Environmental Factors Regulate Plant Secondary Metabolites.

Abiotic environmental stresses can alter plant metabolism, leading to inhibition or promotion of secondary metabolites. Although the crucial roles of these compounds in plant acclimation and defense are well known, their response to climate change is poorly understood. As the effects of climate change have been increasing, their regulatory aspects on plant secondary metabolism becomes increasingly important. Effects of individual climate change components, including high temperature, elevated carbon dioxide, drought stress, enhanced ultraviolet-B radiation, and their interactions on secondary metabolites, such as phenolics, terpenes, and alkaloids, continue to be studied as evidence mounting. It is important to understand those aspects of secondary metabolites that shape the success of certain plants in the future. This review aims to present and synthesize recent advances in the effects of climate change on secondary metabolism, delving from the molecular aspects to the organismal effects of an increased or decreased concentration of these compounds. A thorough analysis of the current knowledge about the effects of climate change components on plant secondary metabolites should provide us with the required information regarding plant performance under climate change conditions. Further studies should provide more insight into the understanding of multiple environmental factors effects on plant secondary metabolites.

Individual and interactive effects of temperature and light intensity on canola growth, physiological characteristics and methane emissions.

Earlier studies have shown that plants produce methane (CH4) under aerobic conditions, and that this emission is not microbial in nature. However, the precursors of aerobic CH4 remain under debate, and the combined effects of environmental factors on plant-derived CH4 requires further attention. The objective of this study was to determine the interactive effects of temperature and light intensity on CH4 and other relevant plant parameters in canola (Brassica napus L.). Plants were grown under two temperature regimes (22/18 °C and 28/24 °C, 16 h light/8 h dark) and two light intensities (300 and 600 µmol photons m-2 s-1) for 21 days after one week of growth under 22/18 °C (16 h light/8 h dark). In this study, higher temperature had little effects on CH4 emissions from plants, indicating the mitigating effects of higher light intensity. Higher light intensity, however, significantly decreased CH4, which was inversely related to plant dry mass. Higher light intensity decreased stem height, leaf area ratio, chlorophyll, nitrogen balance index, leaf moisture, methionine (Met) and ethylene (C2H4), but increased specific leaf mass, photochemical quenching, flavonoids, epicuticular wax, lysine and tyrosine. The results revealed that increased CH4 emissions from plants could be related to changes in plant physiological activities, which portrayed themselves in increased C2H4 evolution, and methylated amino acids, such as Met. We conclude that higher light intensity reduces Met and, in turn, CH4 and C2H4 emissions, but lower light intensity enhances CH4 formation through cleavage of methyl group of amino acids by reactive oxygen species, as previously suggested.

Environmental Factors Influence Plant Vascular System and Water Regulation.

Developmental initiation of plant vascular tissue, including xylem and phloem, from the vascular cambium depends on environmental factors, such as temperature and precipitation. Proper formation of vascular tissue is critical for the transpiration stream, along with photosynthesis as a whole. While effects of individual environmental factors on the transpiration stream are well studied, interactive effects of multiple stress factors are underrepresented. As expected, climate change will result in plants experiencing multiple co-occurring environmental stress factors, which require further studies. Also, the effects of the main climate change components (carbon dioxide, temperature, and drought) on vascular cambium are not well understood. This review aims at synthesizing current knowledge regarding the effects of the main climate change components on the initiation and differentiation of vascular cambium, the transpiration stream, and photosynthesis. We predict that combined environmental factors will result in increased diameter and density of xylem vessels or tracheids in the absence of water stress. However, drought may decrease the density of xylem vessels or tracheids. All interactive combinations are expected to increase vascular cell wall thickness, and therefore increase carbon allocation to these tissues. A comprehensive study of the effects of multiple environmental factors on plant vascular tissue and water regulation should help us understand plant responses to climate change.

Unravelling the effects of blue light on aerobic methane emissions from canola.

It is now well documented that plants produce methane (CH4) under aerobic conditions. However, the nature of methane production in plants and all the potential precursors and environmental factors that can be involved in the process are not fully understood. Earlier studies have suggested several chemical compounds, including the amino acid methionine, as precursors of aerobic methane in plants, but none have explored other amino acids as potential precursors or blue light as a driving force of methane emission. We examined the effects of blue light, and the promoter or inhibitor of endogenous ethylene on methane and ethylene emissions, amino acids, and some plant physiological parameters in canola (Brassica napus). Plants were grown under four light conditions: no supplemental blue light, and low, medium, or high blue light, and exposed to three chemical treatments: no chemical application, ethylene promoter (kinetin), or ethylene inhibitor (silver nitrate). Regardless of chemical treatment, blue light significantly increased methane emission, which was accompanied by decreased plant biomass, gas exchange, and flavonoids, but by increased wax, and most amino acids. This study revealed that blue light drives aerobic methane emission from plants by releasing of methyl group from a number of amino acids, and that the methane production in plants may have several pathways.

Light quality and quantity regulate aerobic methane emissions from plants.

Studies have been mounting in support of the finding that plants release aerobic methane (CH4 ), and that these emissions are increased by both short-term and long-term environmental stress. It remains unknown whether or not they are affected by variation in light quantity and quality, whether emissions change over time, and whether they are influenced by physiological parameters. Light is the primary energy source of plants, and therefore an important regulator of plant growth and development. Both shade-intolerant sunflower and shade-tolerant chrysanthemum were investigated for the release of aerobic CH4 emissions, using either low or high light intensity, and varying light quality, including control, low or normal red:far-red ratio (R:FR), and low or high levels of blue, to discern the relationship between light and CH4 emissions. It was found that low levels of light act as an environmental stress, facilitating CH4 release from both species. R:FR and blue lights increased emissions under low light, but the results varied with species, providing evidence that both light quantity and quality regulate CH4 emissions. Emission rates of 6.79-41.13 ng g-1 DW h-1 and 18.53-180.25 ng g-1 DW h-1 were observed for sunflower and chrysanthemum, respectively. Moreover, emissions decreased with age as plants acclimated to environmental conditions. Since effects were similar in both species, there may be a common trend among a number of shade-tolerant and shade-intolerant species. Light quantity and quality are influenced by factors including cloud covering, so it is important to know how plants will be affected in the context of aerobic CH4 emissions.