ELONGATED HYPOTCOTYL5 and SPINE BASE SIZE1 together mediate light-regulated spine expansion in cucumber.

Plant trichome development is influenced by diverse developmental and environmental signals, but the molecular mechanisms involved are not well understood in most plant species. Fruit spines (trichomes) are an important trait in cucumber (Cucumis sativus L.), as they affect both fruit smoothness and commercial quality. Spine Base Size1 (CsSBS1) has been identified as essential for regulating fruit spine size in cucumber. Here, we discovered that CsSBS1 controls a season-dependent phenotype of spine base size in wild-type plants. Decreased light intensity led to reduced expression of CsSBS1 and smaller spine base size in wild-type plants, but not in the mutants with CsSBS1 deletion. Additionally, knockout of CsSBS1 resulted in smaller fruit spine base size and eliminated the light-induced expansion of spines. Overexpression of CsSBS1 increased spine base size and rescued the decrease in spine base size under low light conditions. Further analysis revealed that ELONGATED HYPOTCOTYL5 (HY5), a major transcription factor involved in light signaling pathways, directly binds to the promoter of CsSBS1 and activates its expression. Knockout of CsHY5 led to smaller fruit spine base size and abolished the light-induced expansion of spines. Taken together, our study findings have clarified a CsHY5-CsSBS1 regulatory module that mediates light-regulated spine expansion in cucumber. This finding offers a strategy for cucumber breeders to develop fruit with stable appearance quality under changing light conditions.

Antibacterial and antibiofilm performance of low-frequency ultrasound against Escherichia coli O157:H7 and its application in fresh produce.

Ultrasound technology has been focused on due to its unique advantages in biofilm removal compared with traditional antibacterial methods. Herein, the anti-biofilm properties of low-frequency ultrasound (LFUS) were studied against Enterohemorrhagic Escherichia coli O157: H7 (E. coli O157:H7). After ultrasonication (20 kHz, 300 W) for 5 min, the removal rate of biofilm from polystyrene sheets reached up to 99.999 %. However, the bacterial cells could not be inactivated completely even extending the duration of ultrasonic irradiation to 30 min. Fortunately, this study indicated that LFUS could efficiently weaken the metabolic capacity and biofilm-forming ability of bacterial cells separated from biofilm. It could be associated with the removal of cell surface appendages and damage to cell membrane induced by mechanical vibration and acoustic cavitation. Besides, the genetic analysis proved that the transcription level of genes involved in curli formation was significantly down-regulated during ultrasonic irradiation, thus impeding the process of irreversible adhesion and cells aggregation. Finally, the actual application effect of LFUS was also evaluated in different fresh produces model. The results of this study would provide a theoretical basis for the further application of ultrasound in the food preservation.

Increasing the performance of cucumber (Cucumis sativus L.) seedlings by LED illumination.

Light is one of the most important limiting factors for photosynthesis and the production of plants, especially in the regions where natural environmental conditions do not provide sufficient sunlight, and there is a great dependence on artificial lighting to grow plants and produce food. The influence of light intensity, quality, and photoperiod on photosynthetic pigments content and some biochemical and growth traits of cucumber seedlings grown under controlled conditions was investigated. An orthogonal design based on a combination of different light irradiances, ratio of LEDs and photoperiods was used. Treaments consisted of three light irradiance regimes (80, 100, and 150 µmol m-2 s-1) provided by light-emitting diodes (LEDs) of different ratios of red and blue (R:B) (30:70, 50:50, and 70:30) and three different photoperiods (10/14, 12/12, and 14/10 h). The white light was used as a control/reference. Plant height, hypocotyl length, stem diameter, leaf area, and soluble sugar content were highest when exposed to LM9 (150 µmol m-2 s-1; R70:B30; 12/12 h) light mode, while the lowest values for the above parameters were obtained under LM1 (80 µmol m-2 s-1; R30:B70; 10/14 h). Higher pigments contents (chlorophyll a, chlorophyll b, and carotenoid) were obtained when light regime LM9 (150 µmol m-2 s-1; R70:B30; 12/12 h) was applied. In general, cucumber seedlings grown under the LM9 regime showed a significant increase in growth as well as photosynthetic capacity. It seems that the content of photosynthetic pigments is the key factor responsible for the performance of cucumber seedlings grown under different lighting modes, compared to other traits studied. We recommend monitoring the content of chlorophyll a, b, and their ratio value when studying the light requirement of cucumber plants.

Downsizing in plants-UV light induces pronounced morphological changes in the absence of stress.

Ultraviolet (UV) light induces a stocky phenotype in many plant species. In this study, we investigate this effect with regard to specific UV wavebands (UV-A or UV-B) and the cause for this dwarfing. UV-A- or UV-B-enrichment of growth light both resulted in a smaller cucumber (Cucumis sativus L.) phenotype, exhibiting decreased stem and petiole lengths and leaf area (LA). Effects were larger in plants grown in UV-B- than in UV-A-enriched light. In plants grown in UV-A-enriched light, decreases in stem and petiole lengths were similar independent of tissue age. In the presence of UV-B radiation, stems and petioles were progressively shorter the younger the tissue. Also, plants grown under UV-A-enriched light significantly reallocated photosynthates from shoot to root and also had thicker leaves with decreased specific LA. Our data therefore imply different morphological plant regulatory mechanisms under UV-A and UV-B radiation. There was no evidence of stress in the UV-exposed plants, neither in photosynthetic parameters, total chlorophyll content, or in accumulation of damaged DNA (cyclobutane pyrimidine dimers). The abscisic acid content of the plants also was consistent with non-stress conditions. Parameters such as total leaf antioxidant activity, leaf adaxial epidermal flavonol content and foliar total UV-absorbing pigment levels revealed successful UV acclimation of the plants. Thus, the UV-induced dwarfing, which displayed different phenotypes depending on UV wavelengths, occurred in healthy cucumber plants, implying a regulatory adjustment as part of the UV acclimation processes involving UV-A and/or UV-B photoreceptors.

Genetic and Transcriptomic Analysis Reveal the Molecular Basis of Photoperiod-Regulated Flowering in Xishuangbanna Cucumber (Cucumis sativus L. var. xishuangbannesis Qi et Yuan).

Xishuangbanna (XIS) cucumber (Cucumis sativus L. var. xishuangbannesis Qi et Yuan), is a botanical variety of cucumber cultivars native to southwest China that possesses excellent agronomic traits for cucumber improvement. However, breeding utilization of XIS cucumber is limited due to the current poor understanding of its photoperiod-sensitive flowering characteristics. In this study, genetic and transcriptomic analysis were conducted to reveal the molecular basis of photoperiod-regulated flowering in XIS cucumber. A major-effect QTL locus DFF1.1 was identified that controls the days to first flowering (DFF) of XIS cucumbers with a span of 1.38 Mb. Whole-genome re-sequencing data of 9 cucumber varieties with different flowering characteristics in response to photoperiod suggested that CsaNFYA1 was the candidate gene of DFF1.1, which harbored a single non-synonymous mutation in its fifth exon. Transcriptomic analysis revealed the positive roles of auxin and ethylene in accelerating flowering under short-day (SD) light-dark cycles when compared with equal-day/night treatment. Carbohydrate storage and high expression levels of related genes were important reasons explaining early flowering of XIS cucumber under SD conditions. By combining with the RNA-Seq data, the co-expression network suggested that CsaNFYA1 integrated multiple types of genes to regulate the flowering of XIS cucumber. Our findings explain the internal regulatory mechanisms of a photoperiodic flowering pathway. These findings may guide the use of photoperiod shifts to promote flowering of photoperiod-sensitive crops.

Early seedling response of six candidate crop species to increasing levels of blue light.

Light emitting diode (LED) lighting technology for crop production is advancing at a rapid pace, both in terms of the technology itself (e.g., spectral composition and efficiency), and the research that the technological advances have enabled. The application of LED technology for crop production was first explored as a tool for improving the safety and reliability of plant-based bioregenerative life-support systems for long duration human space exploration. Developing and optimizing the lighting environment (spectral quality and quantity) for bioregenerative life-support applications and other controlled environment plant production applications, such as microgreens and sprout production, continues to be an active area of research and LED technology development. This study examines the influence of monochromatic and dichromatic red and blue light on the early development of six food crop species; Cucumis sativa, Solanum lycopersicum, Glycine max, Raphanus sativus, Pisum sativum, and Capsicum annum. Results support previous findings that light responses are often species specific. The results also support the assertion that monochromatic light can interfere with the normal interaction of various photoreceptors (co-action disruption) resulting in intermediate and sometimes unpredictable responses to a given light environment. The nature of the responses reported inform both bioregenerative life-support designs as well as light quality selection for the production of controlled environment crops.

A New Perspective on the Effect of UV-B on l-Ascorbic Acid Metabolism in Cucumber Seedlings.

This study aimed to examine the effects of UV-B on AsA and gene expression in cucumber seedlings. Particular emphasis was placed on identifying genes that were responsive to UV-B to increase AsA levels and elucidate the key UV-B response pathway. We found that the activities of myo-inositol oxygenase (MIOX), galactono-1,4-lactone dehydrogenase (GLDH), ascorbate oxidase (AO), ascorbate peroxidase (APX), glutathione reductase (GR), dehydroascorbate reductase (DHAR), and the transcript levels of CsMIOX1, CsGLDH, CsAO2, CsAO4, CsGR1, CsAPX5, and CsDHAR1 significantly increased with UV-B exposure. These observations indicate that UV-B induces the expression of genes involved in d-mannose/l-galactose and myo-inositol pathways and the ascorbate-glutathione system. Moreover, several genes related to the low and high UV-B fluence responses were considered. CsHY5 and CsMYB60 were involved with the low-fluence response and appeared to be responsive from 2 to 28 h. Together, these data show that these genes respond to UV-B to increase AsA levels through the low-fluence UV-B response pathway.

Exogenous putrescine alleviates photoinhibition caused by salt stress through cooperation with cyclic electron flow in cucumber.

When plants suffer from abiotic stresses, cyclic electron flow (CEF) is induced for photo-protection. Putrescine (Put), a primary polyamine in chloroplasts, plays a critical role in stress tolerance. However, the relationship between CEF and Put in chloroplasts for photo-protection is unknown. In this study, we investigated the role of Put-induced CEF for salt tolerance in cucumber plants (Cucumis sativus L). Treatment with 90 mM NaCl and/or Put did not influence the maximum photochemical efficiency of PSII (Fv/Fm), but the photoactivity of PSI was severely inhibited by NaCl. Salt stress induced a high level of CEF; moreover, plants treated with both NaCl and Put exhibited much higher CEF activity and ATP accumulation than those exhibited by single-salt-treated plants to provide an adequate ATP/NADPH ratio for plant growth. Furthermore, Put decreased the trans-membrane proton gradient (ΔpH), which was accompanied by reduced pH-dependent non-photochemical quenching (NPQ) and an increased the effective quantum yield of PSII (Y(II)). The ratio of NADP+/NADPH increased significantly with Put in salt-stressed leaves compared with the ratio in leaves treated with NaCl, indicating that Put relieved over-reduction pressure at the PSI acceptor side caused by salt stress. Collectively, our results suggest that exogenous Put creates an excellent condition for CEF promotion: a large amount of pmf is predominantly stored as Δψ, resulting in moderate lumen pH and low NPQ, while maintaining high rates of ATP synthesis (high pmf).

UV regulates the expression of phenylpropanoid biosynthesis genes in cucumber (Cucumis sativus L.) in an organ and spectrum dependent manner.

Expression of cucumber (Cucumis sativus) genes encoding the phenylpropanoid and flavonoid biosynthetic enzymes phenylalanine ammonia lyase (PAL), cinnamic acid 4-hydroxylase (C4H), and chalcone synthase (CHS), was studied under control light conditions (photosynthetically active radiation, PAR) in root, stem, and leaf. Furthermore, the expression was quantified in leaves illuminated with PAR and supplemental ultraviolet-A (315-400 nm) or ultraviolet-B (280-315 nm) radiation. The expression patterns of all twelve CsPAL, three CsC4H, and three CsCHS genes were established. Among the genes regulated by UV two general expression patterns emerge. One pattern applies to genes primarily regulated by enriched UV-A illumination (pattern 1). Another pattern (pattern 2) was found for the genes regulated by enriched UV-B. Three of the pattern 2 genes (CsPAL4, CsPAL10, and CsCHS2) displayed a particular sub-pattern (pattern 2b) with transcription enriched by at least 30-fold. In contrast to the other genes studied, the promoters of the genes regulated according to pattern 2b contained a combination of a number of cis-acting regulatory elements (MREs, ACEs, and G-boxes) that may be of importance for the particularly high enhancement of expression under UV-B-containing light. The regulation of phenylpropanoid and flavonoid biosynthesis genes in cucumber resembles that of a number of other plants. However, cucumber, due to its greater size, is an attractive species for combining more detailed studies of the morphology, physiological parameters and fine regulation of spatial and temporal expression of key genes. This, in turn, can facilitate the quantitative investigation of the relationships among different promoter motifs, the expression levels of each of these three genes, and metabolite accumulation profiles.

Sensory Evaluation of Cucumbers Treated with Blue Light.

Blue light delivered at wavelengths of 405 to 470 nm has been demonstrated to inhibit growth of bacteria on foodstuffs. This study investigated the effect of a narrow band of visible light on the color, texture, and flavor (organoleptic) properties of cucumbers. Previous research in this area has focused on either broad-spectrum light or specifically the UV bands of energy. Two experiments were performed, a sensory evaluation and a discriminative test. in both experiments, half of the cucumbers were irradiated with 464 nm at 18 J/cm2 and half were left untreated. For the sensory evaluation, each evaluator received a treated cucumber slice and an untreated cucumber slice, then rated each slice based on organoleptic properties using a 9-item scoring sheet. For the two-out-of-five test, each evaluator received five slices, two slices of treated cucumber and three slices of untreated cucumber. The evaluators were asked to group the cucumber slices based on how the slices were prepared. Statistical analysis revealed that trained sensory evaluators were unable to distinguish between treated and untreated samples using sensory assessment. Blue light does not diminish the organoleptic qualities of the tested vegetables and appears to be at least as acceptable, from an organoleptic perspective, as other light decontamination methods.

Quantification of excitation energy distribution between photosystems based on a mechanistic model of photosynthetic electron transport.

Absorbed light energy is converted into excitation energy. The excitation energy is distributed to photosystems depending on the wavelength and drives photochemical reactions. A non-destructive, mechanistic and quantitative method for estimating the fraction of the excitation energy distributed to photosystem II (f) was developed. For the f values for two simultaneously provided actinic lights (ALs) with different spectral distributions to be estimated, photochemical yields of the photosystems were measured under the ALs and were then fitted to an electron transport model assuming the balance between the electron transport rates through the photosystems. For the method to be tested using leaves with different properties in terms of the long-term and short-term acclimation (adjustment of photosystem stoichiometry and state transition, respectively), the f values for red and far-red light (R and FR) were estimated in leaves grown (~1 week) under white light without and with supplemental FR and adapted (~10 min) to R without and with supplemental FR. The f values for R were clearly greater than those for FR and those of leaves grown with and adapted to supplemental FR tended to be higher than the controls. These results are consistent with previous studies and therefore support the validity of the proposed method.

High light aggravates functional limitations of cucumber canopy photosynthesis under salinity.

Background and Aims: Most crop species are glycophytes, and salinity stress is one of the most severe abiotic stresses reducing crop yields worldwide. Salinity affects plant architecture and physiological functions by different mechanisms, which vary largely between crop species and determine the susceptibility or tolerance of a crop species to salinity. Methods: Experimental data from greenhouse cucumber (Cucumis sativus), a salt-sensitive species, grown under three salinity levels were interpreted by combining a functional-structural plant model and quantitative limitation analysis of photosynthesis. This approach allowed the quantitative dissection of canopy photosynthetic limitations into architectural and functional limitations. Functional limitations were further dissected into stomatal (Ls), mesophyll (Lm) and biochemical (Lb). Key Results: Architectural limitations increased rapidly after the start of the salinity treatment and became stronger than the sum of functional limitations (Ls + Lm + Lb) under high salinity. Stomatal limitations resulted from ionic effects and were much stronger than biochemical limitations, indicating that canopy photosynthesis was more limited by the effects of leaf sodium on stomatal regulation than on photosynthetic enzymes. Sensitivity analyses suggested that the relative importance of salinity effects on architectural and functional limitations depends on light conditions, with high light aggravating functional limitations through salinity effects on stomatal limitations. Conclusions: Salinity tolerance of cucumber is more likely to be improved by traits related to leaf growth and stomatal regulation than by traits related to tissue tolerance to ion toxicity, especially under high light conditions.

Daily light integral and day light quality: Potentials and pitfalls of nighttime UV treatments on cucumber powdery mildew.

Nighttime ultraviolet (UV) radiation, if applied properly, has a significant potential for management of powdery mildews in many crop species. In this study, the role of growth light duration, irradiance, a combination of both (daily light integral) and light spectral quality (blue or red) on the efficacy of UV treatments against powdery mildew caused by Podosphaera xanthii and the growth performance of cucumber plants was studied in growth chambers. Increasing daily light integral provided by high-pressure sodium lamps (HPS) decreased efficacy of nighttime UV treatments against P. xanthii, but it increased plant growth. Furthermore, the efficacy of nighttime UV decreased when day length was increased from 16 to 20h at a constant daily light integral. The efficacy of nighttime UV increased if red light was applied after UV treatment, showing the possibility of day length extension without reducing the effect of UV. Increasing the dose of blue light during daytime reduced the efficacy of nighttime UV in controlling the disease, whereas blue deficient growth light (<6% of blue) caused UV mediated curling of young leaves. Furthermore, application of blue light after nighttime UV reduced its disease control efficacy. This showed the importance of maintaining a minimum of blue light in the growth light before nighttime UV treatment. Findings from this study showed that optimization of nighttime UV for management of powdery mildew is dependent on the spectral composition of the photosynthetically active radiation.

Overexpression of the rubisco activase gene improves growth and low temperature and weak light tolerance in Cucumis sativus.

Rubisco activase (RCA) is an important enzyme that can catalyze the carboxylation and oxygenation activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), which is involved in the photosynthetic carbon reduction cycle. Here, we studied the effects of changes in RCA activity on photosynthesis, growth and development, as well as the low temperature and weak light tolerance of RCA overexpressing transgenic cucumber (Cucumis sativus) plants. CsRCA overexpression increased the plant height, leaf area and dry matter, and decreased the root/top ratio in transgenic cucumber plants compared with the wild-type (WT) plants. Low temperature and low light stress led to decreases in the CsRCA expression and protein levels, the photosynthetic rate (Pn) and the stomatal conductance (Gs), but an increase in the intercellular CO2 (Ci) concentration in cucumber leaves. The actual photochemical efficiency and maximal photochemical efficiency of photosystem II in cucumber seedlings also declined, but the initial fluorescence increased during low temperature and weak light stress. Transgenic plants showed a lower decrease in the CsRCA expression level and actual and maximal photochemical efficiencies, as well as increases in the Ci and initial fluorescence relative to the WT plants. Low temperature and low light stress resulted in a significant increase in the malondialdehyde (MDA) content; however, this increase was reduced in transgenic plants compared with that in WT plants. Thus, the overexpression of CsRCA may promote the growth and low temperature and low light tolerance of cucumber plants in solar greenhouses.

Elimination of diazinon insecticide from cucumber surface by atmospheric pressure air-dielectric barrier discharge plasma.

The food industry is in a constant search for new technologies to improve the commercial sterilization process of agricultural commodities. Plasma treatment may offer a novel and efficient method for pesticide removal from agricultural product surfaces. To study the proposed technique of plasma food treatment, the degradation behavior of diazinon insecticide by air-dielectric barrier discharge (DBD) plasma was investigated. The authors studied the effect of different plasma powers and treatment times on pesticide concentration in liquid form and coated on the surface of cucumbers, where the diazinon residue was analyzed with mass spectroscopy gas chromatography. Our results suggest that atmospheric pressure air-DBD plasma is potentially effective for the degradation of diazinon insecticide, and mainly depends on related operating parameters, including plasma treatment time, discharge power, and pesticide concentrations. Based on the interaction between reactive oxygen species and electrons in the plasma with the diazinon molecule, two degradation pathway of diazinon during plasma treatment are proposed. It was also found that produced organophosphate pesticides are harmless and less hazardous compounds than diazinon.

Sensitivity of Seven Diverse Species to Blue and Green Light: Interactions with Photon Flux.

Despite decades of research, the effects of spectral quality on plant growth, and development are not well understood. Much of our current understanding comes from studies with daily integrated light levels that are less than 10% of summer sunlight thus making it difficult to characterize interactions between light quality and quantity. Several studies have reported that growth is increased under fluorescent lamps compared to mixtures of wavelengths from LEDs. Conclusions regarding the effect of green light fraction range from detrimental to beneficial. Here we report the effects of eight blue and green light fractions at two photosynthetic photon fluxes (PPF; 200 and 500 µmol m-2 s-1; with a daily light integral of 11.5 and 29 mol m-2 d-1) on growth (dry mass), leaf expansion, stem and petiole elongation, and whole-plant net assimilation of seven diverse plant species. The treatments included cool, neutral, and warm white LEDs, and combinations of blue, green and/or red LEDs. At the higher PPF (500), increasing blue light in increments from 11 to 28% reduced growth in tomato, cucumber, and pepper by 22, 26, and 14% respectively, but there was no statistically significant effect on radish, soybean, lettuce or wheat. At the lower PPF (200), increasing blue light reduced growth only in tomato (41%). The effects of blue light on growth were mediated by changes in leaf area and radiation capture, with minimal effects on whole-plant net-assimilation. In contrast to the significant effects of blue light, increasing green light in increments from 0 to 30% had a relatively small effect on growth, leaf area and net assimilation at either low or high PPF. Surprisingly, growth of three of the seven species was not reduced by a treatment with 93% green light compared to the broad spectrum treatments. Collectively, these results are consistent with a shade avoidance response associated with either low blue or high green light fractions.

Interaction between the spectral photon flux density distributions of light during growth and for measurements in net photosynthetic rates of cucumber leaves.

The net photosynthetic rate of a leaf becomes acclimated to the plant's environment during growth. These rates are often measured, evaluated and compared among leaves of plants grown under different light conditions. In this study, we compared net photosynthetic rates of cucumber leaves grown under white light-emitting diode (LED) light without and with supplemental far-red (FR) LED light (W- and WFR-leaves, respectively) under three different measuring light (ML) conditions: their respective growth light (GL), artificial sunlight (AS) and blue and red (BR) light. The difference in the measured photosynthetic rates between W- and WFR-leaves was greater under BR than under GL and AS. In other words, an interaction between supplemental FR light during growth and the spectral photon flux density distribution (SPD) of ML affected the measured net photosynthetic rates. We showed that the comparison and evaluation of leaf photosynthetic rates and characteristics can be biased depending on the SPD of ML, especially for plants grown under different photon flux densities in the FR waveband. We also investigated the mechanism of the interaction. We confirmed that the distribution of excitation energy between the two photosystems (PSs) changed in response to the SPD of GL, and that this change resulted in the interaction, as suggested in previous reports. However, changes in PS stoichiometry could not completely explain the adjustment in excitation energy distribution observed in this study, suggesting that other mechanisms may be involved in the interaction.

Inheritance and quantitative trait locus analysis of low-light tolerance in cucumber (Cucumis sativus L.).

The low-light tolerance index was investigated in a set of 123 F2:3 lines during the seedling stage across 2 seasons, and the heredity of low-light tolerance was assessed via different ge-netic analysis methods. The results of the classical analysis showed that low-light tolerance is controlled by an additive-dominant poly-gene, and the polygenic inheritance rate of separate generations was >30%. In addition, 5 quantitative trait loci (QTLs) exhibited a low-light tolerance index across both seasons, including 2 QTLs (Llti1.1 and Llti1.2) on the 1st linkage group (variances of 6.0 and 9.5%) and 3 QTLs (Llti2.1, Llti2.1, and Llti2.1) on the 2nd linkage group (variances of 10.1-14.0%). The classical analysis method and QTL information on the heredity of low-light tolerance showed that it is controlled by several major genes and a mini-polygene. The results will facilitate the breeding of resistance to low-light stress in cucumber.

Rate Constants of PSII Photoinhibition and its Repair, and PSII Fluorescence Parameters in Field Plants in Relation to their Growth Light Environments.

The extent of photoinhibition of PSII is determined by a balance between the rate of photodamage to PSII and that of repair of the damaged PSII. It has already been indicated that the rate constants of photodamage (kpi) and repair (krec) of the leaves differ depending on their growth light environment. However, there are no studies using plants in the field. We examined these rate constants and fluorescence parameters of several field-grown plants to determine inter-relationships between these values and the growth environment. The kpi values were strongly related to the excess energy, EY, of the puddle model and non-regulated energy dissipation, Y(NO), of the lake model, both multiplied by the photosynthetically active photon flux density (PPFD) level during the photoinhibitory treatment. In contrast, the krec values corrected against in situ air temperature were very strongly related to the daily PPFD level. The plants from the fields showed higher NPQ than the chamber-grown plants, probably because these field plants acclimated to stronger lightflecks than the averaged growth PPFD. Comparing chamber-grown plants and the field plants, we showed that kpi is determined by the incident light level and the photosynthetic capacities such as in situ rate of PSII electron transport and non-photochemical quenching (NPQ) [e.g. Y(NO)×PPFD] and that krec is mostly determined by the growth light and temperature levels.

Water balance altered in cucumber plants infected with Fusarium oxysporum f. sp. cucumerinum.

Fusarium wilt is caused by the infection and growth of the fungus Fusarium oxysporum in the xylem of host plants. The physiological responses of cucumbers that are infected with Fusarium oxysporum f. sp. cucumerinum (FOC) was studied in pot and hydroponic experiments in a greenhouse. The results showed that although water absorption and stem hydraulic conductance decreased markedly in infected plants, large amounts of red ink accumulated in the leaves of infected cucumber plants. The transpiration rate (E) and stomatal conductance (gs) of the infected plants were significantly reduced, but the E/gs was higher than healthy plants. We further found that there was a positive correlation between leaf membrane injury and E/gs, indicating that the leaf cell membrane injury increased the non-stomatal water loss from infected plants. The fusaric acid (FA), which was detected in the infected plant, resulted in damage to the leaf cell membranes and an increase in E/gs, suggesting that FA plays an important role in non-stomatal water loss. In conclusion, leaf cell membrane injury in the soil-borne Fusarium wilt of cucumber plants induced uncontrolled water loss from damaged cells. FA plays a critical role in accelerating the development of Fusarium wilt in cucumber plants.