Julian C. Collins

The mechanism of zinc tolerance in grasses

Abstract The mechanism of zinc tolerance in non‐tolerant and tolerant clones of Deschampsia caespitosa and Anthoxanthum odoratum has been investigated. Analysis of non‐tolerant and tolerant clones of these two grasses showed that the tolerant roots accumulated more zinc than the non‐tolerant ones. The zinc contents of the shoots of both clones were similar and contained less zinc than the roots. Compartmental flux analysis using 65Zn suggested that both clones of D. caespitosa were capable of actively pumping zinc across the plasmalemma into the external medium. However, only the tolerant clone was capable of actively pumping zinc out of the cytoplasm of root cells into vacuoles when exposed to levels of zinc up to 1mM, this process was inhibited above 0.1mM zinc in the non‐tolerant clone. Analysis of D. caespitosa for organic acids showed that only the tolerant clone, grown in the presence of zinc accumulated high levels of malic acid. Cytoplasmic sensitivity to zinc was measured by estimating the effect...

Accumulation of amino acids, proline, and carbohydrates in response to aluminum and manganese stress in maize

Abstract Synthesis of amino acids, proline, and carbohydrates was studied in roots and shoots of 5 maize accessions, differing in aluminum (Al) and manganese (Mn) tolerance, in response to Al and Mn stress at the seedling stage in solution culture. The concentrations of these metabolites increased in roots and shoots of the seedlings in the nutrient solution with added Al (0.22 mM), and Mn (2.0 mM). Both Al and/or Mn tolerant and non‐tolerant accessions accumulated more metabolites under stress than control. Generally, the tolerant accessions accumulated more solutes than the non‐tolerant maize accessions examined.

Effects of salinity on growth of Baltic and Atlantic Fucus vesiculosus

Vegetative apices of intertidal Atlantic and permanently sublittoral, brackish water, Baltic Fucus vesiculosus were cultured in a salinity range (1·5–45 ppt) in the laboratory. Tank experiments with running Baltic sea-water were also conducted under summer (10–20°C) and autumn (7–10°C) temperature ranges. Both populations were able to grow in a wide range of salinity in laboratory culture. The Atlantic population showed better growth in higher salinities and virtually no growth in 1·5 ppt, in which it died after 7 weeks. In contrast the Baltic plants grew better in the lower range of salinity. Baltic material took nearly 4 weeks to recover from upshock in salinities 34 and 45 ppt, and showed 10–15% loss of tissue weight during the first two weeks. Growth then started, but in the highest salinity (45 ppt) growth was negligible. When cultured in a semi-natural Baltic environment, in a tank experiment, Atlantic plants could not survive whereas Baltic plants showed vigorous growth. The combination of continuo...

The Influence of Variations in Salinity upon Photosynthesis in the Marine Alga Porphyra purpurea (ROTH) C. AG. (Rhodophyta, Bangiales)

Summary Steady-state photosynthetic responses of plants immersed in a range of concentrated and diluted seawaters have been determined. Net photosynthesis under hyposaline conditions was found to decrease in direct proportion to the reduction in salinity. Photosynthetic activity was increased in less extreme hypersaline media; in all other concentrated seawaters it was reduced. Photosynthetic activity of plants subjected to quasi-estuarine salinity fluctuations has been studied. Photosynthesis under such conditions was shown to decrease and increase in a synchronous manner, the rates of photosynthesis at any given point in time being similar to steady-state values for dilute seawaters of comparable salt content. Plants subjected to a single cycle of reduced salinity exhibited similar photosynthetic responses to those maintained under such conditions for 15 cycles.

Comparative reproductive biology of the Gulf of Finland and the Irish Sea Fucus vesiculosus L.

Abstract Variation in reproductive characters of two geographically distinct populations of Fucus vesiculosus L. (Phaeophyta, Fucales) from both open and sheltered shores of Baltic, the Gulf of Finland and Atlantic, the Irish Sea coast has been quantified. The period during which the population contains fertile plants is longer on Atlantic than on Baltic coasts, where all receptacles are shed by the end of July. There are differences in reproductive allocation, the value of Atlantic plants being double that of the Baltic population. The mean oogonial length is greater in the Atlantic populations and the size frequency is different, with Atlantic plants bearing some immature oogonia at peak fertility time. Baltic plants have oogonia of more uniform size. Receptacles of Baltic plants have a looser web-like organisation of hyphae in the medulla, which is also characterized by presence of enlarged air cavities formed by schizogeny. The hyphal cells are wider in Atlantic plants than in Baltic plants. Atlantic ...

Effects of Salinity on Growth, Ionic Relations and Solute Content of Sorghum Bicolor (L.) Monench

ABSTRACT The effects of increasing levels of calcium (Ca2+), potassium (K+), and sodium chloride (NaCl) salinity on the growth and ionic relations of Sorghum bicolor (L.) Monench, cv. ‘ICI-5521’ seedlings are reported. Increasing levels of Ca2+ in the solution culture enhanced growth, lowered sodium (Na+) uptake, and increased K+:Na+ ratio significantly. Elevated K+ level also improved growth significantly, but had no significant effect on Na+, Ca2+, or magnesium (Mg2+) accumulation of either roots or shoots. Accumulation of K+ and consequently K+:Na+ ratio increased with external K+ concentration. The effects of sodium chloride (NaCl) versus potassium chloride (KCl) salinity on the growth and ionic relations of sorghum (‘ICI-5521’) were also examined. Growth inhibition was greatest when KCl alone (160 mM) was used, but was enhanced when a mixture of NaCl and KCl (15:1) was used. The influence of salinity on the accumulation of proline, amino acids and carbohydrates and total osmolality is also discussed.