Biomedical subjects

H L Gorton

Publications and source records attributed to H L Gorton.

10 recordsLinked to original sources

PubMed2001

The light environment and cellular optics of the snow alga Chlamydomonas nivalis (Bauer) Wille.

The alga Chlamydomonas nivalis lives in a high-light, cold environment: persistent alpine snowfields. Since the algae in snow receive light from all angles, the photon fluence rate is the critical parameter for photosynthesis, but it is rarely measured. We measured photon irradiance and photon fluence rate in the snow that contained blooms of C. nivalis. On a cloudless day the photon fluence rate at the snow surface was nearly twice the photon irradiance, and it can be many times greater than the photon irradiance when the solar angle is low or the light is diffuse. Beneath the surface the photon fluence rate can be five times the photon irradiance. Photon irradiance and photon fluence rate declined exponentially with depth, approximating the Bouguer-Lambert relationship. We used an integrating sphere to measure the spectral characteristics of a monolayer of cells and microscopic techniques to examine the spectral characteristics of individual cells. Astaxanthin blocked blue light and unknown absorbers blocked UV radiation; the penetration of these wavelengths through whole cells was negligible. We extracted astaxanthin, measured absorbance on a per-cell basis and estimated that the layer of astaxanthin within cells would allow only a small percentage of the blue light to reach the chloroplast, potentially protecting the chloroplast from excessive light.

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PubMed1989

Repeated measurements of aperture for individual stomates.

Measurements of stomatal aperture in epidermal peels are used in a variety of physiological studies, but variability between stomates often hinders experimentation. We mount epidermal peels of Vicia faba over a microscopic grid that enables us to map the positions of individual stomates and thus measure the same individual stomates repeatedly, using a simple digitizing system. Repeated measurements of the same population of 15 stomates show much lower variability than measurements of different populations either on the same peel or on different peels.

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PubMed1989

Circadian Stomatal Rhythms in Epidermal Peels from Vicia faba.

Circadian rhythms in stomatal aperture and in stomatal conductance have been observed previously. Here we investigate circadian rhythms in apertures that persist in functionally isolated guard cells in epidermal peels of Vicia faba, and we compare these rhythms with rhythms in stomatal conductance in attached leaves. Functionally isolated guard cells kept in constant light display a rhythmic change in aperture superimposed on a continuous opening trend. The rhythm free-runs with a period of about 22 hours and is temperature compensated between 20 and 30 degrees C. Functionally isolated guard cell pairs are therefore capable of sustaining a true circadian rhythm without interaction with mesophyll cells. Stomatal conductance in whole leaves displays a more robust rhythm, also temperature-compensated, and with a period similar to that observed for the rhythm in stomatal aperture in epidermal peels. When analyzed individually, some stomata in epidermal peels showed a robust rhythm for several days while others showed little rhythmicity or damped out rapidly. Rhythmic periods may vary between individual stomata, and this may lead to desynchronization within the population.

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PubMed1988

Inhibition of phytochrome synthesis by the transaminase inhibitor, 4-amino-5-fluoropentanoic Acid.

Gardner and Gorton (1985 Plant Physiol 77: 540-543) demonstrated that the transaminase inhibitor gabaculine (5-amino-1,3-cyclohexadienyl-carboxylic acid) inhibits the initial synthesis and resynthesis of spectrophotometrically detectable phytochrome in vivo. Another mechanism-based transaminase inhibitor, 4-amino-5-fluoropentanoic acid (AFPA), is examined in this report for its effects on phytochrome synthesis in developing etiolated seedlings. Preemergence treatment with AFPA was found to inhibit initial phytochrome synthesis in peas (Pisum sativum L.), corn (Zea mays L.), and oats (Avena sativa L.). In general, reduction in phytochrome correlated with reduction in chlorophyll. However, the extent of inhibition of phytochrome synthesis was not as great as that of chlorophyll synthesis. These results confirm those with gabaculine, indicating that both initial synthesis and resynthesis of phytochrome require de novo synthesis of chromophore as well as apoprotein. AFPA was a more effective inhibitor of both chlorophyll and phytochrome synthesis than was gabaculine, suggesting that AFPA may be the preferred tool with which to probe the physiological consequences of the inhibition of phytochrome biosynthesis.

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PubMed1987

Water Relations in Pulvini from Samanea saman: I. Intact Pulvini.

The movement of Samanea leaflets depends upon changes in the curvature of the pulvinus at the base of each leaflet. Pulvinar bending and straightening, in turn, are driven by the movement of water between opposing (extensor and flexor) sides of the pulvinus. Although water movement depends on water potential (Psi) and thus on osmotic potential (pi) and hydrostatic pressure (P), none of these parameters have been measured in Samanea. In this investigation, Psi and pi were measured and P was calculated for extensor and flexor tissues of excised, whole pulvini that were open in the light and closed in the dark. In fully open pulvini, pi in the extensor was generally between 800 and 1000 milliosmol per kilogram and exceeded pi in the flexor by 300 to 450 milliosmol per kilogram. In fully closed pulvini the reverse was true, with pi in the flexor between 800 and 1000 milliosmol per kilogram, exceeding pi in the extensor by 300 to 450 milliosmol per kilogram. To obtain approximate values of Psi of pulvinar tissues, shallow cuts in extensor and flexor sides of oil-covered pulvini were filled with droplets of polyethylene glycol solutions of known Psi. Droplets maintaining constant size were assumed to have the same Psi as the tissue. Extensor and flexor halves of open pulvini had very different Psi (extensor, about -1.4 MPa; flexor, about -0.3 MPa), but both sides of closed pulvini had similar Psi (about -0.3 MPa). Measurements of Psi and pi and calculations of P indicate: (a) In open pulvini, P is about the same in extensor and flexor. The large Psi gradient is caused by a large osmotic gradient. (b) In closed pulvini, P is approximately 50% higher in the flexor than in the extensor. This difference in P compensates for differences in pi such that the Psi gradient is small. (c) Pulvini close as P increases in the flexor and reopen as flexor P decreases; extensor P values are similar in open and closed pulvini.

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PubMed1987

Water Relations in Pulvini from Samanea saman: II. Effects of Excision of Motor Tissues.

Pulvinar motor tissues of Samanea saman are often excised for in vitro studies of ion transport. Because ion transport may be regulated in part by hydrostatic pressure (P), this study explores how P and water potential (Psi) change when motor tissues are excised. Water potential (Psi) of excised extensor and flexor tissues was measured by the Chardakov method and compared with Psi measurements made on extensor and flexor tissues of intact pulvini (HL Gorton 1987 Plant Physiol 83: 945-950). Psi values for excised extensor and flexor tissues were always substantially more negative than for the same tissues in intact pulvini. Extensor tissues excised from open pulvini had slightly more negative Psi than excised flexor tissues, and the opposite was true for closed pulvini. Extensor and flexor tissues elongate immediately when excised from open or closed pulvini, suggesting that in intact pulvini they are constrained from elongating by the nonextensible vascular core. In addition, both tissues in both open and closed pulvini are under compression imposed by oppositely positioned motor tissue. Excision relieves constraint and compression, decreasing P, and thus decreasing Psi. This finding may explain, at least in part, the difference between Psi measurements on intact and excised motor tissues. Implications of these data for the planning and interpretation of in vitro experiments requiring excised strips of extensor and flexor tissues are discussed.

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PubMed1985

Inhibition of phytochrome synthesis by gabaculine.

Gabaculine (5-amino-1,3-cyclohexadienylcarboxylic acid), a transaminase inhibitor, also inhibits chlorophyll formation in plants, and the effect of this compound can be counteracted by 5-aminolevulinic acid (ALA) (Flint, personal communication, 1984). Since it is probable that ALA also serves as a precursor to phytochrome, the effects of gabaculine on phytochrome synthesis in developing etiolated seedlings were examined using in vivo spectrophotometry. Preemergence treatment with gabaculine was found to inhibit initial phytochrome synthesis in peas (Pisum sativum L.), corn (Zea mays L.), and oats (Avena sativa L.). In general, reduction in phytochrome correlated with reduction in chlorophyll. However, the extent of inhibition of phytochrome synthesis was not as great as that of chlorophyll synthesis, perhaps due to preexisting phytochrome in the seed. Foliar treatment of etiolated pea seedlings prior to light-induced destruction of phytochrome inhibited subsequent phytochrome resynthesis in the dark. These results suggest that both initial synthesis and resynthesis of phytochrome require de novo synthesis of chromophore as well as apoprotein.

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PubMed1984

Extensor and flexor protoplasts from samanea pulvini : I. Isolation and initial characterization.

Protoplasts were isolated from extensor and flexor regions of open pulvini of the nyctinastic tree Samanea saman. Both types of protoplasts undergo many changes during isolation. Extensor protoplasts are univacuolate in vivo, but some become multivacuolate. All flexor protoplasts are univacuolate. In an open pulvinus, extensor cells have a higher osmotic pressure than flexor cells. However, both types of protoplasts can be isolated with optimal yield using the same osmoticum (0.5 molar sorbitol) in the digestion medium. This suggests that some leakage of osmoticum occurs during harvest or digestion, especially from extensor tissue. Despite these changes, both types of protoplasts extrude protons in response to 10 micromolar fusicoccin (1.6-1.8 nanoequivalent/10(6) protoplasts/minute), demonstrating that the protoplasts are metabolically active and that proton transport mechanisms must be at least partially functional. The changes in vacuolar structure and osmotic pressure are what one might expect if the protoplasts, which are isolated from open pulvini, take on characteristics of cells in a closed pulvinus.

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PubMed1984

Extensor and Flexor Protoplasts from Samanea Pulvini : II. X-Ray Analysis of Potassium, Chlorine, Sulfur, Phosphorus, and Calcium.

Concentrations of K, Cl, P, S, and Ca in extensor and flexor protoplasts from open pulvini of the nyctinastic tree Samanea saman were estimated using x-ray microanalysis. This technique is particularly suitable when absolute numbers of protoplasts are low, because less than 100 protoplasts are required to obtain statistically significant data. Flexor protoplasts contain similar concentrations of P and S but almost twice as much K and Cl as extensor protoplasts. Low levels of total measurable osmoticum suggest that extensive leakage has occurred during protoplast isolation. Both extensor and flexor protoplasts appear to contain some unidentified osmoticum not detectable by x-ray analysis. Extensor protoplasts must have more unidentified osmoticum to compensate for their lower levels of K and Cl.

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PubMed1980

Phytochrome Responses to End-of-Day Irradiations in Light-grown Corn Grown in the Presence and Absence of Sandoz 9789.

Corn seedlings were grown in white light in the absence and presence of the chlorosis-inducing herbicide San 9789. The resulting green and achlorophyllous seedlings were used to investigate phytochrome-mediated responses to end-of-day far red irradiation and reversal of these responses by subsequent red irradiation. Mesocotyl and coleoptile elongation increased in response to end-of-day far red irradiation, whereas the anthocyanin content of the coleoptiles was decreased. All three responses were reversible by red irradiation following the far red. Dose-response curves for far red induction and red reversal of these responses did not differ significantly for plants grown in the presence or absence of San 9789. Thus, San 9789 appears to affect neither phytochrome itself nor the response system involved. Chlorophyll screening likewise does not affect phytochrome relationships for these responses.

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