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Amyloplasts
Amyloplasts are a type of plastids, double-enveloped organelles in plant cells that are involved in various biological pathways. Amyloplasts are specifically a type leucoplast, a subcategory for colorless, non-pigment-containing plastids. Amyloplasts are found in roots and storage tissues and store and synthesize starch for the plant. The precise mechanisms that must occur for starch synthesis has been under much debate, but it generally known that synthesis relies upon the transportation of carbon from the cytosol.

Amyloplasts have also been shown to play a major role in nitrate assimilation in some species.

Role in Gravity Sensing
Amyloplasts are thought to play a vital role in gravitropism. Statoliths, a specialized starch-accumulating amyloplast, are denser than cytoplasm, and are able to settle to the bottom of the gravity-sensing cell, called a statolith. This settling is a vital mechanism in the plant's perception of gravity, triggering the asymmetrical distribution of auxin that causes the curvature in roots and stems. A plant lacking in phosphoglucomutase (pgm), for example, is a starchless mutant plant, preventing the settling of the statoliths. This mutant shows a significantly weaker gravitropic response as compared to a non-mutant plant. A normal gravitropic response can be rescued with hypergravity.

In roots, gravity is sensed in the root cap, a section of tissue at the very tip of the root. Upon removal of the root cap, the root looses its ability to sense gravity. However, if the root cap is regrown, the root's gravitropic response will recover. In roots, the asymmetrical distribution of auxin causes the root to grow along the gravity vector.

In stems, gravity is sensed in the endodermal cells of the shoots. Unlike roots, the differential distribution of auxin causes stems to grow against the gravity vector.