Studies on the Starch Contained in the Tissues of Rice Plants : XIV. Electron microscobic observations of plastids of various organs and tissues

Abstract

Plastids of various organs and tissues were observed by electron microscope comparing with the observations under light microscope. Leaf mesophyll cells contained chloroplasts with well developed grana and stroma lamellae, containing progressively larger assimilation inner the mesophyll and nearer the vascular bundle they situated. Plastids in the parenchyma of both vascular bundle (parenchymatous vascular bundle sheath) and midrib were rather amyloplasts with far less lamella structure. The amounts of chlorenchyma of leaf-sheath and stem decreased and those of parenchyma increased basipetally, the former tissues containing chloroplasts almost similar to those of leaf-blade and the latter amyloplasts with a trace of lamella structure. The amyloplasts at their basal parts contained larger compound starth grains which are called transitory starch. The initials of shoot apex contained no amyloplast. The corpus cells two to three layers beneath the initials and the cells of slightly elongated leaf primordia began to contain small amyloplasts with small compound starch grains, becoming larger as the cells enlarged. These starches are to be consumed by the cells which contain them for the successive rapid cell expansion, which have been called waiting by Sato. The initials of root apek and periblem cells contained small plastids with starch grains and a trace of lamella structure. Very young meta-vessel cells near the root apex had larger amyloplasts than the other plerome cells. These starches also disappear during the rapid expansion of the cells. Tiny and larger amyloplasts were found in the calyptrogen and mature root cap, respectively, the latter forming the statolith. Mature pollens prior to anthesis contained many specific starch grains, cach of them being composed of one oval single grain in contrast to the other compound starch grains commonly found in the tissues. The mesocarp of ovary seven days after fertilization contained many large amyloplasts except the inner two layers which had plastids with abundant lamella structure, thw outer layer containing large compound starch drains and the inner very small grains. The amyloplasts of endosperm contained compound starch with a greater number of single grains than those of other tissues. These starch should be called reserve starch, which enlarge with maturation especially rabidly at the central part of the endosperm.