Tissue culture: why do auxin and cytokinin ratios decide roots vs shoots, and is the pomato real or a failure?
Pooja Iyer12th Sample
23 Sept 2026 · 1 min read
Tissue culture is giving me dramatic confusion this week. I understand totipotency (any living plant cell can grow into a whole plant, given the right conditions) and that we take an explant, put it on a nutrient medium with growth regulators, and get a callus. But then the details start slipping.
- Growth regulators: I read that the ratio of auxin to cytokinin decides what you get. Which ratio gives roots and which gives shoots? I keep swapping them.
- Virus-free plants: NCERT says even if the plant is infected, the apical meristem is free of virus, so we can culture meristem to get healthy plants. But why? Why doesn't the virus get into the meristem if it is in the plant?
- Somatic hybridisation: protoplast = cell without wall. I wrote that we use "pectinase" to remove the wall. Is that enough? And what is used to fuse the protoplasts? Then the pomato. Did it actually work?
I did make a mnemonic for the regulators but I'm scared I memorised it backwards. Help me, someone who has done this chapter!
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[+][–]Tanvi Deshmukh12thSample· 26d ago
Okay roots/shoots: high auxin : low cytokinin = roots, high cytokinin : low auxin = shoots. My trick: auxin → "A for Anchor" (roots). Cytokinin → "K for Kids" (new shoots, new buds, new cell divisions). Both together in the medium and the cells divide to form a callus.
[+][–]Pooja Iyer12thSample· 26d agoAuthor
omg "Kids" is exactly the mnemonic I needed, my version was backwards 😭 thank you thank you
[+][–]Tanvi Deshmukh12thSample· 26d ago
yay!! always write the auxin one first, A comes before K, high auxin first = roots first 😄
[+][–]Meera Patel11thSample· 26d ago
Pooja, one correction on the protoplast. Pectinase alone is not enough. Plant cell walls have cellulose in them, so you need cellulase and pectinase: cellulase digests cellulose, pectinase digests pectin of the middle lamella and wall. Then the naked protoplasts of two different species are fused using polyethylene glycol (PEG) or with an electric current, and the fused cell is grown to a hybrid.
[+][–]Siddharth RaoDropperSample· 26d ago
Pomato: the fusion of protoplasts of potato and tomato gave a hybrid plant that grew, but NCERT notes that it did not have all the desired characters of a useful crop. Don't write "pomato was successful" in a descriptive answer, write "it demonstrated that distant species can be fused but the practical outcome wasn't a useful crop". That is how I'd phrase it for a 3 mark.
[+][–]Diya Menon11thSample· 26d ago
Meristem virus thing: the textbook just states it as fact. In class our teacher said a few reasons are usually given. The apical meristem cells are dividing really fast, and it doesn't have well-developed vascular tissue, and viruses mostly spread in plants through the vascular system and plasmodesmata. So the meristem tip stays virus-free or has very little, and you can grow a clean plant from it. Not 100% sure which reason NCERT prefers, but for MCQs the answer is simply "meristem culture gives virus-free plants".
[+][–]Farhan ShaikhDropperSample· 26d ago
Practical note: the cells that come out of tissue culture are called somaclones and they are genetically identical to the parent. This is why micropropagation is used for tomato, banana and apple on a commercial scale. Quick exam point: it's "micropropagation" when you make many plantlets quickly from small plant parts.
