Histological and microarray analysis of the direct effect of water shortage alone or combined with heat on early grain development in wheat (Triticum aestivum)

Based on the in silico analysis of the representation of expressed sequence tags (ESTs) in wheat grain-related cDNA libraries, a specific 15k oligonucleotide microarray has been developed in order to monitor environmental stress-dependent gene expression changes in the wheat caryopses. Using this array, the effect of water withdrawal, with and without additional heat stress, has been investigated during the first five days of kernel development on two wheat cultivars differing in their drought sensitivity. Water shortage affected (more than twofold change) the expression of only 0.5% of the investigated genes. A parallel heat treatment increased the ratio of responding genes to 5-7% because of the temperature stress and/or the increased water deficit because of enhanced evaporation. It could be established that the two cultivars, differing in their long-term adaptation capabilities to drought, responded to the short and direct stress treatments on the same way. In response to the combined drought and heat treatment, the coordinately altered expression of genes coding for storage proteins, enzymes involved in sugar/starch metabolism, histone proteins, heat shock proteins, proteases, tonoplast aquaporins as well as several transcription factors has been observed. These gene expression changes were in agreement with histological data that demonstrated the accelerated development of the embryo as well as the endosperm.