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

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.

Fruits of wild and semi‐domesticated Diospyros tree species have contrasting phenological, metabolic, and antioxidant activity profiles

“…This suggested that the significantly lower NSCs accumulation detected in the D. rekoi fruits from 2015 was not due to an impaired and or developmentally regulated capacity to convert starch into reducing sugars, as described in kiwifruits . The previously reported lower nitrogen reserves available to D. rekoi trees at the sampling site also led to discarding the possibility that high nitrogen availability could have negatively affected soluble sugars and starch contents in fruits and other tissues of D. rekoi trees, as shown previously in certain D. kaki varieties . Moreover, they disagreed with a study showing that wild apple fruits, although significantly more acidic than cultivated apples, had average sugar concentrations that were similar to cultivated genotypes .…”

“…Thus, fewer fruits could be sampled, specifically from one and two tree specimens in the 2015 and 2016 winter seasons respectively. The observed difference most probably reflected the fact that D. rekoi fruits were sampled from trees growing in the wild, whereas domesticated D. digyna trees were raised under more controlled conditions . D. rekoi fruits were much smaller, had a higher seed/edible pulp ratio, and a lower edible portion percentage (Table ).…”

“…Fruit samples were obtained in two different locations in western Mexico as described previously . Briefly, D. digyna fruits were sampled in an agro‐forestry settlement in the municipality of Taretan, Michoacán, localized at 1100 m above sea level with a mean annual temperature of 22 °C and 1100 mm of average rainfall per year.…”

“…D. rekoi fruits were sampled in the municipality of Teocuitatlán de Corona, Jalisco, localized at 1800 m above sea level, with a mean annual temperature of 20 °C and 531 mm of average rainfall per year. Five trees were randomly chosen for analysis in each sampling site . Trees selected for sampling were 10–12 m high, with mean tree trunk diameters at chest height of 40 cm and 25 cm for D. dygina and D. rekoi respectively.…”

“…The fruits D. digyna and D. rekoi , locally known as ‘zapote negro’ and ‘zapotillo negro’ respectively, are highly appreciated by the local population, although a fluctuating international demand for the exotic ‘zapote negro’ is common. Contrary to fruits of D. kaki and of other well‐studied species, information of Mesoamerican species such as D. digyna and D. rekoi is scarce to non‐existent . Whereas semi‐domesticated D. digyna fruits have been reported to have high vitamin E content, in addition to relatively abundant levels of carotenoids and phenolic compounds, the latter of which were associated with a strong antioxidant activity, practically no information is available regarding the physicochemical characteristics of wild D. rekoi fruits.…”