We investigated anthocyanin concentration and the expression of anthocyanin biosynthesis related genes in strawberry ‘Sachinoka’ (Fragaria×ananassa Duch.) grown at control regime (20/15°C, 14/10 h, day/night) or high temperature regime (30/15°C, 14/10 h). In Experiment 1, fruits were harvested at different color stages. In the control treatment, the anthocyanin concentration increased as fruit ripened, and was highest at the fully ripe stage. In the high-temperature treatment, however, it was significantly lower at the fully ripe stage. These results were relevant with the peak value of expression of anthocyanin biosynthesis genes which was inhibited in fruits grow at high temperature regime. In Experiment 2, we applied high temperature at different fruit color stages to test the effect of the timing of high temperature stress on coloring. When exposed fruit to high temperature after half ripe stage, the anthocyanin concentration and gene expression in fully ripe fruit were not significantly different from the control. But in fruit exposed before half ripe stage, the anthocyanin concentration and gene expression significantly reduced. These results indicate that the level of gene expression of anthocyanin biosynthesis is affected by the timing of exposure fruit to high temperature stress.
When chlorophyll fluorescence is measured on leaves with restricted gas exchange by a transparent film or Vaseline seal, the obtained electron transport rate in photosystem II (JPSIIseal) was reported show a positive linear correlation with the maximum photosynthetic activity. This is because in a sealed leaf, the CO2 substrate for ribulose-1,5-bisphosphate-carboxylase/oxygenase is derived primarily from photorespiration. Our objective was to clarify whether the JPSIIseal also corresponds to photosynthetic activity in tomato leaflets. The JPSIIseal of a leaflet had a positive linear relationship with the gross photosynthetic rate at 30 mmol mol−1 oxygen. This suggests that the JPSIIseal represents the photosynthetic carbon fixation activity. Maintaining a tight seal with the transparent film was difficult because of the gap between the film and leaflet during transpiration. In contrast, the tight seal with Vaseline enabled measurements for at least 30 min. Additionally, the measurements could be completed faster for the Vaseline-sealed leaflets. The variation in the JPSIIseal of tomato leaflets increased with increasing leaf age. The leaf JPSIIseal (i.e., calculated based on 10–13 leaflets) decreased with increasing leaf age. We propose that chlorophyll fluorescence measurements for Vaseline-sealed leaflets may be useful for comprehensive analyses of tomato leaf photosynthetic characteristics.
To evaluate the effects of leaf wetting on midday depression of photosynthesis in horticultural crops, we analyzed leaf gas exchange (transpiration rate, stomatal conductance, photosynthetic rate) of tomato plants under two different treatments (the Wet treatment and No-wet treatment as control). The gas exchange was measured at 11:00 (the time at which leaf gas exchange was assumed to be active) and 14:00 (the time at which leaf gas exchange was assumed to be inactive due to midday depression) on the clear days of November 2 to 7, 2016. The gas exchange measurements in the Wet treatment were conducted just after droplets on the leaf surface had evaporated. In the No-wet treatment, transpiration rate, stomatal conductance, and photosynthetic rate at 14:00 were decreased compared to those at 11:00. This suggests that midday depression occurred due to stomatal closure induced by excessive transpirational water loss. In contrast, in the Wet treatment, there was no such depression of leaf gas exchange, suggesting that leaf wetting might contribute to maintaining stomatal aperture through improving leaf water status. Thus, leaf wetting could avoid midday depression of photosynthesis in tomato plants.
Solar simulating light (SSL) has been widely used for evaluating the performance of photovoltaic cells and algal photosynthesis. Green plants and algae utilize chlorophylls, thus, the chlorophyll-targeting light components mostly contribute to photosynthesis. In contrast, near infrared (NIR) light hardly energizes photosynthesis. Since SSL spectrum covers a wide range of light from ultraviolet to NIR, we examined the roles of NIR components in SSL during photosynthetic O2 evolution in Synechocystis (sp. PCC6803), by selectively and step-wisely eliminating the NIR using several NIR-cut filters. Here, the effects of intact SSL spectrum and the NIR-cut filtered SSL spectra (lacking NIR light greater than 690, 710, 750, or 810 nm) were examined. We observed that the 750 nm shortpass filter lowered the maximal photosynthetic velocity (Pmax), and concomitantly, the Michaelis constant-like value for light intensity (Kj), whereas no significant change was observed with the 810 nm shortpass filter. We concluded that the 750–810 nm band may contain the photosynthesis-stimulating NIR component acting differently from the known phenomenon (Emerson effect). In contrast, Synechocystis unexpectedly regained the photosynthetic performance by eliminating all range of NIR (>710 nm), suggesting that 710–750 nm far-red band corresponding to the absorption band for bacterial phytochrome is possibly inhibitory to photosynthesis.