The negative impact of shade on photosynthetic efficiency in sugarcane may reflect a metabolic bottleneck

Author(s)

Sales, Cristina R. G. ; Ribeiro, Rafael, V ; Marchiori, Paulo E. R. ; Kromdijk, Johannes ; Machado, Eduardo C.

• Document type: Journal article
• Source: ENVIRONMENTAL AND EXPERIMENTAL BOTANY; v. 211, p. 11-pg., 2023-05-10.

Abstract

Plants with C-4 metabolism normally have higher photosynthetic rates than C-3 ones. As a result, several of the most productive species known are NADP-ME C-4 grasses, such as sugarcane and maize. However, the advantages of the C-4 cycle are most evident under high light as the CO2 concentrating mechanism comes at the expense of additional ATP. Recent works have suggested a negative impact of shading across NADP-ME C-4 grasses, causing a downregulation of maximal quantum efficiency of CO2 assimilation (phi CO2,max). The mechanisms behind the loss in photosynthetic efficiency and whether these results apply for other C-4 crops species and within germplasm of a species remain unclear. We analysed the photosynthetic acclimation to shade in four sugarcane genotypes with contrasting yield. To find out whether the effects of leaf history, i.e., shading a leaf developed under full sunlight and exposed later on to shade differ from a leaf fully developed under shading, these two types of leaves were evaluated. Shaded sugarcane plants showed decreased CO2 assimilation efficiency compared to plants grown under full sunlight. Based on the fluorescence measurements, it seems that this reduction coincided with a more reduced Q(A) redox state, which could point to a metabolic limitation downstream of the light-dependent reactions. The results were similar for all genotypes and were observed regardless of whether leaves developed under shade or under full sunlight conditions and exposed subsequently to shade, suggesting that light is the main factor affecting photosynthetic efficiency. This study reinforces the notion that this negative impact of shade could reflect a common bottleneck across NADP-ME C-4 grasses. (AU)

• FAPESP's process: 08/57495-3 - Integrating physiological, morphological and anatomical traits to understand the differential sucrose yield in sugarcane genotypes
• Grantee: Eduardo Caruso Machado
• Support Opportunities: Program for Research on Bioenergy (BIOEN) - Thematic Grants