Seasonal variation in non-structural carbohydrates, sucrolytic activity and secondary metabolites in deciduous and perennial Diospyros species sampled in Western Mexico.

Ernesto Ramírez-Briones,Jorge Molina-Torres,John P Délano-Frier,Axel Tiessen,Ramón Rodríguez-Macías,Norma Martínez-Gallardo,Eduardo Salcedo-Pérez,Julia Zañudo-Hernández

doi:10.1371/journal.pone.0187235

Abstract

This study was performed to test the working hypothesis that the primary determinants influencing seasonal driven modifications in carbon mobilization and other key biochemical parameters in leaves of poorly known Diospyros digyna (Ddg; semi-domesticated; perennial) and D. rekoi (Dre; undomesticated; deciduous) trees are determined by environmental growing conditions, agronomic management and physiological plasticity. Thus, biochemical changes in leaves of both trees were recorded seasonally during two successive fruiting years. Trees were randomly sampled in Western Mexico habitats with differing soil quality, climatic conditions, luminosity, and cultivation practices. Leaves of Ddg had consistently higher total chlorophyll contents (CT) that, unexpectedly, peaked in the winter of 2015. In Dre, the highest leaf CT values recorded in the summer of 2015 inversely correlated with low average luminosity and high Chl a/ Chlb ratios. The seasonal CT variations in Dre were congruent with varying luminosity, whereas those in Ddg were probably affected by other factors, such as fluctuating leaf protein contents and the funneling of light energy to foliar non-structural carbohydrates (NSCs) accumulation, which were consistently higher than those detected in Dre leaves. Seasonal foliar NSC fluctuations in both species were in agreement with the carbon (C) demands of flowering, fruiting and/ or leaf regrowth. Seasonal changes in foliar hexose to sucrose (Hex/ Suc) ratios coincided with cell wall invertase activity in both species. In Dre, high Hex/ Suc ratios in spring leaves possibly allowed an accumulation of phenolic acids, not observed in Ddg. The above results supported the hypothesis proposed by showing that leaf responses to changing environmental conditions differ in perennial and deciduous Diospyros trees, including a dynamic adjustment of NSCs to supply the C demands imposed by reproduction, leaf regrowth and, possibly, stress.

Highlights

Plants are constantly challenged by variations in temperature, rainfall, and luminosity during their life cycle
This species was abundant in this region, where 20 m-high trees having tree trunk diameters at diameters at chest-height (DCH) exceeding 70 cm were common
The D. rekoi (Dre) population sampled in Teocuitatlan de Corona were located in a deciduous tropical forest that mingled with shrub sections

Summary

Introduction

Plants are constantly challenged by variations in temperature, rainfall, and luminosity during their life cycle. In order to maintain optimal rates of development under fluctuating ambient conditions, they must employ mechanisms designed to maintain photosynthetic efficiency, as well as to ensure the proper functioning of vital metabolic cycles together with membrane and organelle integrity [1, 2] In this context, plant carbohydrates constitute central players in plant metabolism, as primordial sources of energy, and as signal conveying molecules. The above processes are central for the resolution of the constant conundrum faced by plants growing in a continuously changing environment, in which they must decide between employing costly C resources for growth and reproduction, or for survival under usually multiple, perduring and simultaneous (a)biotic stress conditions This decision is dependent on additional endogenous factors related to the leafs ability to utilize luminous energy, such as age, morphology, weight and/ or anatomy, chlorophyll levels and sugar content [6,7,8]

Methods

Results

Discussion

Conclusion