Changes in Protein Synthesis Induced in Tomato by Chilling

Abstract

Impaired chloroplast function is responsible for nearly two-thirds of the inhibition of net photosynthesis caused by dark chilling in tomato (Lycopersicon esculentum Mill.). Yet the plant can eventually recover full photosynthetic capacity if it is rewarmed in darkness at high relative humidity. As a means of identifying potential sites of chilling injury in tomato, we monitored leaf protein synthesis in chilled plants during this rewarming recovery phase, since changes in the synthesis of certain proteins might be indicative of damaged processes in need of repair. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of proteins pulse labeled with I35Slmethionine revealed discrete changes in the pattern of protein synthesis as a result of chilling. A protein of Mr = 27 kilodaltons (kD), abundantly synthesized by unchilled plants, declined to undetectable levels in chilled plants. Reillumination restored the synthesis of this protein in plants rewarmed for 8 hours. Peptide mapping analysis showed the 27 kD protein to be the major chlorophyll a/b binding protein of the photosystem II light-harvesting complex (LHCP-II). The identity of this protein was confirmed by its immunoprecipitation from leaf extracts by a monoclonal antibody specific for the major LHCP-II species. While chilling abolished the synthesis of the major LHCP-II species, it also induced the synthesis of an entirely new protein of M, = 35 kD. The protein was synthesized on cytoplasmic ribosomes, and twodimensional polyacrylamide gel electrophroesis showed it to exist as a single isoelectric species. This chilling-induced 35 kD protein is structurally distinct from the 27 kD LHCP-II and appears to be synthesized specifically in response to low temperature. While the 35 kD protein was found not to be associated with the chloroplast thylakoid membrane, chilling did cause selective changes in thylakoid membrane protein synthesis. The synthesis of two unidentified proteins, Mr = 14 and 41 kD, and the j-subunit of the chloroplast coupling factor were substantially reduced after chilling. These losses may provide clues as to the causes of the overall reduction in net photosynthesis caused by chilling.Plant species evolutionarily adapted to warm habitats are quite susceptible to injury by low, above-freezing temperatures (0 < T <1 2°C). For in darkness (26). While increased stomatal resistance accounts for some of the inhibition, the major portion of the decrease was due to direct impairment of chloroplast activity (26). Yet plants damaged by chilling in darkness can eventually recover full photosynthetic capacity if they are rewarmed in darkness at high RH (24). Presumably, the damaged biochemical processes are repaired under these conditions.Our research is directed toward identifying those elements that account for the susceptibility of chloroplast activity to chilling. Previous work has shown that dark chilling has vanishing little effect on water oxidation capacity (26), electron transfer reactions (20), or the regulation and activation...

Modifications to Thylakoid Composition during Development of Maize Leaves at Low Growth Temperatures

“…3). There are many reports of the accumulation of plant proteins in response to temperature change (5,17,26), and it has been suggested that stressinduced proteins may function to optimize metabolic activities that have been perturbed by the stress (5). Alternatively, the low molecular mass polypeptides that accumulate in maize at low temperatures may be breakdown products of higher molecular mass proteins, which have been exposed to peptidases as a result of changes in protein folding or membrane organization.…”

“…However, chilling maize leaves at low light results in a large decrease in the quantum yield of carbon assimilation, the basis of which is as yet unresolved, in the absence of any damage to PSII (25). Recently, severe impairment of the synthesis of some chloroplast proteins has been observed at chilling temperatures in rice ( 11) and rape (20), and on rewarming after chilling in tomato (5). Also, the accumulation of a 3 l-kD polypeptide in the thylakoids has been observed on chilling maize leaves; this polypeptide is considered to be an unprocessed precursor of the 29-kD apoprotein of the Chl-protein CP29 and its appearance is probably associated with an inhibition of its processing peptidase at low temperatures ( 12).…”

Chilling Delays Circadian Pattern of Sucrose Phosphate Synthase and Nitrate Reductase Activity in Tomato1

“…Notably, whereas cab and rca gene expression are circadian regulated in chilling-tolerant spinach, the rhythm is not affected in this fashion by low-temperature treatment (Ort et al, 1989). However, cab and rca are exceedingly abundant, stable proteins, and this transitory mistiming in their synthesis in chilling-sensitive plants does not lead to detectable changes in cellular protein level (Cooper and Ort, 1988). Therefore, this mistiming cannot be expected to cause the severe inhibition of net photosynthesis that is observed.…”

Acyl-lipid desaturases and their importance in the tolerance and acclimatization to cold of cyanobacteria

“…Such temperature-induced changes in unsaturation of fatty acids are explained in terms of the regulation of membrane fluidity that is necessary for the proper functioning of biological membranes [14]. However, the contribution of the unsaturation of fatty acids to cold tolerance has not been obvious, since acclimatization to low temperature induces not only desaturation of fatty acids of membrane lipids but also a number of other metabolic modifications [15][16][17]. To determine whether the unsaturation of fatty acids contributes to the ability to tolerate low temperature, it is necessary to alter the extent of unsaturation of fatty acids of glycerolipids exclusively by manipulation of genes for fatty-acid desaturases, thereby minimizing effects on any other metabolic processes.…”

“…Although 18:0 is desaturated to 18:1 (9) in the ACP-bound form in plastids by A9 acyl-ACP desaturase, all other desaturation reactions involve lipid-bound forms and acyl-lipid desaturases [20,34]. 18:1 (9) bound to sn-I and sn-2 positions of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) is desaturated to 18:2 (9,12) and then to 18:3 (9,12,15) in the endoplasmic reticulum by A12 and w3 desaturases. The 18:1(9) bound to the sn-I and sn-2 positions of glycolipids, MGDG and SQDG, and to the sn-I position of PG, is desaturated to 18:2(9,12) and then to 18:3 (9,12,15) in plastids by A12 and w3 desaturases [35].…”