No abstract

Seeds of Braehiaria humidieola were subjected, on a thermogradient plate, to a wide range of alternating-temperature cycles (24 h) and constant temperatures with intermittent exposure to diffuse laboratory light, in the presence and absence of 10 mol m"-^ KNO3. The optimum regime for maximum percentage germination was alternating temperatures of 35 °C for 4hd"' and 13"C for 20 h d"'. Almost no germination occurred at any constant temperature. Thermoperiods in which the warmer temperature was applied for the longer part of the 24 h cycle were much less stimulatory; in the presence of KNO3, however, the gertnination under such regimes was much improved, although there was little effect on seeds experiencing near-optimum alternating-temperature regimes. This investigation is the first step in identifying which of 10 attributes of alternating temperatures are stimulatory, in order to predict the efficacy of different temperature regimes and to identify the stimulatory characteristics that must ultimately be explained by cellular physiology. The work shows that amplitude, thermoperiod and mean temperature must all be incorporated in a quantitative model.

Seeds of Braehiaria humidieola were subjected, on a thermogradient plate, to a wide range of alternating-temperature cycles (24 h) and constant temperatures with intermittent exposure to diffuse laboratory light, in the presence and absence of 10 mol m"-^ KNO3. The optimum regime for maximum percentage germination was alternating temperatures of 35 °C for 4hd"' and 13"C for 20 h d"'. Almost no germination occurred at any constant temperature. Thermoperiods in which the warmer temperature was applied for the longer part of the 24 h cycle were much less stimulatory; in the presence of KNO3, however, the gertnination under such regimes was much improved, although there was little effect on seeds experiencing near-optimum alternating-temperature regimes. This investigation is the first step in identifying which of 10 attributes of alternating temperatures are stimulatory, in order to predict the efficacy of different temperature regimes and to identify the stimulatory characteristics that must ultimately be explained by cellular physiology. The work shows that amplitude, thermoperiod and mean temperature must all be incorporated in a quantitative model.