Sensitivity of Photosynthesis in a C4 Plant, Maize, to Heat Stress

Abstract

Our objective was to determine the sensitivity of components of the photosynthetic apparatus of maize (Zea mays), a C4 plant, to high temperature stress. Net photosynthesis (Pn) was inhibited at leaf temperatures above 38°C, and the inhibition was much more severe when the temperature was increased rapidly rather than gradually. Transpiration rate increased progressively with leaf temperature, indicating that inhibition was not associated with stomatal closure. Nonphotochemical fluorescence quenching (qN) increased at leaf temperatures above 30°C, indicating increased thylakoid energization even at temperatures that did not inhibit Pn. Compared with CO 2 assimilation, the maximum quantum yield of photosystem II (F v /F m ) was relatively insensitive to leaf temperatures up to 45°C. The activation state of phosphoenolpyruvate carboxylase decreased marginally at leaf temperatures above 40°C, and the activity of pyruvate phosphate dikinase was insensitive to temperature up to 45°C. The activation state of Rubisco decreased at temperatures exceeding 32.5°C, with nearly complete inactivation at 45°C. Levels of 3-phosphoglyceric acid and ribulose-1,5-bisphosphate decreased and increased, respectively, as leaf temperature increased, consistent with the decrease in Rubisco activation. When leaf temperature was increased gradually, Rubisco activation acclimated in a similar manner as Pn, and acclimation was associated with the expression of a new activase polypeptide. Rates of Pn calculated solely from the kinetics of Rubisco were remarkably similar to measured rates if the calculation included adjustment for temperature effects on Rubisco activation. We conclude that inactivation of Rubisco was the primary constraint on the rate of Pn of maize leaves as leaf temperature increased above 30°C.It has long been recognized that C4 plant species have a higher temperature optimum for photosynthesis than C3 plants due to the operation of a CO 2 -concentrating system that inhibits Rubisco oxygenase activity (Berry and Bjö rkman, 1980;Edwards and Walker, 1983). In C3 plants, inhibition of net photosynthesis (Pn) at moderately high temperatures has usually been ascribed to an increase in the ratio of Rubisco oxygenase:Rubisco carboxylase activities. As temperature increases, the ratio of dissolved O 2 /CO 2 and the specificity of Rubisco for O 2 increase, thus favoring oxygenase activity (Monson et al., 1982; Jordan and Ogren, 1984; Sage and Sharkey, 1987) and resulting in inhibition of Pn. As a consequence, when C3 plants are exposed to high CO 2 and/or low O 2 , i.e. conditions that reduce oxygenase activity, the temperature optimum for Pn is increased (Berry and Bjö rkman, 1980;Edwards and Walker, 1983).For C3 and C4 plants, the temperature range for optimum Pn is broad, and at temperatures above this range, Pn decreases (Edwards and Walker, 1983). Temperature-induced decreases in Pn in C3 species are closely associated with inactivation of Rubisco (Law and Crafts-Brandner, 1999), and when the activation state of Rubisco and g...

Timing of climate variability and grassland productivity

“…Focusing on the indirect effects of heat waves on water balance allows for a common mechanism that links the effects of heat waves with drought and precipitation pattern, but other mechanisms are possible. For example, the possibility that high temperatures associated with heat waves generated physiological stress directly cannot be ruled out (26). That said, peak temperatures from DOY 190-214 generally were below the optimum temperatures reported for photosynthesis for C 4 grasses (27,28), and increases in peak air temperature that were well below optimum photosynthetic temperatures were associated with lower productivity (Fig.…”

Evaluation of Maize Hybrids for Tolerance to High Temperature Stress in Central Punjab

“…A lot of information on agronomic and physiological traits for high temperature tolerance in maize is available (Steven et al, 2002;Sinsawat et al, 2004). The final plant height reflects the growth behavior of a crop, besides genetic characteristics, availability of essential nutrients, space, water and environmental condition under which it is grown.…”

“…protein denaturation, aggregation, enzyme inactivation, inhibited protein synthesis and its degradation was noted (Dubey, 2005;Kim et al, 2007;Wahid et al, 2007;Ristic et al, 2009). The activation state of RUBISCO decreases at 32.5 0 C (Crafts-Brander and Salvucci, 2002) with almost complete inactivation at 45 o C and plant dies at 54 o C (Smith, 1996 andSteven et al 2002). Heat shock affects the endosperm development in maize and reduces grain yield due to interruption in cell division, aberrant sugar metabolism and starch biosynthesis (Monjardino et al, 2005).…”

Photosynthetic Potential and its Association with Lipid Peroxidation in Response to High Temperature at Different Leaf Ages in Maize

“…However, cotton normally is grown in conditions in which photosynthesis may be limited by high temperature, whereas g s is normally quite high (Radin and others 1994). Crafts-Brandner and Salvucci (2002) reported that the photosynthetic rate of maize declined at leaf temperatures above 38°C, but maximal efficiency of PSII photochemistry (F v /F m ) remained at a relatively constant level up to a leaf temperature of 45°C. High temperature up to 42°C in the present experiment led to decreases in photosynthetic rate (A), g s , and activity of PSII at different leaf ages.…”