Abstract
Agricultural production is predicted to be adversely affected by an increase in drought and heatwaves. Drought and heat damage cellular membranes, such as the thylakoid membranes where photosystem II occurs (PSII). We investigated the chlorophyll fluorescence (ChlF) of PSII, photosynthetic pigments, membrane damage, and the activity of protective antioxidants in drought-tolerant and -sensitive varieties of C3 sunflower and C4 maize grown at 20/25 and 30/35 °C. Drought-tolerant varieties retained PSII electron transport at lower levels of water availability at both temperatures. Drought and heat stress, in combination and isolation, had a more pronounced effect on the ChlF of the C3 species. For phenotyping, the maximum fluorescence was the most effective ChlF measure in characterizing varietal variation in the response of both species to drought and heat. The drought-tolerant sunflower and maize showed lower lipid peroxidation under drought and heat stress. The greater retention of PSII function in the drought-tolerant sunflower and maize at higher temperatures was associated with an increase in the activities of antioxidants (glutathione reductase, superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase), whereas antioxidant activity declined in the drought-sensitive varieties. Antioxidant activity should play a key role in the development of drought- and heat-tolerant crops for future food security.
Highlights
As average global temperatures rise, the frequency of drought events and heatwaves will increase [1,2,3]
The greater retention of photosystem II (PSII) function in the drought-tolerant sunflower and maize at higher temperatures was associated with an increase in the activities of antioxidants, whereas antioxidant activity declined in the drought-sensitive varieties
Analysis of PSII electron transport using chlorophyll fluorescence (ChlF) indicated that drought and heat stress had a greater impact in C3 sunflower than in C4 maize (Figures 3 and 4); a result consistent with gas exchange analysis of CO2 assimilation in the same varieties (Figure 1)
Summary
As average global temperatures rise, the frequency of drought events and heatwaves will increase [1,2,3]. This combination of drought and heat stress will have significant negative implications for agricultural production of both C3 [4,5] and C4 [6] crops. Analysis of the physiological mechanisms involved in crop responses to drought and heat stress may elucidate the photosynthetic and protective behaviors that underpin tolerance to these stresses. The stability of cellular membranes is a key determinant of plant tolerance to heat and drought stress [21]
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