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- Jönsson, Anna Maria, et al.
(författare)
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Frost hardiness in bark and needles of Norway spruce in southern Sweden
- 2001
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Ingår i: Trees. - : Springer Science and Business Media LLC. - 1432-2285 .- 0931-1890. ; 15:3, s. 171-176
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Tidskriftsartikel (refereegranskat)abstract
- Bark necrosis and resin flows in Norway spruce have increased in southern Sweden over the last few decades. Frost damage late in spring has been suggested as a possible cause, but other factors besides the climate may have contributed to the damage. The nutrient status influences the hardening processes and plants with poor nutritional conditions have an increased sensitivity to frost. In this study the sensitivity to frost of bark and the hardiness status of needles of Norway spruce were compared with the nutrient status at two sites with different soil fertility. The trees were 30-40 years old. The hardiness status of the bark and needles was negatively affected by low concentrations of P and Mg.
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- Sjögren, Lars, 1977, et al.
(författare)
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Inactivation of the clpC1 gene encoding a chloroplast Hsp100 molecular chaperone causes growth retardation, leaf chlorosis, lower photosynthetic activity, and a specific reduction in photosystem content
- 2004
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Ingår i: Plant Physiology. - : Oxford University Press (OUP). - 0032-0889 .- 1532-2548. ; 136:4, s. 4114-4126
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Tidskriftsartikel (refereegranskat)abstract
- ClpC is a molecular chaperone of the Hsp100 family. In higher plants there are two chloroplast-localized paralogs (ClpC1 and ClpC2) that are approximately 93% similar in primary sequence. In this study, we have characterized two independent Arabidopsis (Arabidopsis thaliana) clpC1 T-DNA insertion mutants lacking on average 65% of total ClpC content. Both mutants display a retarded-growth phenotype, leaves with a homogenous chlorotic appearance throughout all developmental stages, and more perpendicular secondary influorescences. Photosynthetic performance was also impaired in both knockout lines, with relatively fewer photosystem I and photosystem II complexes, but no changes in ATPase and Rubisco content. However, despite the specific drop in photosystem I and photosystem II content, no changes in leaf cell anatomy or chloroplast ultrastructure were observed in the mutants compared to the wild type. Previously proposed functions for envelope-associated ClpC in chloroplast protein import and degradation of mistargeted precursors were examined and shown not to be significantly impaired in the clpC1 mutants. In the stroma, where the majority of ClpC protein is localized, marked increases of all ClpP paralogs were observed in the clpC1 mutants but less variation for the ClpR paralogs and a corresponding decrease in the other chloroplast-localized Hsp100 protein, ClpD. Increased amounts of other stromal molecular chaperones (Cpn60, Hsp70, and Hsp90) and several RNA-binding proteins were also observed. Our data suggest that overall ClpC as a stromal molecular chaperone plays a vital role in chloroplast function and leaf development and is likely involved in photosystem biogenesis.
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- Sjögren, Lars, 1977, et al.
(författare)
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Structural and functional insights into the chloroplast ATP-dependent Clp protease in Arabidopsis
- 2006
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Ingår i: Plant Cell. - : Oxford University Press (OUP). - 1040-4651 .- 1532-298X. ; 18:10, s. 2635-2649
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Tidskriftsartikel (refereegranskat)abstract
- In contrast with the model Escherichia coli Clp protease, the ATP- dependent Clp protease in higher plants has a remarkably diverse proteolytic core consisting of multiple ClpP and ClpR paralogs, presumably arranged within a dual heptameric ring structure. Using antisense lines for the nucleus- encoded ClpP subunit, ClpP6, we show that the Arabidopsis thaliana Clp protease is vital for chloroplast development and function. Repression of ClpP6 produced a proportional decrease in the Clp proteolytic core, causing a chlorotic phenotype in young leaves that lessened upon maturity. Structural analysis of the proteolytic core revealed two distinct subcomplexes that likely correspond to single heptameric rings, one containing the ClpP1 and ClpR1- 4 proteins, the other containing ClpP3- 6. Proteomic analysis revealed several stromal proteins more abundant in clpP6 antisense lines, suggesting that some are substrates for the Clp protease. A proteolytic assay developed for intact chloroplasts identified potential substrates for the stromal Clp protease in higher plants, most of which were more abundant in young Arabidopsis leaves, consistent with the severity of the chlorotic phenotype observed in the clpP6 antisense lines. The identified substrates all function in more general housekeeping roles such as plastid protein synthesis, folding, and quality control, rather than in metabolic activities such as photosynthesis.
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- Zheng, Bo, et al.
(författare)
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A nuclear-encoded ClpP subunit of the chloroplast ATP-dependent Clp protease is essential for early development in Arabidopsis thaliana
- 2006
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Ingår i: Planta. - : Springer Science and Business Media LLC. - 0032-0935 .- 1432-2048. ; 224:5, s. 1103-1115
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Tidskriftsartikel (refereegranskat)abstract
- ClpP4 is a nuclear-encoded plastid protein that functions as a proteolytic subunit of the ATP-dependent Clp protease of higher plants. Given the lack of viable clpP4 knockout mutants, antisense clpP4 repression lines were prepared to study the functional importance of ClpP4 in Arabidopsis thaliana. Screening of transformants revealed viable lines with up to 90% loss of wild type levels of ClpP4 protein, while those with > 90% were severely bleached and strongly retarded in vegetative growth, failing to reach reproductive maturity. Of the viable antisense plants, repression of clpP4 expression produced a pleiotropic phenotype, of which slow growth and leaf variegation were most prominent. Chlorosis was most severe in younger leaves, with the affected regions localized around the mid-vein and exhibiting impaired chloroplast development and mesophyll cell differentiation. Chlorosis lessened during leaf expansion until all had regained the wild type appearance upon maturity. This change in phenotype correlated with the developmental expression of ClpP4 in the wild type, in which ClpP4 was less abundant in mature leaves due to post-transcriptional/translational regulation. Repression of ClpP4 caused a concomitant down-regulation of other nuclear-encoded ClpP paralogs in the antisense lines, but no change in other chloroplast-localized Clp proteins. Greening of the young chlorotic antisense plants upon maturation was accelerated by increased light, either by longer photoperiod or by higher growth irradiance; conditions that both raised levels of ClpP4 in wild type leaves. In contrast, shift to low growth irradiance decreased the relative amount of ClpP4 in wild type leaves, and caused newly developed leaves of fully greened antisense lines to regain the chlorotic phenotype.
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