The effects of glycine betaine (GB) under heat stress conditions were studied in three marigold cultivars, namely, 'Narai Yellow', 'Bali Gold', and 'Columbus Orange'. GB was foliarly applied to the seedlings 24 hours before transfer to either 25°C/25°C or 39°C/29°C (day/night) conditions for 15 days. Heat stress conditions caused photoinhibition and low levels of CO 2 assimilation rate (A), stomatal conductance (g s ), and transpiration rate (E) in all marigold cultivars compared with those of control plants grown under 25°C/25°C conditions. The accumulation of reactive oxygen species (ROS), lipid peroxidation, and cell death were also higher under heat stress in all cultivars compared with those in the control. However, the effect of heat stress on relative water content (RWC) was statistically significant only in 'Bali Gold'. Foliar applications of GB at 0.5 and 1 mM alleviated photoinhibition and resulted in higher A, g s , and E in all marigold cultivars compared with those in the control under heat stress. Application of GB also resulted in lower levels of hydrogen peroxide, superoxide, lipid peroxidation, and cell death in all cultivars. The effect of GB on improving RWC was significant only in 'Bali Gold'. In most cases, there were no significant differences between the effects of GB at 0.5 and 1 mM. The effect of GB seems to be very consistent across all marigold cultivars, as suggested by the lack of interaction between this effect and cultivars in most of the parameters that were studied. Overall, these results indicate that the foliar application of GB could possibly be used to mitigate the effect of heat stress in marigold.

Understanding the effect of light on stomatal behavior is mandatory for plant cultivation under controlled environmental systems. In this study, the effects of LED light quality and intensity on daily stomatal conductance (gs), stomatal aperture movement and stomatal density were investigated in petunia (Petunia hybrida Vilm.) plants under a semi-closed system. Three petunia cultivars, namely 'Coral', 'Purple' and 'Red', were grown under different light quality and quantity for 1 month and then all the parameters were measured. Results showed that 'Coral' exhibited overall higher gs than 'Purple' and 'Red'. Light quality significantly affected gs, width of stomatal aperture and stomatal density of all cultivars. The effect of light quality on gs and width of stomata aperture was strongly depended upon cultivar and time of day and there was a two-way interaction. Light intensity did not affect daily fluctuation pattern of gs but did affect the amplitude of the fluctuation. In contrast to the effect of light quality, the effect of light intensity was independent of cultivar and time of day. There was no obvious correlation between gs and width of either adaxial or abaxial stomata apertures during photoperiod. Light intensity significantly affected stomatal density which could partially explain an increasing of gs in response to increasing light intensity.

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The flower seed industry is facing a variety of issues related to ongoing climate change. The closed plant production system (CPPS) may be a solution to these issues as the environment inside the system can be fully controlled to allow seed production from many plant species. In this study, the influence of an artificial light condition, one of the key factors influencing plant growth and development in CPPS, on gloxinia (Sinningia speciosa) seed production was investigated. Three types of lights: warm white (3200 K), daylight ( 6500K), and red and blue lights (RB) at a photosynthetic photon flux density of either 150 or 200 μmol•m −2 •s −1 were applied to gloxinia plants. The highest vegetative growth was found in plants grown under 3200 K at 200 μmol•m −2 •s −1 light but this did not correlate with seed yield. Plants grown under RB light exhibited the most compact canopy. Day to anthesis, flower diameter and percentage of pod set were not significantly different among the light treatments. Gloxinia plants grown under RB light at 150 μmol•m −2 •s −1 had the highest seed yield, which is attributed to higher pollen elongation and flower number. The effect of light quality on seed yield is strongly dependent on light intensity. Moreover, treatment with RB light resulted in longer pollen grains and seeds than the other light quality treatments. Gloxinia seeds from all light treatment exhibited more than 80% germination and similar seed vigor. The results from this study suggest that CPPS, with suitable light conditions, may be used for commercial gloxinia seed production.

Abstract. Many studies have investigated the impact of a single calcium salt on plant physiology under heat-stress, but it is difficult to determine the effect of calcium from those of its counterions. To address this, we investigated calcium-mediated heat tolerance in tomato seedlings using foliar sprays of four different salt solutions: CaCl2, CaNO3, MgCl2 or KNO3. The application of CaCl2 and CaNO3 improved the operating efficiency of photosystem II (PSII) in the light-adapted state (ΦPSII), maximum quantum efficiency of PSII in the dark-adapted state (Fv/Fm), and the CO2 assimilation rate under the heat-stress condition. In contrast, the application of MgCl2 and KNO3 had no significant effect on those parameters. The application of CaCl2 and CaNO3 resulted in a lower production of hydrogen peroxide, superoxide, and cell death than the heat-stressed control plants. The application of MgCl2 and KNO3 also resulted in lower hydrogen peroxide and superoxide production, but to a lesser extent. Leaf osmotic potential values of seedlings treated with the salt solutions were lower than the control.The online version of the original article can be found under