Analysis of low-temperature tolerance of a tomato (Lycopersicon esculentum) cybrid with chloroplasts from a more chilling-tolerant L-hirsutum accession

Growth and photosynthesis of an alloplasmic tomato (cybrid), i.e. line AH47, containing the nuclear genome of the chilling-sensitive cytoplasmic albino mutant of L. esculentum Mill. 'Large Red Cherry' (LRC) and the plastome of a more chilling-tolerant high-altitude accession of the related wild species L, hirsutum Humb. & Bonpl. LA 1777, were investigated at an optimal (25/20 degrees C) and suboptimal (16/14 degrees C) day/night temperature regime and their performance compared with that of both euplasmic parents. The cybrid shoot had a similar biomass and development rate to the nuclear tomato (L. esculentum) parent at both temperature regimes. Compared with the biomass production of shoots grown at optimal temperature, the reduction in shoot biomass at suboptimal temperature was smaller for L. hirsutum than for L, esculentum and the cybrid. This difference was related to a stronger inhibition of leaf area expansion in L, esculentum and the cybrid in the suboptimal temperature regime than in L. hirsutum. Irrespective of the temperature regime under which the plants were grown, photosynthetic performance and leaf pigment, carbohydrate and soluble-protein contents of the cybrid resembled those of the nuclear parent. No advantages of the alien L. hirsutum chloroplast with respect to growth and photosynthesis-related characteristics were observed in the cybrid in the suboptimal temperature regime, indicating that the temperature sensitivity of the photosynthetic apparatus is regulated by nuclear genes, An adverse consequence of interspecific chloroplast transfer was the increased susceptibility to chill-induced photoinhibition of the cybrid. It is concluded that cybridization is not a useful tool for improving low-temperature tolerance of tomato. (C) 2000 Annals of Botany Company

There is no direct relationship between N-status and frost hardiness in needles of NH3-exposed Scots pine seedlings

The effect of short-term atmospheric ammonia deposition on frost hardening of needles of three-month-old seedlings of Scots pine (Pinus sylvestris L.) was studied. Plants were frost hardened under short day and moderate temperature conditions in the laboratory during exposure to gaseous NH3 concentrations of 400 or 1000 nl l(-1) for 4 to 6 weeks. Exposure to NH3 resulted in an increase of free ammonium and nitrogen content of the needles. Soluble sugar and starch content were not affected. Photosynthetic capacity and chlorophyll a concentrations were increased as a consequence of NH3 exposure, but chlorophyll b and carotenoid were not influenced. NH3 exposure did not decrease frost tolerance of the needles. Exposure to 1000 nl l(-1) NH3 even resulted in an increase of frost hardiness. It was concluded that frost tolerance of Scots pine seedlings is not negatively affected by the alterations of N-status upon short-term NH3 exposure