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Abstract
Leaf heat tolerances of ‘Saladette’ (heat tolerant) and ‘UC-82B’ (less heat tolerant) tomato (Lycopersicon esculentum, Mill) were evaluated after heat acclimation. When plants of both genotypes were grown in a temperature regime below 30°C, there was no difference in heat tolerance. When plants of both genotypes were exposed to a temperature regime of 35° (day/night), ‘UC-82B’ could reach a higher level of heat tolerance, similar to ‘Saladette,’ but ‘UC-82B’ required 6 cycles of high temperature exposure, whereas ‘Saladette’ needed only a single cycle.
Expansins are extracellular proteins that are involved in cell wall modifications such as cell wall disassembly, cell separation, and cell expansion. Little is known about expansin gene expression during flower development of wintersweet (Chimonanthus praecox). In the present study, an expansin gene, CpEXP1, was isolated from the wintersweet flower cDNA library through random sequencing; this gene encodes a putative protein of 257 amino acids with the essential features conserved, like in other alpha expansins. The CpEXP1 gene exhibited different transcription levels in different tissues and had a significantly higher expression in flowers than other tissues. It is strongly correlated with the development of the flower. The expression of CpEXP1 increased in the flower buds or whole flowers from Stage 1 to 4 and decreased from Stage 5 to 6 during natural opening. Ethephon (an ethylene releaser) treatment promoted cut flower senescence, whereas 1-methylcyclopropene (1-MCP) (an ethylene perception inhibitor) delayed the process of flower wilting. This result is associated with the concomitant lower transcript levels of CpEXP1 in the ethephon-treated samples as well as the steady expression in the 1-MCP-treated samples compared with that in control flowers. The studies show the interesting observation that the expression of an expansin gene CpEXP1 is correlated with the development of Chimonanthus praecox flowers, the upregulation during flower opening vs. the downregulation during senescence.
Despite the increasing popularity in American markets of the fruit of the illustrious lychee (Litchi chinensis Sonn.), unreliable flowering and yield has had serious impacts on lychee growers in southern Florida. Lychee flowering is normally induced by chilling temperatures. Unpredictable weather, high rainfall, and excessive nutrients cause unreliable flowering in southern Florida. Although growers have no control over the weather, they need to be able to manage the growth, vigor, and reproduction of trees through practices that optimize flowering. When excessively watered and fertilized, lychee trees grow vigorously with frequent vegetative flushes every 2 to 3 months. The lack of maturity of these late vegetative flushes prevents flower stimulation from mild temperatures in January and February, when flowering typically occurs on trees that have not experienced vegetative flushes in the late fall or early winter. Thus, by adopting nitrogen fertilizer management practice, growers should be able to induce abundant flowering even in mild winters. Our preliminary results demonstrated that timing and rates of applications of nitrogen fertilizer significantly affected concentrations of soil and leaf N. High nitrogen levels in the leaves induced more vegetative flushes and less flowering, and consequently less fruit yield.
Abstract
Several tuber-bearing Solanum species with different levels of frost hardiness and different capacities for cold acclimation were studied for the interrelationship of freezing and heat tolerance after cold and heat acclimation. Cold acclimation could increase the frost hardiness in some species as previously reported, but except for S. commersonii it did not change the heat hardiness in species studied. Heat acclimation, on the other hand, could increase the heat hardiness in all tested species without affecting their frost hardiness. There is no systematic relationship between freezing and heat tolerance and no correlation in heat hardiness between the controls and the heat acclimated plants. The results indicate that the mechanisms of cold and heat acclimation in the potato appear to be independent of each other.
To compare the effects of various zinc (Zn) foliar fertilizers on correcting citrus Zn deficiency and to explore an effective correcting method, three common Zn fertilizers, Zn sulfate heptahydrate (ZnSO4.7H2O), Zn chloride (ZnCl2), and Zn nitrate hexahydrate [Zn(NO3)2.6H2O], were selected to spray the Zn-deficient citrus leaves, tested at different concentrations, with or without organosilicone surfactant. Zn content, chlorophyll levels, and photosynthesis characteristics of leaves were analyzed. Leaf Zn content was significantly increased with increase of the sprayed Zn concentration of the three Zn fertilizers. However, when the sprayed Zn concentration of ZnSO4.7H2O exceeded 200 mg·L−1, and Zn concentration of ZnCl2 or Zn(NO3)2.6H2O exceeded 100 mg·L−1, obvious necrotic spots formed on leaves. This necrosis disappeared when 0.025% organosilicone was added to the three Zn fertilizer solutions, even at a Zn concentration of 250 mg·L−1. Meanwhile, the Zn contents of leaves increased one to four times for these treatments. Furthermore, foliar application of the three Zn fertilizers significantly improved chlorophyll levels and photosynthetic capacity of Zn-deficient leaves. The data of chlorophyll and photosynthesis characteristics indicate that the correcting effect of ZnCl2 and Zn(NO3)2.6H2O is better than that of ZnSO4.7H2O, and could be further improved via supplement of organosilicone. In conclusion, ZnCl2 or Zn(NO3)2.6H2O containing 250 mg·L−1 of Zn and supplemented with 0.025% organosilicone is a safe and effective formulation of Zn foliar fertilizer for correcting citrus Zn deficiency.
Heat treatment induces resistance to low temperature in horticultural crops. Changes in soluble protein and heat-stable protein (HSP) contents, the total soluble solids (TSS), titratable acidity (TA), reducing sugar, weight loss and firmness of honey peach (cv. Hujingmilu) during heat treatment and refrigerated storage were investigated. Low-temperature storage alone led to decreasing of TA and reducing sugar and caused severe fresh mealiness. The hot-air treatment before low temperature combined with the use of a plastic bag (thickness of 0.03 mm) could counteract this effect. Heat treatment before refrigerated storage increased both soluble protein and HSP contents, and the ratio of heat-stable to soluble protein. The most favorable effect was obtained with 46 °C for 30 minutes. In addition, heat treatment before storage retarded the increase in fruit firmness, maintained the highest contents of the TSS and reducing sugar and inhibited the decline of TA during refrigerated storage. Treatment for 30 minutes at 46 °C before low-temperature storage in combination with a 0.03-mm plastic bag might be a useful technique to alleviate chilling injury (CI) and maintain honey peach fruit quality during cold storage.
Many reports indicate that an abundance of really interesting new gene (RING) play key roles in regulating defense responses against abiotic and biotic stresses in plants. In this study, the cloning and functional characterization of a RING gene, MaRING2, in banana (Musa acuminata) fruit are reported. MaRING2 belongs to the NEP1-interacting protein (NIP) RING-H2 finger protein family. Gene expression profiles revealed that MaRING2 was cold responsive and induced by abscisic acid (ABA) treatment during cold storage. In this study, the MaRING2 under control of the Cauliflower mosaic virus 35S (CaMV 35S) promoter was transformed to tobacco (Nicotiana benthamiana) using agrobacterium (Agrobacterium tumefaciens)-mediated transformation. The resultant MaRING2-overexpressing transgenic plants (35S:MaRING2) exhibited significantly increased tolerance to low temperatures and were hypersensitive to exogenous ABA in terms of germination and early seedling growth. In addition, overexpression of MaRING2 enhanced the expression of stress-responsive genes under normal (before cold stress) or cold conditions. These results demonstrate the biological role of MaRING2 in conferring cold tolerance. Taken together, these results suggest that MaRING2, a C3H2C3-type RING protein, is a positive regulator of the ABA-dependent stress response.
Effects of postharvest oxalic acid (OA) application on chilling injury (CI) in harvested mango fruit (Mangifera indica L.) were investigated using ‘Tommy Atkins’ fruit from Florida and ‘Zill’ fruit from Panzhihua. The OA was applied to harvested fruit as a 5 or 10 mm drench for 10 or 15 minutes at 25 °C. ‘Tommy Atkins’ fruit typically develop external CI symptoms while ‘Zill’ develops internal symptoms. Development of CI symptoms was significantly reduced in OA-treated ‘Tommy Atkins’ fruit stored for 18 days at 5 °C as was the rate of softening upon transfer to 25 °C for 4 days. However, OA treatment did not substantially control fruit decay. For ‘Zill’, CI development was significantly reduced in OA-treated fruit during storage at 10 °C for 49 days and subsequently for 4 days at 25 °C. In addition, membrane integrity was enhanced and the activities of the antioxidant system enzymes superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) were elevated, although there were decreases in both hydrogen peroxide (H2O2) content and superoxide radical production in OA-treated fruit. The activities of some enzymes of the energy cycle were also elevated in the OA-treated fruit, including succinate dehydrogenase (SDH), cytochrome C oxidase (CCO), H+-adenosine triphosphatase (H+-ATPase), and Ca2+-adenosine triphosphatase (Ca2+-ATPase). Thus, OA may enhance CI tolerance in mango fruit by maintaining membrane integrity associated with enhanced antioxidant activity and regulation of energy metabolism. Application of 5 mm OA appears to be beneficial in controlling postharvest CI in mango fruit.
Ethylene is important during the berry development and in the last stages of rachis development or rachis senescence. Since grapes develop in a cluster that comprises both the fruit berry and the nonfruit rachis, we measured the release of ethylene from both tissues. Detached berries from Vitis vinifera ‘Ruby Seedless’ and ‘Thompson Seedless’ showed that ethylene release peaks at the beginning of berry development and at veraison. Ethylene production in the rachis was higher than that in the berry and had an obvious peak before harvest in ‘Thompson Seedless’. In both cultivars, ethephon treatment induced ethylene production in the rachis but not in the berry. Expression of 1-aminocyclopropane-1-carboxylate (ACC) synthase (ACS) and ACC oxidase (ACO) genes showed diverse temporal and spatial patterns in ‘Thompson Seedless’ and ‘Ruby Seedless’. For most gene family members, the low ACS expression levels were observed in berry and rachis. Expression levels of most of the ACS and ACO genes did not correlate with ethylene released in the same organ. The transcriptional level of VvACS1 did correlate with ethylene evolution in rachis of ‘Thompson Seedless’ during berry development and storage, which suggested that VvACS1 may have important roles in rachis senescence. In berries of ‘Thompson Seedless’ and ‘Ruby Seedless’, the transcriptional levels of VvACO1, VvACS2, and VvACS6 coincided with ethylene production, indicating possible roles in berry development. Expression of VvACS2–VvACO9 and VvACO1–VvACO3 was not consistent with ethylene production during storage or in response to ethephon treatment, which suggests that the expression of ACS and ACO was affected by other stress factors after harvest.
Quantitative real-time reverse transcription polymerase chain reaction (RT-PCR) is a sensitive and widely used technique for gene expression analysis that depends on stability of the reference genes used for data normalization. Tree peony (Paeonia suffruticosa), known as one of the most famous traditional ornamental plants in China, is very popular in both domestic and international markets for its showy and colorful flowers. To date, no systematic studies on reference genes have been performed in tree peony with different flower colors. In this study, we evaluated the expression stability of 12 candidate reference genes in different tissues and five flower developmental stages of tree peony with six different colors by three algorithms: geNorm, NormFinder, and BestKeeper. The results showed that protein phosphatase 2A (PP2A), ubiquitin protein ligase (UPL), and ubiquitin (UBQ) were the most stable genes across all samples. Helicase, alpha-tubulin (TUA), and eukaryotic translation initiation factor 5A (EIF5A) also exhibited high expression stability in different tissues, in samples with different colors, and at different flower developmental stages. According to the geNorm analysis, the combination of two most stable reference genes was optimal for normalization in all tested sample sets in this study. To further validate the suitability of the reference genes identified in this study, the expression patterns of two putative homologs of chalcone synthase gene (PsCHS1) and chalcone isomerase gene (PsCHI1) were studied at different developmental stages of white flowers. The results provide information for transcriptional analyses in future studies of gene expression on tree peony flower development and pigmentation.