The ultrastructure of mesophyll chloroplasts of maize (Zea mays L.) was more severely affected by iron deficiency that induced mild chlorosis than was the ultrastructure of bundle sheath plastids. Ferredoxin and ribulose diphosphate carboxylase levels were severely decreased bv iron deficiency. Malic enzyme was less affected, and phosphoenolpyruvate carboxylase activity remained high even under severe iron deficiency.Iron deficient leaves fixed carbon into malic and aspartic acids but the rate of entrance of carbon into the sugar phosphates and sucrose was greatly reduced compared to the control. Chlorophyll a/b ratios ranged from low values of less than 2 in severelv iron deficient leaves to high values exceeding 4 in leaves showing little iron deficiencv.In C4 plants such as maize, CO2 is first fixed through /3-carboxylation of PEp2 into the C,-dicarboxylic acid, oxaloacetic acid, and then rapidly appears in aspartic and malic acids. It is generally believed that this process takes place in the mesophyll cells of the leaf, and that malate and aspartate then are transported to the bundle sheath cells where they are decarboxylated and the CO2 that is released is fixed by the action of ribulose diP carboxylase in the normal C3 cycle (11,12).Such a mechanism involves a spatial separation of activities between mesophyll and bundle sheath cells in the leaf, but at the same time necessitates a considerable and rapid movement of small molecules such as malate, aspartate, pyruvate, glycerate-3-P, and trioses out of one type of plastid across a series of membrane barriers and into a second plastid type in another cell. Although such a rapid shuttling of material between the two adjacent cell types (mesophyll and bundle sheath) seems feasible (18), the exact situation still requires considerable clarification. One method of studying the problem would be to inhibit preferentially the activity of one of these cell types in vivo and study the

Stocking, C. Ralph, and Alpaslan Ongun. (U. California, Davis.) The intracellular distribution of some metallic elements in leaves. Amer. Jour. Bot. 49(3): 284–289. Illus. 1962.—A comparison of the potassium, sodium, calcium, magnesium, and nitrogen levels of chloroplasts isolated in an aqueous sucrose medium and by the nonaqueous method reveals that large amounts of these elements are lost from the plastids during their isolation in sucrose solution. Nonaqueously isolated chloroplasts of bean and tobacco leaves contained over 40% of the total leaf potassium, magnesium, and calcium. High levels of nitrogen up to 70% of the total leaf nitrogen were found associated with nonaqueously isolated chloroplasts. As much as 40–50% of this nitrogen is lost when chloroplasts are isolated in a sucrose solution. Electron photomicrographs of nonaqueously isolated chloroplasts reveal only a partial disruption of the internal structure and a loss of the plastid membrane during isolation.

1. Enzyme distribution between chloroplasts and the nonchloroplast parts of green leaf cells of Spinacia oleracea, Nicotiana rustica, Vicia faba, and Phaseolus vulgaris have been investigated by use of the nonaqueous chloroplast isolation technique. Whereas pyruvate kinase and peroxidase were located only or mainly outside of the chloroplasts, the other enzymes studied, isocitric dehydrogenase, glutathione reductase, NAD- and NADP-dependent pyridine nucleotide quinone reductase, malic dehydrogenase, NAD- and NADP-dependent glyoxylate reductase, glutamate-oxaloacetate transaminase, NAD-dependent glutamic dehydrogenase, and NADP-dependent aspartic dehydrogenase were both inside and outside of the plastids. In contrast, NADP-dependent glyceraldehyde-3-phosphate dehydrogenase is located only within the chloroplasts.2. Intact isolated spinach chloroplasts incorporated only a very small amount of labeled carbon from 14CO2 into amino acids in the light. The addition of NH4Cl did not increase the amount of labeled amino acids and had no effect on the total amount of 14C fixed during short time photosynthesis. However, NH4⊕ caused changes in the pathway of carbon during photosynthesis. In the presence of NH4⊕, more 14C was incorporated into sugar monophosphates and phosphoglyceric acid than in the absence of NH4⊕.3. 14C-labeled glycine and serine fed to intact isolated spinach chloroplasts were neither accumulated nor transformed into other compounds, but 14C-labeled glutamic acid was converted into glutamine. This transformation took place only in the light in chloroplasts containing an intact outer envelope. The addition of NH4⊕ and certain substrates and cofactors did not increase the rate of transformation.4. The penetration of some amino acids and substrates through the outer envelope of the chloroplasts was investigated on aqueously isolated spinach plastids. It was found that a-ketoglutarate, oxaloacetate, pyruvate, aspartate, and alanine are able to penetrate the envelope although at least for some of these compounds the outer membrane of the chloroplasts acts as a partial barrier.5. From the experiments reported here and in connection with the results published by other investigators it can be concluded that the most common amino acids such as glutamic acid, aspartic acid, alanine, glycine, and serine are able to penetrate through the outer envelope of the chloroplasts and the synthesis of these amino acids can occur in the leaf cells inside as well as outside of the chloroplasts.

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tissue (18). This is particularly evident at the electron microscopic level where one must contend with stabilizing the movement of the water-soluble compounds in question and at the same time assure adequate preservation of the tissue so as to make the electron photomicrograph informative. The most widely used techniques to date have been those of freeze-substitution of the plant tissue in acetone or propylene oxide (13,14,22) or the freeze-drying of the plant tissue followed by infiltration with xylene and embedding in plastic or paraffin (15,19