Johannsen's gene and genotype in the light of plant molecular biology

Abstract

It is particular pleasure for me to give the Wilhelm Johannsen lecture. In searching out some of Johannsen's writings, I was given access to lot of material by his former university, the University of Copenhagen; this was kindly facilitated by Diter von Wettstein. In Johannsen's papers were original manuscripts of four lectures that he gave at Columbia University in 191 1. I was struck by the clarity of those lectures which could still, to this day, provide the basis for course in analytical genetics. Johannsen first gave us the word 'gene' and it was he who crystallized the distinction between genotype and phenotype. In the period of the clarity of understanding of inheritance of distinct morphological characters that came from the rediscoverers of Mendel's work, there was still clouded mass of uncertainty about the inheritance of quantitatively varying characters. Johannsen stood out like beacon at that time in his perception of the value of working with pure lines in probing this question, showing that the quantitative differences behaved and were understandable according to Mendelian laws. In criticizing the mathematical geneticists of his day, Johannsen emphasized the value of experimental biology and experimentation characterized his work. He didn't get everything right. In 1923, he still felt it was an absurdity to believe that genes always may be special particles, but he did see that alleles were different states or chemisms in the same locus of chromosome. He defined the genotype-as the sum total of all genes in gamete. Yet he could not ascribe all growth and development to the genes per se and he postulated a great something as yet not divisible into separate factors, this in addition to the genes. Some of Johannsen's early botanical work at the University of Tiibingen concerned the study of respiration of plant seedlings under reduced levels of oxygen and that is the topic I would like to talk about today. I'll describe the progress that we have made in studying the genes involved in the plant's response to anaerobic stress and I hope to show you that we have made some progress towards understanding Johannsen's central something in terms of the control of gene action. When the roots of plants are flooded, as in irrigation practices, oxygen tension is reduced in the cells of the root and the plant's metabolism changes dramatically. Roots respire at surprisingly high rate and they need efficient energy recharge to provide for the uptake and redistribution of water and nutrients through the plant. Prolonged hypoxia can lead to yellowing of the leaves and to plant death. However, most plants can survive 2 to 3 days of reduced oxygen tension. They have special response'mechanism, response that is not present in vertebrate cells, which can survive only very short periods of oxygen deprivation. Some years ago, Sachs and Freeling showed in maize roots that all protein synthesis ceases within minutes of oxygen deprivation, so that the pattern of polypeptide synthesis, the aerobic pattern, would become blank shortly after the removal of oxygen. Then within the space of 3 to 4 h, distinctive set of polypeptides begin to be synthesized, the so-called anaerobic polypeptides; and they are shown on the right-hand pattern in Fig. 1. That response is true for most plants that have been looked