RESUMEN

This experiment aimed to investigate the status of tomato plants in terms of sink or source-limitation of 2 cultivars of greenhouse tomato (Solanum lycopersicum L.), i.e., 'Grandella' and 'Isabella' under the greenhouse conditions of Iran and to improve the yield and plant growth by manipulating the sink-source balance. To this end, 4 treatments were applied: leaves were not pruned and fruits were pruned to one per truss (1F/3L), leaves were not pruned and fruits were pruned to two per truss (2F/3L), leaves were not pruned and fruits were pruned to three per truss (3F/3L) and no leaf and fruit pruning (control). The results showed that truss pruning reduced the sink demand and consequently, increased the amount of available assimilate for the growth of the remaining fruits or vegetative parts. The negative correlation between the leaf area index and the net assimilation rate and no significant difference in the net assimilation rate between different sink/source ratios showed that the excess leaf area index does not contribute in increasing the  assimilate production and hence, total yield. Total fruit weight, harvest index, and the ratio of the ripe fruits to the total fruit led to the highest yield for control plants. No changes in chlorophyll, protein content and nitrate reductase activity were the evidence for the fact that sink/source ratio  do not affect light-harvesting and light-utilizing components of photosynthesis. Since the individual weight of fruits increased with decreasing fruit number per trusses, the growth of individual fruits in both cultivars was source-limited and truss pruning can decrease this limitation. Future studies should be carried out to determine the best level of sink/source ratio that in addition to producing an acceptable amount of yield, meets the needs of consumers in the current stressful world by increasing the antioxidant and nutriceutical content of fruits.

RESUMEN

Due to insoluble iron (Fe) sources in soil, limited Fe availability leads to the disruption of the photosynthetic apparatus; this affects the growth and productivity of plants such as quince (Cydonia oblonga) that are very sensitive to low Fe content. Plant growth-promoting rhizobacteria (PGPR) play an important role in the regulation of Fe uptake under its limited availability. Therefore, in this research, two PGPR (Pseudomonas fluorescens and Microccucuce yunnanensis), at two Fe levels [50 µM (Fe-sufficiency) or 5 µM (Fe-deficiency)], were used to investigate the impact of the given bacteria on improving the acquisition of Fe in quince seedlings. Upon Fe-deficiency, the highest shoot and root biomass (7.14 and 6.04 g plant-1 respectively), the greatest chlorophyll concentration (0.89 mg g-1FW), and the largest Fe concentrations in roots and shoots (30% and 48.7%, respectively) were shown in the quince treated with M. yunnanensis. Both PGPR increased the root citric acid and the phenolic compound concentration. Two days after Fe-deficiency and PGPR treatments, a 1.5- fold increase, was observed in the expression of HA7. The highest PAL1 gene expression and the greatest PAL activity (95.76 µmol cinnamic acid g-1FW) were obtained from the M. yunnanensis treatment. The expression of the FRO2 gene was also affected by Fe-deficiency and PGPR treatments, resulting in an increase in the FCR activity and a surge in the Fe concentrations of leaves and roots. It could, therefore, be concluded that the PGPR modulated Fe acquisition in the quince seedlings upon Fe-deficiency by influencing the physico-chemical and molecular responses.

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RESUMEN

To examine the physiological role of hexose transporters in determining the sink strength of individual fruits, the regulation of hexose transporters gene expression was studied when the sink/source ratio was artificially altered under the greenhouse condition; this was done in two cultivars of tomato, i.e. Grandella and Isabella. The sink/source ratio treatments included: saving one fruit per truss (1F), two fruits per truss (2F), three fruits per truss (3F) and no fruit pruning (control). The results showed that fruit thinning could increase starch, sucrose, and hexose contents in the fruits; it could also modulate the activity of the key enzymes and the expression of tomato hexose transporter genes (LeHTs). Based on the relative transcript levels, all examined LeHTs were unregulated at the end of cell division and the cell expansion stage of fruit development, but the strongest expression level observed at the onset of ripening was related to LeHT1 and LeHT2. Given the concomitancy of cell wall invertase (EC 3.2.1.26) activity and the LeHTs relative expression cell wall, invertase activity seemed to be involved in the expression level of LeHTs. The increased trends of the LeHTs expression with the decrease of the sink/source ratio confirmed the role of hexose transporters in determining the sink strength of the tomato fruits.

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Synthetic antioxidants can reduce postharvest losses, but consumers are concerned about chemical residues in the product. There is a growing interest in using natural compounds for the preservation of foods. In this study, the efficiency of juices or extracts obtained from three fruit species with high antioxidant activity as browning inhibitors was measured and then compared with that obtained from pomegranate by-product (PBP). The aim was to offer the most significant contributions concerning fresh-cut fruit preservation, using 'Shahmive' pear as the fruit model. Slices of pear were dipped in pomegranate juice (PJ) or extract (PE), kiwifruit juice (KJ) or extract (KE), grape juice (GJ) or extract (GE), PBP and chitosan before being stored at 4 °C. The total phenolic content of solutions ranged from 11 to 127.5 mg gallic acid/100 mL. Extracts of pomegranate peel and grape had the uppermost and the lowermost antioxidant activity (%DPPH), respectively. In comparison with other treatments including the control one, the minimum peroxidase (POD) activity, the maximum ascorbic acid content and the retention of firmness were seen in the fruit which was treated with kiwifruit extract. PJ + GJ treatment decreased POD and polyphenol oxidase activity and improved L* and a* values in the slices. The use of fruit juice or extracts had no adverse effect on the sensory quality of slices, with the exception of samples subjected to PJ or GJ + KJ treatments. Improving antioxidant capacity of fresh cut pear treated with KE and PJ + GJ would have a big advantage of preventing enzymatic browning.

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Many reports have already been published regarding the removal of heavy metals from aqueous solutions onto activated carbon. However, the biosorbents' effect on the plant response still needs further investigation. In this study, activated carbon derived from the pomegranate peel [pomegranate activated carbons (PAC)] was used to see the effects of the addition of PAC on growing strawberry in Cd-contaminated sand. Cd accumulation and toxicity to strawberry was investigated by measuring the concentration of Cd in plant tissues and various biochemical activities of plant. Our results suggested that PAC had a high sorption capacity for Cd. Strawberry plant tried to deal with the Cd-induced oxidative stress by strengthening its antioxidant competences and decreasing Cd absorption. In comparison with the control, PAC applied to the sand decreased the level of lipid peroxidation and enhanced the carotenoid content. The greater tolerance of strawberry toward the level of Cd due to the application of PAC was associated with improving the physical conditions of the soil, increasing the amounts of some essential elements and decreasing the level of Cd absorption. Gaviota strawberry cultivar exposed to 5 or 10 mg kg-1 Cd was able to adopt a new metabolic equilibrium, allowing the plant to cope with this metal.

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The physicochemical composition changes during palm ripening were studied. The activities of invertase and cell wall-modifying enzymes, namely pectin methylesterase (PME), ß-galactosidase (ß-Gal), endo-1,4-ß-D-glucanase (EGase), and cellulase were monitored during growth and ripening of Shahani, Piarom and Deiry cultivars with different textures. Also, we estimated the concentrations of six organic acids by HPLC. Reducing sugars, most of organic acid, pH and TSS increased up to the full-ripe stage of all date types. On the contrary, moisture, macro and microelements and proteins decreased during the same period. Despite a considerable rise in invertase activity (200 units) during ripening of Shahani, no significant trend could be discerned in Deiry cultivar (8 units) at different stages. Our results also showed that cell wall enzymes were increased in activity during ripening and these increases were coincident with fruit softening. Furthermore, our results showed that the composition and the variation of the chemical compositions mainly depended on the cultivar and maturity stage.

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