Structure of the Grain
The endosperm occupies the major part of the seed. The endosperm consists of only parenchymatous cells, containing starch grains of compound type. The rice grain is broadly divided in to two types viz glutinous (Waxy) and non glutinous (non-waxy) depending upon the ratio between the amylase content and the amylopectin content of starch. The glutinous types are characterized by having low amylose content and a high amylopectin content, whereas the non-glutinous types have high amylose content, the rest of the starch being amylopectin.
The pericap consist of epidermis, parenchymatous mesocarp, chlorophyllous cells, tube cells and an inner integument. The ovary is superior, monocarpellary and unilocular with a single anatropous ovule. The development of the embryo in inter specific hybrids in rice showed that in such hybrids unreduced female gametes were produced quite frequently and a few ovules showed full development.
During germination the radicle emerged first and then the plumule. But under submergence, the plumule emerged first. The coleoptile is the protecting sheath of the plumule. In the early stage, it is a tubular structure with a small pore at its tip, but later it splits longitudinally and becomes scale like. Two vascular bundles which run parallel from the base of the coleoptile slowly converge on the tip. The stomata are the most interesting part of the coleoptile. The stomata of the coleoptile have kidney shaped guard cells. The range of temperature under which varieties germinated was from 6 degrees – 47 degrees centigrade
There are two types of roots in rice, seminal roots having primordial inside and the embryo and adventitious which arise from the nodes of the stem
Stem of the rice plant has two parts, the underground part and the aerial part. The basal internodes, which remain inside the soil, are condensed with crowded nodes and adventitious roots, at times presenting a pseudo-rhizomatic appearance. The stem above the ground level has well defines solid nodes and hollow internodes
Each tiller developing from an axillary bud is enclosed by a special leaf called, called prophyll which structurally resemble the first leaf. The main culm (Mother Tiller) bears the largest number of leaves, and the number of leaves on a tiller decreases progressively with the rise in the tillering order. The lamina of the last leaf (flag or boot leaf) is wider and shorter than that of the other leaves. The angle of the flag leaf is oriented more vertically that the preceding leaves.
Inflorescence and anthesis
The inflorescence of the rice is a terminal panicle, borne on a long penduncle, which is the last internode of the culm. Normally anthesis starts shortly after the panicle emerges from the flag leaf. Even though the blossoming starts from the tip of the panicle, the process does not proceed to the bottom in a regular sequence
In stem there is a single layered epidermis covered with cuticle. Below the epidermis is a cylinder of the sclerenchymatous tissue, the hypodermis. The thickness of this layer varies in different varieties. The ground parenchyma extends from the hypodermis to the hollow pith. It is not differentiated into cortex or endodermis. The fibro-vascular bundles are arranged roughly in to two rings, the outer or pheripheral ring and the inner ring. The pheripheral bundles are smaller and are separated from the hypodermis by a few layers of closely placed parenchyma. Each bundle is surrounded by a fibrous sheath and alternates with a cortical air-chamber. The thickness of the cell wall and the size and the arrangement of the papillae differ in different species of Oryza. The air cavities and the vascular bundles were larger and the mewophyll is thicker in tetraploid strains
The origin and cytogenetics of rice reported 12 as the basic haploid number and 24 as the diploid number of Oryza sativa. It is established that all cultivated species have the same basic chromosome number ie, 24. The haploid complement of 12 chromosomes include 2 chromosome with median centromere and 2 pairs of chromosomes were satellited, the satellite of one being larger than that of the other.

During the first 72 hours of germination, the hydrolysis of endospermic proteins and the translocation of soluble N products to embryo predominated,, whereas in the second phase proteins were synthesized in the embryo from the products of translocation. The high nitrogen content increased the soluble protein in the plant resulting in the higher protein content in the grains.

Source - Studies on charecterization of Indegenous Medicinal Rice Njavara and selected cultivars of Oryza sativa L by Mr. Suresh V, Dept. of Botany, Govt. Victoria College, Palakkad

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