The conversion of spring wheat into winter wheat and vice versa: false claim or Lamarckian inheritance.

ABSTRACT

Paul Kammerer, an Austrian biologist, argued strongly in favour of the Lamarkian view on the inheritance of acquired characters. In his most controversial experiment, Kammerer forced midwife toads, which live and mate on land, to mate and lay their eggs in water. Most of the eggs died, but a few (3–5%) of offspring that survived had lost the terrestrial habits of their parents and, by the third generation, they began to develop black nuptial pads on their forelimbs, a character common to water-dwelling species. This experiment is often cited as an example of scientifi c fraud. Recently, however, Vargas (2009) has re-examined Kammerer’s midwife toad experiments and argues that these experiments show signs of epigenetic inheritance. An immediate discussion on this topic has been published in a recent issue of Science (Pennisi 2009). This new analysis reminds us of several recent reports on the inheritance of acquired behaviour adaptations and brain gene expression in chickens, which may have been transmitted to the offspring by means of epigenetic mechanisms (Lindqvist et al. 2007; Natt et al. 2009). It especially reminds us of Trofi m Lysenko’s converted wheat, a situation exactly analogous to Kammerer’s midwife toad. The characteristic of winter wheat is that if sown in the spring it fails to form ears. It has been shown that the capacity to form ears depends on the plant’s passing through a defi nite internal qualitative change. It was Lysenko who coined the term jarovization, which was later translated into vernalization. It is defi ned as ‘the acquisition or acceleration of the ability to fl ower by a chilling treatment’. The characteristic feature of winter wheat is its requirement of rather low temperature for vernalization. The usual duration of the process of vernalization in most winter wheat at low temperatures (0o–10oC) is 30–50 days, depending upon the variety. Once this stage has been accomplished, the plant becomes capable of forming fl owers in favourable conditions. Spring wheat differs from winter wheat in that it does not require vernalization, and is thus able to ear when sown in spring. Winter and spring habit, as a Mendelian character transmitted by gametes, is a hereditary property in wheat. Before 1930, Lysenko had shown that vernalization of winter wheat can be accomplished before it is sown. The process is to allow the grains to take up water and swell, and then to keep them for the required time at a temperature of 0–3°C. The grains are then dried off they show no signs of germination but when subsequently sown in spring they ear normally, indicating that they have passed the phase of vernalization. This treatment has no effect on the hereditary behaviour of the plants. That is to say, the progeny of the pre-vernalized spring-sown wheat is still winter wheat; if sown (without pre-vernalization) in the following spring it will not form ears (Morton 1951; Lysenko 1954). However, in a series of experiments carried out between 1935 and 1940, Lysenko and his colleagues established that permanent changes in heredity can be induced by appropriate changes in external conditions at the critical period of vernalization. In the earliest experiments, winter wheat was sown in the greenhouse and kept at a temperature higher than the temperature required for vernalization in normal conditions. After 152 days, 30–40% of the plants eared and gave ripe seed, indicating that these plants had succeeded in completing the vernalization stage, although very slowly, at the higher temperature. The seeds were sown and raised again in the same conditions. This time the plants eared in 77 days. A third generation was raised in the same way and gave ears at 46 days. The seed from the three generations that had passed the vernalization stage at the higher temperature was then sown in the fi eld. The experimental plants behaved as spring forms and eared, but the control plants from the original seed material did not ear at all. Lysenko suggested that the later stage of vernalization was the critical period, in which the change would become hereditarily fi xed. Thus, concretely, to change winter wheat.