HEAT STRESS-INDUCED ABORTION OF BUDS AND FLOWERS IN PEA - IS SENSITIVITY LINKED TO ORGAN AGE OR TO RELATIONS BETWEEN REPRODUCTIVE-ORGANS

A short period of hear stress can cause a significant increase in abor tion frequency of floral buds and flowers in pea, but a large variabil ity in sensitivity exists among reproductive organs (ROs) within a pla nt or between plants. We have analysed spatial distribution of abortio n frequency in plants subjected or not subjected to heat stress in: (1 ) four controlled environment experiments in which apex temperature wa s increased to 31 degrees C for 6 h per day for 4 d (moderate stress); (2) one field experiment with a similar level of stress; and (3) one experiment with 2 d with 33/30 degrees C day/night (severe stress) in addition to treatment (1). Influence of neighbouring organs on sensiti vity to heat stress was analysed by partial flower removal. Severe hea t stress caused rapid interruption of RO development followed by absci ssion while, in moderate stress, at lear 4 d elapsed between cessation of stress and first symptoms of abortion. In both moderate stress and control treatments, abortion frequency followed a consistent pattern along the stem with no abortion on the lowest reproductive phytomeres, a temperature-dependent abortion frequency on intermediate phytomeres and 100% abortion on apical phytomeres. Regardless of temperature, th is pattern was shifted by four positions if ROs were removed on the lo west four reproductive phytomeres, and no abortion was observed if you ng pods were sequentially removed. Moderate heat stress increased the effect of developing ROs on abortion frequency of younger ROs located above them. We suggest that the effect of mild stress should be viewed as the acceleration of a programme linked to the normal termination o f phytomere production during the plant cycle, rather than as an abrup t event linked to stress. (C) 1997 Annals of Botany Company.