Modification of abscission by UV-induced alteration in RNA and protein metabolism.

Low irra(liances of 254 nm UV photoreversibly interfere with the capacity of plant cells properly to tutilize auixin for cell division, enlargement and (lifferentiationi (3,8,17). This UV-induced auixinrecalcitrance does not seem to be caused by activation of aulxin oxidase or by alteration of auxin metal)olism, penetration, or translocation. In view of the role of nucleic acid and protein metabolism in aulxini iutilization (1, 7), a sttudy of the interactionis of UVi and( antimetabolites seeme(l warranted. The experiments reported here were base(I oln the hypothesis that if UV induces auxin-recalcitrance l)y interfering with nuicleic acid or protein synthesis involved in auxin-indutce(d growth, there shouldl bc a synergistic interaction of UV and a test anitimetabolite visuialized by increase(d abscission. The reqlluirements for establishing synergistic interactions have been eluicidated by Lockhart (10) aind are ftulfilled in these experiments. Repressioln of abscission of explanlts of the puilvinuiis zonie of primary bean-leaf petioles is (lepeii(lnent ulpoll auxinl and growth (5). Puilvinuis explanits (2) were incubated in agar containiing 10 MM IAA at 200; uinder these conditions, 50 % of the explanits absciss in 72 hoturs (9). Irradiation of explanits at zero time with 5 mJ/cm2 UV had no effect on abscission with this concentration of auxin, althouigh higher irradiances increased the percentage abscission (8). Concentration-response experiments with selectedI anitimetabolites and antibiotics presente(d at zero time were conducted to select a concentration which had little or no effect on abscission; higher concentrationis invariably increased abscission. The abscissioni-inicreasing effect of at least 1 antimetabolite from each group was reversible by the appropriate metabolite. All experiments were repeated 3 times with abouit 25 explants per variable: resuilts are presented as the averaged percent abscission. There was no interaction between UV andl any tested anti-thymine (table I). This finding, plu1s the fact that treatments which split or negate thymine dlimers (temperature shock, addition of thymidine, etc.) wvere ineffective in ameliorating UV7-