Iron Deficiency and the Structure and Physiology of Maize Chloroplasts

Abstract

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

Limiting Factors in Photosynthesis

“…Stocking (20) (22). These facts suggest that the effects of short-term Fe stress on lamellar development are reasonably specific.…”

Limiting Factors in Photosynthesis

“…Since Fe stress did not significantly change the Chl a/Chl b ratio, there was no evidence that the amount of lightharvesting complex per photosynthetic unit was affected by Fe stress. Fe stress did not change the Chl a/b ratio in tomato (23) or spinach (8), although Stocking (24) found that the ratio was decreased in Fe-stressed maize. The composition of the lightharvesting complex may have changed, however, with respect to carotenoid content since there were significant increases in the molar ratio of fl-carotene to Chl(a+b) and in the ratio of xanthophyll to Chl(a+b) with Fe stress (26).…”

“…ii.. (24,28), tomato and spinach (28), tradescantia (15), and xanthium (7). Since Fe stress has a relatively small effect on chloroplast volume, chloroplast protein content, and RuBP carboxylase activity, and no effect on several leaf attributes including the number of cells or chloroplasts per unit area (25,26), the chloroplast lamellae seem to be most affected by Fe stress.…”

Nitric Oxide Improves Internal Iron Availability in Plants

“…Chlorophyll quantification has been widely used to estimate the effect of iron deficiency on plant metabolism (Thoiron et al, 1997). Therefore, we first evaluated the effect of NO on chlorophyll content in maize plants growing under iron-insufficient conditions (50 m Fe-EDTA; Stocking, 1975). The younger leaves were more drastically affected by iron deficiency than the older ones.…”