1. Department of Molecular Biology and Ecology of Plants; Tel-Aviv University; Tel-Aviv 6997803 Israel
2. Mathematics and Computer Science Division; Argonne National Laboratory; Argonne IL, 60439 U.S.A
3. Institute of Plant Biology, Biological Research Centre; 6726 Szeged Hungary
4. Department of Biological Sciences; Purdue University; West Lafayette IN 47907 U.S.A