Abstract
Temperature is an important factor that influences the growth of plant individuals and plant tissues in vitro. Plant individuals often grow better under different day and night temperature conditions than under constant day and night temperature conditions. However, plant tissues in vitro are usually cultured at constant day and night temperatures and in most of the cases, rice anther culture is conducted at temperatures in the range of 25 to 28°C. In this study, experiments were focused on the effects of different day and night temperatures on callus induction and plant regeneration from anthers. Four Japonica rice cultivars were used. Anthers including mid- to late uninucleate pollen grains were incubated in growth chambers that provided about 3, 000 lx of fluorescent light under a 12 hr photoperiod. The frequencies of callus formation and plant regeneration were examined by using two chambers controlled at day -30°C/night -20°C (30/20°C) and 25/25°C with the daily average temperatures being synchronized. When the anthers of a cultivar ‘Kitaake’ were inoculated on liquid medium, in the 30/20°C culture the rate of callus induction per anther significantly increased, with an average value of 102% for the four years tested, compared with 53% for the 25/25°C culture. In addition, for the calli induced at 30/20°C, the frequency of albino plant differentiation decreased compared with that at 25/25°C. The effect of the 30/20°C culture on the increase of the callus formation rate was recognized in the other three cultivars ‘Kirara397’, ‘Yukihikari’ and ‘Aya’, too. Moreover, such effect was revealed not only in liquid medium but also on solid medium. The frequency of green plant regeneration from calli increased when the calli were cultured at 30/20°C during the regeneration period. When anthers were cultured at 30/20°C throughout the period from anther inoculation to plant regeneration, the rates of callus formation per anther, of the calli that regenerated green plants and of green plant regeneration per anther were 96%(1.6times of that at 25/25°C), 42%(1.4times) and 41%(2.4times), respectively, as an average of six experiments including different cultivars and years. The 30/20°C culture is recommended as an effective method for increasing the yield of haploid plants from rice anther.
