EFEKWARNALIGHTEMITTINGDIODE(LED)TERHADAP EKSPRESIGENYANG TERLIBAT DALAMMETABOLISME DAN BIOSINTESISASAM ASKORBATPADABUNGA BROKOLI

Chandra Kurnia Setiawan, Dr. Ir. Supriyadi, M.Sc.

2013 | Tesis | S2 Ilmu dan Teknologi Pangan

Asam Askorbat merupakan salah satu antioksidan yang banyak ditemukan di tanaman. Asam askorbat berfungsi sebagai pelindung dari cahaya, mengikat reaktif oksigen spesies (ROS) yang dihasilkan oleh proses oksigen fotoproteksi dan fotorespirasi. Biosintesis dan metabolisme asam askorbat melibatkan 10 macam enzim yaitu, BO-VTC1, BO-VTC2, BO-GLDH, BO-APX1, BO-APX2, BOsAPX, BO-MDAR1, BO-MDAR2, BO-DHAR, BO-GR. Penelitian mengenai efek penggunaan LED pada ekspresi gen yang terlibat dalam biosintesis dan metabolisme di bunga brokoli varietas “Ryokurei”, dilakukan menggunakan LED warna merah (660 nm) dan biru (470 nm) sebagai sumber cahaya serta LED warna putih dan perlakuan tanpa cahaya sebagai kontrol. Ekspresi gen yang terlibat dalam biosintesis dan metabolisme asam askorbat, kandungan asam askorbat, warna, kandungan klorofil dan produksi etilen bunga brokoli diamati selama 4 hari. Hasil penelitian menunjukan setelah perlakuan selama dua hari, LED merah signifikan (p<0,05) dapat menghambat penurunan kandungan asam askorbat dibandingkan dengan kontrol (tanpa cahaya) dan LED putih. Hasil tersebut diperkuat dengan hasil pengamatan menggunakan Real-Time Quantitative RT-PCR menunjukan LED merah dapat menekan level mRNA BOAPX1, BO-APX2 dan BO-sAPX pada hari ke-tiga. Pengamatan level mRNA BOGLDH yang meningkat pada hari ketiga menunjukan penyinaran lampu LED merah meningkatkan biosintesis asam askorbat hingga level transkripsi. Enzim yang kemungkinan bertanggungjawab pada metabolisme dan biosintesis asam askorbat berturut-turut Askorbat Peroksidase (APX) dan L-Galaktono-1,4-Lakton Dehydrogenase (GLDH). Pengaturan ekspresi gen tersebut mungkin berkontribusi terhadap penghambatan penurunan kandungan asam askorbat oleh perlakuan lampu LED merah pada bunga brokoli. LED warna merah juga menunjukan penghambatan yellowing dan penurunan kandungan klorofil pasca panen bunga brokoli.

Ascorbate is one of the most abundant soluble antioxidant in plant. Multiple functions of ascorbate in photoprotection have been proposed, including scavenging of reactive oxygen species generated by oxygen photoreduction and photo respiration. Biosynthesis and metabolism of ascorbic acid involves 10 kinds of enzymes, that are BO-VTC1, BO-VTC2, BO-GLDH, BO-APX1, BO-APX2, BOsAPX, BO-MDAR1, BO-MDAR2, BO-DHAR, BO-GR. The effect of light-emitting diodes (LED) light on ascorbate (AsA) biosynthesis and metabolism in broccoli (Brassica oleracea L. variety italica) cultivar “Ryokurei”, were studied using red (660 nm), blue (470 nm) and white LED lights as the light source and also no light treatment as the control. Gene expression involved in the biosynthesis and metabolism of AsA, AsA content, color, chlorophyll content and ethylene production rate on the postharvest broccoli were observed in 4 days. The result showed that after 2 days, red light treatment significantly (p < 0,05) delayed the decrease of ascorbate content. The result was supported by observations using Real-Time Quantitative RT-PCR showed that red light treatment can suppress mRNA level of BO-APX1, BO-APX2, and BO-sAPX in third day. Observations of BO-GLDH mRNA level was increased in the third day exposure of red LED light. Therefore red LED light showed up-regulated AsA biosynthesis transcriptional level. Enzymes which possibility responsible for AsA metabolism and biosynthesis in a row were Ascorbate Peroxide (APX) and LGalactono- 1,4-Lactone Dehydrogenase (GLDH). The regulation of this gene expression might contribute to the suppression of AsA reduction by red LED light treatment in broccoli. Red LED also showed suppression of yellowing and decline the chlorophyll content in postharvest broccoli.

Kata Kunci : Asam Askorbat, LED, Brokoli, Ekspresi Gen, Real-Time Quantitative RT-PCR