Ethylene and auxin participation in pollen induced fading of vanda orchid blossoms.

Blossomiis frolmi several varieties of orchids fade prematurely when their pollinia are removed or disturbed (2,3, 7), and also if the 'flowers are gassed with ethylene (8, 9, 10), pollinated (3, /7), or treated with an auxin (3, 7). Durinig natural ifading as wel' as that indu'ced by removal, of the 'pollinia, ethylene is evolved (2, 3, 9, 10), and therefore it has been inferred that the gas is the causative agent. Ethylene evolution also is stimulated w^hen plant tissues are exposed to auxin (1,4), and wve now present evidence that this response is the basis for flower fading inlucecl by pollination or auxin, application. Blossoms from I anla Pcthimbocran or Vand(ia Rose N1'ariw mere placed witlh tlheir cut ends in a beaker of water, and( sealed tindera 200 ml bell jar having a grounld glass< base aAd a silde arml closed with a rubber vaccilne cal). Other flowvers wvere pollinated, emasculated (pollinia remiloved), self-pollinated, or treated with 5 iixs IAA in lanolin or 0.1 mm carboxyl labeled 14C-IAA in 0.8 % agar (specific activity = 8 mc/nmmole) applied to the stigmas, and then the fl-owers were sealed under a bell jar. Air samples, removed with a hypodermic syringe, were analyzed bygas chromatography to determine the ethylene content (4), and at least every 10 hours the chambers were completely aerated. Ethylene evolution by isolated sepals and petals, columns or lips was measured by incubating each tissue in a 50 ml, flaslk fitted with a vaccine cap, and sampling the air in the flask at hourly intervals. Cutting the floral iparts induced a wound response, lasting about 1 hour, during which time 1.5 mMl of ethylene 'per gram of cut control tissue was produced. Treated cut tissue wvas only considered to produce ethylene if the total evolution exceedled this value, and if the extra evolution continued at a nearly constant rate for at least 4 hours. Intact blossolmls were also placed in desiccators and gassed for 3 to 24 hours Nvith 10 ppm etllylene. Ill .uch cases the flowvers were aerated for at -least 1 lhour 'before ethyl;ene production was measured in order to remlove any ethylene contained within the tissue. The spread of '+C-IAA from the stigmas of the flower wvas determined iby excising the ifloral parts from representative blossomiis after 3, 6, aind, 24 hours and dividing these into pieces as illustrated in figure 3. Each piece was ground with ethanol on a planchet, dried, and counted with a 21 % efficient gas flow counter. When blossoms of V. Rose Marie were emasculated, ethylene evolution, began after a 10 hour lag period ('fig 1), and fading became obvious after an additional, 8 to 12 hours. A similar time course of ethylene production and fadin'g has been reported for V. Miss Agntes Joaqutim 'blossoms after removal of their pollinia (2), whereas V. Petamboeran, a semiterete of heavy texture, fades after a considerablv longer lag (fig 2). That remiioval of the pollinia per se is not responsible for floral fading is indicate(d by experiments with Phalecnopsis Paniala (7) whichi have shown that distur.bance of the coninectioni between the rostelluin (tthe structure supporting the pollinia) and the upper surface of the sticky disk with which it is in intinmate contact, suffices to induce the response. There is no indication that this type of fading involves a release or production of auxin. for it does not result in swelling of the col.umn Nwhereas both auxin application and pollination bring about such an effect. Self ,pollination induces ethylene formation within 1 hour in V. Rose Marie, and flower fading within 8 to 10 hours ('fig 1). A simiilar time course was observed, with V. Petamboerant even when the flower was pollinated with its ow%n ipollinia intact (fig 2). This response was duplicated by applying enough IAA (5 mM) in lanolin paste to fill the stigmatic cavity (fig 2), and exactly the same result was obtained using 0.1 mM 1*C-IAA in 0.8 % agar. Other cases .n which the fading response caused by pollination is stimulated by auxin have been reported (3, 7), and 'led to the suggestion that the large quantity df auxin contained in the pollen is responsible 'for the pollination effect (/7). As auxin stimulates ethylene evolution in these blossoms anfd other plant tissues within an hour, and since ethylene causes floral fading, it is logical to conclude that this is the mechanism involved. Auxin induced ethvlene formation must also influence the growth of the coluimnIi for within 2 hours after application of pollinia or auxin this structure