Effects of UV-B radiation on photosynthesis and growth of terrestrial plants.

The photosynthetic apparatus of some plant species appears to be well-protected from direct damage from UV-B radiation. Leaf optical properties of these species apparently minimizes exposure of sensitive targets to UV-B radiation. However, damage by UV-B radiation to Photosystem II and Rubisco has also been reported. Secondary effects of this damage may include reductions in photosynthetic capacity, RuBP regeneration and quantum yield. Furthermore, UV-B radiation may decrease the penetration of PAR, reduce photosynthetic and accessory pigments, impair stomatal function and alter canopy morphology, and thus indirectly retard photosynthetic carbon assimilation. Subsequently, UV-B radiation may limit productivity in many plant species. In addition to variability in sensitivity to UV-B radiation, the effects of UV-B radiation are further confounded by other environmental factors such as CO2, temperature, light and water or nutrient availability. Therefore, we need a better understanding of the mechanisms of tolerance to UV-B radiation and of the interaction between UV-B and other environmental factors in order to adequately assess the probable consequences of a change in solar radiation.

The effects of ultraviolet-B radiation on photosynthesis of different aged needles in field-grown loblolly pine.

We examined the effect of supplemental UV-B radiation (290-320 nm) on photosynthetic characteristics of different aged needles of 3-year-old, field-grown loblolly pine (Pinus taeda L.). Needles in four age classes were examined: I, most recently fully expanded, year 3; II, first flush, year 3; III, final flush, year 2; and IV, oldest needles still present, year 2. Enhanced UV-B radiation caused a statistically significant decrease (6%) in the ratio of variable to maximum fluorescence (F(v)/F(m)) following dark adaptation only in needles from the youngest age class, suggesting transient damage to photosynthesis. However, no effects of enhanced UV-B radiation on other instantaneous measures of photosynthesis, including maximum photosynthesis, apparent quantum yield and dark respiration, were seen for needles of any age. Foliar nitrogen concentration was unaffected by UV-B treatment. However, the (13)C/(12)C carbon isotope ratios (delta(13)C-a time integrated measure of photosynthetic function) of needles in age classes II and IV were 3% (P < 0.01) and 2% (P < 0.05) more negative, respectively, in treated plants than in control plants. Exposure to enhanced UV-B radiation caused a 20% decrease in total biomass and a 4% (P < 0.05), 25% (P < 0.01), and 9% (P < 0.01) decrease in needle length of needles in age classes I, II, and IV, respectively. The observed decreases in delta(13)C, and F(v)/F(m) of the needles in the youngest needle age class suggest subtle damage to photosynthesis, although overall growth reductions were probably a result of decreased total leaf surface rather than decreased photosynthetic capacity. Needles of age class IV had lower light- and CO(2)-saturated maximum photosynthetic rates (39%), lower dark respiration (34%), lower light saturation points (37%), lower foliar nitrogen concentration (28%), and lower delta(13)C (14%) values than needles of age class I. Apparent quantum yield and F(v)/F(m) did not change with needle age. The observed changes in photosynthesis and foliage chemical composition with needle age are consistent with previous studies of coniferous trees and may represent adaptations of older needles to shaded conditions within the canopy.

Self-compression plates for orbital rim fractures.

The development and principles of self-compression plating, as well as a series of patients treated with this technique, are described. The use of such plates has specific advantages over other techniques for disorders encountered by the oculoplastic surgeon. The indications for plating were displaced trimalar fracture, displaced trimalar fracture with orbital rim fragment, and comminuted orbital rim fracture. Results were good; no complications have been observed to date. Comparison of compression plating to other methods for repair of orbital fractures is made. Self-compression plating with Vitallium plates is an effective modality for the treatment of a broad spectrum of patients with orbital rim fractures.

Interaction of Elevated Ultraviolet-B Radiation and CO(2) on Productivity and Photosynthetic Characteristics in Wheat, Rice, and Soybean.

Wheat (Triticum aestivum L. cv Bannock), rice (Oryza sativa L. cv IR-36), and soybean (Glycine max [L.] Merr cv Essex) were grown in a factorial greenhouse experiment to determine if CO(2)-induced increases in photosynthesis, biomass, and yield are modified by increases in ultraviolet (UV)-B radiation corresponding to stratospheric ozone depletion. The experimental conditions simulated were: (a) an increase in CO(2) concentration from 350 to 650 microliters per liter; (b) an increase in UV-B radiation corresponding to a 10% ozone depletion at the equator; and (c) a and b in combination. Seed yield and total biomass increased significantly with elevated CO(2) in all three species when compared to the control. However, with concurrent increases in UV-B and CO(2), no increase in either seed yield (wheat and rice) or total biomass (rice) was observed with respect to the control. In contrast, CO(2)-induced increases in seed yield and total plant biomass were maintained or increased in soybean within the elevated CO(2), UV-B environment. Whole leaf gas exchange indicated a significant increase in photosynthesis, apparent quantum efficiency (AQE) and water-use-efficiency (WUE) with elevated CO(2) in all 3 species. Including elevated UV-B radiation with high CO(2) eliminated the effect of high CO(2) on photosynthesis and WUE in rice and the increase in AQE associated with high CO(2) in all species. Elevated CO(2) did not change the apparent carboxylation efficiency (ACE) in the three species although the combination of elevated CO(2) and UV-B reduced ACE in wheat and rice. The results of this experiment illustrate that increased UV-B radiation may modify CO(2)-induced increases in biomass, seed yield and photosynthetic parameters and suggest that available data may not adequately characterize the potential effect of future, simultaneous changes in CO(2) concentration and UV-B radiation.

Field Study of the Interaction between Solar Ultraviolet-B Radiation and Drought on Photosynthesis and Growth in Soybean.

Soybean, Glycine max (L.) Merr. cv Essex, plants were grown in the field in a 2 x 2 factorial design, under ambient and supplemental levels of ultraviolet-B (UV-B) radiation (supplemental daily dose of 5.1 effective kilojoules per square meter) and were either well-watered or subjected to drought. Soil water potentials were reduced to -2.0 megapascals by the exclusion of natural precipitation in the drought plots and were maintained at approximately -0.5 megapascal by supplemental irrigation in well-watered plots. Plant growth and gas exchange characteristics were affected under both drought and supplemental UV-B radiation. Whole-leaf gas exchange analysis indicated that stomatal limitations on photosynthesis were only significantly affected by the combination of UV-B radiation and drought but substrate (ribulose bisphosphate) regeneration limitations were observed under either stress. The combined effect of both drought and UV-B radiation on photosynthetic gas exchange was a reduction in apparent quantum efficiency and the rapid appearance of biochemical limitations to photosynthesis concomitant with reduced diffusional limitations. However, the combination of stresses did not result in additive effects on total plant growth or seed yield compared to reductions under either stress independently.

Pretarsal fixation of gold weights in facial nerve palsy.

Implantation of a gold weight in the pretarsal space was performed on 17 patients with poor eyelid closure secondary to facial nerve weakness. Successful results were obtained in 14 (82%) of 17 patients. Postmortem histopathology of such a case demonstrated firm fibrous encapsulation of the weight. Although some authors advocate fixation of lid weights to the orbital septum, fixation in the pretarsal space is preferred for the following reasons: (a) "cheesewiring" is less likely to occur, (b) a limited levator recession may be more easily performed, (c) greater mechanical benefits are obtained, and (d) the potential for inferior migration is less.

The pathogenesis of retinal detachment with morning glory disc and optic pit.

A child with nonrhegmatogenous retinal detachment associated with morning glory disc underwent first a vitrectomy and then, some months later, an optic nerve sheath fenestration. The latter procedure led to retinal reattachment. It also produced a biopsy specimen that confirmed the perineural herniation of poorly differentiated retinal tissue in this condition, similar to that in congenital pit of the optic nerve. It demonstrated continuity of the vitreous cavity with the perineural space, both histologically and by the fact that gas injected through the pars plana into the vitreous cavity bubbled out the window in the optic nerve sheath. The authors suggest that morning glory disc and optic pit share similar anatomic features, differing more in degree than in kind, and that the porous nature of the poorly differentiated tissue herniated around the optic nerve into the subarachnoid space in these conditions makes several sources of subretinal fluid possible.

Eyelid anaphylactic reaction to atracurium with general anesthesia.

Atracurium is a relatively new neuromuscular blocking anesthetic with known histamine release effects which has become popular in ophthalmic anesthesia. This report describes the IV use of Atracurium causing an anaphylactic reaction manifested by localized edema of all four eyelids, conjunctival chemosis and mild laryngeal edema requiring scheduled ptosis and strabismus surgery to be cancelled.

Cryosurgery in ophthalmic practice.

Cutaneous cryosurgery is useful in an ophthalmic practice in the treatment of basal cell carcinoma, trichiasis, and other benign cutaneous disorders. Indications and techniques for using liquid nitrogen and nitrous oxide instruments are discussed.

Cryosurgery for trichiasis.

A series of 41 cases of trichiasis was treated with cryosurgery using a standard retinal cryoprobe. The failure rate was approximately 50 per cent. The results should be improved by using properly designed equipment capable of cooling the lash follicles to -20 degrees C, and ensuring that this temperature is achieved by using a tissue thermocouple. A double freeze-thaw cycle should be used and a long-acting local anaesthetic containing adrenaline. The main complication is depigmentation which is a problem only with heavily pigmented patients. Cryosurgery does have potential for the treatment of trichiasis.

The use of cryotherapy for trichiasis.

Cryosurgical destruction of aberrant eyelashes was performed on 72 eyelids. Seven of nine failures occurred following major deviation from recommended technique. All but one recurrence were successfully re-treated. Notching of the eyelid was observed in one patient. The technique utilized a nitrous oxide gas-cooled cryoprobe. Tissue temperature was monitored by a subcutaneous microthermocouple in the region of the lash follicle to -20 C in a double freeze-thaw cycle.

Cryotherapy of basal cell carcinoma in oculoplastic surgery.

Cryotherapy was an effective modality in the treatment of basal cell carcinoma in the eyelid and periorbital area and cured 93% of the 29 lesions in 25 patients. This method was especially advantageous in patients with blood clotting disorders; those with medical contraindications to, or who refused, classical surgery; patients who had prior radiation or surgery; patients with the basal cell nevus syndrome or xeroderma pigmentosa; and in patients with medial canthal tumors. Experimental cryotherapy in the albino rabbit showed their lacrimal system is not adversely affected by freezing in the temperature range required for tumor death.

Cryosurgery for treatment of trichiasis.

We cryosurgically destroyed eyelashes in rabbits and applied the technique to treat 23 selected patients with trichiasis. Liquid nitrogen was sprayed on the eyelid margin by using a double, rapid-freeze, slow-thaw cycle monitored by a subcutaneous thermocouple to -30 degrees C. It was an improvement on electrolysis and a simple alternative to surgery.

Lower eyelid reconstruction by tarsal transposition.

We reconstructed the lower eyelids of 13 patients using a tarsoconjunctival flap from the upper eyelid. The laterally based pedicle flap permitted a one-stage repair without prolonged occlusion of the eye. The technique was best suited to lesions involving the lateral aspect of the lower eyelid, but can be applied to lesions of the central and medial eyelid. The functional and cosmetic results were equal or superior to tarsoconjunctival advancement flaps.

Cryosurgery for treatment of trichiasis.

We cryosurgically destroyed eyelashes in rabbits and applied the technique to treat 23 selected patients with trichiasis. Liquid nitrogen was sprayed on the eyelid margin by using a double, rapid-freeze, slow-thaw cycle monitored by a subcutaneous thermocouple to -30 degrees C. It was an improvement on electrolysis and a simple alternative to surgery.