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 heat stress can cause a significant increasein abortion frequency of floral buds and flowers in pea, buta large variability in sensitivity exists among reproductiveorgans (ROs) within a plant or between plants. We have analysedspatial distribution of abortion frequency in plants subjectedor not subjected to heat stress in: (1) four controlled environmentexperiments in which apex temperature was increased to 31 °Cfor 6 h per day for 4 d (moderate stress); (2) one field experimentwith a similar level of stress; and (3) one experiment with2 d with 33/30 °C day/night (severe stress) in additionto treatment (1). Influence of neighbouring organs on sensitivityto heat stress was analysed by partial flower removal. Severeheat stress caused rapid interruption of RO development followedby abscission while, in moderate stress, at leat 4 d elapsedbetween cessation of stress and first symptoms of abortion.In both moderate stress and control treatments, abortion frequencyfollowed a consistent pattern along the stem with no abortionon the lowest reproductive phytomeres, a temperature-dependentabortion frequency on intermediate phytomeres and 100% abortionon apical phytomeres. Regardless of temperature, this patternwas shifted by four positions if ROs were removed on the lowestfour reproductive phytomeres, and no abortion was observed ifyoung pods were sequentially removed. Moderate heat stress increasedthe effect of developing ROs on abortion frequency of youngerROs located above them. We suggest that the effect of mild stressshould be viewed as the acceleration of a programme linked tothe normal termination of phytomere production during the plantcycle, rather than as an abrupt event linked to stress. Pisum sativum; heat stress; abortion; abscission; age; organ-to-organ relations     

Physiological factors regulating polyandry in Lobesia botrana (Lepidoptera: Tortricidae)

Abstract. The effects of several physiological factors related to female multiple mating in the monandrous Lobesia botrana Denis and Schiffermuller (Lepidoptera: Tortricidae) were studied under laboratory conditions. Polyandry was assessed observing the induction of re-calling in previously once-mated females. Female age at first mating had no effect on induction of re-calling during practically the whole of the female lifetime, but in older females it was significantly lower. The percentage of re-calling was negatively correlated with the volume of the spermatophore received, ranging from ≅ 23% with the largest spermatophores to ≅ 75% with the smallest ones. Furthermore, the smaller the spermatophore volume, the earlier the re-calling was induced, significantly reducing die female refractory period after the first mating. Heavy females showed a significantly higher rate of re-calling (52.8%) than light ones (37.0%), but no differences were observed when females received only small spermatophores. This finding was explained by die allometric relationship between me female weight and the size of its reproductive system that affects relative replenishment by the spermatophore. Females with a supply of water displayed a significantly higher rate of re-calling (41.2%) than control females (22.8%), highlighting the effect of adult feeding (or drinking) status on the re-calling behaviour. The short-distance presence of virgin males with once-mated females promoted a re-calling rate (and subsequent matings) close to 37%, significantly higher than that of isolated females (20%). It is concluded mat re-calling and polyandry in L. botrana are controlled, as expected, by a number of mating-derived stimuli, but also to a great extent by other physiological stimuli unrelated to mating. The reproductive strategies in relation to polyandry and the mechanisms controlling female sexual inhibition are discussed.