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Biomedical subjects

N K Boardman

Publications and source records attributed to N K Boardman.

At least 37 records · Page 2Linked to original sources
PubMed1972

Lipid Composition of Pea and Bean Leaves during Chloroplast Development.

The changes in composition of the complex lipids were followed during the greening of dark-grown pea (Pisum sativum) and bean (Phaseolus vulgaris) seedlings. No significant changes in glycerolipid concentrations in the leaves were observed during the early stages of greening (0-8 hour for peas and 0-12 hour for beans). On further greening, there was an increase in the proportion of galactolipids and a decrease in the phospholipids. The fatty acid composition of the galactolipids remained constant during 24 hours of greening, but there was a slight increase in alpha-linolenic acid at 72 hours in the bean. The percentage of alpha-linolenic acid in the phospholipids and in sulfolipid showed a marked increase between 24 and 72 hours in the bean. Trans-delta(3)-hexadecenoic acid was the major fatty acid of phosphatidyl glycerol in bean leaves at 72 hours, but it was barely detectable at 24 hours. The lipid composition of greening leaves is discussed in relation to the fine structure and photochemical activity of the developing plastids.

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PubMed1971

Formation of chlorophyll B, and the fluorescence properties and photochemical activities of isolated plastids from greening pea seedlings.

Chlorophyll b was first detectable after 10 minutes of illumination of etiolated pea seedlings (Pisum sativum L. var Greenfeast) with continuous white light. The chlorophyll a/b ratio decreased from 300 at 10 minutes to 15 after 1 hour. There was little change in the chlorophyll a/b ratio between 1 and 2 hours, and it declined to 3 between 2 and 5 hours of illumination. In red light, the time courses of total chlorophyll synthesis and chlorophyll a/b ratio were similar to those in white light for the first 5 hours of illumination. But with increasing time of illumination with red light, there was an increase in the chlorophyll a/b ratio to 7 after 30 hours. Illumination with white light of very low intensity also gave high chlorophyll a/b ratios. Seedlings which had been illuminated for varying periods and then returned to darkness always showed an increase in chlorophyll a/b ratio during the dark period. It is concluded that the synthesis of chlorophyll b is controlled by light.The onset of the transfer of excitation energy from carotenoids to chlorophyll a correlated with the appearance of chlorophyll b. The detection of chlorophyll b and the onset of energy transfer from carotenoids to chlorophyll a preceded by several hours the appearance of Hill activity in the isolated pea plastids. The detection of the large fluorescence emission band at 735 nm at 77 K also preceded the observation of Hill activity, but it correlated with the phase of rapid chlorophyll synthesis. There was a good correlation between Hill activity and the formation of grana. The fluorescence kinetics which are characteristic of mature chloroplasts appeared considerably later than grana or the observation of Hill activity.It is concluded that the formation of photosynthetic membranes and the assembly of the photosystems is not a single step process, at least in the initial stages of chloroplast development from the etioplast.

Journal Article↗
PubMed1970

Deficient Photosystem II in Agranal Bundle Sheath Chloroplasts of C(4) Plants.

A method is described for separating mesophyll and bundle sheath chloroplasts from the leaves of C(4) plants. The agranal bundle sheath chloroplasts are inactive in the Hill reaction, whereas granal bundle sheath and granal mesophyll chloroplasts exhibit normal photosystem II activity. The agranal bundle sheath chloroplasts are deficient in photosystem II; they lack cytochrome b-559 and the fluorescence bands associated with photosystem II. All the chloroplasts exhibit photosystem I activity.

Journal Article↗
PubMed1969

Photosynthetic Studies on a Pea-mutant Deficient in Chlorophyll.

A chlorophyll-deficient mutant of pea (Pisum sativum) was found as a spontaneous mutation of the variety Greenfeast. Total chlorophyll of the mutant leaves was about one-half that of normal pea leaves per mg dry weight, and the ratio of chl a:chl b ranged from 10 to 18, compared with 3 for normal pea. In each generation the mutant plants gave rise to normal and mutant plants and lethal plants with yellow leaves.For a normal pea plant, CO(2) uptake was saturated at about 60,000 lux, whereas with mutant leaves, the rate of CO(2) uptake was still increasing at 113,000 lux. At 113,000 lux the mutant and normal leaves showed similar rates of CO(2) fixation per unit area of leaf surface, but on a chlorophyll basis the mutant leaves were twice as active. Hill reaction measurements on isolated chloroplasts also showed that the mutant chloroplasts were saturated at higher intensities than the normal, and that the activity of the mutant was at least double that of the normal on a chlorophyll basis.It is suggested that the photosynthetic units of the mutant chloroplasts contain about half the number of chlorophyll molecules as compared to the normal photosynthetic units.Electron microscopy of leaf sections of normal and mutant leaves showed that the mutant chloroplasts contain fewer lamellae per chloroplast and fewer lamellae per granum. The lethal chloroplasts, which were virtually devoid of chlorophyll, were characterized by an absence of grana.

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