|Year : 2015 | Volume
| Issue : 2 | Page : 89-94
The role of polyamine to increasing growth of plant: As a key factor in health crisis
Mohammad Fazilati, Amir Hossein Forghani
Department of Biology, Payame Noor University, Tehran, Iran
|Date of Web Publication||12-Feb-2015|
Department of Biology, Payame Noor University, Tehran
Source of Support: None, Conflict of Interest: None
Context: There is an increasing concern over predications that the world population will reach 8 billion in the next 25 years. Currently, many regions in Africa and Asia are experiencing a food crisis that is contributing to hunger, malnutrition and starvation. So each way to increasing yielding plant is a key factor to respond this demand. There are several elicitor to reach this target. Polyamines (PAS) are lightweight molecular that are present in all living organisms. PAS are necessary for the growth of prokaryotes and eukaryotes. Putrescine (Put), spermidine (Spd) and spermine (Spm) are the major PAS in plants. In plant cells, Put (diamine) is synthesized from ornithine and arginine by ornithine decarboxylase and arginine decarboxylase, respectively. With regard to the significance of the flower and oilseed of safflower, this research has been done on Put and its effect on the growth and development of safflower. Discussion :This experiment included three separate plans (A, B, C) and each plan has two different culture mediums that were called 'a' and 'b'. Finding and Conclusion: In this work, we found that maximum shoot regeneration belonged to Put A4 and Put A2 (Plan A). Also, the third plan has a significant reduction rather than first and second plan regarding rooting. According to data, the group with the highest shoot regeneration (A plan-Put A4) had maximum peroxidase activity also and the treatments of B plan with the lowest shoot regeneration had lowest enzyme activity.
Keywords: Diamine, polyamines, putrescine, peroxidase, root and shoot regeneration, safflower
|How to cite this article:|
Fazilati M, Forghani AH. The role of polyamine to increasing growth of plant: As a key factor in health crisis. Int J Health Syst Disaster Manage 2015;3:89-94
|How to cite this URL:|
Fazilati M, Forghani AH. The role of polyamine to increasing growth of plant: As a key factor in health crisis. Int J Health Syst Disaster Manage [serial online] 2015 [cited 2021 May 15];3:89-94. Available from: https://www.ijhsdm.org/text.asp?2015/3/2/89/151316
| Introduction|| |
The new millennium promises excitement and hope for the future fuelled by new advancements in medicine, agriculture and technology. However, there is an increasing concern over predications that the world population will reach 8 billion in the next 25 years. Currently, many regions in Africa and Asia are experiencing a food crisis that is contributing to hunger, malnutrition and starvation. The expected population increase will only make the food crisis worse-or will it? Also, in the face of growing population and rising rates of chronic disease, the challenge is to improve public health whilst at the same time reducing healthcare costs, to save billions of pounds. A solution already exists, once the direct link between dietary choices and the major chronic diseases-obesity, diabetes, heart disease-is recognized. So, each way to increasing yielding plant is a key factor to control or to improve this event. There are several plants that is important for human as a food, economical and medical future. The scientific name of safflower is Carthamus tinctorius L. which is called Carthame in French. This plant comes from Asteraceae family and it is growing as annual or biennial. This plant has been cultivated in Egypt since 4,000 years ago because of its flowers.  Safflower oil has a great value because of the presence of significant amounts of unsaturated fatty acids. In recent years, the attention of many people has been attracted by both food crop and medicinal aspect of safflower, especially in developed countries, because of having significant amounts of linoleic acid. Safflower has several industrial and pharmaceutical applications. Safflower cultivars with high levels of linoleic acid and oleic acid have high values. 
Polyamines (PAS) are lightweight molecular that are present in all living organisms. PAS are necessary for the growth of prokaryotes and eukaryotes. Putrescine (Put), spermidine (Spd) and spermine (Spm) are the major PAS in plants. These materials are present either free or combined with some molecules such as phenolic acids, lightweight molecular substances or macromolecules such as proteins, nucleic acids. PAS stimulate deoxyribonucleic acis (DNA) replication, transcription and translation. They have an important role in a wide range of growth stages including aging, protection against environmental stress and fungal and viral penetration. ,,,, In plant cells, Put (Diamine) is synthesized from ornithine and arginine by ornithine decarboxylase and arginine decarboxylase, respectively. Then, Put catalysed to Spd and Spm by transforming of aminopropyl groups from decarboxylated S-adenosylmethionine (dSAM). These reactions were catalysed by a special enzyme and that is called Spd and Spm synthases. In various tissues inplants, activity and distribution of these enzymes are regulated in regard to tissue type and developmental stage. , With regard to the significance of the flower and oilseed of this plant and application of PAS, this research has been done on Put and the effect it has on the growth and development of safflower. This study is done with the help and aid of the Payame Noor University.
| Materials and Methods|| |
Seeds cultivation and explants provision
Safflower seeds (Isfahan spring version) have been provided from seed and plant improvement institute of Iran. Five to seven sterilized seeds with mercuric chloride 0.1% has been cultivated in Murashige and Skoog medium (MS) sterile medium  at a distance from one another. Then the glass doors were closed by cellophane and seeds were kept under a photoperiod of 16 hours light and 8 hours dark light at 22-24 degrees centigrade. After 6-8 days, leaves of cotyledon were cut in 8-10 mm size (explant) and were transferred to the induction medium.
Making induction medium
This experiment included three separate plans (A, B, C) and each plan has two different culture mediums that were called 'a' and 'b'. In the first plan (A), culture medium 'a' contained the MS medium, 2 mg/l naphthalene acetic acid (NAA), 0.5 mg/l benzyl aminopurine (BAP), 50 mμ silver nitrate and several concentrations of Put according with [Table 1]. The slices of cotyledons were transformed into medium 'a'. Then, after 10 days, the explants were moved to media 'b' that was similar 'a' but without NAA and BAP. We transformed the explant in second medium ('b') due to the results to Mandal works. He reported the best concentration for somatic embryogenesis was usage of 2 mg/l NAA and 0.5 mg/l BAP and lessening the NAA through the first stage of embryo genesis can be more effective on it. , The second plan (B) was similar to 'A' project but in medium 'a' Put is not used. As mentioned above, the explants in design B were moved to 'b' medium with several concentrations of Put [Table 1]. In plan C, first of all, the explants were moved to medium (a) containing MS plus NAA with concentration of 2 mg/l and 50 mM silver nitrate and after 10 days they were transferred to medium 'b' involving BAP and several levels of Put.
| Results|| |
Result of seed and tissue culture
Safflower seeds germinated after 24 hours and the growing power was about 97% after 7 days. Nearly, the colour of callus in every plan above was both light green and light yellow colour. In addition, induction callus was viewed about 80-85% in all cases. In each plant, the number of callus that had rooting and inducing shoot was counted separately. Then, results base on clustering was analysed by Statistical Package of Social Sciences (SPSS) software.
Results indicate all treatments are in three groups regarding shoot generation [Figure 1]. Maximum shoot regeneration belonged to Put A4 that with Put A2 are in same group (Group 3). This group has the highest rate of stem formation that is significantly different from the other two groups. Flowering was also observed in the same treatment (Put 4) after 40 days. From the shoot creation point of view, data analysis suggests that all treatments in C plan, except of Put C5, are in group 2 along with Put B2 from plan B. The number of shoot induction in this group is fewer than third group and greater than the first group and the difference is significant. Others concentration of Put in A plan (Put A1, Put A3, Put A5) with its control are in the same group (group 1) where lowest shoot regeneration occurred. In other words, in this group (Group A) shoot regeneration rate is close to zero. In addition, the control of plan B and C are in group 1. The important point is the presence of all treatments of plan B in this group except from Put B2. So, the treatments that were different from controls including Put A2, Put A4, Put B2, Put C1, Put C2, Put C3 and Put C4 [Figure 1] and [Figure 2], [Table 1].
|Figure 2: The effect of diamine on shoot regeneration in Plan A, B and C|
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In the case of rooting, the process was similar. Data analysis and cluster analysis are shown in [Figure 3] and [Figure 4]. According to the terms of rooting, all treatments are in three groups as shoot formation. The third group, with highest rate of rooting that has significant difference with the other two groups at 95%, includes Put A1, Put A5, control A, Put B1, Put B2 and control B. Other treatments of plan A (Put A2, Put A3 and Put A4) with other treatments of plan B (Put B3, Put B4 and Put B5) are in group 2. Rooting rate in this group is fewer than group 3 but is greater than the first group. First group, with the lowest rooting rate consists of all treatments and control of plan C [Figure 3] and [Figure 4]. It seems the main reason for decreasing the rooting rate was due to the absence of BAP in step a (C plan) and high diamine did not effect on it, because the control of this group shows less rooting rate rather than the controls of group A and B. However, it seems that the Put reduced the rooting rate generally. This result is because of most rooting in the control of A and B plan and considering the kind of plan and presence or absence of Put. But, we see the different behaviours regarding concentration of Put and its interaction with BAP. Then, we observed reducing the rooting rate with middle and high concentration of diamine.
In spite of indirect organogenesis in all of the three plans, we only could see somatic embryogenesis in plan C which was so observable and distinct [Figure 5]. Most of the results were taken from the high level of Put (unpublished).
|Figure 5: Somatic embryogenesis in plan C. Up: For Put C5. Down: For PutC4|
Click here to view
Results of peroxidase enzyme activity
The data from peroxidase in all three projects were analysed by using SPSS software in randomized complete block design. The data indicate a significant difference in peroxidase activity at 1%. Maximum peroxidase activity belonged to plan A and Put A4 treatment that maximum shoot regeneration was observed in this treatment, whereas second plan (B) had minimum activity and Put B1 and Put B2 had significant difference by Put A4 and Put A5 at 99%. Also, Put B1 and Put B2 were in the group by the lowest shoot regeneration. The data analyse demonstrated high levels of enzyme activity was during the first plant A so that the highest activity (Put A4) had significantly different from second stage such as Put B1, Put B2, Put B3 and Put B5 which showed the lowest shoot regeneration. But, there was no significant difference with Put B4. On the other hand, data analysis showed a statistically difference between Put A4 and treatments third plan, such as Put C1, Put C2, Put C3 and Put C5. There is no difference between control group and the treatments but treatments are different [Figure 6].
| Discussion|| |
Despite the importance of safflower as an oilseed and medicinal crop, a little information is available about in vitro culture of this plant. However, Mandal et al. observed high somatic embryogenesis in 2 mg/l and 0.5 mg/l concentration of NAA and BAP, respectively, and they also reported formation of bud and new shoot in explants cotyledons of this plant ,, after changing in content of these hormones. Therefore, according this work, we transformed explants to new environment.
PAS are involved in many phases of plant growing such as cell division, embryogenesis, development of reproductive organs, root growth, beginning of flowering, development of flowering and fruit, senescing and stresses. , The internal Put level increased before stages of shoot regeneration, callus induction and rooting in Passiflora.  The effect of Put and spermidine on direct shoot regeneration of cotton was reported and it increased in present 20 mg/L of Put. Although the effect of PAS on shoot growth and development has been reported but the works of Ganesan were the first studies about the effect of these hormones on direct shoot growth.  As mentioned above, there are several reports that suggested effect of these materials on cell growth, somatic embryogenesis and shoot growth. Spermidine is essential for shoot regeneration in cucumber and sugarcane. , Also, in a dicotyledonous plant (Momordica charantia L.), Put, Spm and Spd caused to increase the number stem creation. 
In this work, we found that maximum shoot regeneration belonged to Put A4 and Put A2 that are in the same group (Group 3). This group has a highest rate in stem formation that is significantly different from the other two groups. Since the control of each project was in the first group (with minimum shoot regeneration) and when they were compared with treatments and several concentrations of Put, it can be generally stated that the concentrations of Put caused the increasing shoot regeneration in safflower. Because, the controls stem regeneration in each plan was about zero. These results are consistent with impact of these substances on plant growth and development, especially on stems. But the role of Put concentration and present of BAP and relation between them is different. According to data analysis, it appears that the presence of BAP in 'b' and its absence in stage 'a' (C plan) with Put (regardless of the concentration) increased shoot regeneration in comparison with B plan. So, interactions between these two hormones have an important role in the development of new organs of safflower, especially in the stem. Given that Put A2 and Put A4 in A plan had highest shoot regeneration. So, these two concentrations are key levels in shoot making at this plant. This note is important when all treatment of plan B apart from Put B2 are placed in a control group (minimize shoot generation = 0). Therefore, the concentration of Put and its interaction effects with BAP in shoot growth and development is important. There is a little information about this interaction. The effect of cytokinin and light on PAS has been studied. In this experiment, increasing level of Put because of cytokinin treatment have been reported.  It appears that specific range of Put caused the growth shoot induction that it is interacting with its concentration and BAP because the more concentration reduced shoot regeneration.
The role of PAS in formation and growing of roots has been studied several times. However, more information is on Phaseolus and Vigna.  Jarvis and his colleagues found evidence that PAS not only are associated with starting rooting but also are essential for root growth.  The studies on some plant species showed a relation between a depletion of PAS and inhibition of root growth. In addition, the aging is often associated with decreased levels of PAS. , Thus, the biosynthesis restraint of Put causes reduction starting root growth while rising in external removes this inhibitory. So, Put can be as a marker for differentiation of root. , Also, Ivan (2004) proved that PAS have a major role in control, cell division and primary and secondary roots differentiation. 
In this research, the third plan has a significant reduction rather than first and second plan regarding rooting; the reason might be the absence of BAP in phase 'a' of this plan. Since all treatments of this plan and its control had the lowest rooting rate, the presence of BAP in step 'b' of C plan and its interaction with Put caused decline root growth in comparison with other plans. However, the amount of rooting decreased in B plan with increasing concentration of Put. In other words, according to plan A and B, we can say the presence of BAP in step 'a' and increasing concentration of Put caused this event. Some reports showed effect of Put, Spd and Spm in 0.001 mM on raising roots number and length. Nevertheless, the number and length of root decreased in 1- 0.01 mM. , In some plant species, there is negative relationship between Put aggregation and growth of primary root. Even interceptor of Put increased root growth in tobacco. However, other species such as the Kerguelen cabbage in a wide range of endogenous Put pool (2-12 μ mol.g-1 DW) did not any effect on root growth, but lower concentrations at 2 μ mol.g-1 DW, increased the primary root growth. , . So, the high concentration of PAS inhibits root growth and in this project, we used silver nitrate to prevent vitrification, also it is interceptor of ethylene, which possibly increased endogenous Put. This action with use of external Put may be a barrier for rooting.
Plant peroxidases (POD) involve in many physiological processes such as growth regulation and cell development, Auxin metabolism, fruit development and wood stage. These enzymes involve in many processes such as protection against oxidative factor item for example H2o2, chlorophyll degradation, aging and processes related to browning, wound healing and resistance to drought. , Also, there are some reports that indicate this enzyme have an antifungal role too. Thus, POD is a multifunctional enzyme and one of its functions is Auxin catabolism. Peroxidase has a role in regulation of cells growth by varying the amount of Indole-3-acetic acid (IAA) and IAA oxidative catabolism. Therefore, these enzymes probably limit growth by hardening the cell wall and POD will control the final form of cells by catalyzing reaction of cross-linked cell wall composition. ,
Diamines and PAS decompose by diamine oxidase and polyamine oxidase; and in the aerobic condition, H2O2 is formed by these enzymes. Studies have shown that increased level of PAS and their biosynthesis enzymes caused to raise cell division in many cells such as embryonic of carrots and tomato and tobacco ovum and also associated with fruit development. , abiotic and biotic stress stress effects the releasing of spermidine/spermine to the apoplast in order to acting of diamine and PAS oxidase. The result is the production of hydrogen peroxide. The accumulation of H2O2 dependent on level of internal PAS is associated with resistant response or cell death. ,
Kaur and his colleagues found that PAS affect on flowering in tobacco in 2003. These results and the likes indicate that PAS play a role in the beginning of flowering and its development. Many processes of plant growth and development being regulated by plant hormones such as Auxin and ethylene are linked in changing PAS metabolism. This change in any level of PAS synthesis and its enzymes biosynthesis occur that is special for any tissue. 
According to these data, the group with the highest shoot regeneration (A plan- Put A4) had also maximum peroxidase activity and the treatments of B plan with the lowest shoot regeneration had lowest enzyme activity. Therefore, these results confirm the increase in peroxidase activity during shoot regeneration that is consistent with reports of Rajeswari. He reported increasing peroxidase activity until 15 days after shoot regeneration and afterwards reduction enzyme activity until initiate rooting. , It is important to note that flowering only in the Put 4 =./16g/l Put was obtained. In the other hand, by looking at the overall results, we can say that in second phase and as well as the absence of BAP in first phase (B and C plan), Put reduced peroxidase activity slightly. So, the treatment Put 4 has a key role in growth and development of safflower. There are some reports in controlled laboratory condition that Put increased activity of polyphenols peroxidase and catalase, but this combination reduced the peroxidase activity.  Although pretreatment with some PAS as spermidine and spermine did not effect on activity of this enzyme,  but unlike this, he and his colleagues showed that Put decreases peroxidase activity. So, the result of this project confirm that Put decrease activity of this enzyme. Since this enzyme involves in wide range of reactions, its activity is definitely affected by the growth phase such as shoot regeneration, rooting and callus production.  For example, Joersbo (1989) stated that there was an increase in peroxidase activity in embryo cells one day before globular embryo stage. 
On the other hand, the data analysis indicates significant differences between Put A4 treatment and all treatments of C plan. However, there was no difference among treatments in comparison with controls. But as mentioned above, there was a difference among treatments. The reason may be assumed that the cutting in plant produce a stress that may increase level of peroxidase even in controls group.
| References|| |
Li D, Mündel H-H. Safflower, Carthamus Tinctorius L. ???: Bioversity International; 1996.
Weiss EA. Oilseed crops: Blackwell Sci; 2000.
Aigner-Held R, Daves GD Jr. Polyamine metabolites and conjugates in man and higher animals: A review of the literature. Physiol Chem Phys 1980;12:389-400.
Igarashi K, Kashiwagi K. Characteristics of cellular polyamine transport in prokaryotes and eukaryotes. Plant Physiol Biochem 2010;48:506-12.
Seiler N, Atanassov CL, Raul F. Polyamine metabolism as target for cancer chemoprevention (review). Int J Oncol 1998;13:993-1006.
Tabor C, Tabor H. Polyamines. Annu Rev Biochem 1984;5:749-90.
Tiburcio AF, Kaur-Sawhney R, Galston AW. Polyamine metabolism and osmotic stress. II. Improvement of oat protoplasts by an inhibitor of arginine decarboxylase. Plant Physiol 1986;82:375-8.
Slocum RD, Kaur-Sawhney R, Galston AW. The physiology and biochemistry of polyamines in plans. Arch Biochen Biophys 1984;325:283-303.
Slocum RD, Galston AW. Changes in polyamine biosynthesis associated with postfertilization growth and development in tobacco ovary tissues. Plant Physiol 1985;79:336-43.
Murashige T, Skoog F. A revised medium for rapid growth and bio assays with tobacco tissue cultures. Physiol Plant 1962;15:473-97.
Mandal AK, Chatterji AK, Duta Gupta S. Direct somatic embryogenesis and plantlet regeneration from cotyledonary leaves of safflower. Plant Cell Tissue Organ Culture 1995;43:287-9.
Mandal Ak, Gupta SD, Chatterji AK. Factors affecting somatic embryogenesis from cotyledonary explant of safflower. Biol Plantarum 2001;44:503-7.
Prasad B. Influence of genotype and cold pre-treatment on anther culture response in safflower, Carthamus tinctorius L. Indian J Exp Biol 1990;28:924-7.
Bais H, Ravishankar GA. Role of polyamines in the ontogeny of plants and organ culture. Plant Biol (Stuttg) 2002;69:1-34.
Evans P, Malmberg R. Do polyamines have a role in plant development? Annu Rev Plant Physiol Plant Mol Biol 1989;40:235-69.
Harsha V, Desai AR. Changes in polyamine levels during shoot formation, root formation, and callus induction in cultured passiflora leaf discs. J Plant Physiol 1985;119:45-53.
Ganesan M, Jayabalan N. Infunce of cytokinin, auxin and polyamines on in vitro
mass multiplication of cotton (Gossypium hirsutum L. cv.SVPR2). Indian J Exp Biol 2006;44:506-13.
Uma Shankar CA, Ganapathy M. Manickavasagam, Influence of polyamines on shoot regeneration of sugarcane (Saccharum officinalis L). Egypt J Biol 2011;13:44-50.
Vasudevan A. Leucine and spermidine enhance shoot differentiation in cucumber (Cucumis sativus L.). In Vitro
Cell Dev. Biol Plant 2008;4:300-6.
Muthu TC, Ill-Min, Se-Chul C. Influence of polyamines on in vitro
organogenesis in bitter melon (Momordica charantia L.). J Med Plan Res 2012;6:3579-85.
Mark AW, Dane RD, Erwin B. Effects of cytokinin and light on polyamines during the greening response of cucumber cotyledons. Plant Cell Physiol 1988;29:201-5.
Jarvis BS, Yasmin, Coleman M. RNA and protein metabolism during adventitious root formation in stem cuttings of Phaseolus aureus cultivar berkin. Physiol Plant 1985;64:53-9.
Tisi A, Angelini R, Cona A. Does polyamine catabolism influence root development and xylem differentiation under stress conditions? Plant Signal Behav 2011;6:1844-7.
Hummel I, Couée I, El Amrani A, Martin-Tanguy J, Hennion F. Involvement of polyamines in root development at low temperature in the subantarctic cruciferous species Pringlea antiscorbutica. J Exp Bot 2002;53:1463-73.
Tiburcio AC, Gendy TT. Morphogenesis in tobacco subepidermal cells: Putrescine as a marker of root differentiation. Plant Cell Tissue Organ Culture 1989;19:43-54.
Ivan C. Involvement of polyamines in root development. Plant Cell Tissue Organ Culture 2004;76:1-10.
Gurung S, Cohen MF, Fukuto J, Yamasaki H. Polyamine-induced rapid root abscission in azolla pinnata. J Amino Acids 2012;2012:493209.
Tisi A, Federico R, Moreno S, Lucretti S, Moschou PN, Roubelakis-Angelakis KA, et al
. Perturbation of polyamine catabolism can strongly affect root development and xylem differentiation. Plant Physiol 2011;157:200-15.
Hummel I, El-Amrani A, Gouesbet G, Hennion F, Couée I. Involvement of polyamines in the interacting effects of low temperature and mineral supply on Pringlea antiscorbutica (Kerguelen cabbage) seedlings. J Exp Bot 2004;55:1125-34.
Goldberg R. Development of epidermal cell wall peroxidases along the mung bean hypocotyl: Possible involvement in the cell wall stiffening process. J Exp Bot 1987;38:1378-90.
Lagrimini LM. Wound-induced deposition of polyphenols in transgenic plants overexpressing peroxidase. Plant Physiol 1991;96:577-83.
Ros Barceló A, Pedreño MA, Ferrer MA, Sabater F, Muñoz R. Indole-3-methanol is the main product of the oxidation of indole-3-acetic acid catalyzed by two cytosolic basic isoperoxidases from Lupinus. Planta 1990;181:448-50.
Bruyant P, Schauman A. A effect of light on total proteins and peroxidase activities in culture medium and in the cell wall fraction cultured flax cells. Plant Phys Biol 1996;34:417-23.
Kaur-Sawhney R. Polyamines in plants. J Cell Mol Biol 2003;2:1-12.
Christensen JH, Bauw G, Welinder KG, Van Montagu M, Boerjan W. Purificatin and characterization of peroxidases correlated with lignification in poplar xylem. Plant Physiol 1998;118:125-35.
Gaspar T. A two step control of basic and acidic peroxidases and its significance for growth and development. Physiol Plant 1985;64:418-23.
Cheniany M. Effect of endogenous phenols and some antioxidant enzyme activities on rooting of Persian walnut (Junlans regia L.). Afr J Plant Sci 2010;4:179-487.
Rajeswari V, Paliwal K. Peroxidase and catalase changes during in vitro
adventitious shoot organogenesis from hypocotyls of Albizia odoratissima L.f. (Benth). Acta Physiol Plant 2008;30:825-32.
Lokman Ö, Yavuz D. Effects of putrescine and ethephon on some oxidative stress enzyme activities and proline content in salt stressed spinach leaves. Plant Growth Regul 2003;40:89-95.
Velikova V, Yordanov I, Edreva A. Oxidative stress and some antioxidant systems in acid rain-treated bean plants. Protective role of exogenous polyamines. Plant Sci 2000;151:59-66.
Krsnik-Rasol M. Peroxidase as a developmental marker in plant tissue culture. Int J Dev Biol 1991;35:259-63.
Joersbo M, Andersen JM, Okkeis FT, Rajagopal R. Isoperoxidases as markers of somatic embryogenesis in carrot cell suspension cultures. Physio Plant 1989;76:10-6
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]