The circadian clock, an internal oscillator with a period of approximately 24 hours, plays an important role in the regulation of biological processes, and an understanding of circadian rhythms can be employed to improve the quality of plant production. Many studies have measured the circadian rhythms of plants and estimate their circadian times. However, the circadian time estimation methods used in previous studies are difficult to apply to commercial crops because they require extraction of plant contents such as RNA, which involves destroying plant tissues. In this study, we sought to develop a nondestructive method for estimating circadian time in harvested leaves of green perilla (Perilla frutescens var. crispa f. viridis). The results of RNA sequencing (RNA-Seq) show that the gene expression of perillyl alcohol depend on the circadian time. A hyperspectral camera captured the light reflectance of 141 wavebands from 350 to 1,050 nm on leaves, and machine learning using the reflectance data successfully estimated the circadian time corresponding to the harvest time. The study results demonstrate the potential for the nondestructive use of hyperspectral reflectance data in circadian time estimation and its applicability to improving the quality of plant production.

In this study, we investigated the effect of continuous lighting for efficient plant growth during the reproductive period of everbearing strawberry (Fragaria×ananassa Duch. ‘Elan’) in a plant factory with white LED lighting. The plants were grown under different photoperiods (16 and 24 hours per day) and PPFDs (200, 300, 400, and 500 μmol m^-2 s^-1). The fruit yield was significantly lower at 200 μmol m^-2 s^-1 with either photoperiods and was significantly higher under 24 hours than 16 hours photoperiod. The rate of yield increase by intensifying PPFD was higher under 24 hours than under 16 hours photoperiod. The soluble solids and ascorbic acid content was significantly lower at 200 and 300 μmol m^-2 s^-1 with 16 hours photoperiod and 200 μmol m^-2 s^-1 with 24 hours photoperiod, but not different between the photoperiods. The anthocyanin content was significantly higher under 24 hours than under 16 hours photoperiod. The crop's productivity (g mol^-1) was higher under 24 hours than under 16 hours photoperiod and 300 μmol m^-2 s^-1 was higher than that of different PPFDs. These results indicate that continuous lighting at 300 μmol m^-2 s^-1 is more efficient for cultivating everbearing strawberry.

This research aimed to develop regression models that estimate starch concentration in saffron (Crocus sativus L.) corms from hyperspectral light scattering images. Light scattering images were captured from corms at wavelengths from 650 nm to 1,000 nm in 5 nm intervals. Light decay curves were measured, and the integrated value of the curve at each wavelength (S⋋) was calculated by image processing algorithms. The starch concentration in each captured corm was also measured using the phenol sulfuric acid colorimetric method for validation. A principal component regression method was applied to develop regression models in order to estimate the starch concentration from the S⋋ spectra. The results indicated that the estimation accuracy was high, and this model had practical use based on the ratio of performance to deviation (RPD) criterion (R_cal ² 0.913, standard error of calibration (SEC) = 1.33％ w.b., R_val = 0.932, standard error of validation (SEP) = 1.54％ w.b., RPD = 2.81). The S⋋ was found to be negatively correlated with starch concentration since light scattering increased considerably as starch concentration increased.

It has been proposed that cold stress applied to the root area promotes the production of reactive oxygen species and the increase in antioxidants levels in the plant body. However, changes in the balance between antioxidant activity and oxidative stress in plants under different levels of cold stress remain unexplored. Here, we assessed ascorbic acid content, superoxide dismutase activity, 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity, as proxies of antioxidant activity, and malondialdehyde (MDA) content, as an oxidative stress marker, in spinach. The root area was exposed to cold stress for 2, 4, 5, 6, and 7 days at various temperatures (4℃, 7℃, 10℃, and 14℃). Root chilling at 4℃ and 7℃ induced increases in ascorbic acid and DPPH scavenging levels, which were accompanied by the increase in MDA content, as cold exposure progressed. In contrast, root chilling at 10℃ and 14℃ increased antioxidant capacity without the increase in MDA concentration. The results of this study indicate that moderate cold stress applied to the root area of spinach could increase its antioxidant functions without accumulation of oxidative stress-related substances.

A combination of physical and chemical properties defines the rice quality. During grain filling, kernel location in the panicle and ambient air temperature influence its physicochemical properties thereby affecting the quality of rice. Here, we implemented principal component analysis (PCA) to reduce the dimensionality of 10 characteristics of 719 harvested rice samples, comprised of 10 varieties produced from 2010 to 2017 in regions of Hokkaido, Japan, into latent variables PC-1 and PC-2, which explained 69.7％ of the total variance. The model increased the interpretability of the relationship among physicochemical properties of brown rice and temperatures during grain filling in a visually intuitive manner. Results showed that high temperatures in August lowered the quality of samples produced in some regions in 2013 and 2016 by increasing the percentage of immature kernels and protein. Also, high temperatures in September increased the quality of samples produced in some regions in 2011 and 2012 by increasing the percentage of mature kernels and decreasing amylose and protein levels. Moreover, in 2015 and 2017, low temperatures in August and September increased amylose levels, which negatively affected rice quality attributes. This information could contribute to the production of high-quality and palatable rice demanded by Japanese consumers.

Panax ginseng C.A. Meyer is used extensively in traditional Asian medicines, and requires an efficient cultivation method. However, few studies have examined the effects of different light intensities on growth, photosynthetic rate, and accumulation of photosynthetic products throughout the whole-cultivation period. We investigated plant growth, photosynthetic rates, and accumulation of photosynthetic products in each organ under low (70 μmol m^-2 s^-1) and high (300 μmol m^-2 s^-1) light intensities and discussed methods of promoting productivity. During early growth stages, dry weight and photosynthetic rates under the high light treatment were significantly higher than those under the low light treatment. However, these values under the high treatment suddenly declined and the plants became dormant 30 days earlier than plants that received the low light treatment, which may be possibly related to accumulation of photosynthetic products in lamina. Our results indicate that ginseng's cultivation under high light conditions can shorten the cultivation period.