Role of mitochondria in the origin of chloroplast starch grains: description of the phenomenon.

By phase microscopic observation of living palisade parenchyma cells in sections of Nicotiana excelsior leaves from plants previously placed in the dark for 72 hours, 30 to 45 minutes of light is found to induce mitochondria to remain stationary within the concavity of the chloroplasts and become round. Extending the illumination period to 60 to 90 minutes causes the stationary mitochondria in the concavity to change from a translucent to an opaque appearance, the change coinciding with the first appearance of starch as detected by blue staining of the grains with I(2)-KI. It is speculated that an interaction bearing some resemblance to the previously described interaction between mitochondria and the mobile phase of the chloroplasts may also operate in the starch grain phenomenon.