Absence of ribosomes in Capsicum chromoplasts

The effect of harpin on shelf life of peppers inoculated with Botrytis cinerea

The preservation methods as an alternative to chemical control to prevent postharvest quality losses of peppers were examined. The efficacy of harpin treatments on peppers (Capsicum annuum L. cvs. 'Demre', 'Yalova Charleston' and 'Sari Sivri') was tested in the same conditions in two different years. Peppers grown in greenhouse were applied with four treatments consisting of harpin, Botrytis cinerea, harpin+B. cinerea and control. The harpin in B. cinerea treatments reduced the percentage of rotten fruit in cv. 'Demre' from 42.68% to 22.85%, in cv. 'Yalova Charleston' from 60.87% to 26.59% and in cv. 'Sari Sivri' from 32.83% to 12.82%. The harpin and harpin+B. cinerea peppers had a better overall appearance at the end of shelf-life. Changes in percentage of red fruit and fruit color at the end of shelf life proceeded more slowly in the harpin treated fruit. The treatments of harpin gave the best results in all three cultivars. Moreover, the values obtained from fruits subjected to harpin+B. cinerea were better than those of the fruits picked from the plants only subjected to B. cinerea. In the trials, harpin slowed down the changes leading to quality loss in fruits, in all cultivars. Thus, the positive effect of harpin was revealed more clearly especially in the fruits picked from the inoculated plants.

Plant programmed cell death and the point of no return

The point of no return during programmed cell death (PCD) is defined as the step beyond which the cell is irreversibly committed to die. Some plant cells can be saved before this point by inducing the formation of functional chloroplasts. A visibly senescent tissue will then become green again and live for months or years. The mechanism of this reversal is only partially known. The point of no return in fungi and animals is often associated with lack of mitochondrial function. In plant cells that do not regreen, there is no evidence for PCD reversal that results in a long life. It is unclear why chloroplast-containing cells, in contrast to those with only mitochondria, have long lives after PCD reversal.

Induction and control of chromoplast-specific carotenoid genes by oxidative stress

The differentiation of chloroplasts into chromoplasts involves a series of biochemical changes that culminate with the intense accumulation of long chain chromophore carotenoids such as lycopene, rhodoxanthin, astaxanthin, anhydroeschsoltzxanthin, capsanthin, and capsorubin. The signal pathways mediating these transformations are unknown. Chromoplast carotenoids are known to accumulate in green tissues experiencing stress conditions, and studies indicate that they provide efficient protection against oxidative stress. We tested the role of reactive oxygen species (ROS) as regulators of chromoplast carotenoid biosynthesis in vivo. The addition of ROS progenitors, such as menadione, tert-butylhydroperoxide, or paraquat and prooxidants such as diamide or buthionine sulfoximine to green pericarp discs of pepper fruits rapidly and dramatically induce the simultaneous expression of multiple carotenogenic gene mRNAS that give rise to capsanthin. Similarly, down-regulation of catalase by amitrole induces expression of carotenogenic gene mRNAs leading to the synthesis of capsanthin in excised green pericarp discs. ROS signals from plastids and mitochondria also contribute significantly to this process. Analysis of the capsanthin-capsorubin synthase promoter in combination with a beta-glucuronidase reporter gene reveals strong activation in transformed pepper protoplasts challenged with the above ROS. Collectively these data demonstrate that ROS act as a novel class of second messengers that mediate intense carotenoid synthesis during chromoplast differentiation.

Biochemistry and molecular biology of chromoplast development

Plant cells contain a unique class of organelles, designated the plastids, which distinguish them from animal cells. According to the largely accepted endosymbiotic theory of evolution, plastids are descendants of prokaryotes. This process requires several adaptative changes which involve the maintenance and the expression of part of the plastid genome, as well as the integration of the plastid activity to the cellular metabolism. This is illustrated by the diversity of plastids encountered in plant cells. For instance, in tissues undergoing color changes, i.e., flowers and fruits, the chromoplasts produce and accumulate excess carotenoids. In this paper we attempt to review the basic aspects of chromoplast development.

Chromoplast formation during tomato fruit ripening. No evidence for plastid DNA methylation

Ripening of tomato fruits involves differentiation of chloroplasts into non-photosynthetic chromoplasts. Plastid DNAs isolated either from green leaf chloroplasts or mature red fruit chromoplasts were compared by restriction endonuclease and DNA/DNA hybridization analyses. The same restriction and gene maps were obtained for both types of DNAs, illustrating the lack of major recombinational events during chromoplast formation. Several enzymes were used that discriminate the presence of methylated bases in their target sequences (Pst I, Pvu II, Sal I, Mbo I/Sau 3AI, Msp I/Hpa II, Bst NI/Eco RII). Plastid DNA fragments generated by these enzymes were hybridized against DNA probes encompassing about 85% of the tobacco chloroplast genome. These probes represented genes that follow very different expression behaviors in response to plastid development. Extensive restriction and hybridization analyses failed to reveal any difference between the chloroplast and chromoplast genomes, indicating that no developmentally related DNA methylation was detected by these methods. The results presented here do not support the hypothesis that selective DNA methylation of the chromoplast genome might play a major role in the transcriptional control of gene expression in these non-photosynthetic plastids.