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To investigate thermotolerance in seeds of lettuce (Lactuca sativa L.), primed, nonprimed, or seeds matured at 20/10 and 30/20 °C (day/night on a 12-h photoperiod) were imbibed at 36 °C for various periods and then dissected. Structural changes in seed coverings in front of the radicle tip were observed during germination at high temperature. Thermotolerant genotypes, ‘Everglades’ and PI 251245, were compared with a thermosensitive cultivar, ‘Dark Green Boston’. In all seeds that germinated, regardless of seed maturation temperature or priming, a crack appeared on one side of the cap tissue (constriction of the endosperm membrane near the basal end of the seed) at the micropylar region and the endosperm separated from the integument in front of the radicle tip. Additional changes took place during imbibition in these seeds; the protein bodies in the vacuoles enlarged and gradually depleted, large empty vacuoles formed, the cytoplasm condensed, the endosperm shrank, the endosperm cell wall dissolved and ruptured, and then the radicle elongated toward this ruptured area. The findings suggested that the endosperm layer presented mechanical resistance to germination in seeds that could not germinate at 36 °C. Weakening of this layer was a prerequisite to radicle protrusion at high temperature. Seeds of ‘Dark Green Boston’, ‘Everglades’, and PI 251245 matured at 30/20 °C had greater thermotolerance than those matured at 20/10 °C. Results of the anatomical study indicated that the endosperm cell walls in front of the radicle of seeds matured at 30/20 °C were more readily disrupted and ruptured during imbibition than seeds matured at 20/10 °C, suggesting a reason why these seeds could germinate quickly at supraoptimal temperatures. Similar endosperm structural alterations also were observed in primed seeds. Priming led to rapid and uniform germination, circumventing the inhibitory effects of high temperatures. From anatomical studies conducted to identify and characterize thermotolerance in lettuce seed germination, we observed that genotype, seed maturation temperature, or seed priming had the ability to reduce physical resistance of the endosperm by weakening the cell wall and by depleting stored reserves leading to cell collapse.
‘Fuyu’ perisimmon fruit were treated with 500 nL·L−1 1-methylcyclopropene (1-MCP) for 24 h at 20 °C and then stored at 4 °C for 45 days to investigate the effects of 1-MCP on chilling injury (CI) during storage at 4 °C. Persimmon fruit developed CI, manifested as rapid softening and external and internal browning. Injury symptoms were reduced by 1-MCP treatment. 1-MCP also delayed increases in respiration and ethylene production. Compared with control fruit, 1-MCP-treated fruit exhibited increased superoxide dismutase and catalase activities within the initial storage period and lower membrane permeability, malondialdehyde content, and peroxidase and polyphenol oxidase activities throughout the entire storage period. These results suggest that reduction of CI symptoms in persimmon fruit in response to 1-MCP treatment may be attributed to altered oxidative status.
Continuous monitoring of hydraulic/hydrologic data for managing water for horticultural crops has been a challenge due to factors such as data loss, intensive resource requirements, and complicated setup and operation. The use of state-of-the-art wireless spread spectrum communication technology and wireless data acquisition and control (WDAC) systems for agricultural water management is discussed in this paper. The WDAC technology was applied to a research project where lysimeters were used for water quantity and quality studies for vegetables. Two types of WDAC networks, master–slave and peer-to-peer WDAC networks, are discussed. The WDAC system linked the wireless dataloggers to a network to make real-time data available over the Internet. The use of WDAC made it possible to collect real-time data and control the experiment (e.g., frequency of data collection) remotely through the Internet. The WDAC system for the lysimeter study was compared to a commonly used manual system with regard to potential instrument damage, data loss, ease of data collection and analyses, and total cost of monitoring. The advantages of the WDAC include: reduced equipment losses from natural disasters (e.g., lightning), improved equipment maintenance, reduced data loss from faulty equipment, higher project personnel efficiency, and real-time involvement by a dispersed team. The total cost of the WDAC system ($65,750) was about half that of the manual system ($130,380). The WDAC system was found to be an effective tool for agricultural water management projects.
Cut Rosa ×hybrida L. `Royalty' flowers were used to determine the efficacy of electron-beam irradiation for increasing postharvest quality and decreasing petal infection by Botrytis cinerea Pers. In an experiment for determining the injury threshold, roses received electron-beam irradiation of 0, 0.5, 1, 2, and 4 kGy. Irradiation dosages ≥1 kGy caused necrosis on petal tissue and decreased postharvest life at 20 °C. In a second experiment to evaluate postharvest quality, roses were irradiated at 0, 0.25, 0.5, 0.75, and 1 kGy. Dosages of 0.25 and 0.5 kGy slowed the rate of flower bud opening for 2 days but did not decrease postharvest quality when compared with nonirradiated roses. Roses that received irradiation dosages of 0.75 and 1 kGy showed unacceptable quality. In a third experiment, roses that had or had not been inoculated with B. cinerea were irradiated at 0, 0.25, 0.5, and 0.75 kGy. Irradiation did not control B. cinerea populations, and rose quality decreased as dosage increased. In a fourth experiment to determine the effect of irradiation on B. cinerea, conidia on water-agar plates exposed to dosages ≤1, 2, and 4 kGy germinated at rates of ≈90%, 33%, and 2%, respectively, within 24 h.
Expansins are proteins that have been reported to contribute to fruit softening. In this study, an expansin gene, CDK-Exp3, was identified from persimmon fruit, and the mRNA accumulation of CDK-Exp3 during postharvest softening was examined using real-time polymerase chain reaction (PCR). Sequence analysis showed that CDK-Exp3 contained a putative open reading frame of 765 bp encoding a polypeptide of 254 amino acid residues, which had all the characteristics of α-expansin. As fruit softened, the expression of CDK-Exp3 increased dramatically within the initial 8-day ripening at 20 °C followed by a gradual decline at the late stages of ripening. The expression of CDK-Exp3 was inhibited by gibberellic acid, and the maximum transcript abundance was delayed by 20 days compared with that of the control fruit. The results suggest that CDK-Exp3 might be closely related to softening of persimmon fruit during postharvest ripening.