Ozone Response of Leaf Physiological and Stomatal Characteristics in Brassica juncea L. at Supraoptimal Temperatures

Plants are affected by the features of their surrounding environment, such as climate change and air pollution caused by anthropogenic activities. In particular, agricultural production is highly sensitive to environmental characteristics. Since no environmental factor is independent, the interactive effects of these factors on plants are essential for agricultural production. In this context, the interactive effects of ozone (O3) and supraoptimal temperatures remain unclear. Here, we investigated the physiological and stomatal characteristics of leaf mustard (Brassica juncea L.) in the presence of charcoal-filtered (target concentration, 10 ppb) and elevated (target concentration, 120 ppb) O3 concentrations and/or optimal (22/20 °C day/night) and supraoptimal temperatures (27/25 °C). Regarding physiological characteristics, the maximum rate of electron transport and triose phosphate use significantly decreased in the presence of elevated O3 at a supraoptimal temperature (OT conditions) compared with those in the presence of elevated O3 at an optimal temperature (O conditions). Total chlorophyll content was also significantly affected by supraoptimal temperature and elevated O3. The chlorophyll a/b ratio significantly reduced under OT conditions compared to C condition at 7 days after the beginning of exposure (DAE). Regarding stomatal characteristics, there was no significant difference in stomatal pore area between O and OT conditions, but stomatal density under OT conditions was significantly increased compared with that under O conditions. At 14 DAE, the levels of superoxide (O2-), which is a reactive oxygen species, were significantly increased under OT conditions compared with those under O conditions. Furthermore, leaf weight was significantly reduced under OT conditions compared with that under O conditions. Collectively, these results indicate that temperature is a key driver of the O3 response of B. juncea via changes in leaf physiological and stomatal characteristics.

Mannosylglycerate and Di-myo-Inositol Phosphate Have Interchangeable Roles during Adaptation of Pyrococcus furiosus to Heat Stress

ABSTRACTMarine hyperthermophiles accumulate small organic compounds, known as compatible solutes, in response to supraoptimal temperatures or salinities.Pyrococcus furiosusis a hyperthermophilic archaeon that grows optimally at temperatures near 100°C. This organism accumulates mannosylglycerate (MG) and di-myo-inositol phosphate (DIP) in response to osmotic and heat stress, respectively. It has been assumed that MG and DIP are involved in cell protection; however, firm evidence for the roles of these solutes in stress adaptation is still missing, largely due to the lack of genetic tools to produce suitable mutants of hyperthermophiles. Recently, such tools were developed forP. furiosus, making this organism an ideal target for that purpose. In this work, genes coding for the synthases in the biosynthetic pathways of MG and DIP were deleted by double-crossover homologous recombination. The growth profiles and solute patterns of the two mutants and the parent strain were investigated under optimal growth conditions and also at supraoptimal temperatures and NaCl concentrations. DIP was a suitable replacement for MG during heat stress, but substitution of MG for DIP and aspartate led to less efficient growth under conditions of osmotic stress. The results suggest that the cascade of molecular events leading to MG synthesis is tuned for osmotic adjustment, while the machinery for induction of DIP synthesis responds to either stress agent. MG protects cells against heat as effectively as DIP, despite the finding that the amount of DIP consistently increases in response to heat stress in the nine (hyper)thermophiles examined thus far.

High Maturation Temperature of Lettuce Seeds during Development Increased Ethylene Production and Germination at Elevated Temperatures

Ethylene synthesis and sensitivity, and their relation to germination at supraoptimal temperatures, were investigated in lettuce (Lactuca sativa L.) seeds matured at 30/20 °C [12-h day/night, high temperature matured (HTM)] or 20/10 °C [12-h day/night, low temperature matured (LTM)]. HTM seeds of both thermosensitive `Dark Green Boston' (DGB) and thermotolerant `Everglades' (EVE) had greater germination at a supraoptimal temperature (36 °C), in both light or dark, than LTM seeds of DGB and EVE. HTM seeds of DGB and EVE produced more ethylene during germination than LTM seeds, regardless of imbibition conditions. The ethylene action inhibitor, silver thiosulfate, led to reduced germination in both cultivars. The ethylene precursor, 1-aminocyclopropane-1-carboxylic acid at 10 mm increased germination of both cultivars at supraoptimal temperatures, whereas germination of HTM seeds was greater than that of LTM seeds. No differences in ethylene perception were detected between HTM and LTM germinating seeds using a triple response bioassay. This study demonstrated that at least one method through which seed maturation temperature influences lettuce germination is by affecting ethylene production.