Cells that can become a plant

"Can one plant cell grow into a whole plant?" In 1958, F. C. Steward tested this. He took single cells from the phloem of a carrot and grew them in a liquid with simple sugars and hormones. The cells formed a lump, and the lump grew into a complete plant.

Here is what happened, step by step:

• Dedifferentiation: the specialised cells went back to being able to divide.
• They formed a mass of unspecialised cells.
• Redifferentiation: these cells became roots, a shoot, and finally a whole plant.

This ability is totipotency: one cell can become a whole organism, just as a fertilised egg (zygote) does.

Reading Steward's results (Table 3.6): only cells given light, air and a liquid medium grew, increasing their fresh weight by 20%. Without air (in a solid medium), or without light, their weight went down. Each condition was needed.

Indian scientists in this story: Sipra Guha Mukherjee and S. C. Maheshwari grew complete plants from anthers (the pollen-making part of a flower) on an artificial medium. This anther culture was a breakthrough for improving crops.

From a disease to a tool. Crown gall disease causes tumour-like swellings on stems, because cells there divide rapidly and without control. It is caused by the bacterium *Agrobacterium tumefaciens*, which puts some of its own genetic material into plant cells. Scientists studied how it does this, and now use it to put useful genes into crop plants.

Our bodies have special cells too. Stem cells in the bone marrow can divide and make new blood cells. Bone marrow transplants are used to treat leukaemia and thalassemia.

And to keep the musculoskeletal system healthy: yoga improves flexibility, posture and breathing. International Yoga Day is on 21 June.