THE DIET, PREY SIZE AND CONSUMPTION OF PHILINE ORIENTALIS (OPISTHOBRANCHIA: PHILINIDAE) IN HONG KONG

Philine orientalis occurs on Hong Kong's beaches for {smalltilde}2 months each year, in May and June when it breeds, laysegg capsules and dies. It is believed to have a life span ofone year. Hoi Sing Wan, a sandy beach in the New Territoriesof Hong Kong is dominated at lower levels by the venerid bivalveTapes philippinarum, the population of which in May and June,following spring recruitment, mostly comprises juveniles. P.orientalis, occurring at a density of {small tilde} 1.m^–2,feeds voraciously upon these juveniles consuming, in laboratoryexperiments, a mean of 25.day^–1. At Hoi Sing Wan, P. orientalisappears to be highly prey specific. It is, however, known tofeed on other prey items and probably has a catholic diet, duringits annual migration from deeper to shallower sediments, accordingto the prevailing fauna. In terms of wet weight, P. orientalis consumes a mean of {smalltilde}4.4% (2.2–6.7%) of its body weight day^–1.In terms of dry weight, however, this figure increases to amean of 35.5% and one figure of 208% has been recorded. Althoughthis is because of the large body fluid content of this, essentiallyshell-less, gastropod, using a hydrostatic skeleton to achieveburrowing, such figures further attest to the voracity of thebreeding adults. This study joins others in questioning ourpresent understanding of the scale of energy budgets on suchshores, i.e., are our estimates of loss to predation grosslyunderestimated? ^*Present address: Department of Biology, Baptist College, WaterlooRoad, Kowloon, Hong Kong. (Received 20 May 1989; accepted 3 July 1989)     

A Study of Nitrate Reduction in Mould Fungi

1. The activity of the nitrate-reducing (nitratase) system infungal mycelium was measured by incubation of the mycelium (eitherintact or ground) with nitrate in the presence of sodium fluoridewhich blocks nitrite reduction and causes nitrite accumulation. 2. The nitrate-reducing system in the fungi examined shows rapidchanges in activity in response to some environmental factors.Nitratase activity of mycelium in glucose-nitrate medium fallsto a low value within 1 hour after addition of ammonia and remainsat this value until all added ammonia has been assimilated.The fall in activity appears to depend on the assimilation ofammonia by the mycelium, since it did not occur in conditionswhen assimilation was prevented. 3. Nitrate-reducing activity declines rapidly in the absenceof assimilable carbohydrate, and recovers equally rapidly whencarbohydrate is restored. Recovery is accelerated by nitratebut almost completely prevented by ammonia. 4. Evidence is given that these variations in nitrate reductionare primarily changes in the nitrate reductase link in the enzymesystem. Nutritional behaviour of the fungi investigated is closelycorrelated with the observed changes in activity of their nitratereductase. 5. Nitrate reductase may be formed by these fungi when grownin complete absence of nitrate.     

The distribution of hop latent viroid within plants of Humulus lupulus and attempts to obtain viroid-free plants

The detectability of hop latent viroid (HLVd) was investigated in field-grown hop (Humulus lupulus L.; an herbaceous perennial in which all the aerial parts die at the onset of winter) plants, using dot-blot hybridisation. The viroid was readily detected in all aerial tissues in the second half of the growing season but it could not be detected very early in the season. Between early- and mid-season, HLVd was first detected at the base of the new stems and then apparently spread up them as they grew but only became detectable near the tips of the shoots at mid-season, approximately at the time most elongation growth ended and flowering began. Petioles were the most convenient tissues to test, being easy to collect and, relative to leaf lamina tissue, low in inhibitors. Both dot-blot and in situ hybridisation failed to detect HLVd in shoot tips taken from plants grown at two ‘low’ temperatures (10°C and 15°C). Failure to produce any viroid-free plants by in vitro culture from such tips suggested that they did contain viroid but at levels too low to detect by either method. Lower temperatures and smaller explants are now being investigated as means of producing viroid-free plants.