Every year, almost 10 million hectares of arable land is lost across the globe to salinity caused by irrigation. This was one of the major reasons for the fall of the Mesopotamian civilisation in West Asia some 4,000 years ago.
While most plants perish in saline soil (excess salt in the soil draws water out of plants by the process of osmosis), a few manage to thrive in such soil. M.K. Mathew and his colleagues at the Bangalore-based National Centre for Biological Sciences (NCBS) are trying to understand how such plants survive in salty soil. Understanding what cellular mechanisms the hardy plants resort to may help develop crop varieties with better salt tolerance.
"Plants can't run away from what is there in their surroundings, unlike animals. Plants are exposed to whatever is embedded in the soil, including high salt content," says Mathew. Plants have had millions of years to adapt to salty soil, and one would expect them to have multiple ways of doing so. But till very recently only one such mechanism was known to scientists, says Mathew.
"When I first thought of getting into this field I was told not to waste my time as it was well known how plants coped. However over the last decade or so, we have found at least three previously unreported mechanisms," Mathew told KnowHow . "It is these Aha! moments that one does science for," he exclaims.
Salinity is one of the major causes of crop loss. And it is not a modern problem. The ancient Mesopotamians practised intensive agriculture until they salinised their fields. Then they had to abandon their cities; the rest is history, says the NCBS professor.
Working with a rice variety called Pokkali - known for its high salt tolerance - Mathew and his colleagues had earlier shown that these plants kept sodium levels in the cells low by sequestering it into vacuoles (storage bubbles in the cell).
This insight naturally begged the question; how long can this go on? The scientists then hypothesised that the plant cells may have a way of "dumping" the excess sodium. This is when Mathew's doctoral student Anirban Baral decided to look at this intriguing problem in detail.
Instead of carrying out studies in plant cells cultured in dishes, the NCBS researchers decided to study this phenomenon in the root of a living plant called Arabidopsis thaliana because the root is transparent enough to be easily imaged under a microscope.
Mathew's team, working together with Satyajit Mayor, NCBS director, showed that different cellular mechanisms are in operation in different layers of the root . While vacuoles in a cell on the surface layer are large and can take in more sodium, those in cells in the inner layers are smaller in size. However, if the need arises, they too can form larger vacuoles to accommodate more sodium. This study appeared in a recent issue of the journal Plant Cell.
