Comprehensive Assessment of the Dynamics of Banana Chilling Injury by Advanced Optical Techniques

Green-ripe banana fruit are sensitive to chilling injury (CI) and, thus, prone to postharvest quality losses. Early detection of CI facilitates quality maintenance and extends shelf life. CI affects all metabolic levels, with membranes and, consequently, photosynthesis being primary targets. Optical techniques such as chlorophyll a fluorescence analysis (CFA) and spectroscopy are promising tools to evaluate CI effects in photosynthetically active produce. Results obtained on bananas are, however, largely equivocal. This results from the lack of a rigorous evaluation of chilling impacts on the various aspects of photosynthesis. Continuous and modulated CFA and imaging (CFI), and VIS remission spectroscopy (VRS) were concomitantly applied to noninvasively and comprehensively monitor photosynthetically relevant effects of low temperatures (5 °C, 10 °C, 11.5 °C and 13 °C). Detailed analyses of chilling-related variations in photosynthetic activity and photoprotection, and in contents of relevant pigments in green-ripe bananas, helped to better understand the physiological changes occurring during CI, highlighting that distinct CFA and VRS parameters comprehensively reflect various effects of chilling on fruit photosynthesis. They revealed why not all CFA parameters can be applied meaningfully for early detection of chilling effects. This study provides relevant requisites for improving CI monitoring and prediction.

Proteomics Insight into Imbalanced Down-Regulation of Photosynthetic Components during Blueberry Fruit Maturation

Background: Blueberries are admired for both their delicious flavor and extensive health benefits. In blueberry, fruit photosynthesis provides a large part of the carbon requirements, and is associated with fruit quality. To explore mechanism underlying fruit photosynthesis, photosynthetic ability was determined at three maturation phases (green, pink, and blue) by CO2 gas exchange and chlorophyll fluorescence, and proteomics was conducted by MS/MS shortgun and PRM strategies. Results: The fruit photosynthetic ability gradually decreased as fruit maturation. The gross photosynthesis rate in green fruit accounted for 26.36% of that in the leaf, followed by 16.73% in pink fruit, and 9.11% in blue fruit. Fv/Fm (0.76) was observed in green fruit, comparable to that in leaves (0.78), and followed by 0.66 in pink fruit (no data was generated for blue fruit). Degeneration of fruit photosynthesis was started with imbalances within down-regulation of PS core/LHC, and PSI/PSII. In green/pink, PS core proteins were more down-regulated than LHC proteins. A decreasing ratio of PSII core/LHCII was reflected in the decreasing ratios of Chl a/b and carotenoids/Chl. KEGG analyses also indicated that the down-regulated LHC proteins were enriched in pink/blue, but not in green/pink. In green/pink, PSII was more down-regulated than PSI, while in blue/pink, PSI was more down-regulated than PSII. GO also suggested that down-regulated PSII proteins were enriched in green/pink, whereas down-regulated PSI proteins were enriched in pink/blue. Moreover, down-regulation of FNR and ATP synthase resulted in a decreasing yield of NADPH and ATP, while the down-regulation of both RuBisCO and RCA severely hindered Calvin cycle, and thereby led to a decreased efficiency of carbon fixation. Conclusions: Dynamic imbalances in degeneration of photosynthetic components occured during fruit maturation; this may be related to physiological attributes e.g. carbon contribution and attractiveness to frugivores.

Contents of non-structural carbohydrates in fruiting cape gooseberry (Physalis peruviana L.) plants

Although the cape gooseberry has become the second most important export fruit in Colombia, information is scarce for its carbohydrate partitioning, which plays a major role in plant productivity. Seed-propagated Colombia ecotypes were kept in a greenhouse in 2.5-L plastic containers filled with washed quartz sand and were ferti-irrigated. The plants were pruned to one main vegetative stem with two generative stems. Dry matter (DM) partitioning during the initial plant growth showed the highest accumulation rate in the roots during the first 20 days, whereas, at a later stage of development, the shoot DM gain was higher and the leaf DM gain was lower than that of the roots. Sixty days after transplant, the plant parts were quantified and analyzed for glucose, fructose, sucrose, and starch. The roots were the largest carbohydrate pool for starch, but the sucrose content was lower in the roots than in the vegetative stem and the lower part of the reproductive stems. At 5-15 cm of the vegetative stem base, 6.4 mg of starch, 1.4 mg of monosaccharides and 5.3 mg/100 g of DM sucrose were found, indicating that this lower organ is also important for starch accumulation and, especially, for sucrose transport. In the two reproductive stems, the starch contents were much higher in the base part than in the apical part; the same relationship was found in the leaves. The monosaccharide content was the highest in the apical stem position with 8.2 mg/100 g DM. In contrast, the apical-positioned 10-day-old fruits had maximum starch concentrations (11.6 mg/100 g DM), possibly due to the assimilatory starch from green fruit photosynthesis, whereas the mature basal fruits (60-day-old) mainly accumulated sucrose (25.7 mg) and monosaccharides (21.2 mg/100 g DM).

Fruit Photosynthesis and Phosphoenolpyruvate Carboxylase Activity as Affected by Lightproof Fruit Bagging in Satsuma Mandarin

To clarify why fruit bagging reduces sugar content at harvest, we investigated its effect on carbon dioxide assimilation by Satsuma mandarin (Citrus unshiu) fruit through photosynthesis and phosphoenolpyruvate carboxylase (PEPC; enzyme code 4.1.1.31). Seasonal changes in gross photosynthesis ranged from 70 to 400 μmol·d−2·h−1 O2 with a peak at 99 days after full bloom (DAFB) when the assimilation rate of fruit was comparable to that of leaves. However, a peak showing net photosynthesis appeared at 112 DAFB because of high fruit respiration. When fruit were bagged at 85 DAFB, the net photosynthetic peak disappeared, perhaps as a result of the decline in chlorophyll content in the rind. Sugar and organic acid content in the bagged fruit were 0.3% and 0.16% less, respectively, than controls at the mature stage (204 DAFB). PEPC activity in the rind was much higher than in leaves on a protein basis; it increased between 92 and 112 DAFB and showed a peak of 72 units. The PEPC activity peak was also 90% of control after fruit bagging. Thus, just before their color development, mandarin fruit assimilate CO2 actively through photosynthesis and PEPC. However, these activities are inhibited by bagging, likely resulting in lower sugar content at harvest. The concomitant activation of PEPC and photosynthesis between 99 and 126 DAFB indicates that CO2 fixed by PEPC might be used for photosynthesis in mandarin fruit, because photosynthesis in several fruit such as apple (Malus pumila) and pea (Pisum sativum) is considered to have an intermediate status among C3, non-autotrophic tissue, and C4/CAM photosynthesis.

Uniform ripening Encodes a Golden 2-like Transcription Factor Regulating Tomato Fruit Chloroplast Development

Modern tomato (Solanum lycopersicum) varieties are bred for uniform ripening (u) light green fruit phenotypes to facilitate harvests of evenly ripened fruit. U encodes a Golden 2-like (GLK) transcription factor, SlGLK2, which determines chlorophyll accumulation and distribution in developing fruit. In tomato, two GLKs—SlGLK1 and SlGLK2—are expressed in leaves, but only SlGLK2 is expressed in fruit. Expressing GLKs increased the chlorophyll content of fruit, whereas SlGLK2 suppression recapitulated the u mutant phenotype. GLK overexpression enhanced fruit photosynthesis gene expression and chloroplast development, leading to elevated carbohydrates and carotenoids in ripe fruit. SlGLK2 influences photosynthesis in developing fruit, contributing to mature fruit characteristics and suggesting that selection of u inadvertently compromised ripe fruit quality in exchange for desirable production traits.