Physiological and Ecological Studies of Rice Plant in Well-drained and Ill-drained Field : (10) Seasonal changes in inorganic constituents of roots classified by their age.

Abstract

Seasonal changes in chemical constituents of root of rice plant grown in well-drained and in ill-drained field were reported before in the previous paper (7) in which roots were subjected to the study as a whole. But since the root system is consisted of many roots of varying age from the youngest root to the oldest one, roots were classified into several groups according to their age and the seasonal changes in inorganic constituents of each root group were studied in the present paper. Classificaiton of roots is as follows: Type I: white root without rootlets. (youngest) Type II: rootlets were seen only at basal half of a root, still white or a little coloured root. (young) Type III: rootlets were seen in whole parts except for 2-5 cm at root tip, brown root. (old) Type IV: some of rootlets have fallen off at basal part, deep or dark brown root. (oldest) Accompanying to the growth of root of rice plant, cortex parenchyma was destructed to form aerenchyma of root. This phenomenon must result in the decrease in water contents of root. Fig. 2 and Fig. 3 showed the changes of water contents of root of rice plant. From these figure, it will be considered that the youngest root is most rich in water. Fig. 5 to Fig. 11 showed the iron accumulation on epidermis of root and rootlet at early stage in rice growth, and then epidermis of root and rootlet have fallen off when root has grown up. As shown in Fig. 4 silicate showed same behavior as iron. Phosphate contents of each classified root were shown in Fig. 12. According to this figure, III class rot was most rich in phosphate at early stage in rice growth. It is known that phosphate of root of rice plant is stored in the form of glucose-phosphate. Glucose-phosphosphate is related to catalitic activity of root of rice plant. Potassium and total nitrogen content were highest in youngest and young root, i. e., type I and type II. As above mentioned, high correlation was observed between classification of root and inorganic constituents.