Studies on the Chlorosis Expressed under Low Temperature Condition in Rice, Oryza sativa L. : II. Phenotypic Expression Behaviors

The expression behaviors of 4 types of low temperature-induced chlorosis in cultivated rice, Oryza sativa L., have been studied. The 15℃ and 20℃ can be considered as the critical temperatures to distinguish type 1 from type 0 and type IV from type III, respectively. When treated at 15℃ and then transferred to 20℃, the least duration of 15℃ treatment for the effective induction of chlorosis varies from type to type of chlorosis: 3 days for type III, 5 days for type II, continuous treatment for type I. The duration around 7 days of 15℃ treatment was found as the optimum for the classification of chlorogis types. The seedling development stage most sensitive to low temperature coincides with the stage when the coleoptile reaches from 5 mm to 10 mm in height and the third leaf just develops from the leaf primordium from 0.3mm to 1.4mm in the case of HO 1405. The shift of low temperature treatment from this stage, earlier or later, leads to lessen the effectiveness of the chlorosis induction. Chlorophyll bleaching under high light intensities may be due to the photodestruction of chlorophyll without damage of the chloroplast structure. An extra addition of iron as well as nitrogen into the medium does not affect the chlorophyll yield of the bleached types