlings (<i>Oryza sativa</i> L.) under Physiological Conditions and Cadmium Stress

The aim of this study was to assess the impact of the microalgae Chlorella vulgaris on the rice seedlings at physiological conditions and under cadmium (Cd) stress. We examined the effects of C. vulgaris in the nutrient solution on rice seedlings grown hydroponically in the presence and the absence of 150 μM CdCl₂, using the low (77 K) temperature and pulse amplitude modulated (PAM) chlorophyll fluorescence, P700 photooxidation measurements, photochemical activities of both photosystems, kinetic parameters of oxygen evolution, oxidative stress markers (MDA, H₂O₂ and proline), pigment content, growth parameters and Cd accumulation. Data revealed that the application C. vulgaris not only stimulates growth and improves the functions of photosynthetic apparatus under physiological conditions, but also reduces the toxic effect of Cd on rice seedlings. Furthermore, the presence of the green microalgae in the nutrient solution of the rice seedlings during Cd exposure, significantly improved the growth, photochemical activities of both photosystems, the kinetic parameters of the oxygen-evolving reactions, pigment content and decreased lipid peroxidation, H₂O₂ and proline content. Data showed that the alleviation of Cd-induced effects in rice seedlings is a result of the Cd sorption by microalgae, as well as the reduced Cd accumulation in the roots and its translocation from the roots to the shoots.     

The Effect of Salinity Pretreatment on Cd Accumulation and Cd-Induced Stress in <Emphasis Type="Italic">BADH</Emphasis><Emphasis Type="Italic">-</Emphasis>Transgenic and Nontransgenic Rice Seedlings

The influence of betaine aldehyde dehydrogenase (BADH) and salinity pretreatment on oxidative stress under cadmium (Cd) toxicity was investigated in rice cv. Xiushui 11 and its BADH-transgenic line Bxiushui 11. The results showed that plants previously treated with 4.25 and 8.5 mM NaCl, respectively, for 5 days each had higher Cd concentrations in both roots and shoots of the two rice genotypes compared with the controls. Malondialdehyde (MDA) content in both leaves and roots was increased by salinity pretreatment and was significantly lower in the salinity-pretreatment plants than in the controls when the plants were consequently exposed to Cd stress. Salinity pretreatment also increased proline content and the activities of superoxide dismutase (SOD) and peroxidase (POD) in both leaves and roots. It can be assumed that salinity pretreatment enhances the defensive ability of plants against oxidative stress through increasing activities of antioxidative enzymes. The BADH-transgenic line (Bxiushui 11) had lower Cd and MDA content, higher SOD and POD activities, and higher proline content than its wild type (Xiushui 11). The current results suggest that betaine, a product of BADH expression, improves the tolerance of rice plants to Cd stress through increasing the activities of antioxidative enzymes and osmoprotectant content.     

Effective Phytoextraction of Cadmium (Cd) with Increasing Concentration of Total Phenolics and Free Proline in Cannabis sativa (L) Plant Under Various Treatments of Fertilizers,Plant Growth Regulators and Sodium Salt

The comparative effect of fertilizers (NPK), plant growth regulators (GA₃, IAA, Zeatin) and sodium chloride (NaCl) on Cd phytoaccumulation, proline and phenolics production in Cannabis sativa was evaluated. Proline and phenolices were correlated with Cd contents in plant. Cd significantly reduced the plant growth. Fertilizers application (in combination) most significantly increased the growth (19 cm root and 47 cm shoot) on Cd contaminated soil. All treatments increased the Cd contents in plant tissues. This increase was highly significant in fertilizers treated plants (1101, 121 and 544 ppm in roots, stem and leaves respectively). Significantly positive correlation was found between Cd concentration and dry biomass of root (R² = 0.7511) and leaves (R² = 0.5524). All treatments significantly increased the proline and total phenolics and maximum was recorded in NaCl treated plants followed by fertilizers. Proline was higher in roots while phenolics in leaves. The correlation between proline and phenolics was positive in leaf (R² = 0.8439) and root (R² = 0.5191). Proline and phenolics showed positive correlation with Cd concentration in plant. Conclusively, fertilizers in combination seem to be the better option for Cd phytoextraction. Further investigation is suggested to study the role of phenolics and proline in Cd phytoextraction.     

Responses of nitric oxide and hydrogen sulfide in regulating oxidative defence system in wheat plants grown under cadmium stress

We conducted a study to evaluate the interactive effect of NO and H₂S on the cadmium (Cd) tolerance of wheat. Cadmium stress considerably reduced total dry weight, chlorophyll a and b content and ratio of Fv/Fm by 36.7, 48.6, 26.7 and 19.5%, respectively, but significantly enhanced the levels of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA), endogenous H₂S and NO, and the activities of antioxidant enzymes. Exogenously applied sodium nitroprusside (SNP) and sodium hydrosulfide (NaHS), donors of NO and H₂S, respectively, enhanced total plant dry matter by 47.8 and 39.1%, chlorophyll a by 92.3 and 61.5%, chlorophyll b content by 29.1 and 27.2%, Fv/Fm ratio by 19.7 and 15.2%, respectively, and the activities of antioxidant enzymes, but lowered oxidative stress and proline content in Cd-stressed wheat plants. NaHS and SNP also considerably limited both the uptake and translocation of Cd, thereby improving the levels of some key mineral nutrients in the plants. Enhanced levels of NO and H₂S induced by NaHS were reversed by hypotuarine application, but they were substantially reduced almost to 50% by cPTIO (a NO scavenger) application. Hypotuarine was not effective, but cPTIO was highly effective in reducing the levels of NO and H₂S produced by SNP in the roots of Cd-stressed plants. The results showed that interactive effect of NO and H₂S can considerably improve plant resistance against Cd toxicity by reducing oxidative stress and uptake of Cd in plants as well as by enhancing antioxidative defence system and uptake of some essential mineral nutrients.     

Antioxidant enzyme activities and hormonal status in response to Cd stress in the wetland halophyte Kosteletzkya virginica under saline conditions

Salt marshes constitute major sinks for heavy metal accumulation but the precise impact of salinity on heavy metal toxicity for halophyte plant species remains largely unknown. Young seedlings of Kosteletzkya virginica were exposed during 3 weeks in nutrient solution to Cd 5 µM in the presence or absence of 50 mM NaCl. Cadmium (Cd) reduced growth and shoot water content and had major detrimental effect on maximum quantum efficiency (F_v/F_m), effective quantum yield of photosystem II (Y(II)) and electron transport rates (ETRs). Cd induced an oxidative stress in relation to an increase in O₂^?? and H₂O₂ concentration and lead to a decrease in endogenous glutathione (GSH) and α‐tocopherol in the leaves. Cd not only increased leaf zeatin and zeatin riboside concentration but also increased the senescing compounds 1‐aminocyclopropane‐1‐carboxylic acid (ACC) and abscisic acid (ABA). Salinity reduced Cd accumulation already after 1 week of stress but was unable to restore shoot growth and thus did not induce any dilution effect. Salinity delayed the Cd‐induced leaf senescence: NaCl reduced the deleterious impact of Cd on photosynthesis apparatus through an improvement of F_v/F_m, Y(II) and ETR. Salt reduced oxidative stress in Cd‐treated plants through an increase in GSH, α‐tocopherol and ascorbic acid synthesis and an increase in glutathione reductase (EC 1.6.4.2) activity. Additional salt reduced ACC and ABA accumulation in Cd+NaCl‐treated leaves comparing to Cd alone. It is concluded that salinity affords efficient protection against Cd to the halophyte species K. virginica, in relation to an improved management of oxidative stress and hormonal status.     

Heavy metals content and distribution in basil (Ocimum basilicum L.) as influenced by cadmium and different potassium sources

Abstract

Despite the fact that cadmium (Cd) is a non-essential element for plants, it can influence nutrients and affect human health. Potassium (K) can influence the transportation of heavy metals (HMs) in soil-plant systems. Here, a greenhouse experiment was conducted to evaluate the effect of Cd and K fertilizers on the different partitioning forms of HMs, their concentrations, uptake in the shoots and roots of Ocimum basilicum. Treatments comprised 2 levels of Cd (0 and 40?mg kg^?1) and three levels of K (0, 100, and 200?mg kg^?1) from three sources, i.e. KCl, K₂SO_4, and K-nano-chelate. 40?mg Cd kg^?1 increased the shoot (above ground parts) Cd concentration. Addition of K as KCl, K₂SO_4, and K-nano-chelate increased the presence of Cd in shoots by 86, 82 and 76%, respectively, compared to the control. Using the nano-chelate of K can increase the accumulation of Cd in plants grown on contaminated soils to lesser content than that of the other forms of K. Application of 40?mg Cd kg^?1 reduced the concentration of Zn, Cu, and Mn in the shoot, but increased shoot Fe concentration. Transfer factor (TF), which is the ratio of metal concentration in shoot to its concentration in root, of the studied HMs, was significantly affected by Cd and K treatments. Therefore, the proper form and dose of chemical fertilizers should be applied in Cd-contaminated soils.     

盐生植物盐爪爪的耐盐生理特性探讨

当前土壤盐渍化日益严重,是限制植物生长的一个主要环境因子,然而在盐碱自然环境中生长着许多耐盐植物,为更好地了解盐生植物的耐盐机理,该文从无机离子Na+,K+,Ca2+含量、脯氨酸水平、水势变化、丙二醛含量和盐胁迫的表型等生理参数以及半定量RT-PCR检测脯氨酸合成关键酶基因(P5CS)的表达规律等方面探讨盐胁迫下盐爪爪的耐盐特性。结果表明:(1)随着盐浓度的升高,Na+在根和肉质化的叶中显著地富集,且叶中积累的Na+比根中更多;(2)在盐胁迫条件下,随着盐浓度的增加,脯氨酸的含量和脯氨酸合成关键酶基因的表达显著地增强;(3)Na+和脯氨酸是植物有效的渗透调节剂,可使处于低水势的植物细胞仍能从细胞外高浓度的盐溶液中吸收水分;(4)在0和700 mmol·L-1Na Cl处理下,盐爪爪肉质化叶中丙二醛的含量较其它处理高,这表明植物在这两个处理下可能受到了氧化胁迫;(5)从盐胁迫3个月的生长表型来看,低盐环境中生长的盐爪爪植株的生物量更多,肉质化的叶嫩且绿。综上所述,结合对野外生境的调查和实验室长期的盐胁迫表型结果表明盐爪爪的生长是需盐的,相对低的盐浓度环境对盐爪爪的生长是顺境,而无盐或高浓度盐环境对于盐爪爪的生长来说都是逆境。该研究结果为全面深入研究盐爪爪的耐盐特性,以及更好地利用盐爪爪的生物和基因资源改良土壤和提高作物和林木的耐盐性奠定基础。     

Calcium application enhances growth and alleviates the damaging effects induced by Cd stress in sesame (Sesamum indicum L.)

In this study, the effects of calcium (Ca²⁺) application on acquired systemic tolerance mechanism to cadmium (Cd) stress in sesame (Sesamum indicum L.) were studied. The Cd stress reduced the root and shoot growth of sesame, and plant contents of photosynthetic pigments; however, the application of Ca²⁺ improved these parameters under Cd stress condition. The hydrogen peroxide, malondialdehyde and soluble sugar contents were higher under Cd stress, and were reduced by Ca²⁺ treatment. The antioxidant enzyme activities in the leaves of sesame, superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) were higher under Cd stress, whereas reduced concentration was observed in Ca²⁺-treated plants. Cd stress increased the contents of diacylglycerol and sterol ester; however Ca²⁺ treatment resulted in a significant increase in phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol and phosphatidylserine. Our results indicated that application of calcium enables sesame plants to withstand the deleterious impact of cadmium through upregulating acquired systemic tolerance system as lipid fractions (galactolipids, phospholipids, neutral lipids), antioxidant enzymes (SOD, POD, CAT, APX, GR) hence protect membrane functions.     

重金属Cr6+胁迫对茳芏生理生态特征的影响

采用盆栽模拟试验,研究了不同水平重金属Cr6+对茳芏生理生态的影响,探索了茳芏对重金属的抗性机理,充实有关盐沼植物的污染生态学研究。结果表明:(1)Cr6+胁迫对茳芏生物量具抑制作用;(2)叶绿素含量及叶绿素a/b比值显著降低,并对净光合速率(Pn)、胞间CO2浓度(Ci)、蒸腾速率(Tr)及气孔导度(Gs)产生显著负面影响;(3)各浓度Cr6+胁迫对茳芏根系活力表现为抑制效应;(4)在Cr6+胁迫下,茳芏过氧化氢酶(CAT)活性均比对照低(除50mg/L外),超氧化歧化酶(SOD)活性随Cr6+浓度增加呈降低趋势,而过氧化物酶(POD)活性则持续上升。丙二醛(MDA)、细胞膜透性和脯氨酸(Pro)随Cr6+浓度增加显著增加,表明Cr6+胁迫对茳芏细胞质膜系统及主要细胞器的结构与功能都具有较强的破坏作用。     

Morphological and physio-biochemical characterization of Brassica juncea L. Czern. & Coss. genotypes under salt stress

Abstract

Soil salinity is one of the major factors responsible for the low productivity of crop plants and has become an increasing threat for agriculture. In this context, the selection of tolerant genotype/s may be one of the remedies. Keeping this in view, the effect of NaCl (0–120 mM) stress on shoot length (SL) plant^?1, area (A) leaf^?1, leaf area index (LAI), fresh weight (FW) and dry weight (DW) plant^?1, stomatal conductance (g_s), net photosynthetic rate (P _N), total chlorophyll (Chl) content, malondialdehyde (MDA) content, sensitivity rate index (SRI), leaf- nitrogen (N), potassium (K) and sodium (Na) content, leaf-K/Na ratio, nitrate reductase (NR: EC.1.6.6.1) and ATP-sulphurylase (ATP-S: EC.2.7.7.4) activities and proline (Pro) and glycinebetaine (GB) content of ten genotypes of Brassica juncea L. was studied at 55 and 65 days after sowing (DAS). NaCl treatments decreased all the above parameters, except Pro, GB, MDA, Na and SRI at both stages. Salt stress resulted in accumulation of Pro and GB, in all genotypes. The magnitude of increase in both osmolytes (Pro and GB) was higher in genotype G₈ than the other genotypes. Salt stress increased MDA and Na content while it decreased Chl, N and K content and K/Na ratio, Chl content, NR and ATP-S activities in all genotypes. But the magnitude of increase in MDA and Na content and decrease in SL plant^?1, A leaf^?1, LAI, P _N, g_s, Chl content and NR and ATP-S activities in genotype G₈ was more than that of other genotypes. These results suggest that the salt-tolerant genotype may have better osmotic adjustment and protection from free radicals by increasing the accumulation of Pro and GB content with overproduction of N and K and higher K/Na, NR and ATP-S activities under salinity stress.     

Pretreatment with NaCl induces tolerance of rice seedlings to subsequent Cd or Cd + NaCl stress

Rice (Oryza sativa L.) seedlings were grown hydroponically in Hoagland’s nutrient solution under controlled conditions to investigate the effects of NaCl pretreatment on their response to subsequent application of cadmium (Cd) alone and Cd + NaCl combination. The Cd stress caused growth retardation in all plants, significantly reduced pigment content, stomatal conductance (g_s), and net photosynthetic rate (P_N). Cd stress significantly increased malondialdehyde and proline content. Compared to Cd treatment alone, combination stress had more detrimental effects on the above parameters. However, the NaCl pretreatment was beneficial in improving the plant growth and plant tolerance to Cd alone or combination stress.     

An assessment of Agropyron cristatum tolerance to cadmium contaminated soil

A pot experiment was conducted in a greenhouse to assess the tolerance of Agropyron cristatum plants to cadmium contaminated soils (0, 5, 10, 25, 50, 100, 150, and 200 mg kg^?1) for 100 d. Results indicate that Cd in concentrations of 5–50 mg kg^?1 had no significant impact on growth, relative membrane permeability (RMP), lipid peroxidation measured as malondialdehyde (MDA) content, and chlorophyll (Chl) content relative to the control. Exposure of these plants to high concentrations of Cd (100–200 mg kg^?1) caused a small reduction in growth and Chl content and a slight enhancement of RMP and MDA content compared with the control. In addition, superoxide dismutase (SOD) and peroxidase (POD) activities show an increasing trend with the increase of Cd content in soil. The Cd content in the roots was 4.7–6.1 times higher than that in the shoots under all Cd treatments suggesting that the plant can be classified as a Cd excluder. The translocation factor was low and similar at 25–200 mg kg^?1 Cd treatments. In summary, A. cristatum plants tolerated Cd stress and might have potential for the phytoremediation of Cd contaminated soils.     

Exogenous succinic acid mediates responses of Larix olgensis A. Henry to cadmium stress

Abstract

Trace metal contamination of soil is an increasing problem. Organic acid application can restore trace metal elements such as cadmium (Cd) in contaminated soil. Changbai larch (Larix olgensis A. Henry) is an economically important forestry species in northeast China; however, growth is inhibited by severe Cd contamination. We investigated the effects of different concentrations of exogenous succinic acid (SA) on Cd tolerance and physiological and morphological toxicity in L. olgensis seedlings. Seedlings were planted in pots containing Cd-contaminated or uncontaminated Haplic Cambisol. Seedlings in Cd-contaminated soil were treated daily with SA solution at 0, 0.04, 0.2, 1.0, and 2.0?mmol kg^?1 of soil for 10, 20 or 30?days. Cd treatment induced seedling damage and significantly increased the relative conductivity and malondialdehyde content of the leaves, inhibiting soluble protein and proline contents, superoxide dismutase and peroxidase activity, chlorophyl fluorescence and pigment content. Decreases in the length, surface area, volume of roots and leaves, and specific root length were also observed. Effects increased in control plants with time. SA treatment also reduced the Cd content of the fine roots and leaves and Mg, K, and Ca contents. Moreover, plant growth was significantly promoted and damage was reversed, especially at 5.0 and 10.0?mmol?L^?1 SA for 30?days. SA therefore alleviated Cd-induced injury, improving tolerance to Cd stress. SA application combined with afforestation could therefore help restore Cd-contaminated soil in northeast China. Further studies aimed at determining the detoxification mechanism of L. olgensis seedlings are now required.     

Exogenous spermidine and spermine enhance cadmium tolerance of <Emphasis Type="Italic">Potamogeton malaianus</Emphasis>

In order to investigate the effects of spermidine (Spd) and spermine (Spm) on cadmium stress, the content of chlorophyll, hydrogen peroxide (H₂O₂), malondialdehyde (MDA), soluble protein and proline, the rate of O₂^·− generation, and activities of antioxidant enzymes (superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX), and glutathione reductase (GR)) in Potamogeton malaianus Miq. were measured. Exogenous application of Spd or Spm significantly enhanced the level of proline, retarded the loss of chlorophyll, enhanced photosynthesis, decreased the rate of O₂^·− generation and H₂O₂ content, and prevented Cd-induced lipid peroxidation. Spd and Spm also effectively maintained the balance of antioxidant enzyme activities under Cd stress; however, GR activity was found to increase only slightly in response to polyamines (PAs). The antioxidant systems, which were modified by PAs, were able to moderate the radical-scavenging system and to lessen in this way the oxidative stress. These results suggest that both Spd and Spm can enhance Cd tolerance of P. malaianus.     

Action de la proline exogène sur l'activité de la voie du glycolate chez Nicotiana tabacum cv. Xanthi n.c.

The effect of exogenous proline on the activity of the glycolate pathway in Nicotiana tabacum cv. Xanthi n.c. An exogenous proline supply in the light provokes an increase in free glycine concentration in apical tissues or in leaf disks of vegetative Nicotiana tabacum L. cv. Xanthi n.c. This does not occur in the equivalent tissues of tobacco plants after floral induction, these being naturally rich in proline. In vegetative tobacco, we have tried to determine this specific action of exogenous proline. With ¹⁴C glycine, ¹⁴CO₂ experiments (Pulse-chase) and glycine decarboxylase activity determinations, we observed that glycine-serine transformation was inhibited by proline supply. Presently it is important to determine if endogenous proline acts on the same reaction.