Somaklonal variation Zulfahmi
Definition • Somaclonal variation is the variation seen in plant that have been produced by plant tissue culture
• Types of somaclonal variants – genetic changes • • • •
point mutations (e.g., Adh mutants in wheat) cytoplasmic (maternal inheritance) gene amplification (e.g., incr. gene copy no.) activation of transposable element
• Types of somaclonal variants – genetic changes • cytogenetic (changes to genome structure) » » » »
aneuploidy – gain or loss of 1 or more chromosomes polyploidy – gain or loss of an entire genome translocation – arms of chromosomes switched inversion – piece of chromosome inverted
• Types of somaclonal variants – epigenetic • change in phenotype that isn't stable during sexual propagation • may or may not be stable during asexual propagation • usu. undesirable in a breeding program, not always undesirable in propagation • habituation (most studied epigenetic change)
• Types of somaclonal variants – epigenetic • habituation (most studied epigenetic change) – defn – loss of exogenous requirement for a growth factor ( usu. a PGR); e.g., auxin, cytokinin habituation – detection – callus may lose requirement for a PGR in the process of several transfers to fresh medium
• Types of somaclonal variants – epigenetic • characteristics – often occur gradually – are regularly reversible (esp. in regenerated plants) – are not seed-transmitted
• Possible causes – the dedifferentiation – redifferentiation process • axillary shoot proliferation vs. organogenesis & embryogenesis • hypothesis of D'Amato – somaclonal variants are rare in micropropagated plants (when multiplication is by axillary branching of shoot tips/buds) – more common during shoot organogenesis & somatic embryogenesis (esp. w/a callus phase)
• Possible causes – the "culture environment" • the hypothesis – that tissue culture is inherently stressful to cultured plant cells • environmental stress is known to cause: – DNA methylation – the methylation of cytosine is known to cause gene inactivation; this may occur during the redifferentiation process – gene amplification – can result in incr. gene expression
• Possible causes – the "culture environment" • environmental stress is known to cause: – transpositional changes – inadequate control of the cell cycle (errors in microtubule synthesis, spindle formation) – importance of PGRs » scant evidence of direct mutagenic action » more evidence for transient modifications of phenotype (e.g., dwarfing)
Dalam kultur jaringan Mutasi yang terjadi adalah mutasi somatik Sangat dipengaruhi oleh kondisi sel itu sendiri Sel yang mengalami mutasi Melakukan pembelahan Membentuk sel yang berbeda dengan sel asalnya Tanaman yang berbeda Kultur Jaringan merupakan teknik perbanyakan vegetatif, hal ini membuktikan teknik vegetatif dapat menghasilkan tanaman yang tidak sama dengan tetuanya. Kultur Jaringan Memiliki potensi yang sangat besar dalam meningkatkan keragaman.
Li & Gray, (2005) Faktor-Faktor Yang mempengaruhi Keragaman Somaklonal Faktor Fisiologis
Perlakuan Auksin (2,4-D, 2,4,5-T) pada tanaman kelapa sawit menghasilkan buah yang bersayap
Faktor Genetik Keragaman genetik selama proses regenerasi kultur jaringan
merupakan perubahan pada tingkat kromosom Fenotipe Seolah-olah sama tetapi secara genetik berbeda Penempatan Heterokromatin yang terlambat menyebabkan terjadinya keragaman somaklon pada tan jagung
Faktor Biokimia • Faktor Biokimia merupakan faktor yang paling banyak terjadi (Jayasankar, 2005) • Metabolisme carbon menyebabkan fotosintesa lintasan karoten, biosintesa pati, Metabolisme nitrogen menjadi rendah
Induksi Keragaman somaklonal secara eksogen. 1). Pengaturan Penanaman eksplan • Pengaturan ZPT • Lamanya Pengkulturan • Organogenesis langsung • Induksi Kalus • Kultur Protoplas 2). Mutagen Penginduksi Keragaman Somaklonal • Kimia: (Kolkisin, EMS(Etil Metan Solfonat),DEMS(Dietil Metan Sulfonat)DES(Dietil slfonat)EL(Etilen Amin), ENH(Etit Nitroso Urea), (Metil Nitroso Urea)
• Fisik : Sinar X, Sinar Gamma,
MNH
• Somaclonal variation leads to the creation of additional genetic variability. Characteristics for which somaclonal mutants can be enriched during in vitro culture includes resistance to disease pathotoxins, herbicides and tolerance to environmental or chemical stress, as well as for increased production of secondary metabolites.
• Negative consequences (of somaclonal var.) – introduction of deleterious genes • dominant alleles – albinos, pollen sterility • recessive alleles – off-types that show up in progeny of seed-propagated cultivars – carry-over effect from tissue culture • common with asexually propagated plants • symptom – excessive and multiple branching of regenerated plants (lack of establishment of apical dominance)
• Applications to crop improvement – overcoming barriers to genetic exchange • embryo culture of interspecific hybrids (Lolium, Hordeum) • selection for stable mitosis, fertility in a hybrid; e.g., intergeneric hybrids of barley x canada wild rye
– seed cultivar improvement (e.g., Fusarium resistance in celery, white-flowered Torenia, tomato cultivars with higher soluble solids, better "flesh" color)
Identifikasi keragaman somaklonal
1). Konvensional (Karakterisasi Morfologi) 2). Analisis Molokuler RAPD (Ramdom Amplified Polymorphic DNA) RFLF (Restriction Fragment Length Polymorphism) AFLF ( Amplified Fragment length Polymorphism) 3). Analisis Isoenzim
