Photosynthetic capacity, respiration and growth of two papaya genotypes with different chlorophyll concentrations

Papaya is the most economically important species within the Caricaceae family and it is widely cultivated not only for fruit consumption, but also for the proteolytic enzyme papain, which has several commercial and medical uses. The Golden genotype of papaya (Carica papaya), named for its yellowish leaves, produces fruits very much appreciated by consumers worldwide. However, its growth and yield are considerably lower than those of other genotypes, such as ‘Sunrise Solo’, which has intensely green leaves. Previous work has shown that Golden had similar COuptake rates to ‘Sunrise Solo’, which suggests that physiological processes other than photosynthesis are likely responsible for the reduced growth and yield of Golden. Net leaf carbon gain estimated from leaf photosynthesis alone typically leads to an overestimation of plant performance. Therefore, leaf respiration in the dark and in the light must also be considered to obtain an accurate C-balance estimate.

Papaya genotypes
Golden (A) and Sunrise Solo (B) plants. Image credit: J.S. Paixão.

A recent study by Paixão et al. published in AoBP provides the first complete picture of leaf carbon balance in two economically important genotypes of papaya and demonstrates that neither stomatal effects nor reduced photochemical and carboxylation capacities of the Golden genotype affected COassimilation through photosynthesis. The authors consider that physiological processes other than photosynthesis/leaf respiration (LCB) can also contribute to reduced growth rates and yield of Golden. For example, photorespiration was observed to be increased in Sunrise Solo, which could improve rates of N assimilation into organic compounds, and thus contribute to greater biomass production in Sunrise Solo relative to Golden. Further experiments to evaluate the effects of N metabolism on Golden physiology and growth, as well as measurements of whole canopy gas exchange and phytohormonal balance are required to fully understand the observed responses as these all have the potential to affect both growth and yield.

Researcher highlight

Dr. Eliemar Campostrini

Dr. Eliemar Campostrini received his DSci (Crop Production) at Universidade Estadual do Norte Fluminense, Rio de Janeiro, Brasil in 1997 and has been an Associated Professor (Plant Physiology and Ecophysiology) at the UENF since 1999. He has been a visiting scientist at the Universita Cattolica del Sacro Cuore, in Piacenza, Italy and the University of Almeria, Spain.

Dr. Eliemar and his colleagues have worked extensively on the environmental physiology of tropical and subtropical fruit crops, specially papaya, coffee and grapevine plants. The aims of his research are to provide deeper understanding of the effects of environmental factors on physiological processes (including gas-exchange, sap flow, photosynthetic pigments, chlorophyll fluorescence) of papaya, coffee and grapevine. This research is crucial to minimize the deleterious impacts of suboptimal environmental conditions and to manage these crops for maximum productivity.