A MODEL OF PHOTOPERIOD X TEMPERATURE INTERACTION EFFECTS ON PLANT DEVELOPMENT

The recent whole-plant research reviewed suggests the commonly applied paradigms about vernalization and photoperiodism should be replaced. A simple equation based on new paradigms predictively models with exce llent fit the published days to flowering of at least six plant specie s. The paradigm that the response to photoperiod of the days to flower ing (DTF) of crop plants is revealed adequately by comparing a range o f photoperiods at just one temperature should be replaced with the fol lowing concepts. There is a base (lowest) temperature below which phot operiod gene activity does not occur, and, when the temperature is hig h enough to allow activity, there is always a photoperiod x temperatur e x genotype interaction effect on the days to flowering. Similarly, t he paradigm that vernalization gene activity occurs at low temperature and promotes development should be replaced as follows. Vernalization gene activity occurs only if the temperature is above a base (lowest) temperature that allows activity of the vernalization gene(s), and th is activity delays development to flowering. Development to flowering is accelerated by low-temperature vernalization, because the low tempe rature prevents vernalization gene activity, thereby preventing delay of the DTF. The phenomena called long-day (LD) vernalization and short -day (SD) vernalization are reinterpreted as follows. The apparent rep lacement by short or long daylength of a requirement for low-temperatu re vernalization is actually a replacement by the low temperature of a requirement for long or short day. Just as true low-temperature verna lization results from prevention of vernalization gene activity, these SD and LD promotions of the DTF occur because the photoperiod gene ac tivity is prevented by the low temperature. Rather than requiring an e nvironment that induces flowering, an inherent capability for rapid de velopment to flowering is expressed, if there is no delay of the DTF b y the activity of either or both of the vernalization and photoperiod gene(s). All the above-mentioned effects of temperature are due to the Q(10) effect on:he specified photoperiod or vernalization gene activi ty. The effect of thermal time (due to the accumulated growing degree days) is the integrated Q(10) effect on all additional genes that part ially control the rate of development to the reproductive stage.