The Effects of Zinc, Lead and Cadmium Pollution on the Leaf Surface Microflora of Lolium perenne L.

Abstract

The influence of zinc, lead and cadmium contamination on the phylloplane microflora of Lolium perenne growing at various distances from a smelting complex was investigated. Bacteria, yeasts and filamentous fungi were isolated using a leaf washing method, and relative metal tolerance was assessed by the incorporation of zinc, lead and cadmium salts into the growth media. Numbers of fungal propagules were also assessed by direct observation of leaf segments. Non-pigmented yeastgof the genus Cryptococcus were particularly tolerant to the metals, both in vitro and in vivo. Bacteria were less tolerant in vitro, but populations in the field were found even under the highest levels of metal contamination. Filamentous fungi were more tolerant than bacteria to heavy metals in vitro but population levels appeared to be particularly influenced by lead contamination on the leaf surface. I N T R O D U C T I O NConsiderable zinc, lead and cadmium pollution occurs in the vicinity of a smelting complex at Avonmouth, near Bristol, and metal levels have been extensively studied on grass, moss and lichens (Burkitt et al., 1972), in soil and vegetation (Little & Martin, 1972) and on the leaf surfaces of hawthorn, oak, willow and elm (Little, 1973).Up to 8000p.p.m. zinc, 5000p.p.m. lead and 50p.p.m. cadmium have been detected on vegetation close to the smelting complex (Little, 1973). On pine saplings and cabbages grown in pots and exposed to contamination near the smelter, the numbers and diversity of micro-organisms were reduced compared with those grown at a control site (Gingell et al., 1976). The aim of the present study was to investigate the influence of this pollution on the phylloplane microflora of a plant of the indigenous vegetation, Lolium perenne L., a common grass found near the smelting complex. M E T H O D SSampling procedure. Five grass fields numbered 1 to 5, at approximate distances of 0.35,0.5, 1.4, 1.3 and 1-85 km, respectively, ENE of the Avonmouth smelting complex, were sampled in November 1976. Field 4 was a little nearer to the smelter than field 3 but slightly out of the main line of sampling. Leaves from three patches of Loliurn perenne in each field were collected and placed in sterile containers.Microbiological assay. Eighty leaf discs were cut from each sample (using a 2-5 mm diam. punch), placed in a Universal bottle containing 10 ml sterile distilled water with 5 g glass beads (approx. 3 mm diam.) and shaken for 10min on a wrist action shaker. Samples (0.1 ml) of the suspension and of a 10-fold dilution were each inoculated separately on to the surface of a series of agar plates. Two basic media were used: Martin's Rose Bengal Streptomycin Agar (MRB; Tuite, 1969) and Tryptic Soy Agar [TSA; 3 g Tryptic Soy Broth (Difco 0370) 1-1 plus 20 g agar l-l]. To study relative microbial tolerance to the three metals, cadmium, zinc and lead were added singly (as nitrates) at, respectively, 100, 400 and 800 pg (g wet wt)-' to TSA and 500, 2000 and 2000 ,ug (g wet wt)-l to MRB. Plates of TSA and MRB containing al...

Biological Monitoring of Heavy Metal Pollution

“…zinc, cadmium and lead- Gingell et ai., 1976;Bewley, 1979;Bewley andCampbell, 1980. zinc, cadmium and lead- Gingell et ai., 1976;Bewley, 1979;Bewley andCampbell, 1980.…”

Interactions of fungi with toxic metals

“…Heavy metal pollution of plant surfaces is widespread and, while there may be significant decreases in total microbial numbers (including bacteria) on phylloplanes, numbers of filamentous fungi and non-pigmented yeasts are generally little affected (Bewley, 1979(Bewley, , 1980Bewley & Campbell, 1980; and, if metal-supplemented isolation media are used, only fungi may be isolated (Bewley, 1980). On polluted oak leaves, Aureobasidium pullulans and Cladosporium spp.…”

“…glucose), and by glucose analogues, metabolic inhibitors and uncouplers (Ross, 1977;Norris & Kelly, 1977, 1979Borst-Pauwels, 1981;Gadd, 1986a, 6;Starling & Ross, 1990). In certain fungi, especially yeasts, greater amounts of metal may be accumulated by such a process, in conjunction with internal sequestration, than by metabolism-independent processes (Ross, 1977;Norris & Kelly, 1977, 1979. Many metals are essential for fungal growth and metabolism, e.g.…”

“…In general, minerals with a high cation exchange capacity (CFC) are more effective in reducing toxicity than minerals with a lower CFC (Babich & Stotzky, 1977a, b;Bewley & Stotzky, 1983). Montmorillonite was more effective than kaolinite, with a lower CFC, in protecting fungi from Cd, Ni and Pb toxicity (Babich & Stotzky, 1978, 1979, such effects also being influenced by soil pH (Collins & Stotzky, 1989). …”

OBSERVATIONS ON DRECHSLERA LEAF SPOT ON LOLIUM PERENNE AFFECTED BY CADMIUM

“…There have been numerous investigations into the uptake and efTects of heavy metals on plants including L. perenne (Jarvis, Jones & Clement, 1977;Jarvis & Jones, 1978;Wong & Bradshaw, 1982), and the influence of aerial heavy metal pollutants, particularly Cd, Pb and Zn, on the phylloplane microflora of L. perenne has been described by Bewley (1979). There are no reports, however, of the interaction between heavy metal affected plants and phytopathogenic fungi, although Giri and Sinha (1983) have investigated the use of heavy metal salts to induce phytoalexin production in rice seedlings and so control brown spot infection caused by Drechslera oryzae Subram and Jain.…”