I thought this was a really interesting question, and I was looking forward to some solid answers of those who have expertise in this area. I am far from an expert, but do have an interest in the subject. We started working on a group of species that do produce and accumulate very large amounts of mucilage. Our hypothesis is that it functions very much like hydrenchyma (water-storage tissue) acting as a buffer when the supply of water from soil becomes limiting. For us, this is work in progress, and I cannot give you a conclusive answer at this stage.

Thanks for interesting in this question sir @ Hans Lambers. Im eager to looking forward answer from you sir.

Quince (Cydonia sp.) seeds release a mucilage in water that swells to an amazing extent. I presume this improves the success of germination of seeds in a dry-ish climate. The mucilage contains cellulose and a complex methyl-glucan. See attached for the chemical nature of the glucan.

Some Orient genotypes of Brassica rapa have so called A-type of seed coat of large cells with walls made of some polymer swelling in water. The seed coat is formed by mother plant but A-type is controlled by genes in embryo I have only references in Russian. Ignatov AN, Hida Ken'ichi. Occurrence and inheritance of A-type seed coat in Brassica rapa L. Agricultural biology 2004. - № 3. -C. 123 -127.(Moscow) and some - in Japanese.

Thanks for your contribution for the answer. I really getting impressed on ypur involvement @ Dr. J.H. Martin Willison and Alex Ignatov.

I just searching a chemical (Polymer) used as a water absorbant. Its used to retain water for plants.?

Parthasarathi, I'm not clear about which of two possible questions you are asking:

1. Do you want to know about synthetic (or natural) polymers that can be added to soil (such as potting soil) to increase the ability of the soil to hold moisture?

2. Do you want to know about natural polymers produced by plants under natural conditions that are secreted by roots (or seeds) and increase the water-holding capacity of the rhizosphere?

I am asking the First question only J.H. Martin Willison. Will it be healthy to plants? how long retain water? Examples of synthetic polymers commercially available?

Parthasarathi, it seems we all misunderstood your question and provided interesting but irrelevant answers. Your question needs to be more specific in order to provide advice. For example, is this for an experiment in laboratory or field conditions? Are you trying to measure a plant physiological attribute with varying soil conditions? Why would a hydrophilic polymer be helpful? And so on.

I found some papers on line that I think may be helpful and which were easy to download, so I'll attach them here. I am not expert in this specific field, though I have done some work in plant stress physiology. I can only send one paper at a time, so will make more messages.

Another paper

Third paper

Fourth paper. Please note that I found all of these in about 5 minutes searching, so I think you can do this too.

Thank you sir J.H. Martin Willison. for your information regarding this