Ammonium Ion and the Flowering of Lemna perpusilla

Abstract

'the unique advantages of the Lemnaceae (duckweeds) as experimental organisms include the ease with which flowering can be affected by changes in the composition of the medium (4,5,(7)(8)(9)(10)(11)(12)(13). This characteristic becomes particularly important as these plants are increasingly employed not only in studies of photoperiodism, but also as assay systems for preparations having florigenic activity (e.g., 2).Posner (12,13) The results of two experiments comparing various concentrations of Hutner's and KNO3 media are summarized in Table I; they indicate clearly that the inhibition caused by progressively diluting Hutner's medium under these conditions cannot be observed in KNO3 medium. Vegetative growth in the two different media was indistinguishable in terms of the general appearance of the fronds, but frond number in the KNO medium cultures was generally somewhat lower than in the others.To determine whether the operative difference between the KNO3 and Hutner's media is indeed the presence of ammonium ion, experiments were conducted in which 0.1 X strength KNO3 medium was supplemented with various levels of NH4CI, (NH4)2SO4, NH4NO3 or KNO3. Two such experiments are shown in Table II, which makes it clear that ammonium ion from 1 X 10-' to 3 X 10-3 M is highly inhibitory under these circumstances.Kandeler's work on the effect of ammonium ion on L. gibba G3 (9) The sucrose-ammonium interaction on L. perpusilla is superficially reminiscent of the literature concerning carbohydrate-nitrogen interactions on flowering (1), but it differs in that here both substances are required for an inhibition to occur, rather than acting antagonistically. Kandeler (9-11) has already extensively reviewed the possible ways in which ammonium ion itself might act, e.g., by uncoupling phosphorylation or repressing the synthesis of nitrate reductase. However, no explanation of the relative specificity for flowering is forthcoming. An effect exclusively on photophosphorylation (9, 10) is ruled out by our frequent observation that L. perpusilla growing under nonphotosynthetic (5) conditions is still susceptible to the ammonium-sucrose-dilute medium inhibition of flowering. The possibility that this inhibition results from a level of amino acids inadequate for flowering has also been suggested (13), but again with no explanation for the specificity.The ammonium effect on L. perpusilla differs from that on L. gibba in its dependence on an external supply of utilizable carbohydrate and a low level of several major ions, notably calcium and phosphate (12). WVhether comparable interactions might be discovered in L. gibba is unknown, but clearly the situation in L. perpusilla is at present more susceptible to experimental analysis. This is particularly true since a number of common features indicate a close relationship between these phenomena and the observation (3) that incubation in distilled water daily for a few hours at a particular time of the inductive dark period specifically inhibits flowering in L. perpusilla. Such resul...

Epinephrine, Propranolol, and the Sucrose-Ammonium Inhibition of Flowering in Lemna paucicostata 6746

“…The irradiance was 800 ergs cm-2 s-5. We have found that these growth conditions (3) gave a more reliable and reproducible flowering response to ammonium ion than did those used previously (4,11). However, as noted below, the response was also determined under short days.…”

“…In the SDP4 Lemna paucicostata5 strain 6746, the sucrose inhibition (11) was later shown to be due to an interaction between sucrose and ammonium ion (4).…”

Influence of Temperature on the Flowering of Lemna perpusilla 6746 Grown under Skeleton Photoperiods

“…The containers with a smaller volume show less flowering at all temperatures except 27 C where neither type of culture flowers. This behavior may be partially attributed to the attainment of a higher steady state concentration of some volatile inhibitor, such as CO2 (13) (8). Figure 1.…”

“…Figure 1. Means not having same superscript are significantly different (P = 0.05) as determined by Dun-can's multiple range test (8). Flowering values were subjected to an angular transformation prior to performing the statistical tests (9).…”

“…These were grown axenically in either 50-ml Erlenmeyer flasks containing 20 ml of the stock culture medium or in 25 X 50 cm cylindrical vials (scintillation vials) containing 4 ml of the same medium. In one experiment, full strength Hutner's medium and KNOI medium (8), both supplemented with 1 % (w/v) sucrose, were used as well as the usual half-strength Hutner's medium (Table I). All culture vessels were stoppered with rolled paper plugs.…”