Effect of Elevated Temperature and Excess Light on Photosynthetic Efficiency, Pigments, and Proteins in the Field-Grown Sunflower during Afternoon

Abstract

This study examined the photosynthetic responses of two sunflower hybrids to elevated temperatures and excess light intensity in the flowering stage by measuring the chlorophyll a fluorescence (ChlF) under morning and afternoon field conditions to determine the photosynthetic pigment contents and the relative accumulation of photosynthetic proteins. The morning environmental conditions were considered optimal, while the afternoon was characterised by elevated temperatures and excess light intensity. The minimum fluorescence intensity (F0), the electron-flux-reducing end electron acceptors at the photosystem I acceptor side per reaction centre (RE0/RC), and the D1 protein had significant, high, and positive correlations with the environmental conditions, which indicates that they were the most useful in the sunflower-stress-response research. In hybrid 7, the elevated temperatures and the excess light intensity resulted in the inactivation of the oxygen-evolving complex, which was indicated by the positive L, K, and J steps, the increase in the maximum quantum yield of PSII (TR0/ABS), the decrease in the electron transport further than the primary acceptor QA (ET0/(TR0-ET0)), the reduction in the performance index (PIABS), and the higher relative accumulation of the light-harvesting complex of the photosystem (LHCII). Hybrid 4 had smaller changes in the fluorescence curves in phases O–J and J–I, and especially in steps L, K, J, and I, and a higher PIABS, which indicates a more efficient excitation energy under the unfavourable conditions. As the tested parameters were sensitive enough to determine the significant differences between the sunflower hybrids in their photosynthetic responses to the elevated temperatures and excess light intensity in the flowering stage, they can be considered useful selection criteria. The development of more adaptable sunflower hybrids encourages sustainable sunflower production under stressful growing conditions.

Detailed Insight into the Behaviour of Chlorophyll a Fluorescence Transient Curves and Parameters during Different Times of Dark Adaptation in Sunflower Leaves

“…According to PI total and δR 0 /(1 − δR 0 ), sunflower leaves should be dark-adapted for 15-30 min as the values of both parameters were statistically different after the 45 to 90 min range of dark adaptation (Figure 5d,e). Markulj Kulundžić et al [12] and Pavlović et al [41] proved that δR 0 /(1 − δR 0 ) is the most sensitive component of PI total , which can also be seen from the results of this research. Given the uniform results for each developmental stage, the conclusions above can be applied to all three developmental stages (vegetation-V6, budding and flowering).…”

“…The values for all of the mentioned parameters increased after 15 min of adaptation compared to values without dark adaptation, after which they decreased with the elongation of dark adaptation time for all parameters except ET 0 /(TR 0 − ET 0 ). Figure 5d shows differences between the PI ABS values by developmental stages, which was previously confirmed in the papers of Markulj Kulundžić et al [12]. PI ABS values increase with the aging of sunflower plants [12].…”

“…Figure 5d shows differences between the PI ABS values by developmental stages, which was previously confirmed in the papers of Markulj Kulundžić et al [12]. PI ABS values increase with the aging of sunflower plants [12].…”

“…The application of the ChlF method on sunflowers started immediately after its introduction [7,8]. Some of the resulting research on sunflower deal with the photosynthetic characteristics at different nitrogen inputs into the soil [9], differences under combined salt and drought stress [10], the impact of light and heat stress on sunflower genotypes [11,12], the effect of drought and heat stress on sunflower [13] and by examining the effects of other environmental stresses on sunflower plants.…”

Antioxidative Response and Phenolic Content of Young Industrial Hemp Leaves at Different Light and Mycorrhiza

“…Carotenoids have an important role in protecting cells from oxidation and cellular damage [ 44 ]. Various stresses affect plants by changing the content of chlorophyll and carotenoids [ 45 , 46 ].…”