Arg EXPRESSION IN RELATION TO EPICUTICULAR WAX DISTRIBUTION

PNL Volume 14 1982 RESEARCH REPORTS 53

Marx, G. A. NYS Agricultural Experiment Station, Geneva, NY USA

The gray-green leaves on argenteum (Arg) plants were shown by Hoch

et al. (1) to result from the presence of extensive air spaces located

between the leaf epidermis and parenchyma. At present, this is the only

known effect of Arg. Hoch et al found nothing to show that surface

wax was in any way involved in determining the characteristic gray-green

leaf color. Removal of the surface wax of leaves modifies but does not

fundamentally change Arg mutant expression. This can be demonstrated

directly, by mechanically or chemically removing leaf wax, or in-

directly, by incorporating mutants known to reduce epicuticular wax on

the leaves. In the course of our investigations, Arg has been combined

with nearly all the known wax mutants. In plants bearing the combina-

tion Arg wlo, for example, the upper surface of the leaflets are shiny

and less gray-green than in Arg Wlo plants, but the presence of Arg is

unmistakable.

Still, the gray-green color of Arg plants is not confined ex-

clusively to the leaves but includes the stem and pods as well. The

color contrast between mutant (Arg) and normal (arg) is, however, much

less distinct in the stem and pods than in the foliage. Moreover, the

gray-green color of stems and pods, unlike the leaves, disappears upon

gentle rubbing, thus suggesting that Arg influences pod wax. Also, the

pods of plants with the combination Arg wp are waxless and appear iden-

tical with pods borne on arg wp plants. In arg wel plants all parts

(leaves, stems, and pods) have reduced wax. When Arg is added (i.e.

Arg wel) the leaf parts show the modified expression of Arg similar to

that on the upper surface of the leaflets of Arg wlo plants. However,

the pods and stems of Arg wel plants are shiny green and phenotypi cal ly

identical with pods and stems of arg wel plants. Fig. 1 depicts the

interactions among Arg, wp and wel. These observations imply that Arg

exerts an effect on stems and pods which is different from that on

leaves, thus complicating the interpretation of gene action.

1. Hoch, H. C., Charlotte Pratt, and G. A. Marx. 1980. Amer. J. Bot.

67:905-911.

PNL Volume 14

1982

RESEARCH REPORTS

Fig. 1. A schematic illustration of the phenotypic effects on leaf and

pod wax resulting from the interaction of Arg, wel. and wp. Shading in-

dicates presence of wax; no shading indicates absence of wax. Fine

crosshatching indicates effect of Arg on normal waxy tissue. Coarse

crosshatching indicates effect of Arg on waxless leaf tissue. Note that

in Arg wp and Arg wel plants the pods are waxless, Just as in arg wp and

arg wel plants.