Photosynthetic capacity, leaf respiration and growth in two papaya (Carica papaya) genotypes with different leaf chlorophyll concentrations.

Jéssica Sousa Paixão,Katherine Fraga Ruas,Kevin Lee Griffin,Deivisson Pelegrino Abreu,Weverton Pereira Rodrigues,José Altino Machado Filho,Jefferson Rangel Da Silva,Eliemar Campostrini,Luciene Souza Ferreira,Julian Cuevas Gonzalez,José Cochicho Ramalho,Wallace De Paula Bernado

doi:10.1093/aobpla/plz013

Abstract

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. We undertook an investigation with the goal of evaluating key physiological traits that can affect biomass accumulation of both Golden and Sunrise Solo genotypes. Papaya seeds from two different genotypes with contrasting leaf colour ‘Sunrise Solo’ and Golden were grown in greenhouse conditions. Plant growth (plant height, leaf number, stem diameter, leaf area, plant dry weight), leaf gas exchanges, leaf carbon balance, RuBisCO oxygenation and carboxylation rates, nitrogen, as well as chlorophyll concentrations and fluorescence variables were assessed. Although no significant differences were observed for photosynthetic rates between genotypes, the accumulation of small differences in photosynthesis, day after day, over a long period, might contribute to some extend to a higher C-budget in Sunrise Solo, higher leaf area and, thus, to higher productivity. Additionally, we consider that physiological processes other than photosynthesis and leaf respiration can be as well involved in lower growth and yield of Golden. One of these aspects could be related to the higher rates of photorespiration observed in Sunrise Solo, which could improve the rate of N assimilation into organic compounds, such as amino acids, thus contributing to the higher biomass production in Sunrise Solo relative to Golden. Further experiments to evaluate the effects of N metabolism on physiology and growth of Golden are required as it has the potential to limit its yield.

Highlights

Papaya is the most economically important species within the Caricaceae family and it is widely cultivated for fruit consumption, and for the proteolytic enzyme papain, which has several commercial and medical uses (Villegas 1997; Campostrini and Glenn 2007; Carr 2014)
A previous study showed that Golden had similar CO2 uptake rates to ‘Sunrise Solo’ (Castro et al 2014), which suggests that physiological processes other than photosynthesis are likely responsible for the reduced growth and yield of Golden
Slattery et al (2017) further showed that chlorophyll deficiency led to greater rates of leaf-level photosynthesis per absorbed photon early in the growing season when mutant chlorophyll content was ca. 35 % of the wild-type, but there was no effect on photosynthesis later in the season when mutant leaf chlorophyll approached 50 % of the wild-type

Summary

Introduction

Papaya is the most economically important species within the Caricaceae family and it is widely cultivated for fruit consumption, and for the proteolytic enzyme papain, which has several commercial and medical uses (Villegas 1997; Campostrini and Glenn 2007; Carr 2014). Lower growth vigour and yield were first assumed to be related to the reduced chlorophyll and nitrogen (N) content of the leaves (Torres-Netto et al 2009; Castro et al 2014). A previous study showed that Golden had similar CO2 uptake rates to ‘Sunrise Solo’ (Castro et al 2014), which suggests that physiological processes other than photosynthesis are likely responsible for the reduced growth and yield of Golden. Slattery et al (2017) reported that chlorophyll content can be drastically reduced with little impact to canopy photosynthesis, suggesting an over-investment in chlorophyll and an under-utilization of photosynthetic biochemical capacity in modern soybean cultivars. The small negative effects that were present were likely due to a pleiotropic effect of the mutation that was linked to lower water use efficiency (WUE) that may have dampened any photosynthetic benefits of reduced chlorophyll content, especially since significant drought conditions were experienced during the work (Slattery et al 2017)

Methods

Results

Conclusion