Efficient Regulation of CO2 Assimilation Enables Greater Resilience to High Temperature and Drought in Maize

Abstract

Increasing temperatures and extended drought episodes are among the major constraints affecting food production. Maize has a relatively high temperature optimum for photosynthesis compared to C3 crops, however, the response of this important C4 crop to the combination of heat and drought stress is poorly understood. Here, we hypothesized that resilience to high temperature combined with water deficit (WD) would require efficient regulation of the photosynthetic traits of maize, including the C4–CO2 concentrating mechanism (CCM). Two genotypes of maize with contrasting levels of drought and heat tolerance, B73 and P0023, were acclimatized at high temperature (38°C versus 25°C) under well-watered (WW) or WD conditions. The photosynthetic performance was evaluated by gas exchange and chlorophyll a fluorescence, and in vitro activities of key enzymes for carboxylation (phosphoenolpyruvate carboxylase), decarboxylation (NADP-malic enzyme), and carbon fixation (Rubisco). Both genotypes successfully acclimatized to the high temperature, although with different mechanisms: while B73 maintained the photosynthetic rates by increasing stomatal conductance (gs), P0023 maintained gs and showed limited transpiration. When WD was experienced in combination with high temperatures, limited transpiration allowed water-savings and acted as a drought stress avoidance mechanism. The photosynthetic efficiency in P0023 was sustained by higher phosphorylated PEPC and electron transport rate (ETR) near vascular tissues, supplying chemical energy for an effective CCM. These results suggest that the key traits for drought and heat tolerance in maize are limited transpiration rate, allied with a synchronized regulation of the carbon assimilation metabolism. These findings can be exploited in future breeding efforts aimed at improving maize resilience to climate change.

Maize Intercropping in the Traditional “Milpa” System. Physiological, Morphological, and Agronomical Parameters under Induced Warming: Evidence of related Effect of Climate Change in San Luis Potosí (Mexico)

“…The genotypes from the warm–dry climate ( Altiplano ) were the most affected, even for the two other crops. Studies showed that early closure of stomata and decreasing transpiration were found to be thermal sensitive in maize plants grown at high temperatures [ 63 ], as we reported in our study. In various crop species, such as soybean, tobacco, and grape, global warming has been found to increase stomatal frequency while decreasing stomatal size, though no effect has been recorded in maize [ 64 , 65 , 66 ].…”

Elevated CO2 and Water Stress in Combination in Plants: Brothers in Arms or Partners in Crime?

“…In the NAD-ME type plants, the enzyme has the main function of decarboxylation of malate to produce pyruvate, NADH and CO 2 ; this enzyme uses NAD + , does not decarboxylate Oxalo Acetic Acid (OAA) and is present in mitochondria. Drought and C 4 enzymes, specifically the NAD and NADP malic enzyme action dynamics, have been well studied [ 14 , 67 , 69 , 70 ]. The possible mechanism can be that the entry of CO 2 is restricted under eCO 2 conditions due to reduction in stomatal density and closure, either due to eCO 2 or drought; the ME in C 4 can contribute to higher accumulation of CO 2 in the bundle sheath cells, thus increasing photosynthesis, and in contrast to the commonly accepted view that C 4 plants do not have a distinct advantage under eCO 2 conditions.…”

Elevated CO₂ and Water Stress in Combination in Plants: Brothers in Arms or Partners in Crime?

“…In the NAD-ME type plants, the enzyme has the main function of decarboxylation of malate to produce pyruvate, NADH and CO2, this enzyme uses NAD + and does not decarboxylate Oxalo Acetic Acid (OAA) and is present in mitochondria. Drought and C4 enzymes specifically the NAD and NADP malic enzyme action dynamics have been well studied [67,69,70,14]. The possible mechanism can be that the entry of CO2 is restricted under eCO2 conditions due to reduction in stomatal density and also closure either due to eCO2 or drought, the ME in C4 can contribute to higher accumulation of CO2 in the bundle sheath cells, thus increasing photosynthesis, this is in contrast with the commonly accepted view that C4 plants don't have a distinct advantage under eCO2 conditions.…”