Water deficit significantly reduces growth and production of apples and is detrimental to the quality and size of the fruits. For this reason, water use efficiency is essential when growing apples. An apple tree of good agricultural quality must be able to efficiently use and transport water, which not only provides better tolerance to drought but also secures greater fruit size and hence higher incomes for producers. By altering their own amount and activity, aquaporins can control water transport through cell membranes. Study of the molecular mechanism of water use efficient will allow breeding of drought tolerant apple trees.
Lin Wang, of the China Agricultural University, together with a team of researchers, expressed the drought inducible aquaporin gene MdPIP1; 3 of apple (Malus domestica) in tomato. The resulting transgenic tomatoes showed increased stress tolerance, indicating that the loss of water in their leaves is slower than in the wild type. In addition, the fruits of transgenic tomatoes showed accelerated growth over nontransgenic ones. The fruit size and fresh weight of ripe transgenic tomatoes were also greater than the wild type. At the cell level, an increased size of cells was observed.
Expression of MdPIP1;3 in tomato leads to increased drought tolerance, partly due to reduced water loss in the leaves. Transgenic tomato fruits are larger and heavier due to larger cells and more efficient water transport through the membranes. The results obtained provide new opportunities for molecular breeding for production of large apple fruits through increased water use efficiency under water deficit.