Extreme climatic events: impacts of drought and high temperature on physiological processes in agronomically important plants

Abstract

Climate models predict more frequent and more severe extreme events (e.g., heat waves, extended drought periods, flooding) in many regions for the next decades. The impact of adverse environmental conditions on crop plants is ecologically and economically relevant. This review is focused on drought and heat effects on physiological status and productivity of agronomically important plants. Stomatal opening represents an important regulatory mechanism during drought and heat stress since it influences simultaneously water loss via transpiration and CO 2 diffusion into the leaf apoplast which further is utilized in photosynthesis. Along with the reversible short-term control of stomatal opening, stomata and leaf epidermis may produce waxy deposits and irreversibly down-regulate the stomatal conductance and non-stomatal transpiration. As a consequence photosynthesis will be negatively affected. Rubisco activase-a key enzyme in keeping the Calvin cycle functional-is heat-sensitive and may become a limiting factor at elevated temperature. The accumulated reactive oxygen species (ROS) during stress represent an additional challenge under unfavorable conditions. Drought and heat cause accumulation of free amino acids which are partially converted into compatible solutes such as proline. This is accompanied by lower rates of both nitrate reduction and de novo amino acid biosynthesis. Protective proteins (e.g., dehydrins, chaperones, antioxidant enzymes or the key enzyme for proline biosynthesis) play an important role in leaves and may be present at higher levels under water deprivation or high temperatures. On the whole plant level, effects on long-distance translocation of solutes via xylem and phloem and on leaf senescence (e.g., anticipated, accelerated or delayed senescence) are important. The factors mentioned above are relevant for the overall performance of crops under drought and heat and must be considered for genotype selection and breeding programs.

Divergent strategies displayed by potato (Solanum tuberosum L.) cultivars to cope with soil drought

“…Among the earliest plant responses to soil water deficiency is stomatal closure protecting the plant against excessive loss of water but it concomitantly restricts CO 2 gas exchange (Feller & Vaseva, ; Obidiegwu et al., ). Stomatal conductance decreased significantly in potato cultivars under drought, but tolerant as well as susceptible cultivars had low relative stomatal conductance.…”

Heavy Metals in Crop Plants: Transport and Redistribution Processes on the Whole Plant Level

“…Often interactions between various biotic and/or abiotic stresses affect plant growth and the composition of the biomass [112,113]. High salt concentrations or climatic factors such as drought or heat should be considered in more detail in the context of global change.…”

Selection and Breeding of Suitable Crop Genotypes for Drought and Heat Periods in a Changing Climate: Which Morphological and Physiological Properties Should Be Considered?

“…A reduced stomatal density in halophytes exposed to salt stress (compared to unstressed control plants) was reported by several groups [107][108][109][110] and such adaptations were also considered for selecting/breeding crop varieties with improved abiotic stress tolerance by "learning from halophytes" [109]. Besides the morphological adaptations in drought-exposed leaves, other important mechanisms are based on changes in the protein pattern (e.g., accumulation of chaperonins or increased activities of enzymes involved in the detoxification of reactive oxygen species or the production of compatible solutes [18,103]. Two aspects of abiotic stress impacts relevant for genotype selection and breeding are emphasized here and discussed in more detail: intactness of organelles (especially chloroplasts and mitochondria) and reactive oxygen species (production and detoxification).…”

“…Several recent reviews have summarized the current knowledge of plant response to drought and high temperature stresses at morphological, physiological and phenological levels [16][17][18][19][20][21]. The aim of this review is to identify morphological and physiological properties that are important for drought and/or heat tolerance in crop plants and for sustainable crop production.…”