Michael J. Earnshaw

Altitudinal changes in the incidence of crassulacean acid metabolism in vascular epiphytes and related life forms in papua new guinea

SummaryThe occurrence of Crassulacean acid metabolism (CAM), as judged from δ13C values, was investigated in epiphytes and some related plant species at a series of sites covering the approximate altitudinal range of epiphytes in Papua New Guinea. Comprehensive collections were made at each site and the occurrence of water storage tissue and blade thickness was also determined. Some 26% of epiphytic orchids from a lowland rainforest (2–300 m.a.s.l) showed δ13C values typical of obligate CAM and possessed leaves thicker than 1 mm. A second group of orchids, mostly with succulent leaves, possessed intermediate δ13C values between -23 and -26% and accounted for 25% of the total species number. Some species of this group may exhibit weak CAM or be facultative CAM plants. The remainder of the lowland rainforest species appeared to be C3 plants with δ13C values between -28 and -35%. and generally possessed thin leaves. Obligate CAM species of orchids from a lower montane rainforest (1175 m.a.s.l) comprised 26% of the species total and mostly possessed thick leaves. The remainder of the species were generally thin-leaved with δ13C values between -26 and -35%. largely indicative of C3 photosynthesis. Orchids with intermediate δ13C values were not found in the lower montane rainforest. Obligate CAM appeared to be lacking in highland epiphytes from an upper montane rainforest and subalpine rainforest (2600–3600 m.a.s.l). However the fern, Microsorium cromwellii had a δ13C value of -21.28%. suggesting some measure of CAM activity. Other highland ferns and orchids showed more negative °13C values, up to-33%., typical of C3 photosynthesis. The highland epiphytic orchids possessed a greater mean leaf thickness than their lowland C3 counterparts due to the frequent occurrence of water storage tissue located on the adaxial side of the leaf. It is suggested that low daytime temperatures in the highland microhabitats is a major factor in explaining the absence of CAM. The increased frequency of water storage tissue in highland epiphytes may be an adaptation to periodic water stress events in the dry season and/or an adaptation to increased levels of UV light in the tropicalpine environment.

Acclimation of potassium influx in rye (Secale cereale) to low root temperatures

The influx of K+(86Rb+) into intact roots of rye (Secale cereale L. cv. Rheidal) exposed to a differential temperature (DT) between the root (8° C) and shoot (20° C) is initially reduced compared with warm-grown (WG) controls with both shoot and root maintained at 20° C. Over a period of 3 d, however, K+-influx rates into DT plants are restored to levels similar to or greater than those of the WG controls, the absolute rates of K+ influx being strongly dependent upon the shoot/root ratio. Acclimation in DT plants results in a reduction of K+ influx into the apical (0–2 cm) region of the seminal root which is associated with a compensatory increase in K+ influx into the more mature, basal regions of the root. Values of Vmax and apparent Km for K+ influx into DT plants were similar to those for WG plants at assay temperatures of 8° C and 20° C except for an increase in the apparent Km at 8° C. The influx of K+ from solutions containing 0.6 mol·m-3 K+ into both WG and DT plants was found to be linearly related to assay temperature over the range 2–27° C, and the temperature sensitivity of K+ influx to be dependent upon shoot/root ratio. At high shoot/root ratios, the ratio of K+ influx at 20° C:K+ influx at 8° C for WG plants approached a minimum value of 1.9 whereas that for DT plants approached unity indicating that K+ influx into DT plants has a large temperature-insensitive component. Additionally, when plants were grown in solutions of low potassium concentration, K+ influx into DT plants was consistently greater than that into WG plants, in spite of having a greater root potassium concentration ([K+]int). This result indicates some change in the regulation of K+ influx by [K+]int in plants exposed to low root temperatures. We suggest that K+ influx into rye seedlings exposed to low root temperatures is regulated by the increased demand placed on the root system by a proportionally larger shoot and that the acclimation of K+ influx to low temperatures may be the result of an increased hydraulic conductivity of the root system.

Photosynthetic pathway, chilling tolerance and cell sap osmotic potential values of grasses along an altitudinal gradient in Papua New Guinea.

SummaryA total of 22 grass species were examined from 5 sites spanning the altitudinal range 1550–4350 m.a.s.l. The presence of the C3 or C4 photosynthetic pathway was determined from δ13C values and chilling tolerance was assessed on the basis of electrolyte leakage from leaf slices incubated on melting ice. Most of the grasses studied at the lower altitude sites of 1550 m.a.s.l. (annual mean of daily minimum temperature, 14.6° C) and 2600 m.a.s.l. (9.4° C) possessed C4 photosynthesis and were chill-sensitive. The single except ion was Agrostis avenacea, a montane chill-resistant C3 species which occurred at 2600 m.a.s.l. The three species apparently most sensitive to chilling were Ischaemum polystachyum, Paspalum conjugatum and Saccharum robustum, all occurring at 1550 m.a.s.l. At the higher altitude sites of 3280 (5.6° C), 3580 (4.0° C) and 4350 (−0.7°C) m.a.s.l., most of the grasses exhibited C3 photosynthesis and were chill-resistant. However, an Upland population of the C4 species, Miscanthus floridulus was found at 3280 m.a.s.l. which had acquired chill-resistance as confirmed by additional in vivo variable chlorophyll fluorescence measurements. Cell sap osmotic potential values of the upland grasses at altitudes of 3280–4350 m.a.s.l. were lower (−8.1 to −19.8 bars) than values in grasses from 1550 and 2600 m.a.s.l. (−3.9 to −7.5 bars) due mainly to the presence of non-electrolyte osmoticants, which may be involved in frost avoidance mechanism(s).

The action of heavy metals on the gametes of the marine mussel, Mytilus edulis (L.)—III. The effect of applied copper and zinc on sperm motilityin relation to ultrastructural damage and intracellular metal localisation

Treatment of Mytilus edulis sperm with external concentrations of copper or zinc (0-1-3-3mM) causes a decrease in motility in which zinc is more inhibitory than copper. Zinc also appeared to cause more extensive mitochondrial damage, as revealed by transmission electron microscopy, than did treatment with copper. The relationship between sperm motility and respiration in the presence of the various heavy metal concentrations used indicates that the depression of sperm motility can be explained largely on the basis of respiratory inhibition. However, zinc produces a less pronounced effect on sperm motility than on r respiration. X-ray microanalysis of thick sections of fixed treated sperm showed that copper accumulation occurs in the acrosomes, mitochondria and nuclei, whereas zinc is found in the acrosomes and in mitochondrial granules in association with calcium and phosphorus. No evidence was obtained for zinc accumulation in the nuclei. Treatment with either copper or zinc resulted in considerable reductions of bound calcium and phosphorus in both the acrosomes and mitochondria. It is suggested that the heavy metal ions cause an increase in the permeability of the organelle membranes to calcium and phosphorus. It is concluded that the less marked effect of zinc on sperm motility as compared to respiration may be due to an increase in the cytosolic free calcium concentration which, in turn, may stimulate the flagellar contractile apparatus.

Leaf anatomy, water relations and crassulacean acid metabolism in the chlorenchyma and colourless internal water-storage tissue of Carpobrotus edulis and Senecio ?mandraliscae

Both Carpobrotus edulis and Senecio ?mandraliscae possess leaves with a peripheral chlorenchyma and colourless internal water-storage tissue. Water stress in C. edulis growing under semi-natural conditions resulted in the induction of weak Crassulacean acid metabolism (CAM) whereas well-watered plants of S. ?mandraliscae exhibited a similar degree of CAM. Titratable acidity in the separated water-storage tissue was substantially lower than in the chlorenchyma in both species but, nevertheless, increased during the night and decreased during the day either when sampled from the intact plant or from incubated tissue slices. Indeed, the increase in nocturnal titratable acidity produced by the water-storage tissue in situ accounted for approx. 30% of total acidification on a per-leaf basis. It appears that during the night the water-storage tissue in these species is able to fix CO2 which is subsequently released during the day to enter the photosynthetic carbon-reduction cycle of the chlorenchyma. Diurnal rhythms of water potential (Ψ) and osmotic potential (Ψs) were measured in separated chlorenchyma and water-storage tissue by thermocouple psychrometry. Both parameters increased during the latter part of the daytime and initial nocturnal period and decreased during the rest of the night and into the post-dawn period. The chlorenchyma of water-stressed plants of C. edulis appeared to possess a marked negative turgor pressure (as determined from Ψ-Ψs) but this was caused by a severe underestimation in the measurement of the chlorenchyma Ψ. It is suggested that this artefact arose from release of colloidal polysaccharide mucilage, or possibly tannins, from broken tannin cells producing a lowering of water activity when measured using thermocouple psychrometry.

Changes in leaf water potential and CAM inSempervivum montanum andSedum album in response to water availability in the field

SummaryThe short term effects of irrigation on diurnal changes in Ψleaf and titratable acidity were examined both inSempervivum montanum and inSedum album, a facultative CAM plant, in the Spanish Pyrenees. InSemperivivum, Ψleaf responded rapidly to irrigation and, in both the control and irrigated plants, increased during the day and decreased during the night and early morning. By contrast, Ψleaf inSedum responded more slowly to irrigation and showed a decrease during the day and an increase in the period between evening and early morning. Under the conditions of the short-term experiments, changes in acid metabolism were not observed in either species following irrigation. The results suggest that transpirational water loss together with redistribution of water within the plant are more important than the osmotic concentration of malic acid in determining Ψleaf in both species and that daytime water loss is greater inSedum than inSempervivum.The effect of long-term water stress on Ψleaf and acid levels was also assessed in both species over a 3-week period. Both Ψleaf and acidification inSempervivum decreased over this time period but could, at least partially, be reversed by irrigation. InSedum, Ψleaf also declined but a more gradual reduction in acidification occurred than inSempervivum. Irrigation inSedum at least partially reversed the decline in Ψleaf but produced a complex pattern of acid metabolism. Nocturnal acidification in the irrigated plants was lower than in the non-irrigated control when preceded by a cool day but showed complete recovery following a hot day. It is suggested inSedum album that C3 photosynthesis during the preceding light period, as determined by light intensity and leaf temperature, may be important in determining the extent of nocturnal acidification under field conditions.

The action of heavy metals on the gametes of the marine mussel, Mytilus edulis (L.)-II. Uptake of copper and zinc and their effect on respiration in the sperm and unfertilized egg

The addition of stock copper and zinc nitrate solutions to filtered seawater (pH 7·91) resulted in a large pH shift which was more pronounced with copper. The pH shift was minimized by increasing the buffering capacity of seawater using 10 mm Tris-Tes pH 7·91. Subsequent experimentation was carried out in both unbuffered and buffered seawater. In unbuffered seawater, both copper and zinc had a pronounced inhibitory effect on Mytilus edulis sperm respiration with 50% inhibition occurring at 0.65 mm (41·3 ppm) copper and 1.0 mm (65·4 ppm) zinc. Egg respiration was also inhibited by copper with 50% inhibition occurring at 0.9 mm (57·2 ppm) whereas zinc inhibited egg respiration by only 30% at 1·5 mM (98·1 ppm). In buffered seawater, both copper and zinc produced an inhibitory effect on sperm respiration. However, with copper the inhibition was much reduced whereas zinc had tthe same inhibitory effect as in unbuffered seawater. In contrast to unbuffered seawater, egg respiration was stimulated by copper but zinc produced a comparable respiratory inhibition. The uptake of both copper and zinc in sperm and egg in buffered seawater increased with increasing metal concentration. Metal ion uptake, when expressed as ng ions μl cell volume−1, was approximately 3-fold greater in the sperm than in the eggs and in both cases zinc uptake exceeded copper uptake. At a seawater pH of < 7·5, in the absence of copper or zinc, the respiration of both egg and sperm was inhibited. The maximum levels of inhibition at pH 5·4 were 15% and 30% for sperm and egg, respectively. The differing actions of copper on egg respiration in buffered and unbuffered seawater appear to be due to enhanced copper uptake in unbuffered seawater.

Studies of the effects of zinc on the respiration of mitochondria from different tissues in the bivalve mollusc Mytilus edulis (L.)

Effects of Zn2+ concentrations have been studied on the respiration of mitochondria isolated from the mantle tissue and digestive gland of Mytilus edulis, and compared with rat liver mitochondria. 2. Both types of isolated M. edulis mitochondria had respiratory control indices (RCI) with ADP of 1.5–2.0 compared with 5–6 for rat liver mitochondria. 3. Approximate Zn2+ concentrations giving a 50% inhibition of succinate plus glutamate oxidation are 70 μM for rat liver mitochondria, 135 μM for M. edulis mantle mitochondria and 280 μM for digestive gland mitochondria, 4. These differences are statistically significant at P < 0.001 to P < 0.05.

The action of heavy metals on the gametes of the marine mussel, Mytilus edulis (L.)—I. copper-induced uncoupling of respiration in the unfertilized egg

The direct addition of Cu2+ to unfertilized eggs of Mytilus edulis results in a stimulation of respiration with maximal stimulation occurring at a Cu2+ concentration of ca 0.5 mM. By contrast, the addition of Zn2+ has no effect on egg respiration. The uncoupler CCCP produces a 5/6 fold stimulation of egg respiration but the addition of ADP leads to only a small release of respiration. In contrast, sperm respiration is unaffected by Cu2+, inhibited by Zn2+ and CCCP produces only a small respiratory stimulation. The addition of Cu2+ to respiring Mytilus mantle tissue mitochondria produces an initial stimulation of State 4 oxidation which is then followed by a progressive inhibition. It is suggested that respiration in the unfertilized egg may be inhibited by a high ATP/ADP ratio in the cytosol. Respiration can, therefore, be released by either the addition of a H+-translocating uncoupler or by Cu2+ which may act by stimulating mitochondrial K+ influx.

Does plant growth temperature modulate the membrane composition and ATPase activities of tonoplast and plasma-membrane fractions from rye roots?

Abstract The effect of plant growth temperature on the lipid composition and ATPase activity associated with tonoplast and plasma-membrane fractions from roots of rye ( Secale cereale cv. ‘Rheidol’) was investigated to try and explain the rapid ( K m ), sensitivity to specific inhibitors (nitrate or vanadate), stimulation by KCI and activation energy ( E a ) of the plasma-membrane and tonoplast ATPases were unaffected. The only apparent difference between growth temperature pretreatments was an increase in the specific activity of the plasma-membrane ATPase, but not that of the tonoplast, after long term ( > 3 day) cooling of plant roots. It appears, therefore, that the enhancement of ion transport capacity which is evident upon cooling rye roots is not mediated by changes in activity or properties of the ATPases.