Ectopic Expression of Arabidopsis thaliana zDof1.3 in Tomato (Solanum lycopersicum L.) Is Associated with Improved Greenhouse Productivity and Enhanced Carbon and Nitrogen Use.

A large collection of transgenic tomato lines, each ectopically expressing a different Arabidopsis thaliana transcription factor, was screened for variants with alterations in leaf starch. Such lines may be affected in carbon partitioning, and in allocation to the sinks. We focused on 'L4080', which harbored an A. thaliana zDof (DNA-binding one zinc finger) isoform 1.3 (AtzDof1.3) gene, and which had a 2−4-fold higher starch-to-sucrose ratio in source leaves over the diel (p < 0.05). Our aim was to determine whether there were associated effects on productivity. L4080 plants were altered in nitrogen (N) and carbon (C) metabolism. The N-to-C ratio was higher in six-week-old L4080, and when treated with 1/10 N, L4080 growth was less inhibited compared to the wild-type and this was accompanied by faster root elongation (p < 0.05). The six-week-old L4080 acquired 42% more dry matter at 720 ppm CO2, compared to ambient CO2 (p < 0.05), while the wild-type (WT) remained unchanged. GC-MS-TOF data showed that L4080 source leaves were enriched in amino acids compared to the WT, and at 49 DPA, fruit had 25% greater mass, higher sucrose, and increased yield (25%; p < 0.05) compared to the WT. An Affymetrix cDNA array analysis suggested that only 0.39% of the 9000 cDNAs were altered by 1.5-fold (p < 0.01) in L4080 source leaves. 14C-labeling of fruit disks identified potential differences in 14-DPA fruit metabolism suggesting that post-transcriptional regulation was important. We conclude that AtzDof1.3 and the germplasm derived therefrom, should be investigated for their 'climate-change adaptive' potential.

Postharvest internal browning of pineapple fruit originates at the phloem.

A typical symptom of postharvest chilling injury (PCI) in pineapple fruit (Ananas comosus (L.) Merr.) is internal browning (IB) near the fruit core. Since vascular bundles (VBs) are localized to this region, it was hypothesized that the VBs might be the site of IB. To test this, the anatomy and histochemistry of VBs during chilling stress in four pineapple cultivars with different levels of sensitivity to PCI were examined. Fruit were stored at 10°C for up to three weeks to stimulate translucency symptoms (TS; the initiation of IB). After three weeks of chilling exposure, the cultivars 'MD2' showed 0%, 'Pattavia' and 'Savee' showed 10-16%, and 'Trad Sri Thong' showed 100% TS and IB symptom. Scanning electron microscopy and in situ histochemical staining techniques that detect enzymes and substrates commonly associated with IB initiation were used in parallel. The TS of pineapple fruit coincided with the collapse of the phloem tissue. The VBs in the tissue where IB was initiated (i.e., the flesh adjacent to the core or F/C) had the highest activity of polyphenol oxidase, hydrogen peroxide, and phenolic compounds. The IB-resistant 'MD2' genotype had fewer VBs, but a greater proportion of sclerenchyma fibers (P<0.05) than did the susceptible 'Trad Sri Thong'. Based on these data, the first report of pineapple IB occurrence in the phloem was proposed.

Comparison of leaf and fruit metabolism in two tomato (Solanum lycopersicum L.) genotypes varying in total soluble solids.

Sink and source activity in two tomato (Solanum lycopersicum L.) genotypes that vary in fruit Brix were investigated to identify differences that potentially underscore this trait. Solara (Brix 9%) accumulated almost twice the glucose, fructose, and sucrose in ripe fruit and had a higher horticultural yield (25% greater) compared to Moneymaker (Brix 5%). 14C-glucose feeding suggested large disparities in sucrose metabolism in ripe fruit between genotypes. Biochemical pathways in the leaf adjacent to a fruiting truss at night were also analyzed since in many species, this is the period when leaf reserves are mobilized to feed the plant. Surprisingly, leaf metabolism, i.e., starch and sugar content, the levels of polar metabolites assayed by GC-TOF MS and 14CO2-pulse-chase fluxes in detached leaves, did not change between the day and night in either genotype. Solara has a higher morphological source-to-sink ratio, and this may contribute to higher Brix in that genotype.

Starch molecular structure shows little association with fruit physiology and starch metabolism in tomato.

The aim of this work was to determine if the molecular structure of starch from tomato ( Solanum lycopersicum L.) is influenced by fruit physiology and carbohydrate metabolism. The effect of fruit size, fruit ripening behavior, and assimilate availability on starch granule accumulation was examined in nine tomato samples. The percentage of (14)C-glucose partitioning to starch was similar among samples, but starch contents varied 10-fold, suggesting differences in metabolism. In contrast, granule size (10-20 microm), amylose content (19-23%), degree of crystallinity (26-31%), and enthalpy of gelatinization (14.8-17.2 degrees C) were similar. Some differences in structure were detected in starch from the largest and smallest fruit using more sensitive analyses such as thermal properties, chain length distribution of amylopectin, and susceptibility to in vitro alpha-amylase digestion. However, overall, our results suggest that granule characteristics are highly conserved in tomato fruit, and we conclude that this is likely due to inherent metabolic constraints.

Starch granules in tomato fruit show a complex pattern of degradation.

Starch is transiently accumulated in tomato fruit with near complete degradation achieved by maturity. Surprisingly, (14)C-pulse-chase analyses indicated that the rate of starch degradation was highest in immature fruit [10 days post anthesis (DPA)] when maximal synthesis occurs, but was almost undetectable at 45 DPA when there is net breakdown of starch. Further analysis of starch accumulation, rate of synthesis, particle size analysis, and confocal laser scanning microscopy of starch granules from developing fruit suggests that the rate of starch degradation does increase after 40 DPA, but it may not occur at the same site at which starch is synthesized. Furthermore, the degradation rate at maturity is lower than that measured in early development. Overall, the results suggest that starch degradation in developing tomato is biphasic with separate regiotemporal occurrences. This mechanism may have evolved to offer flexibility in balancing starch accumulation and utilization in the developing fruit.

Structural investigations and morphology of tomato fruit starch.

The physicochemical properties of starch from tomato (Solanum lycopersicum L.) pericarp and columella of cv. Moneymaker fruit at 28 days post anthesis (DPA) were investigated, providing the first description of the composition and structure of tomato fruit starch. Starch granules from pericarp were mainly polygonal, 13.5-14.3 microm, and increased in size through development, being largest in ripening fruit. Amylopectin content was 81-83% and was of molecular weight 1.01 x 10(8) g/mol; the phosphorus content was 139 ppm, and starch showed a C-type pattern with crystallinity of 30%. Starch characteristics were similar in columella except granule size (16.8-17.8 microm) and crystallinity (40%), although 6-fold more starch accumulated in the pericarp. Solara, a high-sugar tomato cultivar, was also studied to determine if this affects starch granule architecture. There were few differences from Moneymaker, except that Solara columella starch crystallinity was lower (26%), and more starch granule-intrinsic proteins could be extracted by sodium dodecyl sulfate-polyacrylamide gel electrophoresis.