Hi,

I think that drought stress as environment factor should affect composition of phenolic acids.

Please check these PDF attachments.

As my experience we saw increase in phenolic compound of leaves and root exudate in drought 

Thank you all dear fellows

in our studies on natural resources, mainly medicinal and aromatic plants in different localities in Egyptian deserts, we can see plants can accumulate a high percentages of secondary metabolites under harsh desert conditions especially drought or salinity. So during summer months all plant parts especially aerial parts accumulate  a high percentages of phenolic compounds.

Dear Fatma Aly,

I agree with you as I found a likewise trend in my study that with increasing drought stress, the accumulation of phenolic acids increased but what opinion or experience you have if there is increased humidity in summer?? Does rainfall improves secondary metabolites accumulation in comparison with dry months??

Dear Wasif Nouman

          Specimens of same plant species growing under different environmental conditions show significant differences in the production and accumulation of the primary and secondary metabolites. Influenced by environmental factors, respective group of secondary metabolites act as a chemical interface between the plant and its environment. The chemical interaction between plants and their environment is mediated mainly by the biosynthesis of secondary metabolites, which exert their biological roles.

          Therefore, the study of these variations is very useful in the chemical characterization of plants of the same species which are collected from different regions and this is when the different geographical origin of a plant material is taken into account.

          Some processes can be the main sources of variation in the levels of metabolites for individual plant species. These processes involve long term acclimation or local adaptation, seasonal differences related to phenology or environmental changes in the biotic and abiotic factors, geographical differences involving different populations (genetic differences within a plant species), or different environmental conditions of the growth location of the species individuals, especially when they have genetic homogeneity (i.e. cultivars and/or clones).

          The environmental factors include temperature, rainfall, humidity and solar radiation as well as the amount of soil macro-and micronutrients which proved to correlate to variations in the sugar and nucleoside content as well as secondary metabolite composition of the plants.

          An interesting aspect that can be observed is that the environmental factors do not seem to exert a constant effect on the entire metabolism of the plant, so that each respective plant part responds differently to changes in environmental conditions.

          Several climate factors such as water availability, temperature and solar radiation are well described as being able to influence the production of metabolites. Thus, plants under conditions of stress induced by climate factors (i.e. drought, high temperatures, freezing, wide thermal amplitude, high levels of solar radiation) may show changes in the production of different metabolite classes. The availability of water is a known factor related to the variation in the production of metabolites in plants.

          It can be observed that samples collected during the rainiest periods tend to cluster and were rich in primary metabolites such as sugars and nucleosides. Leaf and stem samples collected during the drier periods were rich in secondary metabolites particularly in the cold months. Collected samples of plants during the transition period between the dry and rainy seasons yielded intermediate levels of both primary and secondary metabolites.

          The mechanism involved in the influence of climate factors on the plant metabolism appears to be related to seasonal induction of stress factors in the plants, such as: (i) drought stress, which can cause a reduction in photosynthetic rate with a consequent increase in production of reactive oxygen species (ROS), therefore resulting in an increase in the production of phenolic compounds (natural antioxidants) during the dry season as a defense mechanism; (ii) thermal stress caused by large temperature variation range during the year, especially during drier periods, which can affect metabolic regulation, permeability to water and CO2 and the rate of intracellular reactions as well as improve the antioxidant properties with an increase availability of carbohydrates; and (iii) stress by solar radiation, particularly UV-B radiation (280–320 nm), which mainly affects the production of phenolic compounds (tannins, anthocyanins, flavonoids and other trans-cinnamic acid derivatives) which, besides contributing to absorption and/or dissipation of solar energy, provide protection against the deleterious effects of UV radiation, such as tissue damage induced directly by UV-B or formation of free radicals and other oxidative species.

          Thus, the approach reported herein may be useful in the study of other invasive and highly adaptable species as well as in the study of the effects of environmental changes in the development of plants, which can also be extended to explore quality control or biological properties of further economically important crops, food species or medicinal plants, the latter responsible for the accumulation of active substances that exert pharmacological effect in humans.

Reference:

Bruno Leite Sampaio, RuAngelie Edrada-Ebel, and Fernando Batista Da Costa. Effect of the environment on the secondary metabolic profile of Tithonia diversifolia: a model for environmental metabolomics of plants. Sci Rep. 2016; 6: 29265. Published online 2016 Jul 7. doi:  10.1038/srep29265.

 Mid season drought did not affect phenolic content in seeds. However, phenolic content in leaves and stems reported to be increased under drought stress.