Table 5.

Effect of the applications of two growth regulators (cytokinins (CK) or brassinosteroids (BR)) on the photosynthetic variables of rice plants of genotype Federarroz 2000 subjected to combined heat stress (40°C day/30°C night) at R2 (88 DAE) or R8 (108 DAE).

Treatment	Pn	E	gs	Ci	WUE	Pn/Ci	Fv/Fm	NPQ
Phenological stage (S)	***	NS	NS	NS	**	***	*	*
Treatment (T)	***	NS	NS	*	**	***	**	**
Interaction (SxT)	***	NS	NS	NS	**	***	**	**
Absolute control (AC)-R2	9.38 bc	8.19 a	0.74 a	346.78 a	37.59 b	0.026 bc	0.65 ab	0.55 d
Heat stress control (SC)-R2	9.02 bc	8.28 a	0.69 a	324.72 a	12.25 b	0.026 bc	0.61 c	1.78 a
Stress-R2 + CK3	6.71 cd	9.60 a	0.25 a	326.08 a	31.82 b	0.020 bc	0.67 a	0.98 b
Stress-R2 + BR3	22.53 a	13.20 a	0.21 a	326.29 a	90.81 a	0.036 b	0.67 a	1.12ab
Absolute control (AC)-R8	11.88 b	10.97 a	0.45 a	356.45 a	28.82 b	0.016 c	0.67 a	0.70 c
Heat stress control (SC)-R8	6.10 cd	8.70 a	0.41 a	337.15 a	14.06 b	0.010 c	0.59 c	1.84 a
Stress-R8 + CK3	4.39 d	9.11 a	0.45 a	355.83 a	17.02 b	0.070 a	0.62 b	1.21 ab
Stress-R8 + BR3	8.71 cd	10.49 a	0.49 a	337.14 a	27.53 b	0.026 bc	0.63 b	1.17 ab
CV (%)	15.38	30.70	86.41	4.35	44.91	19.97	3.91	4.51

Photosynthesis (P_n), transpiration (E), stomatal conductance (g_s), intercellular carbon (C_i), water use efficiency (WUE), carboxylation efficiency (P_n/C_i), F_v/F_m ratio, and non-photochemical quenching (NPQ). The treatments evaluated were as follows: absolute control (AC), heat stress control (SC), three foliar sprays of CK (CK3), and three foliar sprays of BR (BR3). Data represent the mean of five data points ± standard error (n = 5). Data followed by different letters indicate statistically significant differences according to Tukey’s test (P ≤ 0.05). Equal letters indicate that the means are not statistically significant (≤0.05). NS, *, ** or *** not significant or significant at P ≤ 0.05, 0.01 or 0.001, respectively. C.V., coefficient of variation.