FOTOSENTETİK KARBON FİKSASYONUNDA ROL ALAN ENZİMLERİN ANTİSENSE İNHİBİSYONU

Bir yapraktaki fotosentetik aktivite Calvin döngüsü içindeki çeşitli enzimlerin aktivitesitarafından regüle edilebilir. Calvin döngüsü içindeki spesifik enzimlerin antisenseinhibisyonu, bu döngünün metabolik regülasyonunun anlaşılması için önemli ip uçlarıvermektedir. Sedoheptulose-l,7-bifosfataz antisense bitkileri üzerinde yapılan analizler, buenzimin aktivitesindeki %35’ lik bir düşüşün bile fotosentetik karbon asimilasyonununazalması için yeterli olduğunu göstermiştir. Bu sonuçlara karşıt olarak, indirgenmiş ribuloz-1,5 bifosfataz/oksijenaz, fruktoz-l,6-bifosfataz, fosforibulokinaz ve gliseraldehit-3-fosfatdehidrogenaz aktivitelerine sahip transgenik bitkilerde ise, fotosentetik karbonasimilasyonunda herhangi bir etki görülmesi için bu enzimlerin aktivitelerinde %65 ve %90arasında bir azalmaya gereksinim olduğu bulunmuştur. Ayrıca tüm antisense bitkilerdeCalvin döngüsü enzimlerinin inhibisyonu nişasta miktarını düşürürken sukroz miktarındaönemli değişimler kaydedilmemiştir. Fakat fotosentezde görülen bu değişimin bitkininbüyüme ortamına veya kısa ya da uzun süreli deney ortamına bağlı olarak değiştiğisaptanmıştır.

Anahtar Kelimeler:

Antisense, Calvin döngüsü, transgenik bitkiler

Antisense Inhibition of Photosynthetic Carbon Fixation Enzymes

The photosynthetic capacity of a leaf might be regulated by the activity of various enzymesof the Calvin cycle. The antisense inhibition of specific enzymes in Calvin cycle haveprovided important tools to understand metabolic regulation of the cycle. The analysiscarried out on the sedoheptulose-l,7-bisphosphatase antisense plants indicated that even35% reduction in the ezymes activity was enough to reduce photosynthetic carbonassimilation. In contrast to these results, transgenic plants with reduced levels of ribulose-1,5- biphosphatase/oxygenase, fruktose-l,6-bisphosphatase, phosphoribulokinase andglyceraldehyde-3- phosphate dehydrogenase, reductions of between 65% and 90% in theactivities of these enzymes were required before any effect on photosynthetic carbonassimilation was observed. Also antisense inhibition of all Calvin cycle enzymes resulted inreduced starch level while sucrose level was maintained. However, it was shown thatchanges in photosynthesis was depend on the environmental conditions and short or longterm experimental sudies.

Keywords:

Antisense, Calvin cycle, transgenic plants,

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