The grana as structural units of chloroplasts of mesophyll of Nicotiana rustica and Phaseolus vulgaris

• Published in: Journal of ultrastructure research Vol. 8; no. 1; pp. 122 - 143
• Main Authors: Weier, T.E., Stocking, C.R., Thomson, W.W., Drever, H.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.01.1963
• ISSN: 0022-5320; 1878-2345
• DOI: 10.1016/S0022-5320(63)80024-6

Grana are compartmented structures in which contiguous compartments or discs share common partitions; thus regularly ordered stroma lamellae do not enter into their structure. This is graphically demonstrated in swollen grana which may be obtained in situ in plastids taken from plants returned to light after a sojourn in darkness, from plants grown in a nutrient medium deficient in zinc, and from plants whose leaves have been treated with atrazine. Grana in isolated plastids and isolated grana may be made to swell by a variety of methods. The swelling is confined to the loculi, and adjacent loculi swell. The common partitions of contiguous compartments remain flat, and margins separating all compartments from stroma graphically demonstrate that the compartments are all alike and that stroma lamellae do not pass through the grana at regular intervals to separate special grana discs. Profiles obtained after three washings indicate that grana break apart by fracturing margins. Grana may exist in situ without a fretwork, indicating that stroma membranes are not essential in their structure. Isolated plastids, lacking stroma and a limiting membrane, maintain their identity as long as the profiles indicate the presence of a fretwork system. After the destruction of the fretwork, the grana separate. This would indicate that the fretwork, at least in isolated chloroplasts, serves a structural function in holding the grana in place. After KMnO 4 fixation the partitions have an ordered granular structure complementing face views of grana discs or partitions reported by Frey-Wyssling and by Calvin. The partitions after KMnO 4 fixation are thicker, the loculi thinner, than after OsO 4 fixation. This difference in partition thickness coincides with Sjöstrand's view that KMnO 4 stains layers of molecules outside of those by OsO 4. Partitions after OsO 4 fixation are granular and give indication of a double nature not shown by KMnO 4.