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Different intensities of high temperatures affect the growth of photosynthetic cells in nature. To elucidate the underlying mechanisms, we cultivated the unicellular green alga Chlamydomonas reinhardtii under highly controlled photobioreactor conditions and revealed systems-wide shared and unique responses to 24-hour moderate (35°C) and acute (40°C) high temperatures and subsequent recovery at 25°C. We identified previously overlooked unique elements in response to moderate high temperature. Heat at 35°C transiently arrested the cell cycle followed by partial synchronization, up-regulated transcripts/proteins involved in gluconeogenesis/glyoxylate-cycle for carbon uptake and promoted growth. But 40°C disrupted cell division and growth. Both high temperatures induced photoprotection, while 40°C distorted thylakoid/pyrenoid ultrastructure, affected the carbon concentrating mechanism, and decreased photosynthetic efficiency. We demonstrated increased transcript/protein correlation during both heat treatments and hypothesize reduced post-transcriptional regulation during heat may help efficiently coordinate thermotolerance mechanisms. During recovery after both heat treatments, especially 40°C, transcripts/proteins related to DNA synthesis increased while those involved in photosynthetic light reactions decreased. We propose down-regulating photosynthetic light reactions during DNA replication benefits cell cycle resumption by reducing ROS production. Our results provide potential targets to increase thermotolerance in algae and crops.

Genetic variation is an important attribute of forest tree populations enabling them to adapt to spatial and temporal variations in environmental conditions. In particular, Scots pine (Pinus sylvestris L.) has an exceptionally broad area of dispersal covering different climates and soil conditions, but the genetic variability in extreme conditions has not been studied. We hypothesized that the genetic variability of P. sylvestris is enhanced at its soil fertility limit in bogs where stunted trees form a sparse canopy with reduced light competition, but in highly turbulent conditions generating ideal conditions for distant pollen dispersal. A total of 180 individuals were studied from three bog populations using five nuclear (nSSR) and five chloroplastic (cpSSR) polymorphic microsatellite loci (simple sequence repeats, SSR). According to both marker systems, high and similar level of genetic diversity (ca. 99 % within the populations and 1 % among the populations) was observed for nuclear (F ST = 0.007 and R ST = 0.022) and chloroplast (F ST = 0.015 and R ST = 0.023) genomes. Despite the low genetic differentiation among the populations, there was evidence of geographic genetic differentiation in the chloroplast genomes, suggesting that isolation by distance might be a possible mechanism shaping the present distribution of genetic variability. In addition, significant but low spatial genetic structure along habitat wetness gradient was found in nuclear genomes in one site. Significant cyto-nuclear linkage disequilibrium was shown between one of the cpSSR loci to all nSSR loci. The results demonstrate a huge within-population genetic variability in these sites and underscore the importance of pollen gene flow in homogenizing populations on these geographic scales.

Knowledge of pistachio genetic diversity is necessary for the formulation of appropriate management strategies for the conservation of these species. We analysed amplified fragment length polymorphisms in a total of 216 pistachio accessions, which included seven populations from three wild species (Pistacia vera, Pistacia khinjuk and Pistacia atlantica subsp. kurdica) and most of the important cultivars from Iran, together with some foreign cultivars. High levels of genetic diversity were detected within the Iranian cultivars, and they showed a clear separation from foreign cultivars, as revealed by unweighted pair group method with arithmetic averaging and supported by analysis of molecular variance. The lowest amount of polymorphism was observed in P. atlantica subsp. kurdica, which showed the lowest number of total bands as compared to the other species. This revealed strong genetic erosion of P. atlantica subsp. kurdica, which reflected a severe decline in habitat and over-exploitation. Based on these findings, strategies are proposed for the genetic conservation and management of pistachio species and cultivars.

Iran is one of the two major centres of Pistacia diversity and the main producer of pistachios in the world. About 282 Iranian pistachio genotypes (Pistacia spp.), together with 22 foreign cultivars (P. vera), were genotyped using 10 simple sequence repeat (SSR) markers to analyse the genetic diversity and relationships among Pistacia species and cultivars. The results revealed that the genetic diversity within P. atlantica subsp. kurdica was considerably lower than in P. vera or P. khinjuk. Principal coordinate analysis revealed a clear separation between the different Pistacia spices, as well as between the Iranian and foreign cultivars. AMOVA analysis showed that the variation between the species, between different populations, and within populations accounted for 41, 9, and 50% of the total variation, respectively. The results demonstrated that the study of genetic diversity and relationships among Pistacia species and cultivars using SSR markers provides important information for the collection and conservation of pistachio germplasm. In addition, the Iranian cultivars had a broader genetic background than that of the foreign cultivars. Thus, they are very important for genetic conservation and the planning of future breeding programmes. We also determined the different levels of genetic diversity that exist between and within the species and populations and showed that gene flow occurs between the Iranian cultivars and wild-type P. vera populations. The study provides practical information that policy-makers and scientists can apply to the conservation and sustainable use of all the species studied. © Springer Science+Business Media B.V. 2009.