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

Differential response of domestic and wild Lycopersicon species to chilling under low light: Growth, carbohydrate content, photosynthesis and the xanthophyll cycle

The response of five Lycopersicon species to 14 days moderate chilling at 10 degrees C under low light (75 mu mol m(-2) s(-1)) and subsequent recovery was examined by measurements on relative shoot growth rate, leaf dry matter and carbohydrate content, CO2-exchange and pigment composition. In addition, the susceptibility to dark chilling and temperature dependence of chloroplast electron transport were analyzed by Chl a fluorescence measurements. During 7 days of recovery at 25/20 degrees C subsequent to chilling, the domestic tomato Lycopersicon esculentum (L.) Mill. cv. Abunda exhibited a small capacity for shoot regrowth (39%) compared to the low-altitude wild species L. pimpinellifolium (Jusl.) Mill. PI187002 (82%) and three wild species originating from high altitude: L, peruvianum Mill. LA 385 (92%), L, hirsutum Humb, & Bonpl. LA 1777 (67%) and L. chilense Dunn. LA 1970 (71%). The inter-specific differences in chilling sensitivity at the chloroplast level, analyzed by the decline of the maximum rate of induced Chl fluorescence rise (F-R) after 40 h at 0 degrees C and the temperature at which q(P) reached the value 0.5, correlated in general well with the measured differences at whole plant level, measured by the post-chilling regrowth capacity. Chilling resulted in a larger increase in leaf dry matter content in L. esculentum (45%) and L. pimpinellifolium (37%) compared to the high-altitude species (13-16%), which could be attributed to a stronger accumulation of both soluble sugars and starch in mature leaves of the domestic and low-altitude species. Photosynthetic and dark respiration rates during chilling could not account for this difference, The recovery of photosynthesis was better in the high-altitude species, Chl content per unit leaf area decreased more throughout the experiment in the domestic and low-altitude species (63-73%) than in their relatives from high altitude (8-29%), In response to chilling, the domestic and low-altitude species showed an increase in the total xanthophyll cycle pool on Chl basis, whereas the de-epoxidation state of the xanthophyll cycle increased in the high-altitude wild species. Both responses resulted in increased zeaxanthin levels in chilled leaves of all Lycopersicon species