A rapid photoreversible response of barley root tips in the presence of 3-indoleacetic Acid.

For several years I have observed that root tips of some species of plants adhere to glass surfaces in water. Examination of this phenomenon shows that under suitable conditions the root tips of barley adhere to glass within 30 seconds when irradiated with red light and detach from the glass within 30 seconds when irradiated with far-red light. This rapid reversibility has been repeated for five or more cycles in numerous trials with different lots of seedlings. 3-Indoleacetic acid at very low concentrations and several other compounds are required for the reversible process. Methods and Materials.-About 14 gm of barley seeds (Hordeum vulgare L., var Compana) are washed several times with deionized water. They are then spread over cheesecloth supported on a stainless steel wire net hung inside a porcelain crock. Six liters of deionized water from which chlorine has been removed by passing through charcoal are poured into the crock until the net just touches the water surface. The seeds are held in darkness for 2 days at 23CC with the water aerated continuously. After 2 days, the seedlings are exposed to dim white light (0.3 ft-c) from a tungsten filament lamp for at least 1 hr before use in a constant-temperature room at 230C. The dim light is used in subsequent handling of seedlings. Roots, after gentle blotting on filter paper, are placed on a ruled plastic block and 1-mm sections are quickly cut with a stainless steel razor blade from tips of the first two seminal roots of a seedling. Ten tips are washed into a Pyrex glass beaker (tall form) of 200-ml capacity containing about 25 ml of deionized water. The water is poured off after a few seconds and 10 ml of solution of the following composition is added immediately to the beaker: sodium adenosine-5'triphosphate (ATP), 2.5 X 10M; 3-indoleacetic acid (IAA), 10-8 M; L-ascorbic acid (AA), 10-6 M; MnCl2, 2 X 10-M; MgCl2, 2 X 10-4 M; KCl, 10-4 M; and HCl, 5 X 10-5 M. Solutions of the organic chemicals are freshly prepared each day. The pH of the final solution is 5.0. The beaker is immediately placed in red light. After mixing with a gentle rotary motion for about 10 sec, the tips are allowed to settle and remain undisturbed in the central portion of the bottom for 20 sec. The beaker is then raised a few millimeters on one edge and very gently swirled 3 or 4 times. Sudden or jerky movements are avoided. The number of tips adhering, or showing signs of adhering, to the glass surface is then counted. Tips that do not adhere move smoothly away from the spot on which they have settled. After the gentle swirling motion, the tips are left undisturbed for about 5 sec. This process of dislodging, counting, and settling is repeated three times. A good count of the average number of tips adhering to the glass can be obtained by the end of the fourth dislodging. After 1 min in red light, the tips are exposed to far-red light for 1 min during which time the procedure done in red light is repeated. The red and far-red irradiation cycle is carried out for 5 cycles. The source of red light is a 15-watt daylight fluorescent tube filtered with 2 layers of red cellophane. Both ends of the tube are covered with 15 cm of black plastic. The beaker is placed 55 cm from the tube where the radiant flux is 7.9 MAw/cm2 in the region of 600-700 nm.1 The far-red light source is a 60-watt tungsten filament lamp covered with 6 sheets of red cellophane and 2 sheets of blue cellophane. The lamp is inverted so that the far-red light passes through 5.5 cm of water contained in a glass dish with a