Table 2.
Effect of combined heat stress (40°/30°C day/night) on leaf photosynthetic pigments [total chlorophyll (Chl total), chlorophyll a (Chl a), chlorophyll b (Chl b) and carotenoids Cx+c)], relative chlorophyll content (Atleaf units), and chlorophyll fluorescence parameters (initial fluorescence (F0), maximum fluorescence (Fm), variable fluorescence (Fv), maximum efficiency of PSII (Fv/Fm), maximum quantum yield of PSII photochemistry (Fv/F0), and the Fm/F0 ratio) in plants of two rice genotypes [Fedearroz 67 (F67) and Fedearroz 2000 (F2000)] at 55 days after emergence (DAE).
| Chlorophyll pigments | Chlorophyll fluorescence parameters | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Genotype | Treatment | Chl totalmg g−1 (FW) | Chl a mg g−1 (FW) | Chl bmg g−1 (FW) | Cx+cmg g−1 (FW) | Atleaf units | F0 | Fm | Fv | Fv/Fm | Fv/F0 | Fm/F0 |
| F67 | AC | 2.67cd | 2.08 cd | 0.59 cd | 0.45 cd | 41.93 bc | 829.75 | 3863.75 | 3029.98 a | 0.78 ab | 3.66 | 4.66 |
| (Experiment 1) 1) | SC | 2.36 def | 1.79 de | 0.56 d | 0.52 bc | 33.50 d | 814.50 | 3278.00 | 2456.79 cd | 0.75 bcd | 3.02 | 4.03 |
| AUX | 1.95f | 1.36 fg | 0.59 cd | 0.14 g | 38.0 cd | 733.50 | 3352.75 | 2605.44 bc | 0.78 abc | 3.56 | 4.58 | |
| GA | 1.45g | 1.07 g | 0.38 ef | 0.27 f | 37.59 cd | 814.00 | 3327.25 | 2513.07 bc | 0.76 abcd | 3.16 | 4.16 | |
| CK | 3.25 ab | 2.52 b | 0.73 ab | 0.59 ab | 41.66 bc | 751.00 | 3579.25 | 2826.34 ab | 0.79 ab | 3.76 | 4.76 | |
| BR | 2.14 ef | 1.65 ef | 0.49 de | 0.38 de | 40.30 bc | 763.75 | 3469.50 | 2745.60 abc | 0.79 a | 3.61 | 4.56 | |
| F2000 | AC | 2.80 c | 2.19 c | 0.60 bcd | 0.53 bc | 48.92 a | 1061.40 | 4016.75 | 2955.35 a | 0.74 cde | 2.79 | 3.79 |
| (Experiment 2) | SC | 2.56 cde | 2.09 cd | 0.54 d | 0.50 bc | 33.72 d | 1266.45 | 3218.25 | 2120.15 de | 0.66fg | 1.76 | 2.67 |
| AUX | 2.24 ef | 1.70 e | 0.54 d | 0.35 ef | 47.45 a | 1041.47 | 3462.25 | 2420.78 cd | 0.70 ef | 2.34 | 3.34 | |
| GA | 1.43 g | 1.09 g | 0.33 f | 0.26 f | 39.07 c | 1112.23 | 3063.50 | 1951.27 e | 0.64 g | 1.76 | 2.76 | |
| CK | 3.65 a | 2.87 a | 0.78 a | 0.66 a | 49.30 a | 918.86 | 3510.75 | 2591.89 bc | 0.74 cde | 2.82 | 3.82 | |
| BR | 2.88 bc | 2.19c | 0.69 abc | 0.48 cd | 44.52 ab | 940.69 | 3485.75 | 2545.06 bc | 0.73 de | 2.72 | 3.72 | |
| Significance | *** | *** | *** | *** | *** | NS | NS | * | ** | NS | NS | |
The treatments evaluated in each genotype were: absolute control (AC), heat stress control (SC), heat stress + auxins (AUX), heat stress + gibberellins (GA), heat stress + cytokinins (CK), and heat stress + brassinosteroids (BR). Data represents the mean of five data ± standard error (n = 5). Data followed by different letters indicate statistically significant differences according to the Tukey test (P ≤ 0.05). Equal letters indicate that means are not statistically significant ( ≤ 0.05). NS, *, ** or *** not significant or significant at P ≤ 0.05, 0.01 or 0.001, respectively.