Water Status Related Root-to-Shoot Communication Regulates the Chilling Tolerance of Shoot in Cucumber (Cucumis sativus L.) Plants

Mechanisms by which Bisphenol A affect the photosynthetic apparatus in cucumber (Cucumis sativus L.) leaves

Bisphenol A (BPA), a widely distributed pollutant, suppresses photosynthesis in leaves. In previous studies on higher plants, the plants were treated by BPA through irrigation to root. This method cannot distinguish whether the BPA directly suppresses photosynthesis in leaves, or indirectly influences photosynthesis through affecting the function of root. Here, only the leaves but not the roots of cucumber were infiltrated with BPA solution. The photosystem II and I (PSII, PSI) were insensitive to BPA under darkness. BPA aggravated the PSII but not the PSI photoinhibition under light. BPA also inhibited CO₂ assimilation, and the effect of BPA on PSII photoinhibition disappeared when the CO₂ assimilation was blocked. The H₂O₂ accumulated in BPA-treated leaves under light. And the BPA-caused PSII photoinhibition was prevented under low (2%) O₂. We also proved that the BPA-caused PSII photoinhibition depend on the turnover of D1 protein. In conclusion, this study proved that BPA could directly suppress photosynthesis in leaves, however, BPA does not damage PSII directly, but inhibits CO₂ assimilation and over-reduces the electron transport chain under light, which increases the production of reactive oxygen species (H₂O₂), the over-accumulated ROS inhibits the turnover of D1 protein and consequently aggravates PSII photoinhibition.

Mechanisms by which Bisphenol A affect the photosynthetic apparatus in cucumber (Cucumis sativus L.) leaves

Bisphenol A (BPA), a widely distributed pollutant, suppresses photosynthesis in leaves. In previous studies on higher plants, the plants were treated by BPA through irrigation to root. This method cannot distinguish whether the BPA directly suppresses photosynthesis in leaves, or indirectly influences photosynthesis through affecting the function of root. Here, only the leaves but not the roots of cucumber were infiltrated with BPA solution. The photosystem II and I (PSII, PSI) were insensitive to BPA under darkness. BPA aggravated the PSII but not the PSI photoinhibition under light. BPA also inhibited CO₂ assimilation, and the effect of BPA on PSII photoinhibition disappeared when the CO₂ assimilation was blocked. The H₂O₂ accumulated in BPA-treated leaves under light. And the BPA-caused PSII photoinhibition was prevented under low (2%) O₂. We also proved that the BPA-caused PSII photoinhibition depend on the turnover of D1 protein. In conclusion, this study proved that BPA could directly suppress photosynthesis in leaves, however, BPA does not damage PSII directly, but inhibits CO₂ assimilation and over-reduces the electron transport chain under light, which increases the production of reactive oxygen species (H₂O₂), the over-accumulated ROS inhibits the turnover of D1 protein and consequently aggravates PSII photoinhibition.

Horticultural, systems-engineering and economic evaluations of short-term plant storage techniques as a labor management tool for vegetable grafting nurseries

This transdisciplinary study has a three-fold systems approach in evaluating a horticultural technology: 1) horticultural evaluations, 2) economic and resource analyses, and 3) systems engineering analyses, using low temperature storage as an example technology. Vegetable grafting is a technique to produce value-added seedlings but requires labor intensive nursery operations. Low temperature storage of seedlings for a short period of time can reduce peak production, but has not been evaluated at the extent demonstrated in this paper. Seedlings of 22 genotypes of Cucurbitaceae (cucurbit family) and Solanaceae (nightshade family) were evaluated for storability under selected temperatures and photosynthetic photon flux. Storability of Cucurbitaceous seedlings varied between 2 to 4 weeks at 12°C and 13 μmol m^-2 s^-1. Solanaceous seedlings were generally storable for 4 weeks at 12°C and 13 μmol m^-2 s^-1, but tomato seedlings could be stored for 4 weeks at 10°C and 5 μmol m^-2 s^-1. Capital and weekly operational costs of a low temperature storage system with a design that meets environmental requirements were estimated as $671 to $708 per m² footprint and $0.79 to $2.21 per m² footprint per week, respectively. Electricity costs per plant was less than 0.1 cents for 2 to 4 weeks of storage. Using a schedule-optimization heuristic and a logistics simulator previously developed for grafting nursery operations, six production scenarios consisting of two crops (tomato or watermelon) and three production peak patterns were examined to evaluate the impact of including low temperature storage. While the overall average costs of grafting labor were not significantly different, maximum labor demand and grafting labor cost during the peak production week were reduced by 31% to 50% and 14% to 30% by using storage, respectively. Therefore, low temperature storage can be an effective means to address the issue of labor management in grafting nurseries.

Ultraviolet-B Radiation (UV-B) Relieves Chilling-Light-Induced PSI Photoinhibition And Accelerates The Recovery Of CO2 Assimilation In Cucumber (Cucumis sativus L.) Leaves

Ultraviolet-B radiation (UV-B) is generally considered to negatively impact the photosynthetic apparatus and plant growth. UV-B damages PSII but does not directly influence PSI. However, PSI and PSII successively drive photosynthetic electron transfer, therefore, the interaction between these systems is unavoidable. So we speculated that UV-B could indirectly affect PSI under chilling-light conditions. To test this hypothesis, the cucumber leaves were illuminated by UV-B prior or during the chilling-light treatment, and the leaves were then transferred to 25 °C and low-light conditions for recovery. The results showed that UV-B decreased the electron transfer to PSI by inactivating the oxygen-evolving complex (OEC), thereby protecting PSI from chilling-light-induced photoinhibition. This effect advantages the recoveries of PSI and CO₂ assimilation after chilling-light stress, therefore should minimize the yield loss caused by chilling-light stress. Because sunlight consists of both UV-B and visible light, we suggest that UV-B-induced OEC inactivation is critical for chilling-light-induced PSI photoinhibition in field. Moreover, additional UV-B irradiation is an effective strategy to relieve PSI photoinhibition and yield loss in protected cultivation during winter. This study also demonstrates that minimizing the photoinhibition of PSI rather than that of PSII is essential for the chilling-light tolerance of the plant photosynthetic apparatus.

Characterization of photosynthetic gas exchange in leaves under simulated adaxial and abaxial surfaces alternant irradiation

Previous investigations on photosynthesis have been performed on leaves irradiated from the adaxial surface. However, leaves usually sway because of wind. This action results in the alternating exposure of both the adaxial and abaxial surfaces to bright sunlight. To simulate adaxial and abaxial surfaces alternant irradiation (ad-ab-alt irradiation), the adaxial or abaxial surface of leaves were exposed to light regimes that fluctuated between 100 and 1,000 μmol m(-2) s(-1). Compared with constant adaxial irradiation, simulated ad-ab-alt irradiation suppressed net photosynthetic rate (Pn) and transpiration (E) but not water use efficiency. These suppressions were aggravated by an increase in alternant frequency of the light intensity. When leaves were transferred from constant light to simulated ad-ab-alt irradiation, the maximum Pn and E during the high light period decreased, but the rate of photosynthetic induction during this period remained constant. The sensitivity of photosynthetic gas exchange to simulated ad-ab-alt irradiation was lower on abaxial surface than adaxial surface. Under simulated ad-ab-alt irradiation, higher Pn and E were measured on abaxial surface compared with adaxial surface. Therefore, bifacial leaves can fix more carbon than leaves with two "sun-leaf-like" surfaces under ad-ab-alt irradiation. Photosynthetic research should be conducted under dynamic conditions that better mimic nature.