THE EFFECT OF POLLINATION AND ETHYLENE ON THE COLOR-CHANGE OF THE BANNER SPOT OF LUPINUS-ALBIFRONS (BENTHAM) FLOWERS

In Lupinus albifrons flowers the banner spot of the standard is initially coloured white or pale yellow. Two to three days after reaching the stage of full flower opening, this banner spot develops a pinkish blush and is deep magenta after a further 24 h. The development of this pigmentation is accelerated by exposure to ethylene in a concentration- and time-dependent manner. Flowers with a pinkish banner spot produced the greatest amounts of ethylene and production was much lower in flowers which had either completed the colour change or in which the banner spot colour remained unchanged. Treatments such as stigma removal or pollination increased the rate of ethylene production. Dissection of the flowers showed that while the banner spot is changing colour there is no change in the rate of production of ethylene from the standard, i.e. from the banner spot or surrounding tissue. The major sites of production at this time are the keel and pistil.Isolated flowers withered within 2 d of removal from the plant and therefore did not show any change in the colour of the banner spot unless exposed to ethylene. The increase in banner spot pigment was about fourfold when isolated floweres were exposed to ethylene (0·24 μl 1-1): however, the increase was less than twofold when isolated standards were exposed to ethylene (0·27 μl I-1). Application of silver thiosulphate (STS) to intact isolated flowers, as a 1 h pulse prior to ethylene exposure, partially prevented the pigment accumulation, whilst a continuous supply of STS reduced the ethylene-induced colour change by approx. 50% Low concentrations of cycloheximide (CHI) (0·01 mg ml-1) reduced the accumulation of pigment in the banner spot of ethylene-treated flowers, and higher concentrations (1·0 mg ml-1) completely prevented the ethylene-induced colour change. © 1990 Annals of Botany Company.