Gene W. Miller

Iron chlorosis, a world wide problem, the relation of chlorophyll biosynthesis to iron

Abstract Iron‐Chlorosis is a world‐wide problem, particularly in semi‐arid regions containing calcareous soils. Although most soils contain adequate total iron, the amount available to the plant is dependent on factors such as iron species and plant genotype. Iron is reduced to ferrous form at the root surface if necessary and transported to the leaf through the xylem in a combined form. In the leaf it is used for chlorophyll (Chl) formation as well as for the functioning of various iron‐containing enzymes. Chlorophyll is formed in higher plants from the precursor δ‐amino‐levulinic acid (ALA). This intermediate, ALA, functions for both heme and chlorophyll formation and may be formed through a primary biosynthesis pathway in higher plants requiring a 5‐carbon substrate, such as a ketoglutarate or glutamate. This pathway may be activated by iron, related to aconitase ativity and/or the formation of ferredoxin (Fd). Ferredoxin could be necessary to activate the ALA‐synthesizing enzyme. With plants that are ...

The formation of delta‐Aminolevulinate a precursor of chlorophyll, in barley and the role of iron

Abstract Chlorophyll formation in higher plants is light dependent. Light directly affects the formation of 6‐aminolevulinic acid (ALA) and the conversion of protochlorophyll to chlorophyll. Various chelators that form especially stable compounds with ferrous iron reduce the formation of ALA in etiolated barley leaves. Barley grown under iron stress has little capacity to form ALA unless supplemental iron is added. Chelated iron and FeSO4 are much more effective in restoring ALA formation than FeCl3. Added organic compounds (citrate, α‐ketoglutarate and glucose) also stimulated ALA synthesis. The role of iron in ALA and chlorophyll synthesis is discussed.

The role of iron in higher plant chlorophyll biosynthesis, maintenance and chloroplast biogenesis

Abstract The photosynthetic ability of higher plants has long been known to be adversely affected by iron deficiency. The primary response associated with the unavailability of iron is the loss of chlorophyll. This paper focuses on the role played by iron in the biosynthesis of chlorophyll and its precursors. Special emphasis is placed on the involvement of iron in the formation of δ‐aminolevulinic acid (ALA), the initial committed step in chlorophyll formation. The discussion also surveys the effects of iron deficiency on chloroplast composition, function and ultrastructure. The use of iron fertilization techniques to control and reverse the photosynthetic pigmentation losses associated with iron deficiency is briefly reviewed.

The accumulation of fluoroacetate and fluorocitrate in forage crops collected near a phosphate plant

Abstract Plants were collected from an area high in atmospheric fluoride. Animals grazing on this area showed severe fluoride injury. Analyses of plants indicated accumulation of fluorocitrate and fluoroacetate at concentrations of 896μg and 179 μg/g leaf dry wt. The presence of these compounds was established by chromatographic techniques, inhibition of aconitase and i.r. spectral analysis.

The effects of iron and light treatments on chloroplast composition and ultrastructure in iron‐deficient barley leaves

Abstract The fine structure and major biochemical fractions of iron‐deficient chloroplasts from Hordeum vulgare were examined. Electron micrographic studies of the isolated chloroplasts revealed reduced plastid areas, as well as, reduced thylakoid lamellar profiles. Biochemical analysis of the isolated plastids showed iron involvement in both protein and chlorophyll contents.

Potassium effect on iron stress in tomato. II. The effects on root CO2-fixation and organic acid formation.

Abstract Tomato plants, two Fe‐efficient cultivars and one Fe‐inefficient cultivar, were grown in treatment combinations of normal and low Fe and K concentrations (Normal Fe, Normal K; Low Fe, Normal K; Low Fe, Low K). Iron‐stressed plants with normal K levels were the first to show elevation of root proton excretion and an enhanced ability to regreen. Roots from the Fe‐efficient cultivars had a marked increase in the rate of CO2 dark fixation that was most prominent with a Normal K, Low Fe. The amount of 14C labeling of root organic acids, particularly malate, citrate, lactate and oxaloacetate increased under Fe‐stress conditions in the Fe‐efficient cultivars; Fe stress with low K resulted in less 14C labeling. A scheme for Fe reduction, uptake and transport is discussed related to CO2 fixation and organic acids (malate, citrate and oxaloacetate.) 1Part of the research done by the senior author while on leave at the Institute for Whole Body Metabolism, Inba, Chiba, Japan. The helpful assistance of Mr. Y....

Uptake and translocation of iron from ferrated rhodotorulic acid in tomato

Abstract Micro‐organisms may develop an iron‐deficiency stress when grown in an alkaline environment and secrete ferric‐specific chelators known as siderophores. Some of these siderophores may have stability constants which can exceed 30. This is comparable to the synethetic Fe chelate FeEDDHA. Our objective was to determine if the Fe‐efficient T3238 FER tomato and the Fe‐inefficient T3238 fer tomato could use iron supplied as the siderophore ferrated‐rhodotorulic acid. After these two tomato cultivars were grown with adequate nutrition to obtain plants large enough for experimental testing, they were grown without iron until Fe‐deficiency‐stress symptoms developed and then iron was supplied as ferrated‐rhodoturulic acid. Iron efficient T3238 FER tomato utilized iron supplied as the siderophore and greened whereas, the Fe‐inefficient T3238 fer tomato plants were chlorotic because they could not use the iron in the siderophore. This study demonstrated that some higher plants subjected to various degrees of...

IN VITRO EFFECTS OF FLUORIDE ON TRICARBOXYLIC ACID CYCLE DEHYDROGENASES AND OXIDATIVE PHOSPHORYLATION: PART I

Studies were conducted on the in vitro effect of fluoride on the succinic oxidase system utilizing mitochondria obtained from cauliflower. Preincubation of mitochondria with fluoride did not increase inhibition of succinic oxidase. Various other tricarboxylic acid cycle substrates were used to determine their sensitivity to fluoride; only succinate oxidation was affected. A series of succinate concentrations in the presence and in the absence of fluoride showed increased activity of succinic dehydrogenase, which indicated competitive inhibition. Various concentrations of phosphate in the absence of fluoride showed that phosphate had only slight effects on the succinic 2,6-dichlorophenolindophenol reductase component of the succinic oxidase system. In the absence of phosphate, various concentrations of fluoride showed an initial increase in activity followed by a decrease in activity of succinic 2,6-dichlorophenolindophenol reductase. In the presence of phosphate, fluoride caused marked inhibition of succinic 2,6-dichlorophenolindophenol reductase. It is believed that this inhibition results from an enzyme-fluorophosphate complex which has a lower dissociation constant than that of the enzyme-substrate complex. An oxidative phosphorylation study indicated that both respiration and phosphorylation were inhibited.

Potassium effect on iron stress in tomato. I. The effect on pH, Fe‐reductase and chlorophyll

Abstract Seedlings of Fe‐efficient tomato plants were cultured in nutrient solutions with two concentrations of Fe and K. The pH of the nutrient solution increased initially in all treatments. A subsequent drop in pH of the nutrient solution to 4.4 occurred only in the low Fe, normal K treatment. Ferric iron reduction by root samples was markedly increased only in those producing a decrease in pH of nutrient solution. Most “Fe‐reductant” was released from the swollen elongation zones of young roots. Chlorophyll content in young leaves (after a pH Fe‐stress response) was greater with normal K versus low K for both normal and low iron treatments. Iron‐stressed plants accumulated more K/g dry weight, especially in the roots, than with normal Fe supply.

Riboflavin excretion from roots of iron‐stressed and reciprocally grafted tobacco and tomato plants

Abstract Seedlings of tomato and tobacco were V‐grafted reciprocally and intraspecifically and cultured for 22 days in 2‐liter containers of nutrient solution with normal or no iron. The pH of solutions containing iron increased slightly, while the pH of solutions with no iron decreased. There was little decrease in the pH of tomato grafts on tomato, while the pH of other combinations decreased from 1.5 to 3.1 pH units. Riboflavin concentrations in nutrient solution were highest with tobacco on tobacco, and were about one‐third less with tomato on tobacco. The riboflavin values for tobacco on tomato and tomato on tomato were barely detectable like those for plants supplied with iron. Roots of iron‐deficient tobacco plants at harvest contained much more total riboflavin than roots of iron‐deficient tomato plants and roots of iron‐supplied plants contained less total riboflavin than iron‐deficient plants. Total riboflavin in roots of tobacco plants exceeded that in roots of tomato plants. The total riboflav...