FISIOLOGI TUMBUHAN 4 Pembungaan
Delayota Science Club April 2011
Bunga dan Penggambarannya
Bunga dapat dideskripsikan dalam: Diagram bunga: lukisan bunga dalam bentuk simbolsimbol grafis tertentu yang menunjukkan bagianbagian bunga dan jumlahnya. Rumus bunga: deskripsi bunga dalam bentuk simbolsimbol yang berupa huruf dan angka, menunjukkan bagian-bagian bunga dan jumlahnya.
Pembungaan Tumbuhan berbunga (antophyta) tak membentuk bunga setiap saat. Berdasarkan banyaknya waktu pembungaan selama hidupnya, tumbuhan bunga dibedakan menjadi: Tumbuhan annual: tumbuh dan berbunga lalu mati pada satu musim. Tumbuhan biennial: tumbuh pada satu musim lalu berbunga dan mati pada musim berikutnya.
Proses pembentukan bunga pada tumbuhan berbunga disebut pembungaan.
Tahap-tahap Pembungaan Induksi/Evokasi : meristem vegetatif diprogram untuk berubah menjadi meristem generatif, dipengaruhi oleh faktor endogen dan faktor eksogen. Inisiasi: terjadinya pembentukan kuncup morfologis deteksi secara makroskopis Anthesis: terjadinya pemekaran bagian-bagian bunga. Polinasi: sampainya serbuk sari ke kepala putik, umumnya diikuti dengan fertilisasi (pembuahan).
1. Photoperiodic
2.Autonomous/vernalization
3. Carbohydrate
4. Gibberellin
FRI Integrates signals from all pathways Transcription factor Transcription factor
Establishes floral meristem identity
Four Developmental Pathways Regulating Flowering
Pengaturan Genetis The meristem is replaced by floral organ whorls (concentric circle): sepals, petals, stamens, carpels.
Model yang digunakan untuk menjelaskan mekanisme pengaturan ini adalah model gen ABC. Menurut model ini terdapat: Gen A: Apetala1*, Apetala2 Gen B: Apetala3*, Pistillata* Gen C: Agamous*
Tanda * menunjukkan bahwa gen tersebut juga mengatur kemunculan faktor transkripsi (MADS box).
Mutasi dapat menyebabkan bagian bunga tidak muncul atau berada di tempat yang tidak semestinya.
No sepals No petals
No stamen, no carpel
Mutasi pada gen Apetala2 (gambar tengah) dan mutasi pada gen Agamous (gambar kanan)
Pengaturan Fotoperiodisme Fotoperioda adalah fenomena panjang hari menentukan apakah meristem pucuk /lateral suatu tumbuhan mampu membentuk bunga atau tidak. Dua tipe fotoperioda: Fotoperioda obligat: tidak dapat berbunga apabila panjang hari tidak sesuai Fotoperioda fakultatif: dapat berbunga apabila panjang hari tidak sesuai, dengan cara diinduksi.
Penemuan fotoperioda melalui percobaan: EXPERIMENT
During the 1930s, USDA scientists briefly exposed batches of lettuce seeds to red light or farred light to test the effects on germination. After the light exposure, the seeds were placed in the dark, and the results were compared with control seeds that were not exposed to light.
Dark (control)
RESULTS
Red
Dark
Red Far-red
Dark
The bar below each photo indicates the sequence of red-light exposure, far-red light exposure, and darkness. The germination rate increased greatly in groups of seeds that were last exposed to red light (left). Germination was inhibited in groups of seeds that were last exposed to far-red light (right).
CONCLUSION Red light stimulated germination, and far-red light inhibited germination. The final exposure was the determining factor. The effects of red and farred light were reversible. Red Far-red Red
Dark
Red Far-red Red
Far-red
Tumbuhan memiliki sensor panjang hari (day length) yang terletak pada daun. Plants have specific photoreceptors. Different photoreceptors detect different wavelengths of light, for example: Phytochromes (red and far-red light) Cryptochromes (blue, green, UV-A light) Phototropin (blue light) UV-B receptor (still not identified)
Stimulus pembungaan dapat ditransmisikan melalui sambung pucuk pada tanaman yang sama atau bahkan berbeda spesiesnya Key regulatory interactions in the leaf and at the shoot apex. Direct interactions are indicated by bold lines (regulation of mRNA levels refers to transcriptional control)
Photoperiodic regulation of flowering Short-day plants flower when the day length is less than (or the night length exceeds) a certain critical duration in a 24-h cycle.
Short-day (long-night) plants flower when night length exceeds a critical dark period. Interruption of the dark by brief light treatment prevents flowering.
Long-day plants flower when the day length exceeds (or the night length is less than) a certain critical duration in a 24-h cycle.
Long-day (short-night) plants flower if the night length is shorter than a critical period. In some long-day plants, 15 shortening the night with a night break induces flowering.
Phytochrome is the primary photoreceptor in photoperiodism Short-day (long night) plant
Long-day (short night) plant A flash of red light during the dark period induces flowering in a long-day plant, and effect is reversed by far-red light. → involvement of phytochrome In a short-day plant, red light prevents flowering, and effect is reversed by flash of16 far-red light.
Effects of the duration of the dark period on flowering Treating short- and longday plants with different photoperiods shows that the length of the dark period is critical.
Chrysanthemum Rice, Kalanchoe Poinsettias Morning glory (Pharbitis) Cocklebur (Xanthium) Soybean
Hibiscus Fuchsia Spinach Arabidopsis Sugar beet Radish
Day-neutral plants rice Kidney bean Desert plants Cucumber Tomato
17
Pengaturan Hormonal The flowering signal, not yet chemically identified, is called florigen, and it may be a hormone or a change in relative concentrations of multiple hormones.
