Effects of nitrogen, phosphorus and potassium on the structure and physiology of the vegetative shoot apex in the rice plant

Abstract

The effects of nitrogen, phosphorus and potassium on the structure of the vegetative shoot apices in rice plants were investigated cyto-histologicaiiy, using the variet of paddy rice "Aichi-Asahi" In the first experimcnt (1956, Soil culture), three plots were provided according to the quality of nitrogen, phosphorus and potassium supplied, and in the second experiment (1957, Sand culture), seven plots (1. N, 2. P, 3. K, 4. NP, 5. NK, 6.PK, 7. NPK) were providee, using the Dr. KASUGAI's complete culture solution for rice plants as the standard solution. Dissected stem tips of the young plants of about middle stage of vegetative growth were fixed in modified Navashin's fluid or F. A. A. and embedded in paraffin wax and serial sections cut at about 7μ were stained with the Delafield's hematoxylin. The results obtained in the experiments are as follows : (1) The structure of the vegetave shoot apices in rice plants shows several cyto-histological changes according to different conditions of mineral nutrients. (2) In the plots of high nitrogen supply or nitrogen only, the number of the tunica layers are increased and 2 or 3, sometimes 4 layered tunica is observed. the anticlinal division in the peripheral region of the apices being promoted. (3) On the contrary, in the plots of hlgh phosphorus supply or phosphorus only, the stratification in the tunica is distutbed and thc number of the tunica layers is decreased to 2 or 1 layer, accampanied by the increase of the all direction division in the corpus. (4) Potassium seems to have an effect to establish the topographical differentiation in a apex distinctly and to restrain the one-sided changes in the number of tunica layers by nitrogen or phosphorus supplied. Refering to the writer's observations on the developmental changes in the structural pattern of thc vegetative shoot apices in rice plants, it is considered that high nitrogen supply tends to strengthen the vegetative characteristics in the apices, and the other way, high phosphorus supply tends to diminish the vegetative features in them.