Palavan Narçin ÜNSAL, Serap ÇAĞ, Ergül ÇETİN

The role of meta-topolin in senescence of wheat leaf segments

Birçok araştırma sitokininlerin farklı gelişim olaylarında örneğin kök büyümesi ve dallanmasında, gövdede apikal dominansinin kontrolünde, kloroplast gelişiminde ve yaprak senesensinde teşvik edici veya ket vurucu işlevlere sahip olduğunu ortaya koymuştur. Son yıllarda Strnad ve ark. (1997) meto-topolin adı verilen yeni bir aromatik sitokinin keşfetmişler ve bu maddenin benziladenine potansiyel bir alternatif olduğunu ileri sürmüşlerdir. Biz daha önce buğday yaprak segmentlerinde senesens sırasında klorofil ve proteinin hızlı yıkımının aromatik sitokinin mefa-topolin tarafından önlendiğini gösterdik. Bu araştırmada meta-topolin uygulanan yaprak segmentlerinde peroksidaz aktivitesi kontrol yapraklarına kıyasla arttı, senesens gecikti ve total klorofil içeriğinde de benzer bulgular elde edildi. Ayrıca, mT in yüksek konsantrasyonda (0.5-1 mM) uygulanması poliamin içeriğinde azalışa, düşük konsantrasyonda ise (0.25 mM) artışa sebep oldu. Bundan başka, meta-topolm total klorofil kaybını azalttı ve benzer eğilim total azot içeriğinde de saptandı. Özetle meta-topolin'in antisenesens aktivitede yönlendirici bir mekanizmaya sahip olduğu sonucuna varılabilinir.

Meta-topolinin buğday yaprak segmentlerinin senesensindeki rolü

Numerous reports ascribe a stimulatory or inhibitory function of cytokinins in different developmental processes such as' root growth and branching, control of apical dominance in shoot, chloroplast development and leaf senescence. Recently Strnad et al. (1997) discovered a new aromatic cytokinin, namely mefa-topolin and they suggested this substance as a potential alternative of benzyladenin. hi our previous study we have determined that a rapid breakdown of chlorophyll and proteins in excised wheat leaf segments during the senescence period prevented by aromatic cytokinin meta-topolin . In this study, peroxidase activity was increased and senescence delayed compared to control leaves in meta-topolin treated leaf segments, and total chlorophyll content also exhibited similar results. Application of mT at high concentrations (0.5-1 mM) caused a decrement in polyamine content, but at low concentration (0.25 mM) it reasoned increment. Besides these, meta-topolin decreased the loss of total chlorophyll and it was estimated similar trends for total nitrogen content. In summary, according to the results of our study it can be concluded that mefa-topolin has a contributing mechanism of the antisenescence action.

PDF

___

Altman A. Retardation of leaf senescence by polyamines. Physiol Plant. 54: 189-193, 1982.
Altman A, Kaur-Sawhney R and Galston AW. Stabilization of oat leaf protoplasts through polyamine-mediated inhibition of senescence. Plant Physiol. 60: 570-574, 1977.
Arnon DI. Copper enzymes in chloroplasts, polyphenoloxidase in Beta vulgaris. Plant Physiol. 24: 1-15, 1949.
Bachrach U. Involvement of polyamines in plant growth and senescence. In: Adv Polyamine Res. Caldarera CM, Zappia V and Bachrach U (Ed). 3: 365-375, 1973.
Birecka H, Briber A and Catalfamo JL. Comparative studies on tobacco pith and sweet potato root isoperoxidases in relation to injury, indolacetic acid and ethylene effects. Plant Physiol. 52: 43-49, 1973.
Chen CT and Kao CH Senescence of rice leaves XXX, levels of endogenous polyamines and dark-induced senescence of rice leaves. Plant Cell Physiol. 32: 935-941, 1991.
Cho SC. Effects of cytokinin and several inorganic cations on the polyamine content of lettuce cotyledons. Plant Cell Physiol. 24: 27-32, 1983.
Feller UK, Soong T and Haeman RH. Leaf proteolytic activities and senescence during grain development of field-grown corn (Zea mays L.). Plant Physiol. 59: 290- 294, 1977.
Ford TW and Simon EW. Peroxidase and glucose-6 phosphate dehydrogenase levels in cotyledons of Cucumis sativus ( L.). J Exp Bot. 23: 423-431, 1972.
Galston AW and Kaur-Sawhney R. Polyamines in plant physiology. Plant Physiol. 94: 406-410, 1990.
Gilbert ML, Thompson JE and Dumbroff EB. Delayed cotyledon senescence following treatment with cytokinin, an effect at the level of membranes. Can J Bot. 58: 1797-1803, 1980.
Grover A and Sinha SK. Senescence of detached leaves in pigeon pea and chick pea: Regulation by developing pods. Physiol Plant. 65: 368-507, 1985.
Kaur-Sawhney R, Flores HE and Galston AW. Polyamine- induced DNA synthesis and mitosis in oat leaf protoplasts. Plant Physiol. 65: 368-371, 1980.
Kaur-Sawhney R and Galston AW. Interaction of polyamines and light biochemical processes involved in leaf senescence. Plant Cell Environ. 2: 189-196, 1979.
Kaur-Sawhney R, Shih L, Flores HE and Galston AW. Relation of polyamine synthesis and titer to aging and senescence in oat leaves. Plant Physiol. 69: 405-410, 1982.
Kraus TE, Hofstra G and Fletcher RA. Regulation of senescence by benzylaminopurine and uniconazole in intact and excised soybean cotyledons. Plant Physiol Biochem. 31: 827-834, 1993.
Liu H. A simple method for determining the relative activities of individual peroxidase isoenzymes in a tissue extract. Anal Biochem. 56: 149-154, 1973.
Middleton KR. New Nessler reagent and its use in the direct Nesslerization of Kjeldahl digests.j Appl Chem. 10: 281-286, 1960.
Mukherjee D and Rao KVM. Alteration patterns of hill activity, peroxidase activity and sugars of pigeon pea during maturation maturation and senescence. Indian J Plant Physiol. 36: 13-16, 1993.
Palavan-Ünsal N, Çağ S and Çetin E. Growth responses of excised radish cotyledons to meta-topolin. Canadian Journal of Plant Sciences. 82: 191-194, 2002a.
Palavan-Ünsal N, Çağ S, Çetin E and Büyüktunçer D. Retardation of senescence by mefa-topolin in wheat leaves. j Cell and Mol Biol. 1: 101-108, 2002b.
Parish RW. Studies on senescing tobacco leaf discs with special reference to peroxidase. I. The effects of cutting and of inhibition of nucleic acid and protein synthesis. Planta. 82: 1-13, 1968.
Richmond AE and Lang A. Effect of kinetin on protein content and survival of detached Xanthium leaves. Science. 125: 650- 1957.
Seiler N and Wiechmann M. Die Mikrobestimmung Von Spermin Und Spermidin als I-dimethylamino-naphtalin 5 sulfon saure Derivative. Hoppe S eyler's Z Physiol Chem. 348: 1285, 1967.
Srivastava SK, Raj ADS and Naik BI. Polyamine metabolism during aging and senescence of pea leaves. Indian J Exp Biol. 19: 440-444, 1981.
Srivastava SK, Washi DJ and Naik BL. Control of senescence by polyamines and guanidines in young and mature barley leaves. Phytochem. 22: 2151-2154, 1983.
Stoddart JL and Thomas H. Nucleic acids and proteins in plants. In: Encyclopedia of Plant Physiology. Boulter D and Parthier B (Ed). Springer-Verlag, Berlin and New York. 14A: 592-636, 1982.
Storey R and Beevers L. Proteolytic activity in relationship to senescence and cotyledonary development in Pisum sativum L. Planta. 133: 37-44, 1977.
Strnad M, Hanus J, Vanek T, Kaminek M, Ballantine JA, Fussell B and Hanke DE. Meta-topolin, a highly active aromatic cytokinin from poplar leaves (Populus x canadensis Moench., cv. Robusta). Phytochemistry. 45: 213-218, 1997.
Thimann KV. The senescence of leaves. In: Senescence in Plants, Thimann KV (Ed). CRC Press, Boca Raton, 88- 115, 1980.
Walker MA, Roberts DR and Dumbroff EB. Effects of cytokinin and light on polyamines during the greening response of cucumber cotyledons. Plant Cell Physiol. 29: 201-205, 1988.