New Phytologist

FITZGERALD, MELISSA A.; ORLOVICH, DAVID A.; ALLAWAY, WILLIAM G.

doi: 10.1111/j.1469-8137.1992.tb01052.xpmid: N/A

Pieces of leaf from the halophyte Avicennia marina (Forsk,) Vierh. were freeze‐substituted and sectioned with special precautions to keep specimens always dry. Spot energy dispersive X‐ray microanalysis and X‐ray mapping showed that vacuoles of water parenchyma and palisade mesophyll cells had much more sodium and chlorine than the cytoplasm of the same cells. Potassium and phosphorus were also found in the vacuoles of the palisade mesophyll cells but in the water parenchyma cell vacuoles, sodium and chlorine generated most of the X‐ray counts. This is consistent with a function for the water parenchyma cells of vacuolar salt storage. No sodium and chlorine were detected in the peltate cells of the abaxial epidermal hairs, and there was very little sodium in the vacuoles of their basal cells, potassium apparently being the major cation. Salt crystals were not detected in substomatal cavities. Abaxial epidermal glands contained sodium and chlorine in the collecting cell, stalk cell, secretory cells and the subcuticular cavity. Material just outside the glands gave extremely high X‐ray counts for sodium and chlorine. We conclude that the material was salt that had been secreted, and that the glands are the secretory apparatus on the abaxial surface of the leaves.

NORTH, GRETCHEN B.; NOBEL, PARK S.

doi: 10.1111/j.1469-8137.1992.tb01053.xpmid: N/A

Drought‐induced changes in hydraulic conductivity (Lp) and anatomy were investigated for 1‐, 3‐ and 12‐month‐old roots of Ferocactus acanthodes (Lem.) Britton & Rose and Opuntia ficus‐indica (L.) Miller. Responses were similar for the two species but varied for the three root ages. Drying in soil for 30 d caused little change in Lp or internal structure for 1‐month‐old roots, primarily due to the formation of soil sheaths in the root hair zone. For 3‐month‐old roots, Lp declined three‐ to five‐told after 30 d of drying, partly because of lacunae caused by rupture of cortical cells. For 12‐month‐old roots after 30 d of drying, the dehydration of suberized peridermal layers led to a two‐ to three‐fold decline in Lp. Measurements of axial hydraulic conductance per unit pressure gradient (Kh) before and after pressurization indicated that air embolism, caused by 30 d of drying, decreased Khby 53, 97, and 98% for 1‐ 3‐ and 12‐month‐old roots, respectively. Rewetting after 30 d of drying restored Kh to initial values within 7 d for all three root ages. Lpafter rewetting attained 100 % of its initial value for 1‐month‐old roots arid about 60% for 3‐ and 12‐month‐old roots. The formation of soil sheaths around young roots, the reduction in radial conductivity for older roots by cortical lacunae and peridermal dehydration, and the reduction in Kh by embolism thus caused a moderate, partly reversible decline in Lp that can help limit water loss from roots to the soil during drought.

WILLIAMSON, B.; GOODMAN, B. A.; CHUDEK, J. A.

doi: 10.1111/j.1469-8137.1992.tb01054.xpmid: N/A

Red raspberry (Rubus idaeus) fruits were subjected to nuclear magnetic resonance (NMR) micro‐imaging to study the changes in spatial distribution of mobile protons (1H) during a 3‐day ripening period while the fruit was still attached to the receptacle. All imaging measurements were made using the protons from a single absorption peak at 4.6 ppm, which corresponds to water, and data were collected by pulsed gradient spin‐echo and gradient‐echo methods with voxel dimensions of 70 × 70 × 500 μm. Individual drupelets were clearly visible by this non‐invasive histological method in distal transverse ‘slices’ of a newly harvested red ripe fruit viewed by spin‐echo; highest mobile proton densities were found at the lines of contact between drupelets. The mesocarp tissues of each drupelet showed intermediate grey tones with some evidence of radial striations. In more proximal ‘slices’ the surface of the receptacle and its central vascular cylinder had the highest mobile proton densities. The seeds produced black images in all ‘slices’, indicative of low mobile proton densities or long relaxation times.

REILING, K.; DAVISON, A. W.

doi: 10.1111/j.1469-8137.1992.tb01055.xpmid: N/A

Ozone concentrations in many parts of Europe exceed the proposed UN‐ECE Critical Levels for the protection of ecosystems but there is so little known about the effects on native, herbaceous species, that it is presently impossible to judge what effect, if any, these concentrations are having on this group of plants. This paper reports the results of an initial screening of 32 taxa that was used to select a small number of species for further work. All were exposed to 70 nl 1−1O3 given for 7 h d−1for two weeks and the response measured in terms of mean relative growth rate (R̄), the allometric root/shoot coefficient (K), and changes in induced chlorophyll fluorescence (FR).

OJANPERÄ, K.; SUTINEN, S.; PLEIJEL, H.; SELLDÉN, G.

doi: 10.1111/j.1469-8137.1992.tb01056.xpmid: N/A

Spring wheat, Triticum aestivum L., cv. Drabant, was exposed to different concentrations of ozone in open‐top chambers for one growing season, at a site located in south‐west Sweden. The chambers were placed in a field of commercially grown spring wheat. The treatments were charcoal‐filtered air (CF), non‐filtered air (NF), non‐filtered air + 25 nl 1−1ozone (NF +) and non‐filtered air + 35 nl 1−1ozone (NF++). Ozone was added daily between 11.00 and 18.00 h, starting at anthesis. Fumigation with elevated concentrations of ozone caused chlorosis of the flag leaves. In the NF++ and NF+ treatments chlorosis appeared after 7 and 20 days of fumigation, respectively, and in the CF treatment after about 34 days, A progressive series of changes occurred in the mesophyll cells of the flag leaves after ozone fumigation. Starting at anthesis, the first changes occurred in the cytoplasm and involved a decrease in the amount of cytoplasm and an increase in the vacuolization of the cells. Subsequently the chloroplasts became affected decreasing in area and containing more plasto‐globuli. Finally vesicles were formed between the grana thylakoids and at the same time the plasma membrane came loose from the cell wall and convoluted. The mitochondria remained unaffected until only lipid droplets, oleosomes, were left in the cells. These changes were not specific for ozone as they occurred also in the CF treatment, although later in time. This indicates that ozone causes premature senescence in wheat flag leaves.

FINCHER, JEAN; ALSCHER, RUTH G.

doi: 10.1111/j.1469-8137.1992.tb01057.xpmid: N/A

The death of many mature red spruce (Picea rubens Sarg.) trees in the northeastern United States has sparked controversy over the roles natural factors and air pollutants play. The goal of this work was to investigate the effects of long‐term ozone exposures on development of injury and, in particular, the expression of winter injury in red spruce. Red spruce seedlings were exposed to elevated levels of ozone during two growing seasons, starting just after budbreak, and continuing into the period of early frosts. Trees spent both winter periods under ambient conditions of light and temperature. No visible lesions on foliage that could be attributed to ozone developed during the growing seasons. Yellow and brown needles appeared each winter, with much more injury in the second year. However, in the spring after two seasons of ozone exposure, there was no significant effect of ozone on the overall appearance of the entire population of seedlings. Samples were taken for histology and ultrastructure approximately monthly. Ozone treatments increased mesophyll cell disruption after frosts in early winter in the first year, but not in the second. There was no correlation between histological injury in the autumn and visible symptoms in the spring, indicating that there may be different aspects of the winter injury syndrome. In the second summer from 20 to 40%, of all mesophyll cells were damaged. This damage was not related to ozone treatment, and probably resulted from high summer temperatures.

BYRES, DAVID P.; DEAN, THOMAS J.; JOHNSON, JON D.

doi: 10.1111/j.1469-8137.1992.tb01058.xpmid: N/A

Seedlings from four half‐sib families of Pinus elliottii var. elliottii Engelm. were planted in open‐top chambers, and exposed to ozone and simulated acidic precipitation. Treatments were applied for 11 months per year for 28 months. The ozone concentrations were: charcoal filtered air (CF), nonfiltered ambient air (1×), twice the nonfiltered level (2 ×) and three times the nonfiltered level (3 ×). Ozone exposures were computer controlled to follow natural diurnal fluctuations in ambient ozone concentrations. Simulated acid rain at pH 3.3, 4.3 or 5.3 was delivered weekly at the same volume as average weekly rainfall to all chambers.

WILLIAMS, J. H.; ASHENDEN, T. W.

doi: 10.1111/j.1469-8137.1992.tb01059.xpmid: N/A

White clover plants (Trifolium repens L. cv ‘Grasslands Huia’) were exposed to combinations of gaseous pollutants and acid mists similar to those found in many parts of upland Britain. The gaseous pollutant treatments were (a) charcoal‐filtered air (control), (b) SO2+ NO2 (c) O3 and (d) O3+ SO2+ NO2. The acid mist treatments were 6 mm per week of solutions at pHs of 2.5, 3.5, 4.5 and 5.6. After 12 weeks, canopy reflectance was measured at green, red, near infrared and middle infrared wavelengths using a portable radiometer. Distinct changes in the characteristic spectral reflectance of the clover canopies were noted. The effect of the gaseous pollutants was significant when examined by analysis of variance. The two treatments containing ozone showed particularly marked changes and were statistically separable from the control in a pairwise comparison; the sulphur and nitrogen dioxide treatment was not statistically separable from the control. The acid mists had no significant effect on canopy reflectance. Simple and 4‐waveband vegetation indices showed positive linear relationships with shoot dry weight. The O3+SO2+NO2, in particular, and O3 treatments produced marked decreases in shoot dry weight and vegetation index. The green and near infrared wavebands were the best discriminators of change in canopy reflectance.

BÄCK, JAANA; HUTTUNEN, SATU

doi: 10.1111/j.1469-8137.1992.tb01060.xpmid: N/A

The mesophyll ultrastructure of needles of Norway spruce [Picea abies (L.) Karst.] and Scots pine (Pinus sylvestris L.) seedlings was examined in the course of experimental acid rain treatment lasting three years. The pH 3‐treated needle mesophyll cells exhibited thicker granal packing in their chloroplasts than the dry control needles after one season's irrigation. Starch occurrence had decreased due to pH treatment when the whole hardening and rest period was considered. Chloroplast shapes were seen to vary from ellipsoid to irregular, especially in the pH 4 and pH 3‐treated needles, due to divisions during hardening. The mean area of mesophyll chloroplasts in the hardened state after three seasons, irrigation was largest (10.3 μm2) in the pH 3‐treated needles, which also contained the smallest number of dark‐stained plastoglobuli. Starch occurrence in the hardened mesophyll cells in October reflected disturbances in the hardening processes in the pH 3‐treated needles.

MORGAN, S. M.; LEE, J. A.; ASHENDEN, T. W.

doi: 10.1111/j.1469-8137.1992.tb01061.xpmid: N/A

Nitrate assimilation and photosynthetic responses of Ctentdium mulluscum (Hedw.) Mitt. Homalothecium sericeum (Hedw.) Br.Eur. Pleurusium schreberi (Brid.) Mitt. Hylocomium splendens (Hedw.) Br.Eur. were studied during and after controlled exposures to 35 nl 1−1NO2 and 35 nl 1−1NO. NO2 induced nitrate reductase activity in all species 24 hours after the start of fumigation. The magnitude of the inductions varied between 23 and 89%. In contrast, exposure to NO caused a rapid decline in activity within 24 hours. After 21 days continuous exposure to each of the gases, the plants were supplied with a single application of 10 mM, NaNO3. Nitrate reductase activity was induced only in plants exposed to clean air. NO8exposure caused a loss of nitrate inducibility of NR. There were no marked effects on rates of oxygen evolution. After a three‐week pollution‐free period, the bryophytes regained the capacity for nitrate assimilation.