The response in growth and gas exchange to a flooding condition was characterized with 8 cultivars of greengram (Vigna radiata (L.) Wilczek). Pot-grown plants were subjected to 6-d flooding and 6-d recovery treatment. The flooding treatment had serious effects on the gas exchange and electron transport of 7 cultivars except for cv. KP, while the damages were lenient in cv. KP. KP was characterized by maintaining relatively higher stomatal conductance, mesophyll conductance and photochemical efficiency of photosystem II, which was attributed to sustaining the CO2 assimilation under flooding stress. KP was also superior in photosynthetic sustainment than other 7 cultivars under recovery treatment, which was attributable to the fact that this cultivar recovered stomatal conductance, mesophyll conductance, electron transport and the ratio of photorespiration to total carbon assimilation. These results in cv. KP lead to higher plant growth in relation to leaf area extension and dry matter.
An open-flow chamber equipped with a multiple CO2-gas analyzing system (MGA) was developed for the continuous measurement of the soil respiration rate in a greenhouse. Two fans attached to the chamber facilitate airflow through it. The air from the inlet and outlet of the chamber is sampled, and then, its CO2-gas concentration is analyzed by the MGA, which consists of an infrared gas analyzer, an air pump, a flow meter, and a programmable data logger. The rate of soil respiration is evaluated based on the difference in CO2 concentration between the inlet and outlet air, and on the air flow rate. The chambers were installed into the ridge and the furrow, and the characteristics of soil respiration were then analyzed. The hourly change in the soil respiration rate was almost constant, and it was higher in the ridge (3.2 μmol m−2 s−1) than in the furrow (0.5 μmol m−2 s−1), which can be attributed to the small amount of surface soil in the furrow. On the other hand, the soil respiration rate on a greenhouse scale was roughly estimated and compared with the rate of CO2 loss from the greenhouse to the ambient air. The rates were nearly equal when the CO2 concentration in the greenhouse was constant. These results suggest that the soil chamber with the MGA is a useful tool for the dynamic analysis of soil respiration in greenhouses.
We examined the effects of 25 d of continuous ultraviolet-B (UV-B) irradiation (0.57 W m−2) on cucumber (Cucumis sativus L.) seedlings. The leaf areas of all unfolded true leaves and the plant height were reduced considerably by 25 d of UV-B irradiation. In each true leaf, both the epidermal cell area and the total epidermal cell number were reduced after UV-B treatment. The expression of five cell cycle-related genes (Cs Cyclin A [CsCycA], CsCycB, CsCycD3;1, CsCycD3;2, and Cs Cyclin-dependent kinase A [CsCDKA]) in the shoot apical meristem (SAM) was reduced within 48 h of UV-B exposure. These results indicate that continuous UV-B irradiation inhibits the cell cycle in the SAM and thus reduces cell division and cell expansion in true leaves. On the other hand, the number of unfolded true leaves increased after exposure to UV-B for 15–25 d. Furthermore, 60% of the plants produced male flower buds after exposure to UV-B for 25 d. Therefore, continuous long-term UV-B irradiation affects the SAM of cucumber seedlings, resulting in reduced plant growth, but does accelerate various developmental stages.
Circadian rhythms are observed in many physiological events in plant, and clock genes orchestrate the rhythms of expression of many genes. Precise environmental control of circadian rhythms provides a key technology for enhancing plant growth in artificial environments. In this study, we investigated the basic properties of a circadian rhythm for establishment of its control engineering in lettuce (Lactuca sativa L.). Bioluminescence of transgenic lettuce carrying an AtCCA1::LUC construct as a reporter of circadian gene expression was measured in young lettuce seedlings. We observed three basic properties; free-running circadian rhythms under constant conditions without day-night cycles, entrainment to red and blue light cycles with 12 h light-12 h dark period, and temperature compensation of a free-running period in three lettuce cultivars (Cisco, Cos, Greenwave). In addition, a light-quality dependence of the free-running period and sensitivity to blue-light cycles with small amplitude (20% of variance in average light intensity) and non-24 h period were also observed. The results in this study indicated that it is possible to control lettuce circadian rhythms by non-24 h period light cycles in LED illumination. It will play an important role in the research of control engineering for the circadian clock of lettuce in closed plant factories with artificial lighting.
Recently, microwave power transmission applications have been studied in various situations. When considering microwave power transmission applications in agriculture, the effects of microwave on crops must be carefully examined, especially in strictly controlled environment under long-term exposure. Effects of long-term exposure to 2.45 GHz microwave on the growth of Spinacia oleracea in pots were examined in 1, 3, and 5 week experiments under the controlled environment of a growth chamber. Each plant were scanned and processed by image processing software. Dry matter weight and leaf area was measured and compared between control plots (no microwave exposure) and experimental plots with microwave exposure. In the 1 and 3 week experiments, no significance was found in dry matter, fresh matter (1 week), fresh matter of above-ground part (3 weeks), cotyledon area, the second leaves area (3 weeks), and the third leaves area (3 weeks) at 5% level by Wilcoxon signed-rank test. In the 5 week experiment, a significance was observed in dry matter, fresh matter of above-ground part, and the third leaves area by Wilcoxon signed-rank test at 5% level. The cotyledon area, the second leaves area, and the forth leaves area did not show the significance. The mean dry matter, fresh matter of above-ground part, and the third leaves area of the experimental plot increased by 60%, 52%, and 57% respectively, compared to the control plot. The results indicated the possibility that the outer change of the plants required a certain period after enough accumulated effects. Another Wilcoxon signed-rank test at the 5% significance level for the 5 week experiment, excluding the pots near the patch antenna, indicated the significance of dry matter and fresh matter of the above-ground part. Eliminating the strong thermal effects on plants by this additional analysis, these results suggest little or no difference in temperature.
In order to develop new geranium cultivars with characteristics not found in existing cultivars, such as heat tolerance and odorless leaves, intercrosses between geranium and four wild species of section Ciconium were carried out. The intercrosses between geranium and P. frutetorum, P. inquinans, and P. salmoneum showed relatively high compatibility, regardless of the seed parent. Their F1 plants grew vigorously and developed normally. On the contrary, some F1 plants derived from the intercross with P. acetosum developed chlorosis and variegation in the leaves, with many plants dying in the early stage of growth. However, the F1 plants that survived showed high pollen fertility, and F2 and BC1 generations could be obtained easily. Some F2 plants showed odorless, and all BC1 plants had non-trichome leaves. Heat tolerance trial was carried out in a greenhouse from spring to autumn using all plants of F1, F2 and BC1 obtained from backcrossing to geranium. Favorable plants with an increased number of flowering peduncles even in summer were selected from the BC1 plants derived from P. frutetorum, P. acetosum, and P. salmoneum. These progeny can be used as breeding material for producing promising new heat-tolerant geraniums with odorless leaves.
Night break effect is widely used in chrysanthemum production by applying incandescent (INC) lamps to inhibit flowering of chrysanthemum in order to obtain longer shoots. To save energy, LED lamps had been developed as a new light source and used in agriculture. Since there is limited research on chrysanthemums grown in LED light culture, we studied the night break effect by using several different wavelengths of LED lamps. Red (R) light from LED-630 and LED-660 had perfect inhibition on floral bud differentiation in ‘Jimba,’ but could not inhibit that in ‘Iwa no hakusen’ chrysanthemums. The far-red (FR) light of LED-735 had no effect on the inhibition of floral bud differentiation in ‘Jimba,’ but it was delayed in ‘Iwa no hakusen.’ Treatments of LED-690 and INC lamps inhibited floral bud differentiation in ‘Jimba’ and strongly delayed that in ‘Iwa no hakusen.’ Treatments of a combination of R light of LED-660 and FR light of LED-735 inhibited floral bud differentiation in both the cultivars.
Night-break has an inhibitory effect on flowering in short-day (SD) plants and is widely used in chrysanthemum (Chrysanthemum morifolium Ramat.) production for flowering regulation. Although LED lamps are a new light source in agriculture, there have been few studies on chrysanthemums under LED light cultures. One incandescent (INC) lamp and four monochromatic LED lamps, with peak emissions at 630 nm, 660 nm, 690 nm, 735 nm, and 660+735 nm, respectively, were used as night-break light sources in chrysanthemum cultivation. Shoot elongation was enhanced significantly in both ‘Jimba’ and ‘Iwa no hakusen’ under treatments using light sources that emitted far-red (FR) light (LED-735, LED-660+735, and the INC lamp) compared with SD, LED-630, and LED-660 treatments. Photon flux density (PFD) in the range 700–799 nm was significantly related to the internode length. As shoot elongation under FR light increased internode elongation but not node number, it is probable that internode elongation was caused by gibberellin biosynthesis induced by FR light. Shoot lengths under the LED-630 and LED-660 light regimes, which only emitted red light, were not significantly different from those under control conditions. There was no significant relationship between internode length and P fr/P total, or the R/FR ratio.
The amount of growth and the vaccine productivity of vaccine-producing lettuce with different cultivation periods were examined in order to determine the optimal harvesting time of transgenic lettuce cultivated in a closed plant factory. Lettuce was planted in a hydroponic system and harvested at 20, 30, 40, and 50 d, and the concentrations of the total soluble protein (TSP) and the double repeated B subunit of Shiga toxin 2e (2×Stx2eB) were measured. The dry-matter weight of leaves per plant increased in a linear fashion until 50 d. Although the TSP concentration decreased continually from day 20 to 50 and 2×Stx2eB concentration decreased from day 40 to 50, the yield per plant of both TSP and 2×Stx2eB increased exponentially until day 50. According to the calculation based on these results, the optimal harvesting time to maximize the annual production of 2×Stx2eB was revealed to be 30 d. Since the optimal 30-d harvesting time is the same to the general harvesting time for commercial lettuce production in a closed plant factory, the capability to utilize the existing closed plant factory lettuce production system could be a big advantage for vaccine-producing lettuce in terms of the cost performance.